THE NATURAL

oid OF
la PLANTS

PO

THE

NATURAL HISTORY OF PLANTS

THEIR FORMS, GROWTH,
REPRODUCTION, AND DISTRIBUTION

FROM THE GERMAN OF

ANTON KERNER von MARILAUN

PROFESSOR OF BOTANY IN THE UNIVERSITY OF VIENNA

TRANSLATED AND EDITED
BY

F. W. OLIVER, M.A., D.Sc.

QUAIN PROFESSOR OF BOTANY IN UNIVERSITY COLLEGE, LONDON

WITH THE ASSISTANCE OF

MARIAN BUSK, B.Sc. anp MARY F. EWART, B.Se.

WITH ABOUT 2000 ORIGINAL WOODCUT ILLUSTRATIONS AND SIXTEEN PLATES IN COLOURS

DIVISIONAL VOLUME V.

LONDON: BLACKIE & SON, LimitEp
GLASGOW, EDINBURGH, AND DUBLIN

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I tA aw j er 1 2 2

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MAY V5 1919

CONTENTS OF DIVISIONAL VOLUME V.

LIST OF ILLUSTRATIONS.

Pirate XIV. Funer ar Home.—Drawn by Ernst Heyn, - - - - -

Illustrations in the Text—Fig. 296 to Fig. 372.

THE GENESIS OF PLANT-OFFSPRING.—Continued.

Page

Autogamy—Continued, - = 337
Fertilization and Formation of Fruit in

Phanerogams, - = = > - 401

THE HISTORY OF SPECIES.

1. Toe NATURE oF SPECIES.

Definition of Species, - - =
The Specific Constitution of Pr Stone

- 486
- 487

2. ALTERATION IN THE FORM oF SPECIES.

Dependence of Plant Form on Soil and

Climate, - = - - - 495
The Influence of Mutilation on the Form of
Plants, = - 514

PAGE
to face 492
Page
3. CHANGE IN REPRODUCTIVE METHODS.
Fruits Replaced by Offshoots, - - 452
Parthenogenesis, - - - - 463
Heteromorphism and Alternation of Genera-
tions, - - - - - - - 469
| Alteration of Form by Parasitic Fungi, - 518

| Alteration of Form by Gall-producing Insects, 527

| Genesis of New Forms asa Result of Cr ossing, 554
3. THE ORIGIN OF SPECIES.
The Genesis of New Species, - - - 576
Derivation of Existing Species, - 595
Subdivisions of the Vegetable Kingdom, - 600
Classification of Plants ee by the
Editor, - - 616

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AUTOGAMY BY BENDING OF STAMENS. 337

the approach to the floral receptacle open. _Dehiscence has already taken place in
the case of the anthers of the stamens insert.d in front of the sepals, and their
pollen is available for cross-fertilization by means of insects, but not for auto-
gamy, owing to the fact that the receptive tissue of the style in the same flower
is still inaccessible. (2) The anthers of the stamens inserted in front of the
sepals drop off, or else their filaments become reflexed and are exserted beyond
the periphery of the flower. The styles move asunder and arrange themselves
like the spokes of a wheel in the middle of the flower, where they are liable to
be covered with pollen brought by insects from other blossoms. The anthers
of the stamens inserted in front of the petals are -still closed. (3) Owing to a
growth of the erect filaments of the last-mentioned stamens, their anthers are
brought to the same height as and in direct contact with the spreading stigmas.
Dehiscence ensues, and the liberated pollen is deposited on the receptive stigmatic
tissue. In annual caryophyllaceous plants—e.g. in Silene conica—the whole pro-
cess takes place in the course of a single day, whereas in the perennial Dianthus
glacialis it occupies five or six days, or, if the weather is bad, from seven to nine
days.

One of the commonest contrivances for effecting autogamy is the following.
Anthers and stigmas stand at the same height, though, owing to the position and
direction of the filaments, the anthers are so far from the stigma that no transfer-
ence of the adhesive pollen to it can take place. At the proper moment, however,
the straight and rigid filiform filaments perform certain special movements with the
object of conveying pollen from the anthers to the stigma in the same flower. The
filaments incline themselves towards the centre of the flower, bringing the anthers
into contact with the stigma there situated and pressing the pollen issuing from
their loculi on to the receptive tissue. In some plants belonging to this category
the displacement of the stamens, which is like the motion of the hands of a clock, is
preceded by an elongation of the filaments, and in this respect the plants in question
form a transition from those previously described, in the flowers of which autogamy
is due to the growth of the filaments. As instances of these transitional forms may
be mentioned Azalea procumbens, Draba aizoides, Haplophyllum Biebersteimii, the
numerous Saxifrages comprised in the groups of Aizoonia and Tridactylites, and
more particularly many Alsinez and other Caryophyllacex. The Saxifrages exhibit
a number of individual peculiarities into which we cannot enter in any detail. We
must content ourselves with describing two species as representatives of the two
groups above referred to, and will select for the purpose Sawifraga Burseriana, a
plant which grows in the eastern Dolomites, and flowers in early spring, and Sazi-
Jraga controversa of the group Tridactylites. The flowers of Saxifraga Burseriana
are protogynous, and the two spreading stigmas are already susceptible of pollina-
tion at the time when the petals are only just open, and the anthers are still closed
and held near the bottom of the flower on quite short filaments. During this first
period of flowering the blossom is adapted to cross-fertilization. Soon afterwards

the stamens in front of the sepals lengthen in definite succession, and the anthers,
Vou. II. 72

338 AUTOGAMY.

which meanwhile have undergone dehiscence, are brought to the same level as the
stigma. Although the horizontal distance between the stigma and anthers is very
small, it is still sufficient to prevent the stigma from becoming coated with pollen
from the anthers. Moreover, the stamens standing opposite the sepals incline out-
wards soon after, thus increasing perceptibly the distance between anthers and
stigma. Synchronously with the outward inclination of these stamens there is an
up-growth of those which stand in front of the petals, and here again the operation
takes place according to a definite law of succession, and continues until the anthers
are raised to the height of the stigmas. These anthers, like the others, do not adhere
at first to the stigma, and it sometimes happens that the stigma remains unsupplied
with pollen even on the sixth day of flowering if none is brought by insects. But,
at last, on the seventh or eighth day some, if not all, the filaments move towards the
centre of the flower, and the pollen-covered anthers are pressed against the stigma,
which has not yet lost the power of receiving the pollen. Usually the five stamens
opposite the sepals act in the same manner, and all the ten anthers then ultimately
form a ring surrounding the stigma from which pollen may still be transferred by
insects to other flowers. The flowers of Saxifraga controversa are likewise proto-
gynous, and adapted to cross-fertilization in the first period of flowering. Of the ten
stamens, the first to elongate are the five opposite the sepals; the anthers borne at
their extremities ascend to the level of the stigma and during the process accomplish
their dehiscence. For a short time anthers and stigmas are separated by a small
interval of space, but soon afterwards the filaments incline a little towards the centre
and deposit pollen upon the stigmas. The five stamens in question then slope away
from the centre, and their empty and shrivelled anthers fall off. Meanwhile the
five stamens opposite the petals have grown up to the level of the stigmas and offer
a fresh supply of pollen for dispersion. But this pollen cannot be used for autogamy
owing to the fact that the stigmas shrivel up after they receive the pollen of the first
five stamens, and are no longer capable of playing a part in fertilization. The
second supply of pollen can, therefore, only be appropriated to the fertilization of
younger flowers through the instrumentality of insects. In other words, the five
anthers in front of the sepals devote their pollen to autogamy, whilst the five
opposite the petals devote theirs to cross-fertilization.

As in these Saxifrages so also in Alsinez we find two whorls of stamens opposite
the sepals and petals respectively, and a certain general resemblance unmistakably
exists in the whole arrangement of the various parts of the flowers. The Alsinex
that we here have to deal with are protandrous, and as examples may be taken
Cerastium longirostre, Malachiwm aquaticum, Sagina saxatilis, Spergula arvensis,
and Stellaria media. Dehiscence takes place in the anthers opposite the sepals
synchronously with the opening of the corolla, and the pollen exposed thereby 1s
available for cross-fertilization. At that period the styles are still coherent, and the
stigmatic tissue, which is composed of short transparent hairs, is inaccessible. Soon
afterwards, however, the styles part asunder, and the stigmatic tissue assumes such
a position as to ensure cross-fertilization in case insects bringing pollen from other

AUTOGAMY BY MOVEMENTS OF STAMENS. 339

flowers should visit them in quest of honey. In a short time the stamens opposite
the petals raise their anthers to the same height as the stigmatie tissue of the
divergent styles; but the filiform filaments slope away from the axis, so that there
is always some interval, however small it may be, between anthers and stigmas, and
there is still no autogamy. It is not till the last moment, when the flowers begin
to close, that the stamens opposite the petals ineline towards the centre of the
flower, and, laying their anthers upon the stigmatie tissue, cover it with a quantity
of their still abundant store of pollen. In most of the Alsinex, of which we are
speaking, the anthers in front of the sepals also come into contact with the stigmas
at the same moment, but in a few cases they project above the stigmas and petals,
and their pollen is then not available for autogamy. It is remarkable that in the
the latter, which may be represented by Sagina sawatilis, the characteristic fact
of the pollen of the five stamens opposite the sepals being devoted to cross-fertiliza-
tion, and that of the five stamens opposite the petals to autogamy, is exactly the
reverse of the arrangement found to exist in the Saxifrages above described.

Next to this series of plants of which the Saxifrages of the Aizoonia and Tridac-
tylites groups and the Alsinee above-named are the chief representatives, comes
another composed predominantly of Crucifere. They are for the most part annual
species with small flowers, which are but little visited by insects, and the majority
of their fruits must be looked upon as products of autogamy. Cochlearia Green-
landica, Draba borealis, Draba verna, Clypeola Messanensis, Lobularia nummu-
laria, Hutchinsia alpina, Schieverekia Podolica, Lepidium Draba, Alyssum
calycinum, are a few examples, and the selection shows incidentally that the range
of the cruciferous plants in question extends from the extreme North to the latitude
of the Sahara, and from high altitudes to the level of the deep-lying steppes; in fine,
that this same process of autogamy recurs under the most diverse external condi-
tions. All these Crucifer& are protogynous, and have six stiff stamens, four long
and two short. The anthers of the former are still closed when the flower opens,
but are already on the same level as the stigma. Autogamy is, however, prevented
immediately on the dehiscence of the anthers, owing to there being a little horizontal
interval between them and the stigma. It is not till the flower is almost over that
the erect filaments move sufficiently towards the middle of the flower to deposit the
pollen upon the stigma. The pollen of the shorter stamens does not get transferred
at all to the stigma in the same flower except in a few species. It is carried away
by insects and used for cross-fertilization, whilst the pollen of the longer stamens
mainly subserves the purpose of autogamy. Lepidiwm Draba exhibits a curious
contrivance to prevent the four longer stamens from being touched by insects and
despoiled of their pollen during the first part of the time that the flower is open.
The stamens referred to bend outwards and hide themselves for a time behind
the petals. The advantage of this movement is that in no circumstances can there
be a deficiency of pollen for the ultimate process of autogamy. In Hutchinsia
alpina usually only one of the four longer stamens approaches sufficiently near to
the stigma to cover it with pollen, and after it has effected this object, it removes

340 AUTOGAMY.

itself again away from the axial position. All these movements are performed as
a general rule with great rapidity. In Alysswm calyeinwm they take a few hours,
in Draba verna the interval between morning and evening.

Some annual species of the Wood-sorrel genus—such as Oxalis stricta, for

example—have five short and five long stamens in each flower. The anthers of the
latter are of the same height as the stigmas, but begin by being at a little distance
from them, so that at this period cross-fertilization may be effected by insects
alighting upon the stigmas. Within the space of a few hours, however, the longer
stamens incline towards the stigmas and deposit their pollen upon them. Here,
again, the pollen of the five shorter stamens does not reach the stigma in the same
flower, but is devoted to cross-fertilization. As in these annual species of Wood-
sorrel, so also in the majority of species of St. John’s-wort (Hypericum), the unequal
length of the stamens, combined with the fact of the non-simultaneity of sexual
maturity (dichogamy), is of advantage to the plant in that it ensures that auto-
gamy shall take place just before the flower fades, whilst permitting at an earlier
period cross-fertilization by the pollen of other flowers through the agency of insects.
In Hypericum perforatwm, which may be chosen as our example, the pistil is encom-
passed by a number of filiform filaments of unequal lengths, so arranged that the
longest are in close proximity to the central pistil and the shortest near the peri-
phery of the flower. The anthers do not liberate their pollen simultaneously, but
one group does so after another. Dehiscence takes place first in the short stamens,
next in those of median size, and last of all in the long ones. As soon as an anther
opens, the filament bearing it inclines inwards, and thus one after another, the
short, median, and long filaments stand up and approach the middle of the flower.
It being only the anthers of the longest stamens that are on the same level as the
stigmas, autogamy cannot occur till quite at the last, not long before the flower
withers.

The widely-distributed Star of Bethlehem (Ornithogalum wmbellatwm) exhibits
on the opening of the flower six stamens arranged in two whorls with three in each
whorl. The stamens of the inner whorl are the longer, and their anthers dehisce
a day sooner than the others. All six filaments look erect in the newly-opened
tlower, but are really sloped slightly outwards, with the result that the anthers are
separated by an interval of about 3 mm. from the small stigma in the middle of
the flower. So long as they maintain this position the pollen cannot be directly
deposited upon the stigma, and the aim of the flower at this stage is to secure cross-
fertilization through the intervention of honey-seeking insects. Towards the end
of the flower’s period of bloom both the long and the short stamens approach the
centre, but only the anthers of the three shorter ones are applied to the stigma and
besmear it with pollen; the other three do not come into contact with the stigma
owing to their standing at a higher level. Thus the Star of Bethlehem differs from
the cases previously described in that it devotes the pollen of the shorter stamens
to autogamy and those of the longer stamens to heterogamy (cross-pollination).
This is partly due to the circumstance that the anthers of the three longer stamens

AUTOGAMY BY MOVEMENTS OF STAMENS. 341

are placed just in front of the approach to the nectaries of the ovary and in such a
position are certain to be brushed by insects, whilst no honey is to be found behind
the anthers of the three shorter stamens, and insects, therefore, make no attempt to
enter past them. These anthers, consequently, retain their pollen, and when the
flower is nearly over yield it up for the purpose of autogamy.

A curious contrivance is exhibited by Aphyllanthes Monspeliensis, a plant
indigenous to Southern Europe. Like the Star of Bethlehem, it has three long and
three short erect stamens in each flower, and the anthers are not at first in contact
with the stigma. But before the final closing of the perianth all the stamens slope
towards the stigma, which is subdivided into six lobes, three at the top and three
lower down, so that the pollen of the three shorter stamens is deposited on the lower
stigmatic lobes, and soon afterwards that of the three longer stamens is deposited
on the three upper stigmatic lobes.

In many plants where all the stamens are of the same length, and where the
anthers are already on the same level as the stigma at the time when the flower
opens, the process of autogamy is essentially identical with that above described.
The anthers are held by erect filaments at a little distance from the stigma, but
later on, after various movements have been accomplished by the filaments, they
adhere to the stigma and deposit their pollen upon it. This is the case, for instance,
in Paris quadrifolia, in several species of Scilla, in Chelidonium and Remeria, in
Samolus Valerandi, in Androsace elongata, A. maxima and A. septentrionalis, in
Lysimachia nemorum and in Swertia perennis and 8. punctata. It is not possible
here to discuss all these plants individually, and only a few points in connection
with them will be referred to. In the Herb Paris (Paris quadrifolia) the period
during which each flower remains open is very long. The stiff stamens at first
stand out radially, but later they describe an angle of 80° towards the middle of
the flower, where they converge over the pistil and press their anthers upon the
stigmas. In the plants of the order Primulacee—viz. Samolus Valerandi, Androsace
elongata, A. maxima, and A. septentrionalis—the corolla is salver-shaped, and the
short filaments, which are adnate to the tube of the corolla, only need to incline
slightly towards the axis in order to transfer their pollen to the stigma in the
same flower. The majority of these plants are protogynous; the flowers of Swertia
perennis and S. punctata alone are markedly protandrous. There is, therefore, in
the case of the latter no chance of eross-fertilization at the beginning of the period
of flowering, the stigma being still closed. On the other hand, pollen is available for
transport by insects to flowers that happen to be at a later stage of development.
The next step is for the stigma to open and so dispose its two lobes that flies
arriving with a supply of pollen from younger blossoms are obliged to effect eross-
fertilization. To prevent restriction or frustration of this process of heterogamy,
and also to ensure the preservation of some pollen for autogamy in the opposite
case of an absence of insect-visitors, the five stamens bend outwards simultaneously
with the opening of the stigma, exserting their anthers and hiding them under the
stellately-expanded petals. If no insects come, and cross-fertilization is therefore

342 AUTOGAMY.

excluded, the filaments straighten themselves again and then move like the hands
of a clock towards the middle of the flower, where they press their anthers, which
still retain a little pollen, upon the stigma.

The stamens, which are instrumental in effecting autogamy by movements of
inclination in the direction of the stigma, are straight at the commencement of the
period of flowering in all the plants above enumerated. Sometimes they curve

Mi
Fig. 296.—Autogamy effected by the inclination of curved stamens,

2

1 Pseudo-hermaphrodite male flowers of the Venus’ Comb (Scandia Pecten-Veneris). 2, 3, 4 Successive positions assumed by the
true hermaphrodite flowers of the Venus’ Comb at first with a view to cross-fertilization, afterwards with a view to autogamy.
5, 6, 7 Successive positions assumed by the true hermaphrodite flowers of the Fool's Parsley (Ethusa Cynapium) at first
with a view to cross-fertilization, afterwards with a view to autogamy. All the figures magnified.

outwards for a short time, but before the flower fades, and particularly at the
moment of autogamy, they are invariably erect again.

There is, however, another group of plants to be considered in which the
filaments are already inflexed in the bud, and continue so at the time when pollen
from the anthers at their extremities is deposited upon the adjacent stigmas.
The most important examples of plants exhibiting this autogamy by means of
an inclination of inflexed filaments are afforded by several annual Umbellifers
with protogynous flowers (#thusa Cynapium, Caucalis daucoides, Scandia Pecten-
Veneris, Turgenia latifolia, &e.). Two kinds of flowers are associated together
in the umbels of the Venus’ Comb (Scandix Pecten-Veneris; see fig. 296% * 4),

AUTOGAMY BY MOVEMENTS OF STAMENS. 343

namely, pseudo-hermaphrodite (cf. p. 294) male flowers (fig. 2961) and true her-
maphrodite flowers (figs. 296 %%*). The latter open earlier than the former,
which, indeed, never come into play until the hermaphrodite flowers have cast
both stamens and petals. Directly the petals open in the hermaphrodite flowers
a finely-granulated honey-secreting dise and two short styles are revealed in the
middle of the flower. The stigmas at the extremities of the styles are already
mature, but the stamens are incurved like hooks and have their anthers still closed
(fig. 296°). The day after, also, when the petals have opened further back and

Fig. 297.—Autogamy effected by inclination of curved stamens.

1 Circea alpina. * A newly-opened flower of Circ@a alpina with the front petal removed. 3, 4 The same flower at a later stage
of development. 5 Fruit of Circewa alpina. ® Agrimonia Eupatoria. 7,8, 9, 10 Successive phases of a flower of Agrimonia
Eupatoria, which is at first adapted to heterogamy (cross-pollination) and subsequently to autogamy. 11 Young fruit of
Agrimonia Eupatoria. 1, °, ! natural size; the rest of the figures magnified.

the filaments have straightened out (fig. 296 °), the anthers surrounding the stigma
in a circle are still closed, so that pollination can only take place at this period in
the event of insects bringing pollen from other flowers. The anthers and filaments
have, however, now entered upon an active phase. The curved stamens bend
successively at short intervals, one after the other (after one has started, the next
to follow is the stamen next but one to the left, and so on till all have done)
towards the centre of the flower, bringing their anthers, which have meanwhile
undergone dehiscence and are covered with pollen, into contact with the stigmas
precisely in the manner shown in fig. 2964. Each stamen only stays a short time
in this position, and then executes a backward movement and makes way for the
next in order. When all the stamens have accomplished these evolutions, they as
well as the petals become detached and fall to the ground. The secretion of honey

344 AUTOGAMY.

on the rough surface of the pad of tissue in the middle of the flower ceases, the
pollinated stigmas turn brown, and the period of bloom for that partieular flower
comes to an end. The imperfect staminiferous flowers do not unfold until all the
hermaphrodite flowers are over, a fact which can only be interpreted as indicating
that their pollen is to be devoted to the fertilization of protogynous hermaphrodite
flowers of other individuals which are still in the first stage of flowering. Fool’s
Parsley (Bthusa Oynapium, see figs. 296 % &7) differs from the Venus’ Comb and
the other annual Umbellifers above referred to in that all the flowers of an umbel
are hermaphrodite, and that the filaments, which in the bud are tucked in like
springs (fig. 296°), not only straighten out when the flower opens, but elongate,
and thus raise the anthers to a higher level than the stigma. Also in Fool’s Parsley,
as has been mentioned before, the anthers are not laid right against the stigmas,
but remain a little higher, and let their pollen fall upon them from above (see
fig. 2967). This at least is what I saw in the case of the common Fool’s Parsley or
Athusa Cynapium; the small Zthusa segetalis, on the other hand, according to
my observation, much more frequently brings its anthers into contact with the
stigmas in the same manner as the Venus’ Comb (see fig. 296 *).

Autogamy of the same type as that described in the above instances of annual
Umbellifers also takes place in many small-flowered Bed-straws (e.g. Galiwm infes-
tum, G. Mollugo, G. tricorne), in the Dodder (Cuscuta), in the Alpine Enchanter’s
Nightshade (Circea alpina), and in Agrimony (Agrimonia Eupatoria). Of the
Enchanter’s Nightshade (see figs. 29714234), it is only needful to note that the
number of stamens is limited to two, and that sometimes one anther alone is laid
upon the stigma (297°), but not infrequently both subserve the purpose of auto-
gamy in that manner (297). In the latter case the stigma looks as if it were
grasped by the two limbs of a pair of tongs. The flowers of Agrimony have from
12 to 20 stamens, and are protogynous. The anther-filaments are very slightly
incurved, each corresponding to about a sixth part of the circumference of a circle
(fig. 2977), but as soon as dehiscence takes place the filaments bend one after
another towards the centre of the flower (see fig. 297°) until they are in the form
of semicircles, and some of the anthers covered with pollen come into direct contact
with the stigmas, which are still in a receptive condition (fig. 297°). Soon after the
stigmas have thus been furnished with pollen the anthers drop off the filaments,
and the latter coil up still more as is shown in fig. 297 ™.

Several species of Stonecrop (e.g. Sedum annuum, 8. atratum, 8. dasyphyllum),
and some House-leeks (e.g. Sempervivum montanum, S. Ruthenicum) have two
kinds of stamens in each flower, namely, those inserted in front of the sepals and
those inserted opposite the petals. The anthers of the former are the first to open,
and as they are quite close to the stigmas only a slight inclination of the curved
filament is necessary to bring about autogamy. After a deposition of pollen upon
the stigmas has already taken place, the filaments opposite the petals also curve
over inwards, and the anthers, which meantime have undergone dehiscence, are
held right over the stigmas. But, seeing that the latter are by this time withered

AUTOGAMY BY MOVEMENTS OF STAMENS. 345

and have no further need of pollen, we are bound to infer that this fresh supply is
offered for the purpose of effecting by insects’ aid the fertilization of other flowers
in which there is as yet no available pollen although the stigmas are accessible and
mature. Opuntias and all the numerous species of the Rose genus (Rosa) behave in
a similar manner. In them also some of the anthers devote their pollen to auto-
gamy, whilst the others devote theirs to eross-fertilization. The filiform filaments
are curved and of unequal lengths. The anthers borne by the innermost whorl of
filaments open first, but their pollen is of no use for autogamy, notwithstanding the
proximity of the stigmas, because the anthers are lower than the stigmas and do
not spontaneously come into contact with them. Only the filaments of the outer-
most whorl are of the right length, and these alone curve over and lean towards the
middle of the flower until their anthers rest immediately upon the stigmas. As,
however, these anthers are the last to dehisce, autogamy does not ensue till the very
last moment of flowering; for the whole of the time up till now the flower is
adapted to eross-fertilization only.

In a number of Ranunculaces, such as Anemone Hepatica, A. Transsylvanica,
Ranunculus alpestris, R. acer, and R. montanus, the structure of the flowers
resembles to a certain extent that of Roses. A group of pistils with short styles
and almost sessile stigmas rises up in the middle of the flower, and is surrounded by
a large number of stamens which are arranged in several whorls and are in their
turn encompassed by the petaloid sepals. The flowers are protogynous, and at the
commencement of their period of bloom can only undergo eross-fertilization through
the agency of insects. At a subsequent stage also after the dehiscence of the
anthers of the outer whorl and the exposure of their adhesive pollen, the flowers are
still adapted to heterogamy; for the distance of these anthers from the stigmas is
comparatively great, and insects always alight on the group of carpels in the centre
and make their way from them over the anthers to the circumference, whence they
again take flight in order to visit another flower. But by degrees the stamens of
the inner whorl also mature; the filaments, which hitherto have been very short,
grow considerably and curve inwards, laying upon the stigmas their anthers which
have meanwhile burst open, The sepals of these Ranunculacez close up when it
begins to get dark, and the flowers assume a nodding position owing to a slight
inflection of their pedicels. It might be supposed that these movements also are
accessory to autogamy, and, as a matter of fact, in many other Ranunculacez, which
will be the subject of discussion later on, such co-operation does occur; but, in the
Anemones and Ranunculuses above referred to, no supplementary action of the kind
is necessary, and the closing and nodding of the flowers in wet weather and during
the night are resorted to merely with the object of protecting the pollen from
moisture.

To this long list of plants with protogynous flowers must now be added a few
protandrous species from the genera Gypsophila, Saaifraga, and Cuphea. The
flower of Gypsophila repens contains ten stamens, of which five are inserted in front
of the sepals and five in front of the petals. In the bud they are all tucked in like

346 AUTOGAMY

hooks; in the open flower they are straight and slope outwards. Contact with the
central stigmas, which meanwhile have become mature, is impossible so long as the
stamens maintain the latter position; but shortly before the flower fades, the stamens
become inflexed, and their anthers are thus brought against the stigmas. The
Saxifrages also have two circles of stamens in each flower. In the species of the
sub-genus Cymbalaria (Sazifraga Cymbalaria, S. Huetiana, &e.), the first to
straighten out are those standing opposite the sepals. Their anthers open and
display their pollen at a time when the adjacent stigmas are closed together, and
are not as yet capable of taking up pollen. This supply of pollen is not therefore
used for autogamy, but is obviously available for crossing with other flowers.
After exposing their pollen one after another in definite order for a couple of days,
these stamens incline outwards and let their anthers fall. The styles, now, for the
first time, move asunder, and their stigmas become capable of receiving pollen. As
the anthers of the stamens opposite the sepals have dropped off, and those of the
stamens opposite the petals are still closed, the stigmas are only liable at this stage
in the development of the flower to be dusted with pollen from other flowers or
other plants. Eventually signs of vitality are also exhibited by the stamens
opposite the petals. They become strongly inflexed, their anthers dehisce, and, the
stigmas being still receptive, the period of the flower’s duration is brought to a close
by the anthers being pressed against the stigmatic surface and effecting autogamy.
The same sort of thing is observed in the case of the protandrous flowers of several
species of the genus Cwphea, as, for instance, in Cuphea eminens. These flowers,
of which mention has already been made on p. 235 (figured on p. 237), face sideways
and contain eleven stamens of varying length whose anthers are disposed in two
irregular rows above the expanded calyx-tube. The style is short at the commence-
ment of flowering, and is concealed, together with the immature stigma, underneath
the anthers. Dehiscence occurs on the upper faces of the anthers which are turned
away from the style, and the pollen issuing from the sutures is fated by its position
to be rubbed off by honey-sucking insects, and to be eventually used for cross-
fertilization. Two days later the style, which has in the meantime increased in
length some 11 mm., projects above the stamens, bringing the stigma into the line
of entrance to the honey (fig. 262°, p. 237). Should insects now visit the flower,
bringing with them foreign pollen, cross-fertilization is certain to ensue. But, in
the event of an absence of insects, the longest stamen bends up to the stigma and
presses that face of the anther which is coated with pollen against the stigma.

The degree of inflection of the filaments in the cases hitherto described scarcely
corresponds to the third of the circumference of a circle, and is but seldom actually
spiral. But that more pronounced movements of inflection do oceur for the purpose
of effecting autogamy, is shown by the case of Nicandra, a plant belonging to the
Solanacex, and that of Calandrinia compressa, belonging to the order Portulacez.
In Vicandra the long filaments bend down to the extent of at least a semicircle
to reach the stigma in the event of a failure of pollen from extraneous sources, and
in the ephemeral flowers of Calandrinia compressa, the filiform filaments curve

AUTOGAMY BY SHORTENING OF PISTIL. 347

gently away from the velvety stigma at 9 A.M. %.e. shortly after the expansion of
the petals, whilst three or fours hours later, when the petals close up again, they
undergo spiral inflection from right to left and lay their anthers upon the stigmas.

The cases in which the stigmas are the agents in the operation of transfer to
themselves of pollen from the anthers of the same flower may be classed in two
divisions, (1) those in which a direct contact between the stigma and the anthers is
effected by some definite bending or other movement of particular parts of the
pistil; and (2) those in which the pollen is first deposited by the anthers and stored
in some part of the flower other than the stigma; ultimately the stigmatic tissue is
brought in contact with it in the same manner as in (1), i.e. by some movement on
the part of the pistil.

The cases comprised in the first division fall naturally into four groups.

To the first group belong all those in which autogamy is produced by contraction
of the style. The Cactiform plants of the Mexican plateaux, in particular, various
species of the genera Cereus, Echinopsis, and Mammillaria, exhibit in their flowers a
number of filiform stamens, arranged in a close spiral around the passage leading to
the honey secreted on the floral receptacle. In the midst of this thicket of stamens
stands a long style which terminates in a stellate stigma. The anthers are already
covered with pollen when the petals unfold, but the stigma, which projects consider-
ably beyond the anthers, is still closed, its fleshy lobes being coherent and forming
a kind of elub, so that there can be no possibility of its being dusted with pollen.
Thus the flowers are markedly protandrous, and the pollen liberated during the first
part of their period of bloom can only be used for cross-fertilization. The next step
is the opening of the stigma and spreading out of its lobes into a star in front of the
entrance to the nectary. Insects now alighting are obliged to brush against the
stigma before they can get at the nectar, and in so doing they deposit a portion of
the store of foreign pollen with which they are laden upon the stigma and initiate a
process of cross-fertilization. This stage may last a few hours only, or several days,
or over a week, according to the species. When the term of the flower’s duration is
nearly reached the style contracts in length, and the stigma, which has hitherto been
above the anthers, is drawn into the midst of them, so that it cannot fail to get
covered with the pollen, of which there still remains a quantity clinging to the
anthers. In Cereus dasyacanthus the stigma soon after the opening of the flower
projects 1 em. beyond the anthers. The length of the style bearing the stigma is at
that time 20 cm. When the flower is nearly over, the style is only 16°5 em. long,
and the stigma is therefore drawn in through a space of 3°5 em. and no longer
surmounts the stamens, but, on the contrary, is 25 cm. lower than the anthers
of the longest stamens.

The second group includes all cases where autogamy is brought about by an
elongation of the ovary or the style. Epimedium alpinum, a native of the warm
valleys of the Southern Alps, has four sepals arranged crosswise and beneath these
—the flowers being partially inverted as shown in figs. 2984%%—four petals
fashioned like little slippers and containing an abundance of honey in their blunt

348 AUTOGAMY.

saccate interiors. The ovary is spindle-shaped, and bears at the end of a short style
a stigma covered with little papille. The stamens, four in number, rest with their
dorsal surfaces in contact with the ovary; their anthers face outwards, are lanceolate
in shape, and each carries on its apex a small foliaceous scale like the point of a
spear (see fig. 298*). The flowers are protogynous, or, in other words, the papillose
stigma, which is hemmed in by the four scales just referred to, is already mature at
a time when the anthers are still closed (fig. 2981). At this stage the stigma may
be dusted with pollen from other flowers. The next step is the dehiscence of the
bilocular anthers, which takes place in a very peculiar manner. The wall of each
anther-half which faces outwards becomes detached, and is lifted up in the form of
a flap with the whole of the pollen of the corresponding cavity sticking to its inner
surface. The two flaps then shrivel and roll up, with the originally internal surface
outside, until the only point of attachment is just below the pointed scale at the
apex of the anther; the free flaps arch over this foliaceous anther tip (fig. 298°),
and also over the stigma, which is close to the scale (fig. 298°). The process is simul-
taneous in all four anthers, the result being that the stigma is roofed over by a vault
composed of eight curved flaps, and as the exposed surfaces of the latter are thickly
coated with pollen, the whole arch presents externally a continuous covering of that
material (see fig. 2987). Should insects now visit the flower to obtain the honey
stored in the slipper-shaped petals they must brush past this pollen-covered vault;
nor can they fail to be besmeared at the very spot where at a previous stage in the
flower’s development they would have had to brush against the stigma. This con-
dition of affairs lasts usually for two days. In the meantime changes affecting the
pistil are taking place which, notwithstanding their inconspicuous nature, are of the
greatest importance in relation to the eventual accomplishment of autogamy. If the
stigma is not dusted by insects with foreign pollen at the first expansion of the
flower the pistil now elongates sufficiently to raise the stigma into the vaulted cavity
just described; and as the flaps composing the vault curl up still more (fig. 298 °)
as the flower approaches its end, the stigma must inevitably come into contact
with the pollen adherent to them (ef. fig. 298°).

A similar process is observed to take place in several Cruciferze, of which the
Charlock (Sinapsis arvensis) is a typical instance. The flowers of this plant are
protogynous. The bud opens early in the morning, revealing still closed anthers
with their faces turned inwards (¢ntrorse), whilst the stigma is already mature and
projecting somewhat above the anthers. At this stage of development no pollen
except what is brought by insects can be deposited on the stigma. A day later the
flower presents quite a different appearance. The four longer stamens have stretched
and curved a little away from the axis, and the anthers are lifted above the stigma.
By a rapidly executed twisting of the filaments the anthers have been turned round
so as to face outwards, and extrorse sutural dehiscence has meantime taken place.
The stigma is completely withdrawn from observation, and is also safe from any
possibility of being dusted with pollen, for the anthers in the same flower have
turned away their pollen-coated faces, nor is it possible for any extraneous pollen

AUTOGAMY BY ELONGATION OF PISTIL. 349

that may happen to be brought by insects to be transferred to the stigma, owing to
the anthers forming a hood over it. At this stage every other object is subordinated
to the dispersion, through the agency of insects, of the pollen exposed by the flower.
After the interval of another day the observer finds a third aspect of the flower pre-
sented to him. The filaments have straightened themselves out, and so brought the
anthers nearer to the stigma; the coating of pollen has spread all over the anthers,

Fig. 298.—Autogamy brought about by elongation of the pistil.

1, 2,3 Flower of Epimedium alpinum at successive stages of development, showing primary adaptation to cross-fertilization
and subsequent adaptation to self-fertilization. 4 Front view of a closed anther. 5 Side view of the same. The front
(right-hand) wall of each of the two loculi has become detached and been raised up as a flap or valve. ® The same anther;
the flap has curled up more tightly and now forms a sort of cowl arching over the spear-like apex. 1,2,3 x10; 4,5, 6 x25.

and the ovary has undergone elongation, carrying the stigma into the midst of the
dome of anthers, where it becomes thickly overlaid with pollen

Again, in the nodding flowers of Atragene alpina, and in these of Clematis
integrifolia, which grows freely in the swampy meadows of the Hungarian plains,
we find autogamy effected by means of an advance of the pistil into proximity to
the anthers laden with pollen. Both plants are protogynous—the stigmas being
mature for a short time before the anthers dehisce—and in both the newly-opened

350 AUTOGAMY.

flowers are adapted to eross-fertilization. The stamens lie one upon another like the
tiles of a roof, and together form a short tube at the bottom of which are a number
of closely-clustered carpels, whilst at the free edge of the tube the anthers expose
their store of pollen. The first anthers to open are those pertaining to the outer-
most and longest stamens, the next belong to those of median length, and the last
to the shortest, which are in the immediate vicinity of the carpels. The pollen of
the outermost anthers serves mainly for cross-fertilization, and can hardly ever be
used for autogamy on account of its position; but even in the case of the latest
anthers belonging to the shortest stamens, no pollen could reach the stigmas were
it not for the elongation of the carpels, which occurs during the last two days of the
flower’s duration. The anthers still contain pollen at this late period, and a quantity
adheres, besides, to the silky hairs clothing their filaments, so that the slightly
divergent stigmas get covered with an abundant supply of pollen as the carpels
lengthen and push them up through the pollen-coated tube (see fig. 246°, p. 174).

The flowers of the Lady’s Mantle (Alchemilla vulgaris) are likewise protogynous.
When a flower opens, the anthers of the four short stamens are still closed, whilst
the stigma is already mature, and is seen in the middle of the flower projecting
through and slightly above a kind of diaphragm which is stretched across the floral
interior and secretes honey. At this stage cross-fertilization alone is possible; but
in the course of twenty-four hours the style grows in an oblique direction, until its
extremity bearing the stigma strikes against one of the four anthers, which have
meanwhile undergone transverse dehiscence; it thus receives a sprinkling of pollen
(see fig. 226°, p. 125). The pollen of the three other anthers is still available for
transference by flies to the stigmas of other flowers.

The above are a few instances of the methods in which autogamy is effected by
elongation of the style or of the entire pistil. Taken generally this process must
be classed among the rarer forms of the phenomenon, though it is surprising that
it should be so considering the frequency of autogamy by means of the elongation
of stamens. The accomplishment of autogamy through the inclination of a style
otherwise straight is of even less usual occurrence. The most striking example of
this process is afforded by the bilabiate flowers of the North American Collinsonia
Canadensis. In the newly-opened blossom the long style stands midway between
two exserted stamens which are almost as long as the style. Towards the end of
the flower’s period of blossom, the style begins to slope towards one of the stamens,
moving like the hand of a clock through an angle of from 20° to 40° until its stigma
comes against the pollen-covered anther borne by the stamen in question.

A much more common method of bringing about autogamy is for parts of the
pistil—usually the style—to bend so as either to bring the stigmas into direct
contact with the anthers belonging to the same flower, or to place them in such a
position beneath the anthers as to ensure their catching any pollen that may fall
out of the loculi. The direction of the style’s inflection depends upon the form and
mode of insertion of the flower, and more particularly on the position assumed by
the anthers. The flowers of the Great Mullein (Verbaseum Thapsus), of the Corn-

AUTOGAMY BY THE BENDING OF THE PISTIL. 351

salad (Valerianella Auricula, V. carinata, &e.), and of the non-twining species of
Honeysuckle (Lonicera alpigena, L. nigra, L. Xylostewm) are protogynous, and the
style is so placed when the corolla opens that its stigma must of necessity be brushed
by insects as they make their way to the receptacle. There is evidently at this stage
no possibility of any but cross-fertilization. Later on, when the anthers open and
expose their pollen, the stigma is taken quite out of the way, the style becoming
bent downwards or to one side, so that the stigma cannot come into contact with
anthers of the same flowers either spontaneously or through the agency of insects.
Not till the flowering period is nearly over does the style return to its original
position; when this happens, the stigma is raised by the straightening up of the
style, and is pressed against the anthers, which are still coated with pollen. The

flowers of the Martagon Lily (Liliwm Martagon) are nodding, and have their
7 6

Fig. 299.—Autogamy effected by means of an inflection of the style.

4 Flower of Tricyrtes pilosa in the first stage of its development. 2 The same in the last stage of development. 3 Flower of
Morina Persica in the first stage of development. #4 The same in the last stage of development. 5 Stigma of Morina
covered with pollen from anthers belonging to the same flower. © Flower of Euphrasia minima in the first stage of
development. 7 The same in the last stage of development. All the figures slightly magnified. In figs. 2, 8, 4, Sand 7 the
front part of the flower is cut away

perianth-lobes strongly reflexed. In each petal there is a groove which is roofed
over and closed in the middle by two coalescing rims, so that the honey stored in
the groove can only be sucked out by insects at the two extremities where the
groove is open. The flowers are protogynous, and, when they are newly open, the
style is straight and holds its stigma in such a position that it is sure to be touched
by insects sucking honey from the inner orifice of the groove. As the anthers are
still closed at this stage, only foreign pollen can be affixed to the stigma. Subse-
quently dehiscence ensues, and the position of the anthers in front of the external
orifice of the groove ensures their pollen being brushed off by insects trying to suck
the honey at that end, whilst the stigma is left untouched by them. In this second
stage of the flower’s development the style begins to bend a little to one side, and,
towards the end, the curvature increases to such an extent that the stigma comes
into contact with one or sometimes two of the anthers, and dusts itself with pollen.
Often enough, it is true, the stigma misses its mark, and in consequence autogamy
is not so certain to occur in the Martagon Lily as in most of the other cases. It

352 AUTOGAMY.

must also be noted that the infleetion of the style only takes place should the stigma
have not previously been supplied with extraneous pollen. If there has been eross-
pollination at the commencement of flowering the inflection either does not oceur at
all or is so trifling as to be of no significance.

The transference of pollen to the stigma by means of a bending down of the
style is observed in various species of Trieyrtes, Morina, Enothera, and Epilobium,
in several Rhinanthacez, Caryophyllacex, and Ranunculacew, and in most of the
Malvacex. The flowers of Trieyrtes pilosa, of which figures are given above, are
protogynous. Each of the three styles is bent down, and has a bifurcated extremity,
so that it looks not unlike a claw. The stigmatic tissue is situated at the end of
the claw, and is brushed by insects on their alighting to suck honey from the saccate
bases of the perianth-segments. The free extremities of the filaments curve down
in semicircles, and the anthers are suspended under the claws of the style (fig. 299 *).
At the time when the anthers have their pollen exposed they are so situated as to
stand in the way of insects coming in quest of honey. Without the assistance of
insects there could be no transference of pollen to the stigma so long as stigmas and
anthers remained in the same relative positions, and the flower remained upright.
But the chance of insects not visiting the flower is provided for by a downward
bending of the claws of the style, which continues until the stigmatic tissue at their
extremities comes into direct contact with the pollen-coated anthers (see fig. 299 *).

The process above described takes place in the course of a week in T’rieyrtes
pilosa, but in Morina Persica, one of the Dipsacez (see figs. 299% #5), it is all
accomplished within a few hours. The difference between the times at which
stigmas and anthers respectively attain maturity in Morina is scarcely half an
hour, but even this short interval suffices to render cross-fertilization possible
during the first stage of flowering, whilst in the second stage autogamy obtains. All
the species of the genus Morina—including Morina Persica, the type here selected
for illustration—unfold their flowers at dusk. As soon as the corolla-limb expands
the thick pulvinate stigma becomes visible in the middle of the flower just above
the entrance to the honey. The receptive tissue is on the upper surface of the
stigma, The two anthers are stationed behind the stigma, and when insects insert
their probosces into the long honey-filled tube of the corolla they are certain to
effeet cross-fertilization, provided they have previously visited flowers at a some-
what later stage of development. In the case of other plants whose flowers open
in the morning it would be scarcely likely that insects should alight immediately
after the opening of the passage to the honey, but the flowers of Morina are
adapted to erepuscular and nocturnal moths, which only have two or three hours of
darkness in which to get the honey, and must, therefore, make great haste and
employ the whole of the time if they are not to fail in their quest. As a matter of
fact the moths in question leave their haunts within a quarter of an hour of the
time when the flowers of Morina open, and one may be sure that wherever Sphin-
gids and Noctuz with probosces 3 or 4 centimetres in length abound, one or more
will come flying to suck the honey as soon as the floral receptacle becomes acces-

AUTOGAMY BY THE BENDING OF THE PISTIL. 353

sible. Thus, dichogamy, involving hardly half-an-hour’s interval between the
attainment of maturity in stigmas and anthers respectively, is sufficient to ensure
cross-fertilization at the commencement of the period of bloom in each flower of
this kind of night-flowering plant. A further adaptation with a view to hetero-
gamy is shown in the position of the stigma in front of the anther in the first stage
of floral development (see fig. 299°). On the intrusion of insects—Sphingide,
Noetus, &c.—into the interior of the flower the large stigma is the first object
encountered, and next to it come the anthers, and there is therefore a possibility
that even during the time that the anthers are open and have their pollen exposed
cross-fertilization may take place through the agency of insects. If, however, no
insects visit the flower the style bends down the very next morning in an open
curve and lays the stigma flat upon the anthers (see fig. 299*). The pollen readily
adheres to the surface of the stigma, as may be seen by removing that organ after
it has become appressed to the anthers, when a thick layer of pollen will be found
sticking to it (fig. 299°).

Inflections of the style-in all respects similar to those exhibited in Morina occur
in the flowers of numerous Rhinanthacex, eg. in Rhinanthus minor, Trixago
apula, Melampyrum pratense, Ewphrasia minima (see figs. 299° and 299°). In
these plants we find, in general, a repetition of the entire process above described,
except for the circumstance that the pollen is not adhesive but mealy, and is not
transferred to the receptive tissue by appression of the stigma to the anthers—it
being sufficient to place the stigma under the anthers by means of an inflection of
the style. The stamens in this case are of the sugar-tongs type (cf. p. 271). In
the first and second stages of floral development the mealy pollen only falls out of
the anthers on the occasions when the stiff filaments of the stamens are forced apart
by insects. Should no insects visit the flower the pollen remains in the loculi. In
the third stage of flowering the filaments become flaccid, as does also the portion of
the corolla adjacent to them, and in consequence the anthers, which have hitherto
been closely coherent, move a little apart from one another and let the pollen fall
out. Meanwhile the style has bent down sufficiently to bring the viscid stigma
under the front pair of anthers, so that a portion of the pollen is caught upon its
glistening surface, with the result that autogamy is effected (see fig. 2997). It is
not uncommon for the inflection of the upper third of the style to be so strong as
to amount to an involution, and the stigma is then pushed between the disuniting
anthers and comes into contact with the hairs which clothe the anthers, and which
are usually powdered all over with pollen.

Trieyrtes, Morina, and the Rhinanthacex just mentioned, are all protogynous,
whilst on the other hand, the Evening-primrose, Willow-herb, Campion, and Mal-
low, in which autogamy likewise occurs in consequence of the style bending down
to the anthers, are protandrous. When the petals of the Evening-primrose (@no-
thera biennis, (E, mwricata, &e.), or of the large-flowered species of Willow-herb
(Epilobium hirsutum, E. angustifolium, see fig. 300) expand, the four branches of

the style, which bear the receptive tissue and constitute the stigmas, are closely
Vou. II. 73

,

354 AUTOGAMY.

coherent, whilst a further condition, which would also render pollination impossible,
consists in a lateral inclination or sharp inflection of the style which removes the
stigma out of the way leading to the honey. The eight anthers then stand in front
of the spots where honey is to be obtained, and liberate their pollen in turn. A
little later—half an hour in Evening-primroses, and 24 hours in the large-flowered
species of Willow-herb—the style straightens itself and takes up a central position

in the flower, whilst its four

branches open back and present
themselves in the form of a
cross in front of the entrance to
the honey. The stigmas remain
in this position for a short time,
and there is no need to enter
into more detail to make it evi-
dent that cross-pollination may
now be effected by the humble-
bees which come in search of
honey and bring with them a
store of pollen from younger
flowers. Soon afterwards, the
four stigmas bend or roll back,
bringing their receptive tissue
into contact with the pollen still
adhering to the anthers (see
fig. 300, the lower flowers). This
act of autogamy is usually pro-
moted also by the stamens becom-
ing rather more erect and by an
inflection of the stalk-like infe-
rior ovary in a gentle curve to-
wards the ground, the result of

Fig. 300.—Autogamy in the flowers of the Willow-herb - =
(Epilobium angustifolium). which is that the flowers nod,

i.e. are half-inverted.

Of the Ranunculacez, a few species of Love-in-a-mist (Nigella) exhibit the same
kind of contrivance. The flowers are protandrous. The first event to take place
after the expansion of the sepals is a bending of the stamens in regular sequence
towards the periphery of the flower, whereby the open anthers are posted just
above the nectaries full of honey. Insects coming in search of honey must inevitably
rub against the anthers in that position and dust themselves with the pollen.
After the stamens have all accomplished these movements, the styles, which have
hitherto stood stiffly erect and stationary, enter upon an active phase and bend
outwards until their terminally-placed stigmatic tissue, which, meantime, has be-
come mature, rests over the nectaries. In this position the stigmas are certain to

AUTOGAMY BY THE BENDING OF THE PISTIL. 355

be dusted with pollen from younger flowers brought by the insects which come in
search of honey. The process of outward inflection of the styles is, however, not
yet completed, but continues until the stigmas strike against the anthers and take
from them some of the pollen still clinging to their surfaces.

There are also some caryophyllaceous plants (Lychnis alpina, Alsine Gerardi,
Cerastium arvense, C.lanatum, Stellaria graminea, S. Holostea) which exhibit, just
before the flowers wither, inflections enabling the stigmas to possess themselves of
the pollen of the anthers in the same flower. The flowers are incompletely protan-
drous. First of all, the stamens inserted opposite the sepals come to maturity while
the stigmas in the same flower are still incapable of receiving pollen. The pollen
offered by these stamens can therefore only be used for cross-fertilization. The
next day their filaments bend as far as possible towards the periphery of the flower,
and many of them lose their anthers. Meanwhile, the stamens standing opposite
the petals grow longer and their anthers dehisce so that their pollen also is ren-
dered available for transference by insects. A day later these stamens bend
slightly towards the periphery of the flower, but they never lose their anthers,
which continue to offer their pollen till the flower withers. On the fourth day the
styles, which have hitherto stood in the middle of the flower, separate from one
another, curve over backwards, and, in some species, become twisted into spirals.
The stigmas are thus brought into contact with the anthers last mentioned and take
up some of the pollen with which they are covered.

In the Caryophyllacese whose names are given above the inflections of stamens
and styles take four or five days; in Mallows (Malva borealis, M. rotundifolia,
&c.) the same processes are completed within 48 hours, and in Hibiscus Trionum,
and in Abutilon Avicenne within from three to eight hours. When the flower of a
Mallow is just open a sheaf of filaments bearing round anthers covered with pollen
may be seen enveloping and roofing over the styles. Soon after, however, the fila-
ments of which the sheaf is composed become reflexed and a bundle of styles is
then seen occupying the place previously filled by the stamens. The stigmatic
tissue has matured in the meantime. The parts of the flower do not remain
long in this position, which is obviously adapted to eross-fertilization by insect
agency; the styles coil into the shape of an S and at the same time bend down
until the fringe of papills constituting the stigmatic tissue comes into contact with
the pollen of the anthers which have shortly before been lowered by the inflection
of their filaments. In Abutilon Avicenne, which grows abundantly in Hungary
on the banks of the river Theiss, the sheaf of filaments does not at any time form a
roof over the style, but, from the moment the petals unclose, five slender styles,
terminating in spherical red stigmas with velvety surfaces, may be seen projecting
above the anthers. Insects alighting upon the velvety stigmas or brushing against
them may cause heterogamy at this period; but a couple of hours later the styles
curve down, and the stigmas are appressed to the anthers which are covered with
an abundant store of pollen. Other Malvacez, e.g. Anoda hastata, behave in an
opposite manner as regards the inflection of the style. In the buds of these plants

356 AUTOGAMY.

both filaments and styles are sharply bent over towards the floral receptacle. After
the expansion of the petals, the filaments straighten out and together constitute a
sheaf of filiform stalks, each of which bears an anther covered with pollen. A little
later it is the turn of the styles to become erect. They perform the same move-
ments as have previously been executed by the stamens, and push themselves into
the midst of the stamens. By these evolutions the stigmas of the longer styles are
placed a little above the anthers, whilst those of the shorter styles are brought into
direct contact with the anthers, and take from them some of the pollen of which
there is always a certain quantity left so that autogamy invariably ensues.

The method of self-fertilization adopted by the Sun-dew (Drosera) is somewhat
like that just described. In Drosera the spherical ovary supports three styles, each
of which divides into two spatulate lobes bearing the stigmatic tissue on their
upper surfaces. The open flower is cup-shaped, and in it these lobes may be seen
spread out horizontally like the spokes of a wheel (see fig. 279", p. 279). The
stamens, on the other hand, are erect, and cross the lobes at right angles, holding
the anthers above the stigmatic tissue. As soon as the petals begin to close, the
stigmatic lobes rise up until they touch the anthers.

In several Labiates and Lentibulariacee autogamy is dependent on inflections,
not of the style but of the stigma. This occurs, for instance, in the Hemp-Nettle
(Galeopsis ochroleuca, G. Tetrahit, &e.), where the flowers are protandrous, and so
adapted as to ensure cross-fertilization in the event of insects visting them.
Towards the end of the flower’s period of bloom the stigmatie extremity of the
lower arm of the style bends downwards and backwards until it touches the pollen-
coated anthers of the longer stamens; in the case of many species of the Wound-
wort genus (Stachys palustris, S. sylvatica, &e.) both stigmatic arms bend down
a short time before the flower fades and take the pollen from the anthers. The
flowers of the Butterwort (Pinguicula; see vol. i. plate II. p. 142), which face
sideways, contain two ascending stamens terminating in patelliform anthers, and
above them an egg-shaped ovary surmounted by a large lobate sessile stigma. The
lower border of the stigma which bears the receptive tissue hangs down like a cur-
tain over the anthers. Insects, in the act of inserting their probosces into the
honey-containing spur, brush first against this stigmatic border, and next against
the anthers behind it. Thus they dust the stigma with the pollen they bring from
other flowers, and the next moment load themselves with a fresh store which they
carry off to yet other plants. The conditions are, in the first instance, adapted to
eross-fertilization, and very frequently this form of reproduction occurs in the
plants in question; but if no insects visit a flower the pendent stigmatic border rolls
up sufficiently to bring the receptive tissue against the anthers. There being still
plenty of pollen on the anthers, autogamy is then certain to ensue. The same
phenomena may be observed in flowers of the Bladder-wort (Utricularia), and
probably in those of the majority of Lentibulariacez.

A comparatively rare method of autogamy is for both filaments and style to coil
up in spirals and become entangled just before the flower fades, the stigmas being

AUTOGAMY BY COILING OF STAMENS AND PISTIL. 357

brought in the process of involution into contact with the pollen of one or more
anthers. Most of the plants which exhibit this curious phenomenon have the
common property of being ephemeral, but they belong to most different families.
In a number of Commelynacew—Commelyna cwlestis, for example (see fig. 301)—
the stigma is situated in front of and lower than the anthers when the flower,
which faces sideways, is quite newly open (fig. 301"). Honey is secreted on curious
palmately-lobed nectaries, and if in this first period of the flower’s development
insects come in quest of the honey they make use of the anthers to alight on, and
in so doing besmear themselves with the pollen, which is already emerging through
the lateral sutures of dehiscence of the anthers. Soon afterwards the stamens
become spirally coiled, and the style, which meanwhile has grown to the same
length as the stamens, curves in such a manner as to bring the stigma to a some-
what higher position than it previously occupied, and to make it the most con-

Fig. 301.—Autogamy by means of spiral twistings of stamens and style.

1 Flower of Commelyna ceelestis in its first stage. 2 In its second stage. % In its third stage of development. All in
longitudinal section and slightly magnified.

venient place for insects to settle upon (fig. 3017). The arrival of insects which
have visited younger flowers is at this stage sure to be accompanied by cross-fer-
tilization. This state of affairs, however, only lasts a very short time. The style
then winds itself into a spiral, and becomes entangled with the coiled stamens, with
the inevitable result that the stigma comes into contact with one or other of the
anthers, and gets covered with pollen (fig. 301°). The whole process occurs in
almost exactly the same manner in the flowers of Allionia violacea, of Mirabilis
Jalapa, and several other Nyctaginacew. As regards Allionia violacea, it is only
necessary to observe that the flowers are protogynous, that the stigma is higher
than the anthers at 6 am., when the flower opens, that a few hours later the
anthers are raised to a higher level than the stigma in consequence of certain pecu-
liar movements of the style and stamens, and that by 10 o'clock the involution of
the filaments resulting in autogamy has already begun. In the newly-opened
flower of the Marvel of Peru (Mirabilis Jalapa) the dot-like stigma is situated in
front of the anthers, and in the event of insects coming in search of honey, it is first
the papille of the stigma and afterwards the anthers that are touched by the
intruders. No raising and lowering of filaments or style takes place in this case,

358 AUTOGAMY.

but a process of involution like that exhibited in Allionia ensues, and as soon as
autogamy has been initiated the limb of the perianth folds up, turns pulpy, and
then forms a kind of stopper above the knot of twisted filaments and style. The
flowers of the Purslane (Portulaca oleracea) differ from those of Commelyna, Allio-
nia, and Mirabilis in having five stigmas which are like delicate feathers in form,
and are spread out in a star in the middle of the erect flower-cup. The stamens
project obliquely from the receptacle, and are arranged in a circle round the stigma;
but when the flower opens first, there are little spaces between anthers and stig-
mas, and this prevents a spontaneous transference of pollen to the stigmas. After
the lapse of a few hours the petals, which in the sunshine are expanded in the form
of a cup, draw together, and the flower begins to close up; all the five feathery
stigmas bend over to the same side and gradually coil up into spirals. The thread-like
stamens also undergo inflection, at first into semicircles, and subsequently into
spirals, and the pollen-coated anthers are in consequence pressed against the stig-
mas. At this period, in the Purslane as in the Marvel of Peru and other plants
whose flowers are ephemeral, the petals may be seen in a pulpy condition covering
over the knot of tangled filaments.

As has been said before, this form of autogamy occurs chiefly in flowers which
last only a single day. Where the whole period during which the flower is open is
but a few hours the movements in question may all be followed by the observer.
In the few species, which resemble the foregoing in respect of autogamy, but differ
from them in that their flowers remain open two or three days, or even longer,
these movements of inflection and torsion take place much more slowly. Thrifts
(Armeria alpina, A. vulgaris, &e.) display in the middle of each of their cup-
shaped flowers five stigmas disposed in the same manner as those of Purslane-
flowers. The stigmas in this case, however, are not feathery, but in the form of
slender cylinders covered with short, closely-packed papille, which give them a
velvety appearance. The stamens are adnate to the short corolla-tube, and rise
up in front of the petals holding their anthers between the rays of the stigma.
Notwithstanding the proximity of the anthers to the stigmas, neither in the first
nor in the second stage of the flower’s development is any pollen transferred, with-
out extraneous aid, to the receptive stigmatic tissue. At first the stamens are so
placed as to have their anthers brushed by insects visiting the flower, whilst the five
stigmas are still erect. A little later the anthers and stigmas change places as in
so many other cases; the stamens stand up and bring the anthers together nearer
the middle of the flower, whilst the stigmas diverge from one another, and place
themselves close to the way leading to the honey. Attention has been so often
directed to the connection between an interchange of position of this kind and
the accomplishment of cross-fertilization that it is needless to repeat the facts of
the case. Supposing, however, that insects do not visit the flower, and that, in
consequence, heterogamy fails, the styles wind themselves up spirally, and move at
the same time towards the middle of the flower, where they become entangled with
the filaments, which have likewise undergone spiral torsion. In these eircum-

AUTOGAMY BY A CONTRACTION OF STYLE-BRANCHES. 359

stances, the velvety stigmas cannot fail to receive the pollen that still adheres to
the anthers.

It appears from what has been said concerning autogamy that in a large number
of plants the pollen developed in the anthers, especially if it be of the adhesive
variety, still oceupies the recesses of the anthers, or sticks to the reflexed margins
of the lobes after their dehiscence, at the time when the flower fades. Even after
insects have brushed off a portion of the pollen and transported it to other flowers,
there is still invariably an abundant supply for the purpose of autogamy, and it is
only in rare eases that loculi, in which adhesive pollen has been matured, are com-
pletely emptied by the end of the flowering period. In some plants, however, the
adhesive pollen is swept out or removed in some other way from the anthers by
means of special contrivances as soon as it is mature, and is then deposited on some
particular spot in the flower where it is exposed for dispersal. In the case of the
pollen of Composites it is well-known that it is pushed out of the tube of connate
anthers by the style, owing to the growth of the latter organ which is sheathed
within the anther-tube, and that it appears at the top of the tube in the form of a
lump capping the extremity of the style. In Bell-flowers (Campanula), the entire
contents of the anthers are stored upon the surface of the style, and the same thing
happens in the various species of the Rampion genus (Phytewma) and in some small-
flowered Gentians. The shrivelling of the anthers is in many plants the cause of
their shedding a portion of their pollen, and it may then collect on capillary append-
ages of the ovary, in cup-shaped petals, or on some other part of the flower where it
is stored up for future use. It must often happen, too, that when insects are in the
act of taking the honey they push against the stamens, and that the pollen shaken
out of the anthers by their impact adheres to particular parts of the corolla, calyx,
or perianth. This pollen is just as available for fertilizing purposes as that which
remains sticking to the anthers, and we meet with cases where the stigmas fetch the
pollen developed in the same flower from its temporary resting-place, and so bring
about autogamy. Contrivances for this purpose are not numerous, but the number
of species in which this form of autogamy prevails is extremely large. The abstrac-
tion of pollen deposited on the outer surface of the stylar column or its arms by
stigmatic tissue situated on the edges or the inner surface of these style-branches
occurs in hundreds of Campanulas and thousands of Composites, and shall therefore
be chosen as our first example of this type of process.

Two modes of operation may be distinguished : first, a crossing; and, secondly, a
spiral revolution of the style-branches. The former process is observed particularly
in the Asteroidee (Aster, Bellidiastrum, Erigeron, Solidago), especially in the
tubular flowers in the middle of the capitula of these plants; but it is also seen in
many Composites possessing ligulate flowers only. In Aster alpinus, the species
selected for illustration (see figs. 302 »%®), the stylar arms are short and thickish;
their inner surfaces are smooth and flat, whilst their outer surfaces are a little
arched, and towards the free extremities are furnished with papilla-like sweeping-
hairs. The receptive stigmatic tissue is situated on the margins of the style-

360 AUTOGAMY.

branches below the sweeping-hairs, and may be recognized by the granulated
appearance of its turgescent cells. The behaviour of the stylar branches from the
commencement to the termination of a flower’s bloom is shown in fig. 3021, where
the three tubular florets are in successive stages of development. Almost simul-
taneously with the opening of the tubular corolla the two style-branches are pushed
up above the anther-tube, and the pollen is swept out of the tube by the hairs pre-
viously referred to. The style-branches at this period are in close contact, and the
receptive tissue of the stigmas is not yet accessible (fig. 3021, left-hand floret).

Fig. 302.—Autogamy by means of a crossing or a bending back of the style-branches.

1 Aster alpinus. Portion of a capitulum, including a marginal female floret with ligulate corolla and three tubular florets of
the disc. The latter are in the successive stages which lead to autogamy (left to right). 2 Style-branches of Aster alpinus
which have just separated but still have some pollen clinging to their hairs. 3 The style-branches crossed so as to transfer
the pollen from the collecting-hairs of the one to the stigmatic tissue of the other. 4, 5, $ Florets from the centre of a
capitulum of Centaurea montana in successive stages leading to autogamy. 7 The two style-branches rolled back suffi-
ciently to bring the stigmatic tissue into contact with the pollen on the collecting-hairs. ® Campanula persicifolia;
longitudinal section through a newly-opened flower. ® The same with the style-branches rolled back so as to bring the
stigmatic tissue into contact with the pollen on the exterior surface of the stylarcolumn. 1° Flower of Phyteuma orbiculare
in process of transition from the first to the second stage of development. 11 The same flower in the last stage of develop-
ment. 8, ® natural size; the rest magnified.

Neither cross- nor self-fertilization of the flower in question can at present be
effected, and the pollen is only exposed that it may be carried away by insects to
fertilize other blossoms. The two style-branches are subsequently lifted still
higher and move a little apart, with the result that the pollen clinging to their
hairs, if not already removed by insects, is for the most part pushed off, falls down,
and is appropriated to the purpose of geitonogamy (see p. 321). A small remnant of
pollen is, however, invariably left hanging to the lower collecting-hairs, and this it

AUTOGAMY BY THE BENDING BACK OF STYLE-BRANCHES. 361

is which is devoted to autogamy (see fig. 302°). The process of self-pollination is
the last to take place. The two style-branches bend and cross one another, and in
so doing bring the pollen adhering to the lower hairs of the one arm into immediate
contact with the receptive tissue on the margin of the other arm. In this position
the two style-branches resemble the beak of a eross-bill, as may be seen in fig. 302°.
The style-branches of those Composites whose capitula consist entirely of ligulate
florets, are always much longer than those of the Asteroidew; they are of thread-like
appearance, and the lower parts of their external surfaces are beset with collecting-
hairs. In one section of these Composites, including, for instance, Crepis grandiflora,
Hieracium umbellatum, and Leontodon hastile, there is likewise, shortly before the
flowers fade, a simultaneous inflection and spiral involution of the two branches of
the style resulting in autogamy; it reminds one, even more forcibly than the case
of Asteroidex, of the action of a person when he crosses his arms.

The second kind of process, viz. the spiral re-volution or bending back of the
style-branches, may be particularly well seen in the Groundsels—Senecio Fuchsii
and S. nemorensis—and in Centaureas. We will select as an example Centawrea
montana (see figs. 302%%®%?), which grows abundantly in the lower Alps. The
styles are fashioned quite differently from those of the composite flowers to which
reference has been made above. The stigmatic tissue is spread out over the inner
surface of the style-branches, especially over the part near the free extremity, and
the collecting-hairs are confined to a narrow zone underneath the point of bifurca-
tion of the style. The pollen is swept out of the anther-tube (see fig. 3024) in the
same manner as in the other Composites, but in Centawrea the process of extru-
sion is accelerated by a sudden contraction of the irritable filaments of the stamens
when they are touched by insects (cf. p. 252). After most of the extruded pollen
has been removed by insects or scattered by the divergence of the style-branches
(fig. 302°), the receptive inner faces of the latter are so disposed as to ensure cross-
pollination in the event of insects coming laden with pollen from other capitula.
This state of affairs, however, only lasts a short time; the two style-branches soon
roll back and bring the receptive tissue of their originally inner faces into contact
with the pollen left upon the hairs, thus effecting autogamy (see figs. 302° and 3027).

Bell-flowers (Campanula) exhibit for the most part the same bending back of
the style-branches, and the phenomenon has the same significance in them as in
composite flowers, but the manner in which the pollen is transferred to the external
surface of the style is somewhat different. Within the closed bud the long anthers
are adjacent to the central column of the style, as in Composite, and form a kind of
tube round it. These anthers open inwards, too, and deposit the whole of their
pollen on the outside of the style, which is furnished with delicate transparent
papille, and is in consequence well adapted to the retention of the pollen. The
pollen is not, however, swept out of the tube of anthers, but the anthers, after
depositing their pollen upon the stylar column, separate from one another and
shrivel up, and only persist as shrunk and empty relies at the bottom of the flower
(see fig. 302°). The style-branches are by this time divergent, and occupy a posi-

362 AUTOGAMY.

tion in the mouth of the corolla, which necessitates contact between the receptive
tissue at their tips and the bodies of the humble or hive bees, which find their way
to the flower in search of honey. If these insect-visitors bring with them pollen
from other flowers, cross-fertilization is inevitable. As they push lower down into
the flower, the bees receive an additional load of pollen from the stylar column, the
surface of which is coated with it, and this new store they may convey to other
blossoms. When the time for the flower to fade is near at hand, the style-arms
become revolute, and press the receptive tissue of their tips upon the stylar column,
taking from it a coating of pollen, of which there is still a sufficient quantity cling-
ing to the surface (see fig. 302°). The large-flowered Campanula persicifolia has
been selected as a type of these Bell-flowers. The style-arms in this species are
from 1 em. to 1'6 em. long, and they coil into spirals of from 1} to 2 involutions.
In most of the other Bell-flowers (e.g. C. barbata, C. carpatica, C. pyramidalis, C.
Rapunculus, C. spicata) the revolute style-branches have only from 1 to 1} coils in
each spiral, whilst in some few (e.g. C. patula, C. rapunculoides) there are rather
more than 2 complete coils in each. The Rampion genus (Phytewma), here exempli-
fied by Phyteuma orbiculare (see figs. 302!" and 30211), differs from the Bell-flowers,
which are its nearest allies, in the circumstance that the deposition of pollen and
retraction of the emptied anthers occurs at a time when the tips of the petals are
still connate into a tube. For a short time the end of the stylar column may be
seen covered with pollen projecting beyond the corolla, and in this position the two
arms disunite and expose their stigmatic tips to pollination by insects (see fig. 302 1°).
If no insects visit the flower the style-branches roll back and bring their tips into
contact with the pollen on the stylar column (see fig. 302"). In all the species that
have been examined (Phytewma confusum, P. hemisphericum, P. Halleri, P.
orbieulare, P. spicatwm) the style-branches are wound into from 1 to 2 complete
coils. In the case of Phytewma Halleri the further observation was made, that
after the accomplishment of autogamy the transparent hairs on the stylar column
and the pollen adherent to them rapidly dry up, whilst the branches of the style
unroll again.

Of the Gentians, the little Gentiana prostyata, which grows on the mountains
in the vicinity of the Brenner Pass in Tyrol, affords a striking example of the
phenomenon in question. The flowers are protandrous; the anthers in the bud are
contiguous to the short style and closed stigma, and, when they open, their pollen
is deposited upon those organs. Upon the expansion of the corolla, the pollen is
available for other flowers through the agency of insects. Somewhat later the
stigmatic lobes part, and if after this insects visit the flower, they brush against the
receptive spots of the stigma, and may dust them with extraneous pollen. Lastly,
the two stigmatic lobes curl back until the receptive tissue upon their upper sur-
faces reaches the residue of pollen still sticking to the short style.

Much less common modes of operation are for the revolute stigmas to take the
pollen from the edge of the tube of connate anthers, from hairs on the corolla, from
bristles on the pappus, or from depressions in the petals. The case of abstraction

AUTOGAMY BY THE BENDING BACK OF STYLE-BRANCHES 363

of pollen by stigmas from the edge of the anther-tube I observed in several Com-
posites, as, for instance, in the species of the genera Adenostyles and Cacalia, and
in Arnica montana. The external surface of the style in Adenostyles is beset with
papilla, which give it the rough glandular appearance whence it derives its name of
Adenostyles (= glandular style); it has no collecting-hairs, and the pollen is therefore
not swept but squeezed out of the anther-tube. The edge of the tube is furnished
with prongs, each of which is slightly revolute and is concave almost to the extent
of being boat-shaped, so that it is able to retain some of the extruded pollen. This
pollen is only used for autogamy in the event of the stigmas not being dusted in
any other way. In that case the two style-branches roll back until the receptive

Fig. 303.—Autogamy effected by means of an inflection of the style-branches.

1, 2,3 Flowers of Arnica montana in successive stages leading to autogamy. 4Style-branches of Arnica in contact shortly after
their extrusion from the anther-tube. Pollen is clinging to the collecting-hairs and to the mouth of the tube. 5 The style-
branches projecting still further from the tube and diverging from one another. $ The style-branches curved back so as
to bring the stigmatic tissue into contact with the pollen sticking to the tube of anthers. 7, ®, 9 Flowers of Senecio viscosus
in the successive stages of development leading to autogamy. 10 A revolute style-branch of Senecio viscosus with its
stigmatic tissue in contact with the pollen sticking to the bristles of the pappus. All the figures magnified.

tissue comes into contact with the edge of the anther-tube. The style-branches in
Arnica montana (see figs. 3031%% 45°) have collecting-hairs on the surface of
their slightly-thickened tips only, and in this case the pollen is regularly swept out
(figs. 303’ and 303*). A small quantity of the pollen is always left behind upon
the 5-toothed edge of the anther-tube. The manner in which the pollen is trans-
ferred to the stigmatic tissue by means of the re-volution of the style-arms is shown
in the accompanying figure 303°.

As illustrations of the abstraction of pollen from the hairs of the corolla we may
take a campanulate, a labiate, and two caryophyllaceous species. The corolla of
the Nettle-leaved Bell-flower (Campanula Tracheliwm) has a thick coating of hairs
on its inner surface. In the bud these hairs are directed horizontally towards the
axis, and touch the style and the anthers. The deposition of the pollen upon the
stylar column takes place in the same way as it does in the Bell-flowers already

364 AUTOGAMY.

discussed (see p. 361), but the moment the anthers are retracted some pollen is
invariably caught by the hairs of the corolla, and when the flower opens a portion
of the pollen is always to be seen adhering to them. The humble and hive bees
which visit the flower may, of course, bring about cross-fertilization, just as they
do in the other Bell-flowers. The style-branches in Campanula Tracheliwm do
not, at the close of the flowering period, roll back so far as the central column; a
less degree of bending is here adequate to bring the receptive tissue on the tips of
the style into contact with the pollen sticking to the hairs.

In Dianthus neglectus, a species of Pink indigenous to the Southern Alps, and
in the Glacier Pink (Dianthus glacialis), the laminz of the petals are beset with
hairs. The pollen is first exposed to the chance of dispersal by insects, but after-
wards the stamens curve outwards, and some of the pollen becomes affixed to the
hairs of the petals, which usually receive in addition a small deposit as a result of
the scattering action of insect-visitors. The flowers are protandrous. The stigmas,
which are situated in front of the entrance to the floral interior, wait till the period
of the flower’s bloom is nearly at an end, for the chance of being touched by insects
bearing extraneous pollen. But sometimes no insects come, and in that case the
pollen stored upon the hairy lamin® of the petals is made use of at the last
moment. The transparent papillose stigmas wind themselves into the shape of the
letter S, and, sweeping like a brush over the petals, collect the pollen from them.
This operation is materially assisted in both the Pinks under discussion by the fact
that the lamin® of the petals grow some millimetres longer during the flowering
period, the result of which is to bring the hairs besmeared with pollen a little nearer
to the stigmas. In Dianthus neglectus there is besides an involution and uprising
of the lamin in the evening, which, likewise, assist the process of sweeping up the
pollen by the stigmas.

In Ballota nigra, a Labiate with protandrous flowers which grows commonly in
hedges on cultivated land, some of the pollen falls at the very commencement of the
flower’s bloom upon the hairs clothing the borders of the upper lip. If no pollen is
brought by insects to the stigma of a flower of this plant, the lower style-arm bends
down at the end of the flowering period and takes up the pollen from the hairy
mantle above referred to. The same kind of thing happens in a few other Labiates,
as, for instance, in Salvia viridis, of the Mediterranean flora, whose style bends
down in the event of a failure of insects, and brings the stigma into contact with a
store of pollen resting upon the under-lip, where it fell at the very commencement
of the flower’s bloom. I have hitherto observed only in the cases of Tozzia alpina
and Pyrola media the phenomenon of a style curving down to take pollen from
cup-shaped hollows in the corolla in which it has lain stored, but it probably occurs
in many other plants besides.

The curious case of the pollen being taken from the hairs of the so-called pappus
by the stigma is illustrated in figs. 3037%%%1° In the Stinking Groundsel (Senecio
viscosus), which will serve for an example, the style-branches are furnished at the
tips only with bunches of collecting-hairs. As the style elongates these hairs sweep

AUTOGAMY THROUGH AGENCY OF COROLLA. 365

the pollen out of the tube of anthers and leave it in a round lump at the top of the
tube (see fig. 303°), whence it may be carried off by insects. At this stage the
corolla and the hairs of the pappus are 6 mm. long. Soon afterwards the two style-
branches, which have undergone rapid elongation, part asunder, and the pollen, if
not already removed by insects, is shaken off, and falls on to the pappus-hairs,
where it is caught by the asperities on their surfaces (see fig. 303°). The receptive
tissue on the inner faces of the style-branches, which are now the upper surfaces,
are in a position to get dusted with pollen brought by insects from other flowers.
Meanwhile an elongation of every part of the flower has taken place; the pappus-
hairs have attained a length of 7 mm., and the corolla of 65 mm. Lastly, the
flower enters upon its third stage of development. The two style-branches curve
down, bringing the stigmatie tissue into contact with the pollen sticking to the
pappus-hairs, which have by that time grown another millimetre, and are therefore
reached all the more easily, as they even project above the arms of the style (see
figs. 303° and 303 7°).

In all the cases hitherto dealt with the only parts of the flower which are con-
cerned in bringing about autogamy are the stamens and pistils. The filaments in
some instances, the parts bearing stigmatic tissue in others, undergo inclination or
inflection, whilst sometimes both organs mutually approach one another. No direet
part in the process of autogamy is taken in any of these plants by the whorls of
petals surrounding the stamens. We will now proceed to describe cases in which
the petals are instrumental in effecting self-fertilization.

The simplest case of the discharge of this function by petals is to be found in
flowers which are in the shape of tubes, cups, or basins, and whose anthers are
adnate to the inner surfaces of the petals, and are brought into contact with the
stigma in consequence of a contraction or closing together of the corolla—Thymelea
Passerina, a low shrub belonging to the Thymelacez, will serve as an example.
The small inconspicuous flowers of this species contain nectar, and by its perfume
attract insects which brush pollen from the anthers as they suck the honey and
convey it to the stigmas of other flowers. The anthers are adnate to the inner face
of the cup-shaped perianth, and are at first at a distance of only $ mm. from the
stigmas. Notwithstanding this proximity the viscid pollen is not spontaneously
transferred to the adjacent stigma when the flower is first open. It is not till the
flower is nearly over that a slight contraction of the upper third of the perianth
causes the anthers to be pressed against the stigma, which stands at the same level
as themselves. In Claytonia perfoliata, one of the Portulacex, autogamy is effected
in the same manner, the only difference being that the anthers are borne on special
filiform filaments which are adnate to the bases of the petals. These filaments,
however, share in all the petals’ movements, and the anthers at their extremities
are pressed exactly upon the stigma when the corolla closes up.

In other cases the epipetalous stamens hold their anthers at the commencement
of the flowering period underneath or behind the stigmas, and are pushed upwards
during the flowering period by an elongation of the petals, in consequence of which

366 AUTOGAMY.

they rest in the last stage against the lateral edges of the stigmas. This process is
very common in plants of the order Solanacew (Hyoscyamus, Lyeiwm, Nicotiana,
Physalis, Scopolia), and it has also been observed in Gentianacex® (e.g. Erythrea
pulchella, Gentiana campestris, @. glacialis). In some of these plants the elonga-
tion undergone by the corolla-tube is very considerable as compared with the size
of the flower. In the American Tobacco plant (Nicotiana Tabacwm) it amounts to
nearly $ cm., whilst in the little Centaury (Zrythrea) it is only 2mm. The elon-
gation of the corolla-tube is accompanied in most instances by a stretching of the
filaments. In consequence of this combined growth the anthers are, in the case of
the short-styled flowers of Lyeiwm barbarum, raised 4 em. in 24 hours. In the
Henbane (Hyoscyamus niger) the anthers are 7 mm. lower than the stigma in the
morning when the flower is nearly open, but by the evening of the same day the
simultaneous elongation of the corolla-tube and of the stamens adnate to it has
raised the anthers to the level of the stigma and pressed them upon it. It is scarcely
necessary to mention that in these plants, which are all protogynous, cross-fertiliza-
tion is possible in the first part of the flowering period, and it is as a matter of fact
very frequently effected through the intervention of insects.

A very curious variety of the phenomenon in question is exhibited by the large-
flowered species of the Eyebright genus (Euphrasia Rostkoviana, E. versicolor,
E. speciosa), and by the allied Yellow Rattles (Rhinanthus angustifolius and R.
hirsutus). The flowers of these plants face sideways, and the corolla has a tri-lobed
under lip and a bi-lobed helmet-shaped upper lip. Four stamens of the pollen-
sprinkling type, which we have compared to sugar-tongs, are adnate to the corolla-
tube. The anthers are concealed beneath the upper lip; the long filiform style is
in the shape of the letter S and lies above the anthers, and when the flower is first
open it projects considerably beyond them (see fig. 277%, p. 273). Stigma and
anthers are then so placed as to make it inevitable that imsects which enter the
flower shall first touch the stigma, and the next moment become dusted with a
shower of pollen from the anthers. If several blossoms are visited in succession
eross-fertilization is certain to take place. If, however, insects stop away, the tube
of the corolla elongates and carries up with it the epipetalous stamens. As the
style retains its original length, the terminal stigma, which hitherto has projected in
front of the anthers, now rests by the side of the anthers or just above them. Thus
the stigma is in a sense overtaken by the anthers. In the large-flowered species of
Eyebright the tense style then presses upon the anthers, forces them asunder, and,
sinking down, brings its stigma between the anther-valves, where it cannot fail to
get coated with the pollen of which they are still full. In the species of Yellow
Rattle above mentioned, the stamens become flaccid towards the end of the flower’s
period of bloom and the pollen falls out and is left sticking to the hairs of the
anthers or to the involute folds of the corolla, so that the style in brushing by
usually removes it.

It is much less common for the calyx to play this part in bringing about
autogamy. Tellima grandiflora, a North American Saxifragacea, is the only case

AUTOGAMY BY THE FALLING OF THE COROLLA, 367

known at present in which the stigma after being at first rather higher than the
anthers is overtaken by them and besmeared with pollen owing to an elongation of
the calyx and consequent raising of the stamens, which are adnate to the tube of
the calyx.

In many plants autogamy depends upon the fact that as the corolla falls off, its
tube slips over the stigma, so that the latter rubs against the anthers, which are
still laden with pollen, or against the inside of the corolla, which is also besmeared
with that substance. This process presupposes that when the flower is in full
bloom the anthers are overtopped by the stigma, and that the latter is still in a
receptive condition at the time the corolla becomes detached and drops. Both these
conditions are as a fact fulfilled in all plants of this category. In the species of the
genus Gilea (Polemoniace»), and in the Brazilian plant Psychotria lewcocephala
(Rubiaceze), the long filiform styles branch into divergent arms, which bear the
delicate stigmatic tissue; and at the period of full bloom, these style-arms project
far above both the limb of the corolla and the anthers. Consequently, insects
alighting on these flowers encounter first of all the stigmas, and if they are laden
with foreign pollen they occasion cross-fertilization. There is, on the other hand,
in this form and position of the stigmas the further advantage, that, in case of a
dearth of insect-visitors, the stigma may still acquire a supply of pollen when the
corolla falls off—that is, at the very last moment of flowering. It is not unusual in
these plants to see the corolla, after it has become detached, hanging for quite a
long time from the long style and divergent stigmas, and this delay in the process of
severance must materially assist the accomplishment of autogamy. The detached
corolla persists in a similar manner in flowers with capitate, or short-lobed stigmas,
as, for instance, in Rhododendron hirsutum, in Digitalis, Anchusa, Cestrwm, and
various other Scrophulariacez, Boraginacex, and Solanacex. In the case of Rhodo-
dendron hirsutum, as the corolla slips along the style, the stigma brushes off the
pollen, which has invariably been discharged from the anthers before the flower
opens and been caught upon the hairs in the interior of the corolla-tube. In
Cestrum aurantiacum, the anthers, which are borne upon stiff and slightly-inflexed
filaments, are pressed against the style, and the corolla is left hanging from the
style, usually for a couple of days after its detachment, and does not fall till after
fertilization has taken place, when the style also drops off. A great variety of con-
trivances exists with the object of promoting this method of autogamy by means of
a falling corolla. A brief account of three of them will now be given. The flower
of the Moth Mullein (Verbascwm Blattaria), which may be taken as the type of a
large number of flowers of Serophulariaces, has a corolla with a very short tube
and the limb spread out at right angles to it (rotate). Adnate to the tube are five
stamens clothed with woolly hairs of a violet colour. The three upper stamens are
a little shorter than the two lower ones, and all of them project obliquely beyond
the limb of the corolla. The central style is still further exserted, and serves as a
perch for insects to alight upon. It is obvious that so long as the parts of the
flower are disposed in this manner every insect which arrives with a supply cf

368 AUTOGAMY.

pollen must effect cross-pollination. As in so many other cases, autogamy is re-
served for the last moment of bloom. With a view to its ultimate achievement, the
two longer filaments cross themselves over the mouth of the corolla-tube in some-
what the same attitude as a pair of folded arms. This brings their two anthers,
which are still full of the orange-coloured pollen, behind the stigma. The corolla
now becomes detached from the receptacle and falls forward, but remains for a
short time suspended to the long style, where it undergoes slight torsion. Finally,
it drops with a gyratory motion, and as it does so the stigma must inevitably be
brushed by one or other of the anthers lying in front of the mouth of the flower.
The Pimpernel (Anagallis), which belongs to the order Primulacex, has a corolla
resembling that of the Moth Mullein in being rotate and in containing five stamens
clothed with violet hairs. The stamens in this case are very long, and the style is
bent to one side, and passes between two of the stamens. Thus the stigma is out of
reach of the anthers, and cannot, in the first stage of the flower’s development, be
dusted with their pollen. On the other hand, cross-fertilization may be effected by
the small insects which creep over the flat limb of the corolla in order to feed on
the hairs of the stamens. The flowers of the Pimpernel belong to the category of
those in which the corolla opens and shuts periodically. The operation of closing is
due to the expanded limb being thrown into superincumbent folds. On the second
occasion of the flower’s closing, the anthers come into contact with the part of the
corolla that is folded in, and leave some of their pollen sticking to it. This pollen
is still to be seen adhering to the inner face of the corolla on the following day,
when the limb expands again, and there it remains till the evening, when the
corolla closes for the third time. After this the corolla does not open any more,
but falls off still closed, and, as it does so, brushes the style, which is held between
two stamens, and leaves upon the stigma the pollen that was sticking to its inner
surface. Again, there is the case of Soldanella alpina, to which we have already
several times had occasion to refer in other connections, and also as affording an
instance of a second form of autogamy (p. 333) besides that now in question. The
style stands up in the form of a column in the middle of the bell-shaped corolla, and
has the five stamens close to it. The anthers are united into a cone, and act as
sprinklers in the dispersion of their pollen. When an insect pushes into a flower it
rubs first against the stigma, and dusts it with foreign pollen, and as it forces its
way further in it displaces the various parts composing the cone of anthers, and is
consequently besprinkled with pollen. If no insects visit the flower the anthers are
still full of pollen when the time comes for the corolla to drop off, and as the style
is drawn through the dislocated cone of anthers, the pollen in the interior of the
latter is caught up by the stigma, and self-fertilization is effected.

Next to these plants, in which autogamy takes place on the fall of the corolla
owing to its tube slipping over the stigma, there comes a group of species in which
the same result is attained in the following manner. At the time when the flower
opens, the petals are slightly smeared with pollen, and this deposit forms a reserve
store. Should the stigma not have received any pollen from extraneous sources, the

AUTOGAMY BY THE CLOSING OF THE COROLLA. 369

flower being nearly over, certain movements are undergone by the petals which
result in the transference of the pollen sticking to their surfaces, margins, lobes, or
folds, as the case may be, to it. The instances of this mode of effecting autogamy
are very numerous, and it will be best to class them in small sub-groups, and to
take a well-known example from each as an illustration.

In Argemone, Hypecoum, and Specularia, which will serve as types of the first
group, there is no considerable elongation of the pollen-flecked petals during the

Fig. 304.—Autogamy effected by the petals.

1 Flower of Argemone Mexicana open in the sunshine. Pollen which has fallen from the anthers is resting upon the concave
petals. 2 The same flower closed; one of the petals besmeared with pollen is laid upon the stigma; the front petal is
removed. * Closed flower of Hypecoum grandiflorum, natural size. *Thesame magnified. 5 Longitudinal section through
the open flower in the first stage of development. $ Open flower in which the pollen-laden lobes of the inner petals are
beginning to separate. 7 The same flower at a later stage. ® One of the two inner petals; the middle lobe is coated with
pollen; at its base is the pit containing the honey. ° Longitudinal section through a closed flower in its last stage of
development. 1° Specularia speculum; longitudinal section through an open flower in the first stage. 11 Transverse
section through a elosed flower in the first stage. !2 Longitudinal section through an open flower in the second stage.
18 Closed flower. 14 Transverse section through a closed flower in the second stage. 15 Longitudinal section through an
open flower in che last stage. 1° Transverse section through a closed flower in the last stage. 1,2, 3 natural size; the rest
magnified.

period of the flower's bloom. This period is only a single day in the case of Arge-
mone, and the process takes place in a very simple manner. In the morning, as
soon as the petals are wide open and the tension of the sheaf of stamens surround-

ing the pistil is somewhat relaxed, there is an immediate fall of pollen on to the

concave surfaces of the petals (see fig. 304"). The flowers are erect, as also is
Vor. IL. 74

370 AUTOGAMY.

the pistil, and the stellate stigma, which offers the best alighting place for insects,
rests at a slightly higher level than the anthers, and at a sufficient horizontal dis-
tance from them to prevent their pollen from reaching, spontaneously, its receptive
tissue. In the course of the day insects arrive with pollen from other blossoms and
cause cross-pollination. When the evening comes the petals close up over the
pistil, and one of them brings its inner surface, which is covered with pollen, into
direct contact with the stigma (see fig. 304”).

The case of the Hypecowm is far more complicated. The flowers of this plant
have two small sepals and four large tri-lobed petals (see figs. 304° and 304%). The
latter are arranged in two pairs at right angles to one another, one pair being
inserted a little higher than the other. The middle lobe of each of the petals
belonging to the upper pair is curiously modified; its surface is concave, and in the
young flower has the shape of a spoon with fringed edges. The function of these
lobes is to collect all the pollen from the anthers at the very commencement of
flowering. The anthers are, like those of Composite, coherent into a tube inclosing
the style; but instead of opening inwards as the latter do, they are extrorse, i.e.
dehisce outwards. At the time of dehiscence and of the discharge of the pollen the
two spoon- or pouch-shaped central lobes of the upper petals are in close proximity
to the anthers, and they receive the whole of the pollen (see fig. 304°). After this
transfer has been accomplished the two lobes now containing the pollen separate
from one another, the first parts to disunite being the free extremities at the top,
then the lateral edges (see fig. 304°). The pollen is thus exposed and may be
carried off by insects which come for the honey concealed in a little depression at
the base of each lobe (fig. 304°). The two linear stigmas being in close contact
at this stage, their tissue is not as yet accessible; they do not disunite till two
days after the first opening of the flower, but when that interval has elapsed they
diverge, and then constitute the most convenient place for insects to settle upon.
‘They are now in exactly the same position as was previously occupied by the
pollen-laden lobes (see fig. 3047), and therefore if an insect alights upon them after
visiting younger flowers, it is sure to dust the stigmatic tissue with foreign pollen.
Meantime the petal-lobes which received the pollen become much more reflexed,
especially at their lateral edges; the back of each lobe, which was originally convex,
is now deeply concave like a boat, and the whole structure is in a manner turned
inside out. The direction of the two divergent stigmas is at right angles to the two
upper petals, and their tips point towards the median line of the two outer ones.
In consequence of this arrangement the stigmas are at such a distance from the
pollen on the lobes that no autogamy could take place without some special inter-
vention. The requisite assistance is afforded by the two outer or inferior petals,
and their mode of action is as follows. When evening comes the flower closes; the
two lateral pollen-free lobes of each superior petal rise up first of all, and then
the two inferior tri-lobed petals wrap themselves over them (see figs. 304° and
3044). On the second or third day, when the margins of the pollen-laden lobes
have curled back, contact ensues between the two closed petals and the revolute

AUTOGAMY BY THE CLOSING OF THE COROLLA. 371

margins of these lobes, and some of the pollen sticks to the petals, so that next day
when the flower opens again a streak of pollen may be seen along the middle line
of each of the outer petals (see fig. 3047). On the last day of bloom the two
stigmatic arms curve down, and when the flower closes once more at dusk, they,
being directed towards the median lines of the outer petals, are brought into contact
with the pollen adherent along those lines (see fig. 304°), and thus at the last
moment autogamy is effected.

The flowers of the Venus’s Looking-glass (Specularia speculum, see figs.
304 1° 11, 12, 18, 14,15) are protandrous like those of the common Bell-flower (Cam-
panula); their anthers form a tube in the newly-opened flower (see figs. 304!" and
3042), dehisce inwards and deposit the whole of their pollen on to the delicate hairs
which clothe the external surface of the stylar column. When the tube of anthers
breaks up through the shrivelling of their empty lobes, an axial column covered
with pollen is exposed to view, and is used by insects as an alighting place. For
the present pollen can only be taken away—not deposited—by insects, for the style-
arms are still united, and the receptive tissue is inaccessible. Every evening the
erect basin-shaped corolla folds up longitudinally in such a manner as to form five
re-entrant angles (see fig. 304°). The in-folded angles of the corolla reach inwards
as far as the central column (see fig. 304), and get besmeared with some of the
pollen with which it is coated. The next morning when the corolla opens linear streaks
of pollen may be seen upon its internal surface. Meanwhile the three short arms
of the style have disunited and spread themselves out, whilst the pollen has fallen
off the stylar column (see fig. 304), or been carried away by insects. If at this
stage insects alight on the divergent style-arms fresh from visiting younger flowers,
eross-pollination is certain to ensue. As night approaches the flower closes in the
same way as on the previous evenings, and the pollen sticking to the lines of the
internal folds comes against the style-arms, which are spread out and slightly
reflexed (see fig. 304'%), and thus effects self-pollination. In the event of the
stigmatic tissue having already received a deposit of foreign pollen, this act of self-
pollination is superfluous, but otherwise the process is effectual, and always results
in the formation of fruit. A similar phenomenon may be observed in the nodding
or pendent flowers of various Solanace, particularly in the Potato plant (Solanwm
tuberosum), for here also there is frequently a transference of pollen to the corolla,
and from the folds of the corolla to the stigma. But in this case the pollen issues
from the anthers through terminal pores, and falls irregularly and not necessarily
upon particular parts of the corolla, so that autogamy is not so certain to take place
in these plants as in Specularia.

From the above descriptions it will be seen that in Argemone, Hypecoum, and
Specularia, although the corolla is the part of the flower which is instrumental in
effecting autogamy, the process does not involve any noticeable elongation of the
pollen-besmeared corolla during the period of flowering. We have now to deal with
another group of plants in which the petals perform just the same function as in
the foregoing cases with respect to autogamy, but in which a very important part

372 AUTOGAMY.

of the operation consists in an elongation of the corolla. Types of this group are
afforded by Gentianacez of the subdivision Coelanthe (Gentiana asclepiadea, @.
Pneumonanthe, &e.), Liliacee (Colchicum), Amaryllidacee (Sternbergia), Iridacesz
of the genus Sisyrinchium, and those Composites whose capitula are furnished with
ligulate florets (Crepis, Hieraciwm, Hypocheris, Leontodon, &c.).

Gentiana asclepiadea (see fig. 305) is one of the sub-alpine species of the Baltic
flora, and has protandrous flowers. The anthers are united into a tube, as in the
case of Composites and Bell-flowers. They do not, however, discharge their pollen
into the tube, but behave in this respect in the same manner as those of Hypecoum,
that is to say, they open by longitudinal fissures down their external faces, so that
after dehiscence the outside of the anther-tube is covered all over with pollen

Fig. 305.—Autogamy effected by means of the corolla.

1 Gentiana asclepiadea. Flower-bud shortly before it opens for the first time. 2 Open flower in the last stage of development.
8 Longitudinal section through a flower which has just opened for the first time. * Transverse section through the same
flower. * Longitudinal section through a flower closed for the first time. Pollen is affixed to the edges of the folds into
which the corolla is thrown. © Longitudinal section through a flower which has opened for the last time. 7 Longitudinal
section through a flower which has closed for the last time. The pollen is being transferred from the folds of the corolla
to the reflexed stigmas. § Tranverse section through the same flower. The anther-tube in %, 5, ®, and 7 is represented in
optical section.

(see fig. 305°). The linear style-branches bearing the stigmatic tissue are at this
stage closely united and as yet immature. Humble-bees are attracted in large
numbers by the rich store of honey in the floral interior, and as the funnel-shaped
corolla is wide open in the daytime the insects enter, and are often entirely engulfed
in the flower. If the visit is paid to a young, newly-opened flower the insect
loads itself with pollen by coming into contact with the tube of anthers. Two days
later the linear stigmas separate and curve over downwards. Their position now
renders it inevitable that they should be touched by the bees, of which a large
number continue to visit the flower, there being still plenty of honey in it. If these
visitors have recently visited younger flowers they are sure to effect cross-fertiliza-
tion. The corolla is disposed in peculiar folds, as is shown in figs. 305! and 305°;
to describe them sufficiently briefly for our present purpose would not be possible.
When the flower expands in the morning these plaits open out; at sunset they are
again drawn in towards the middle of the funnel, and at the same time a movement

AUTOGAMY BY THE CLOSING OF THE PERIANTH. 373

of torsion takes place which brings the folds into the position shown in transverse
section in fig. 305%. The re-entrant angles come into direct contact with the
surface of the anther-tube (see figs. 305° and 305°) and take from it some of the
pollen, which is very adhesive. On the next day,and on the third and fourth days,
the flower opens and shuts again. During that time almost every part of the
flower grows in length; the filaments gain 1 mm., the pistil 3 mm., and the inferior
half of the corolla as much as 5 mm. In consequence of this growth the pollen
transferred to the folds of the corolla from the anther-tube is raised 5 mm., and
rests at the same level as the stigmas, which have in the meantime become diver-
gent. When darkness sets in, and the corolla once more falls into folds and closes
up, the pollen affixed to the re-entrant angles is transferred to the stigmatic tissue.
The process is greatly facilitated by the fact that, at this final stage of flowering,
the internal folds assume a somewhat different form and position (see fig. 305°),
for in consequence of this change the parts besmeared with pollen are brought still
nearer to the middle of the flower. This marvellous contrivance for promoting
autogamy may also be observed in Gentiana Pnewmonanthe, a species which grows
in damp meadows in England and all over the continent of Europe, and in this
instance the elongation of this funnel-shaped portion of the corolla in the interval
between the first and last occasions of the flower’s closing amounts to some 7 mm.
The phenomenon occurs in a much simpler form in Sternbergia and Colchicum,
belonging to the orders Amaryllidacez and Liliacese respectively. The flower of
Sternbergia lutea has an erect funnel-shaped perianth composed of six segments,
three of which are rather longer than the other three. The six upright stamens
have nectar secreted at their bases, and are adnate to the segments of the
perianth; they are arranged in two whorls round the styles, and have their
anthers turned outwards. The styles rise up in the middle of the flower in the
form of three long threads. The stigmas, in which the styles terminate, are higher
than the anthers throughout the period of bloom, and as, after the dehiscence of
the anthers, the pollen adheres to the internal walls of the loculi, it is not spon-
taneously transferred to the stigmas in the same flower. The flowers are protogy-
nous, and at the commencement of their bloom are adapted to eross-pollination
through the agency of insects. Even after the extrorse anthers have dehisced,
insects entering the blossom in quest of honey brush first against the stigmas,
and only subsequently come into contact with the anthers resting at a lower level.
The perianth is open in the daytime alone; in the evening its segments close
together so tightly that their inner surfaces touch the extrorse anthers and become
smeared with pollen. This happens the very first evening following on the dehis-
cence of the anthers. The pollen affixed to the perianth-segments does not reach
the level of the stigmas till the following day. Its ascent is due to an elongation of
the lower regions of the perianth-segments. There is a simultaneous growth of the
other parts of the flower, but it is surpassed by the extraordinary increase in the
length of the perianth-leaves. Whilst the styles grow 4 mm., and the stamen-
filaments from 9 to 10 mm., these segments grow 185 mm. Afterwards, when the

374 AUTOGAMY.

perianth eloses for the night, the pollen is transferred from the inner faces of its
segments to the stigmas. Two subsidiary circumstances co-operate in bringing
about this act of autogamy. ‘The first is, the fact that the free extremities of the
styles which bear the stigmatie tissue curve outwards when the flower's end
approaches, and the second is, the circumstance that the excessive elongation is
especially marked in the three perianth-segments which are opposite the stigmas.

The same events take place in the flowers of the Meadow Saffron (Colchicum
autumnale). Anyone crossing a meadow in the autumn in which this plant is
growing may see what a great difference exists between young and old flowers in
respect of the length of the perianth-segments, and can easily convince himself of
the connection between this diversity and the operation of autogamy as explained
above. In the Meadow Saffron the phenomenon is somewhat complicated by the
circumstance that heterostylism (see p. 302) plays a much more important part
in this instance than in the other Liliacee. Colchicwm possesses long-styled,
mid-styled, and short-styled flowers, which all grow promiscuously together in one
and the same meadow, and the elongation of the perianth-segments is anything but
uniform in these three forms. Careful measurements of some five hundred specimens
gave the following remarkable result. In long-styled flowers the three longer
perianth-segments grow 9 mm. and the three shorter 12:6 mm.; in short-styled
flowers the longer segments grow 10 mm. and the shorter 15 mm., and in the mid-
styled flowers the longer segments grow 13°5 mm. and the shorter 18°5 mm. I shall
return to the subject of heterostylism again presently, and shall then have an oppor-
tunity of entering more fully into its significance; at present it is only necessary to
mention that the stigmas of the short-styled flowers, when the latter are nearly
over, come into contact not only with the pollen sticking to the perianth-segments,
but also with the tips of the anthers themselves, for in this form there is a propor-
tionate growth of the filaments.

This same process, which in Colchicum autumnale, in Sternbergias and in Gen-
tians of the Ccelanthe tribe only culminates in autogamy after the lapse of a week,
is accomplished in the delicate plant Sisyrinchiwm of the order Iridacew in the
course of a few hours. Apart from their ovaries, which are inferior, the flowers
of Sisyrinchiwm are constructed similarly to those of Liliacee. The three small
petaloid stigmas, in which the styles terminate, project above the anthers. The
latter are coherent into a tube and open extrorsely, whilst the flower is still in the
bud state, and the consequence is that some of their pollen is affixed to the con-
tiguous leaves of the perianth. The flower opens out into a cup, and insects may
then cause heterogamy; but on the approach of evening the perianth closes again,
and autogamy takes place owing to the fact, that in the course of those few hours
the petals have lengthened exactly enough to bring the pollen sticking to their inner
surfaces to the level of the stigmas.

Reference must also be made to those Composites in which autogamy is brought
about by means of an elongation of the ligulate corolla, and the consequent uplifting
of the pollen adherent to it. In most and probably in all species of Crepis, Hiera-

AUTOGAMY AIDED BY THE COROLLA. 375

cium, Leontodon, and Hypocheris, in whose capitula the peripheral ligulate florets
are considerably longer than those of the centre, it is easy to see that when the
capitula close in the evening the ligulate petal in each flower rises up and lays its
inner surface upon the pollen which has been extruded from the tube of anthers in
the course of the day. The pollen remains sticking to the petal during the two
succeeding days, and in the meanwhile the latter grows about a couple of milli-
metres in length and carries the pollen up with it. At the same time the style
undergoes elongation and protrudes out of che top of the tube of anthers, holding
its two arms, which are now divergent and expose the receptive stigmatic tissue

Fig. 306.—Autogamy effected by means of the corolla.

1 Pedicularis incarnata. 2 A flower of Pedicularis incarnata which has just become accessible to insects. % Longitudinal
section through the same flower. 4 The same flower in a later stage of development. 5 Longitudinal section through the
flower of +. © The same flower shortly before the corolla fades; the upper lip is bent down and the mealy pollen falling
out of the loosened valves of the anthers is trickling through the tubular upper lip upon the stigma stationed in front of
the mouth of the tube. 7 Longitudinal section through the flower of 6. 1nat. size; the other figures double their nat size.

upon their surfaces, at the same level as the pollen sticking to the ligulate corolla.
When next the capitulum closes, the pollen is transferred to the stigmas, and auto-
gamy ensues. This adaptation of the marginal florets of the capitula is all the more
interesting, seeing that in the central florets in the same plants, geitonogamy has
been found invariably to prevail (cf. p. 319).

One of the most curious contrivances for effecting autogamy consists in a special
inflection of the corolla, on the termination of the flower’s period of bloom, enabling
it to conduct the pollen which falls from the anthers to the stigmas. The pollen in
these cases is of mealy consistence. Two species of the Lousewort genus (Pedicu-
laris) may be used to illustrate this form of adaptation, and we will first take

376 AUTOGAMY.

Pedieularis incarnata (see fig. 306), a species which grows abundantly in Alpine
meadows. The flowers of this plant are arranged in spikes, and their development
proceeds from below upwards (fig. 3061). The corolla is bilabiate; the lobes of the
under lip are at first upturned (see fig. 306), but subsequently are expanded in a
slanting plane (figs. 306 * and 306°). The upper lip is helmet-shaped and rolled into a
tube at the apex (figs. 306%%4567) The stamens are of the sugar-tongs type, and
their anthers are concealed underneath the arch of the upper lip (figs. 306% ® 7).
The long style is bent at an angle to correspond to the form of the upper lip; its
anterior extremity passes through the tube and rests in front of the orifice and at
the same time in front of the entrance to the floral interior. The humble-bees which
make use of this entrance are obliged to rub against the stigma, and if they come
laden with pollen from other flowers eross-fertilization ensues. Owing to the fact
that the flowers are protogynous insect-visitors cannot, in the first stage of bloom
(figs. 306? and 306°), carry off any pollen, but can only leave behind upon the stigma
what they have brought with them; at later epochs, however, the insects, though
still brushing first against the stigma, are next moment besprinkled with the mealy
pollen which falls from the anthers in consequence of the disturbance of the tongs-
like stamens. Under the galeate arch of the upper lip there is a slit (fig. 306 *) to
allow the pollen to fall freely, and whenever an insect enters between the under and
upper lips this gap is enlarged. The head is the part of the humble-bee that
receives the pollen, and the latter may, of course, then be conveyed to other flowers.
If no insects visit a flower, the pollen remains for rather a long time dormant in the
anthers; but, in the last stage of bloom, the filaments become flaccid and give way,
and the pollen then falls of itself upon the edges of the slit. At the same time the
upper lip undergoes a marked downward bending (fig. 306°), whereby that part of
it which is prolonged into a tube, is brought into a vertical position, so that the
pollen rolls down it, and is directed on to the stigma, which hangs right in front of
the mouth of the tube (fig. 3067). Sometimes the stigma is drawn into the tube in
the process of bending above referred to and sticks there, like a cork in the neck of
a bottle; in which case self-pollination takes place inside the tube. Autogamy of
the type exhibited in Pedicularis incarnata occurs with slight variations in all
species which have the upper lip of the corolla produced into a tubular beak. The
cases of this kind especially subjected to investigation were Pedicularis asplenifolia,
P. Portenschlagii, P. rostrata, and P. tuberosa.

Very different behaviour is observed in several species of the same genus in
which the upper lip has the form of a cowl or a helmet truncated in front, as, for
example, Pedicularis Ederi, P. foliosa, P. comosa, and P. recutita. Of these we
will take for illustration Pedicularis (Ederi, which grows abundantly in Alpine
meadows in the neighbourhood of the Brenner Pass in Tyrol. As regards the con-
struction of its flowers, this species differs from P. incarnata in that the stigma is
stationed in front of the truncated helmet forming the upper lip, and also in having
projecting ribs on both sides of the corolla, which act like a system of levers in
causing the inflection just before the flower fades. The entire upper lip at this

AUTOGAMY AIDED BY THE COROLLA. 377

stage bends down so sharply as to look as if the flower had been wilfully broken.
The back of the upper lip, which originally constituted a direct prolongation of the
corolla-tube, now forms with it an angle of 60°, and later an angle of 90°. The
movement is shared, of course, by the style and by the tongs-like stamens concealed
beneath the upper lip. The consequence is that the stigma at the end of the style is
no longer in front of the anthers, but underneath them, and that the anthers, which
hitherto have been held tightly together, move asunder and let their pollen fall. The
stigma is situated in the line of descent of the pollen, and, being very viscid, it catches
a quantity of the particles of the shower, and thus secures the accomplishment of
autogamy (ef. fig. 276, p. 272). The same changes of position, which, spontaneously
initiated at the close of the flowering period lead to autogamy, may, curiously
enough, be brought about at an earlier stage by the humble-bees which fasten on to
the flower, but in that case they result in eross- and not self-fertilization. For a
description of the processes involved the reader is referred to the account of them
given on p. 272, where Pedicularis recutita is the species dealt with. We may here
remark that the whole of the pollen which falls from the anthers in the last stage
of flowering is not devoted to autogamy; the few pollen-cells which stick to the
viscid stigma are sufficient for that purpose. A larger number of pollen-cells fall
past the stigma into the air, where they may be caught up by a gust of wind, and
carried away in the form of a tiny cloud of dust. If mature stigmas of other
Pedicularis-flowers happen to lie in the direction in which the dust-cloud travels,
individual cells of the cloud are left behind on these stigmas, and eross-fertilization
thus ensues in the same way as in the flowers of the Toothwort (see p. 330).

Of the Rhinanthacez most nearly allied to the genus Pedicularis a few species
of the Cow-wheat, which may be represented by Melampyrum sylvaticum, remain
to be mentioned as instances of plants exhibiting the form of adaptation above
described. The sole difference is that in Melampyrum sylvaticum the tube of the
corolla bends at a sharp angle at a point only 2 mm. above the base, whilst the limb
itself, composed of the lips, undergoes no independent flection. The result is the
same as in those species of Pedicularis of which an account has been given, inas-
much as the pollen falls, in consequence of the inflection, from the anthers of
stamens of the sugar-tongs type on to the stigma beneath.

A kindred process to the preceding consists in the anthers with their coating of
pollen being brought into contact with the stigma by means of an inflection of the
corolla. The pollen is not mealy in this case, but adhesive. No one who will take
the trouble to examine the inflorescence in one of the twining species of Honeysuckle
(Lonicera Caprifolium, L. Etrusca, or L. Periclymenum) can fail to notice that
the corolla-tube, in buds which are about to open, ascends in an oblique direction,
that in newly-opened flowers it is horizontal, and that, a short time before a flower
fades, it is bent downwards. The angle through which the axis of the flower is
displaced relatively to the flowering stem varies from 45° to 90°; in the case of
horizontal stems it is less, and in that of erect stems greater, but the object invari-
ably aimed at is that the open corolla shall, as night comes on, be disposed in

378 AUTOGAMY.

the most convenient manner possible for nocturnal moths to visit it. In flowers
adjusted in anticipation of such visits, the stigma takes up a position which pre-
cludes the possibility of its being dusted with pollen from the anthers in the saıne
flower. In the act of introducing their long probosces into the honey secreted in
the interior of the flower, Sphingids come into contact first with the stigma and
then with the anthers, and as they travel from flower to flower they are the means
of effecting cross-pollination in this as in so many other cases. But should no
moths come upon the scene, autogamy invariably takes place through the inflection
of the corolla-tube already referred to. The stamens are adnate to the corolla-tube,
and undergo inflection with it, thus bringing the anthers, still covered with pollen,
into direct contact with the stigma, which, in the horizontal position of the flower,
was stationed a little lower than, and in front of, the anthers.

In respect of the manner of their autogamy the last-mentioned plants exhibit
a transition to a large group in which self-fertilization is prevented during the
early stages of flowering by the relative positions of anthers and stigmas, but is
effected towards the end of the period of bloom, when certain changes in the
position and direction of the flower-stalks have taken place and brought the
pollen and stigmas into conjunction. These alterations of position are usually
associated with one of the many other contrivances already described. ‘Thus, for
instance, the styles or the filaments may undergo elongation and inflection, or the
corolla may grow up and carry with it pollen affixed to its petals, or the stamens
themselves, and so forth; but these processes would not of themselves be sufficient
to induce autogamy if it were not for the part played by the flower-stalks. To put
it briefly, the stigmas and the anthers become, in the absence of cross-fertilization,
so situated by the growth and inflection of the flower-stalk as to render autogamy
inevitable. When we consider that the changes in the position and direction of
pedicels, and the consequent drooping or straightening up of flowers, serve other
purposes of great importance in the life of plants, and that, in particular, to these
inconspicuous movements are often due the protection of pollen from moisture and
the placing of the entrance to a flower in the position most convenient to insects
whose visits are profitable to the plant, we cannot be surprised to find that this form
of adaptation is one of the commonest of all. A combination of advantages, either
simultaneous or in rapid succession, is secured, and contrivances of this kind which
best contribute to the economy of plant-life are found by experience to be invariably
the most widely distributed.

We will first consider flowers in which the stigma begins by being situated
outside the line of descent of the pollen as it falls from the anthers—a circumstance
which is advantageous inasmuch as it favours eross-fertilization—but where subse-
quently the entire flower assumes a different position in consequence of a growth
or an inflection of the flower-stalk, whilst the direction and situation of stamens,
style, and stigmas remain the same as before. In several species of Narcissus, e.g.
the graceful Narcissus juncifolius, and in some Boraginex, such as the common
Wood Forget-me-not (Myosotis sylvatica), the flowers at first have their mouths set

AUTOGAMY BY MOVEMENTS OF THE FLOWER-STALK. 379

in a lateral direetion; the stigma is stationed behind the anthers, and the pollen
that falls out of the anthers does not come upon the stigmas so long as the corolla-
tube is horizontal. During that period the branch of the inflorescence to which
the horizontality of the corolla is due is curved, but it subsequently straightens out
and raises the corolla-tube to a vertical position whereby the stigma is brought
into the line of descent of the pollen as it falls from the shrivelling anthers. This
occurs in T’ulipa sylvestris, Polemonium ceruleum, Saxifraga hieracifolia, Chryso-
splenium alternifolium, Rhododendron Chamecistus, Vaccinium, Arctostaphylos,
Cerinthe, Symphytum, and Cyclamen. The process may be most clearly traced in
the various species of Cyclamen, which are at present so commonly grown 1n pots.
The first day that the flower is open and the petals reflexed, the peduncle, which
rises up from the ground, has its extremity bent over almost at a right angle. The
short bent piece of the stalk is inclined at an angle of from 50° to 60° to the
horizon. The variation in the size of the angle is due to the fact that the longer
inferior part usually ascends obliquely from the ground, and is only in rare cases
quite vertical. From day to day the angle of inclination may be seen to diminish
by about 10° until at the end of the flower’s period of bloom the short down-bent
portion at the top and the long upright portion of the peduncle are almost parallel,
and the whole has the form of a crook. As the style lies in the direct line of
prolongation of the short piece of the peduncle and projects beyond both the tube
of the corolla and the cone of anthers, autogamy cannot take place in the first
stage of the flower’s development, when the style is inclined at an angle of from
50° to 60° to the horizon. Insects visiting the flower at this period first brush
against the stigma at the end of the projecting style, and may occasion cross-
fertilization; but even if it should happen that the displacement of the anthers
caused by an insect’s intrusion has the effect of letting some of the pollen fall out,
the shower does not descend upon the stigma, for it is not yet situated vertically
beneath the anthers. Towards the close of the flowering period, on the other hand,
the stigma is moved by means of the inflection of the peduncle above referred to
into the path along which the pollen descends; the filaments become flaccid, the
anthers disunite, and the pollen stored in the cone is sprinkled upon the still recep-
tive surface of the stigma.

This will be the best place to describe the curious case of autogamy which is
exhibited by the Calceolaria Pavonii of South America. The flowers of this plant
are protogynous, and when first open they are borne on almost horizontal stalks.
The anthers, which are still closed, are concealed beneath the shortly truncate
upper-lip. The style bearing the already mature stigma is borne horizontally, its
tip only being bent down like a hook at a short distance from the stigma (as is
shown in figs. 307 ! and 307 *) so as just to touch the roof of the inflated under-lip.
The short-tongued Hymenoptera which come in quest of the honey secreted
within the lower-lip make use of its roof as an alighting-place. The instant one of
them settles upon it the lip drops as in the case of the Snapdragon, the movement
being regulated by the powerful ribs on each side of the corolla. The result is

380 AUTOGAMY.

twofold: the jaws of the flower are set wide open and the honey-secreting lobe
hitherto concealed in the hollow of the lip is brought out so as to enable the insect
which has caused the movement to lick up the honey without difficulty. In doing
so, however, it rubs its back against the stigma, and should it have previously
visited older flowers cross-pollination ensues. These are the conditions at the
commencement of flowering. The next day or the day after that, the anthers
open by comparatively large pores, one at the top of each loculus. The connectives
are articulated to the fila-
ments, so that when the latter
are pushed the anthers are
set swinging and let fall some
of their mealy pollen. If
under these circumstances a
rather large Hymenopter
alights on a flower in quest
of honey, he must necessarily
knock against the filaments
and be sprinkled by the pol-
len which descends in conse-
quence, especially seeing that
the filaments have meanwhile
increased in length suff-
ciently to bring the upper
lobes of the anthers upon the
highest part of the arched
external surface of the under-
lip. If the flower is not

visited by insects, a quantity
Fig. 307.—Autogamy caused by inflection of the flower-stalk and the adjust- of the mealy pollen falls of

ment of the under lip to form an inclined plane down which the pollen . .

deposited upon the under-lip slides to the stigma: Calceolaria Pavoni. itself upon this convex sur-
1, 2,3 Side view of the flower in the three successive stages leading to auto- face (see fig. 307 2): Soon

gamy. 4 Longitudinal section through a flower in the first stage of de-

velopment. All the figs. slightly magnified. afterwards the flower-stalk

curves down, causing a steep
inclination of the roof of the under-lip, which still bears on its highest part the
heap of pollen deposited by the anthers. The pollen slips down the inclined plane,
and is thus brought into contact with the stigma, which still retains its receptive
power (see fig. 307°).

The acccomplishment of autogamy, by means of a combination of movements
and inflections of the flower-stalks with similar action on the part of the stamens
and style is of as common occurrence as it is varied in respect of details. The
drooping Star of Bethlehem (Ornithogalum nutans) derives its name nutans
from the attitude of its flowers, but the latter really do not assume that position

until quite at the last; in the bud-stage they are erect, and even after the leaves

AUTOGAMY BY A CO-OPERATION OF MOVEMENTS. 351

of the perianth have expanded the pedicels stand out horizontally from the axis
of the inflorescence, and the flowers face sideways. The tlowers are protandrous.
The anthers of the three stamens, situated in front of the little pits in the ovary
in which honey is secreted, dehisce at the same moment as the perianth-leaves
expand, and these anthers are placed in such a position as to be touched by
insects as they enter the flower. The stigma is still immature at this stage.
A little later, when the stigmatic tissue has developed the power of retaining pollen,
the stamens move out of the way of insects towards the periphery of the flower
and thus render it possible for cross-pollination to be effected by such of these
visitors as bring with them pollen from younger flowers. In the third stage of
the flower's duration the pedicel bends down until the flower is at last truly
nodding. The stamens have meantime executed a reverse movement towards the
middle of the flower, and the stigma is found to be just underneath one of the
anthers belonging to a stamen of the shorter class. These anthers always have
some pollen left in them, for they do not open till the second stage of the
flower's development and cannot have undergone contact with insects. The
gradual shrinkage of the anthers now causes this store of pollen to fall out of
them on to the adjacent stigma, and thus autogamy is effected just before the
flower fades.

The hermaphrodite flowers of certain Rosacew — Dryas octopetala, Gewm
coceineum, G. montanum, G. reptans, Potentilla atrosanguinea, P. repens, and
Waldsteinia geoides—and those of some Ranunculacex, viz., Adonis vernalis,
Anemone alpina, and A. baldensis afford particularly instructive examples of
autogamy. In all these plants the flowers are protogynous and are characterized
by having a large number of carpels crowded together in the centre and surrounded
by equally numerous stamens, which are disposed in several whorls. In the
Rosacew in question the stamens are tucked down before the bud unfolds, and
they do not straighten out until the anthers are nearly ready to open. Dehiscence
oceurs first in the anthers which belong to the outermost whorl of stamens, and
are furthest away from the stigmas of the bunch of ovaries in the middle. This
relative position of the two sets of organs excludes all possibility of autogamy,
especially when the flower is erect; on the other hand, eross-pollination is quite
likely to be effected by imsects, which alight on the stigmas, thence proceed
towards the circumference of the flower, licking up honey and collecting pollen
on the way, and finally take wing from the edge to visit other flowers. By
degrees, the stamens of the innermost whorl come to maturity; they straighten
out and elongate, and their anthers with pollen exposed upon them are brought
to the same level as the stigmas of the central pistils. A transference of pollen
to some of these stigmas is now certain to ensue, and is rendered all the more
inevitable by the outward inclination and inflection of the styles belonging to the
pistils most remote from the centre which now take place, and bring the corre-
sponding stigmas into direct contact with the pollen. But if this were all, the
stigmas in the centre might get no share of pollen in the event of an absence

382 AUTOGAMY.

of insect visitors. To obviate this possibility the flower-stalk bends in a gentle
curve to one side so as to bring the last-mentioned stigmas into the line of descent
of the pollen when it falls from the anthers at the end of the flowering-period.
The process in the Ranunculacez referred to only differs from that just described
in trifling respects. In Adonis vernalis no outward inflection of the style can
take place on account of its shortness, but on the other hand the stamens nearest
to the ovaries curve inwards and deposit their pollen upon the adjacent stigmas.
In Anemone alpina the anthers of the innermost whorl of stamens are the first to
open, and the order of development is from that whorl outwards. Owing, however,
to the fact that the styles are crowded close together in a dense tuft at that earliest
stage, autogamy is not effected at once; later on the styles become bent and twisted,
and some of the stigmas touch the anthers in consequence; and when in addition
the pedicel undergoes inflection and causes the flower to nod, the rest of the stigmas
are brought vertically under the anthers and catch the pollen which falls from
them. In Pyrola uniflora (see fig. 308°), a native of fir-woods, autogamy is
brought about at the close of the flower’s period of bloom by means of a marvellous
co-operation of the stamen-filaments and the flower-stalks. The bud about to open
(see fig. 8081) and the young flower whose petals have just expanded (see figs.
308? and 308°) are borne on stalks which are strongly curved, and they are thus
inverted and pendent. The style is vertical, with the stigma pointing downwards.
The filaments are S-shaped and hold the anthers, which are of the pepper-castor
type, with the two pores invariably uppermost so that the pollen does not fall out
of itself or at any rate cannot come upon the stigma (fig. 308°). Insects approach-
ing from below brush first against the stigma and directly afterwards against the
anthers which are in consequence upset, and besprinkle the intruders with pollen.
This pollen is then carried to other flowers of Pyrola wniflora, where it is retained
by the viscid stigmas and fertilizes the ovules. During the period of bloom two
changes are effected, which though not very striking in themselves are yet of
extreme importance with a view to autogamy. In the last stage of the flower
the curve of the pedicel no longer amounts to a semicircle, and consequently the
flower is no longer absolutely pendulous but only facing obliquely down (fig. 308 *);
the style is no longer vertical, but with this new position of the flower points also
obliquely downwards and the stigma is thus brought underneath some of the
anthers. The filaments are still curved in the shape of the letter S but in the
opposite direction to that held by them at the commencement of the flowering-
period (ef. figs. 308° and 308°); the anthers are therefore inverted and have their
pores directed downwards. The least shaking of the slender stem by the wind is
now sufficient to cause a fall of pollen, and, in its present position, the viscid
stigma cannot fail to get sprinkled with some particles from the shower which
descends on such occasions (see figs. 308 * and 308°).

In Phygelius capensis, a plant belonging to the Serophulariacex of the Cape,
and also cultivated elsewhere in gardens for the sake of its deep scarlet flowers, the
branches of the inflorescence and the pedicels stand out nearly horizontally from

AUTOGAMY BY A CO-OPERATION OF MOVEMENTS. 383

the stiff upright stem (see fig. 3091). The pedicels are thickened just where they
pass into the flowers and bent down so as to hold the flowers, when they are newly
open, approximately at right angles to their stalks, which gives a curious appearance
to the inflorescence as a whole. The flowers are protogynous, and, on the first day
that they are open, the stigma can only be dusted with extraneous pollen from older
flowers. The style is originally curved, so that the receptive tissue is held in front
of the entrance to the floral interior where honey is abundantly secreted, and in
this position it is inevitably brushed against by insects visiting the flower (fig. 309 2

Fig. 308.—Autogamy caused by the combined inflections of pedicel and stamen-filaments: Pyrola uniflora.

1 Longitudinal section through a bud about to open. 2 The whole plant with its flower in the first stage of development.
3 Flower in the first stage of development slightly magnified; the front petals are cut away. + The entire plant with its
flower in the last stage of development. 5 Longitudinal section of a flower in the last stage of development; slightly
magnified.

the right-hand flower). The next day the style straightens out, and the stigma is
consequently moved away from the passage to the honey, whilst, on the other hand,
the anthers open and place their pollen-coated faces exactly in the path of insects
coming in search of honey (fig. 3091, the middle flower). On the third day the style
becomes curved again and takes up the same position as it occupied on the first day.
At the same time the pedicel undergoes further inflection and brings the tubular
corolla nearer to the main axis of the inflorescence (fig. 3091, the left-hand flower).
The result of these combined inflections is that the viscid stigma is brought right
under the anthers at the time when they are shrivelling and catches a portion of

354 AUTOGAMY,

the crumbly pollen as it falls from them. Even if the pollen does not fall upon the
stigma autogamy does not fail; for the corolla slips along the style as it drops, and
is certain to touch both anthers and stigma, and to transfer to the latter the last
grains of pollen adhering to the anthers (see fig. 309°).

Reference has often been made in former chapters to the splendid creeper named
Cobea scandens, one of the Polemoniaces native in tropical America, but capable of
thriving luxuriantly in the gardens of Central and Southern Europe, where it is
used for clothing espaliers, which it covers in the height of summer with deep-
purple bell-shaped flowers (see fig. 3107). The anthers are borne on long filaments
with hairy bases, and are situated, at the commencement of the flowering-period,

Fig. 309.—Autogamy ensuing in consequence of the inflection of the pedicel and the disarticulation of the corolla:
Phygelius capensis.

1 Portion of an inflorescence ; the flowers borne by a horizontal branch of the inflorescence in the successive stages of develop-
ment leading to autogamy (from right to left). 2A single flower at the moment of the detachment of the corolla and the
rubbing of the anthers against the stigma.

right in the mouth of the flower, where they are certain to be touched by insects
which enter the flower to get the honey. The style is still short at this stage, and
has its free extremity concealed under the anthers, whilst the three terminal
branches of the style which bear the stigmatic tissue are closed tightly together (see
fig. 310°). A little later anthers and stigmas change places; the filaments elongate
and twist themselves into the form of corkscrews, and the anthers then rest lower
than the three style-arms, which diverge and place themselves in a position to
receive pollen brought by insects from younger flowers (see fig. 310°). If no insects
make their appearance, and there is consequently no eross-fertilization, the pedicel
undergoes inflection to the extent of about 45°, and the flower, hitherto nodding,
becomes completely pendent. At the same time the style curves, and the coils of
the stamen-filaments are drawn closer together. The result of all these move-
ments is that the anthers are brought into contact with the stigmatic tissue, which
is still receptive, and autogamy ensues (see fig. 310 *).

AUTOGAMY BY A CO-OPERATION OF MOVEMENTS, 385

Allium Chamcemoly (see fig. 311!) is an example of the plants, in whose flowers
autogamy is effected by concurrent movements of the pedicel and the style, the
former undergoing inflection, whilst the latter is inclined in the direction of the
spots where the pollen has been deposited. The small white flowers are lifted but
a very little way above the ground; at first they face the sky, and are half hidden
amongst the long green ribbon-shaped foliage-leaves. Nevertheless, they are
assiduously sought out by small insects, the honey, which is secreted in little depres-
sions on the surface of the ovary, being in great request. During the first stage of
flowering cross-pollination alone is possible; the stigma is posted in the middle of

Fig. 310.—Autogamy resulting from an inflection of the pedicel accompanied by spiral torsion of the filaments: Cobea
scandens.

1Side view of a newly opened flower. 2, 3,4 Flowers in the three successive stages of their development which lead to
autogamy. All the figs. somewhat reduced.

the mouth of the flower, and its tissue is already receptive whilst the anthers are
still closed and appressed to the walls of the perianth (see fig. 311”). Later on all
the filaments undergo inclination towards the middle of the flower; the anthers
burst open, become covered all over with the pollen which issues from their loculi,
and together form a yellow knob which occupies the centre of the entrance to the
interior of the flower, and is brushed by all intruding insects. The stigma is at that
stage hidden behind the anthers (see fig. 311°), and is not touched by insects. If,
for any reason whatever, insects do not visit a flower, autogamy takes place in the
third stage of its development. The pedicel curves over downwards and presses the
flower against the ground, and, as a consequence, the delicate white perianth-ieaves
and filiform stamens are displaced, and some of the pollen falls out of the anthers
on to the lower perianth-leaves now resting upon the ground. The style undergoes
slight lateral, zc. in these circumstances downward, inclination and the final result

of all these movements is that the stigma is brought into contact either with the
Vou IL. 75

386 AUTOGAMY,

pollen lying on the lowest perianth-leaf or with that still sticking to one or other
of the anthers (see fig. 311°).

Of the plants in which autogamy is brought about by inflection of the pedicel
combined with inflection or folding of the petals, two groups will be taken here as
representing two different forms of the phenomenon. These groups consist of the
Violaceze of the Melaniwm tribe and the stemless Gentians. The manner in which

the pollen is transferred to the stigma in Violets through the agency of insects has

Fig. 311.—Autogamy resulting from inflection of the pedicel combined with inclination of the style to the place where ths
pollen has been deposited: Alliwm Chamcemoly.

1 Shows the aérial portions of the plant; nat. size. 2, 3, 4 Single flowers with the front perianth-leaves removed; slightly
magnified. They are in the successive stages leading to autogamy.

been already described on p. 280, and illustrated in figs. 279"*® on p. 279. The
pollen thus deposited by insects on the slightly-projecting flap of the capitate
stigma is derived, of course, from other flowers, and the result of its transference is
a crossing between the flowers either of one or of two species. Autogamy is in
general scarcely possible in the Violet during the first part of the flowering-period.
If pollen is shaken out of the cone of anthers on to the proboscis of an insect which
is in the act of dusting the front surface of the stigmatic lobe with foreign pollen,
this new supply may, perhaps, be rubbed off on to the back of the stigmatic lobe as

AUTOGAMY BY A CO-OPERATION OF MOVEMENTS. 387

the proboscis is withdrawn, but it does not even then come upon the receptive
surface of the stigma. As regards the pollen which, though shaken out, is not
carried away by the insect, but left lying underneath the cone of anthers in the
trough of the spurred petal, it also does not reach the stigmatic tissue during the
first stage of the flower’s development, for the groove is still closed by the project-
ing lobe of the stigma. ‘Towards the end of the flower's duration, however, the case
is very different. The Violas of the Melaniwm tribe may be represented by the
Field Pansy (Viola arvensis), it being the most widely-distributed species of the
section. In these plants the cone of coherent anthers gradually breaks up of itself,
and the pollen falls out, and fills the hinder part of the channel of the spurred
petal. At the same time the lamina of this petal bends in such a manner that
its trough is no longer closed by the stigmatie lobe, and the pollen is free to slip
towards the mouth of the flower. The only condition now requisite is some change
capable of setting the pollen in motion, and this is afforded by an inflection of the
flower-stalk. Although the flower-stalk in the Field Pansy, Heart’s-ease (V. tri-
color), and other species of the Melaniwm tribe undergoes sharp inflection (see
vol. i. p. 531) on clear nights, this movement has no influence in promoting auto-
gamy at the time when the flower is in full bloom. At the last, however, it causes
the mealy pollen to slip further and further down the groove in the lowest petal
until it reaches the receptive stigmatic tissue.

There is a remarkable resemblance between this process and that observed to
take place in those Gentians which are called by Descriptive Botanists “acaulescent”
or stemless species (Gentiana acaulis, G. angustifolia, G. Clusii, see fig. 312). The
flowers of these Gentians are of the type of “revolver-flowers” (cf. p. 250). The fila-
ments are adnate to the lower part of the funnel-shaped corolla, and project in the form
of five stout ridges towards the ovary, which appears as a column standing up in the
middle of the flower; the ridges and the ovarian column, coming into contact with one
another, divide the corolla into five tubular passages leading to the honey which is
secreted abundantly at the bottom. The anthers are a little higher than half-way
up the funnel of the corolla, and are connate into a tube which surrounds the style.
Each anther dehisces extrorsely by two longitudinal slits, and immediately after the
flower opens the anther-tube is covered all over with pollen. Above the tube is the
stigma, which is composed of two notched and lacerated white lobes. The positions
of the stigmas and anthers, respectively, ensure cross-pollination through the
instrumentality of the humble-bees which fly from flower to flower. If, however,
unfavourable weather prevails, and the bees stop away, the pollen gradually falls
from the anthers as they shrivel, and is transferred to the stigmas in the same
flower through the agency of the corolla and pedicel in the following manner. As
long as the flower remains upright or ascends obliquely (see figs. 3121 and 312?)
the pollen falling from the shrinking anthers collects above the bases of the fila-
ments, where they coalesce with the corolla, and when the corolla folds up for
the night or to protect the pollen from rain, the pollen falls down between the
folds, which, starting from close to the bases of the filaments, extend nearly to the

388 AUTOGAMY.

mouth of the flower. These furrows constitute, in fact, the channels through which
the pollen is afterwards conducted to the stigmas. The only movements needful for
the attainment of this object are the inversion of the flower, and the placing of the
stigma in such a position that its fringed edges may reach to the furrows in ques-
tion. Both these conditions are complied with. The inversion of the flower is
brought about by a considerable elongation of the pedicel, which is very short when
the flower first opens, and by its semicircular inflection at the approach of night
and in wet weather (see fig. 3127). The introduction of the stigmatic margins into
the furrows is due to the growth of the style, which carries the stigma up into the
conical cavity formed near the apex of the flower when the corolla-limb folds up.

Fig. 312.—Autogamy resulting from inflection of the pedicel combined with the folding up of the corolla.

1 Gentiana Clusii showing the flower as it is when opened for the first time. 2 The same plant with its flower in the last stage
of development, the corolla closed and the pedicel elongated and curved downward in a semicircle. ® Longitudinal
section through a newly-opened flower. 4 Longitudinal section through a flower which has closed for the last time.

All the furrows of the corolla-tube open into this cavity, and converge into such
proximity to the axis of the flower that contact with the edges of the stigmatic
lobes, which occupy the middle of the conical cavity, is inevitable. If, under these
conditions, the drooping flower is shaken by drops of rain falling upon it, or by
gusts of wind, the pollen slips along the smooth furrow right down to the stigma,
and is caught by its fringed margins (see fig. 312*). It is worthy of note that
Gentiana acaulis, G. angustifolia, and G. Clusii—the plants to which the above
description applies—grow for the most part on grassy slopes, and on the ledges of
precipitous rock-faces in the Alps; thousands of flowers of these species may be
seen in situations of the kind with their heads drooping in wet weather so as to lie
parallel to the slope of the ground, and fruits are invariably developed from these
flowers, even after long-continued rain. On the other hand, flowers growing on flat

AUTOGAMY BY A CO-OPERATION OF MOVEMENTS. 389

meadows sometimes have no opportunity of becoming nutant. In them, as might
be expected, autogamy fails, and if the weather is bad, and no humble-bees are
about, eross-fertilization may also be prevented; therefore it is not unusual to find
many ovaries unproductive in level places of the kind.

The Pasque-flowers, Anemone Pulsatilla and A. vernalis, may be taken as
representatives of the cases in which autogamy is achieved by means of an inflection
of the pedicels combined with an elongation of the sepals. The flowers of these
plants have very short stalks and face the sky when they first open. They remain
in that position for about forty-eight hours, opening in the daytime when it is fine,
and closing at night and when it rains. No drooping of the flowers is to be per-
ceived during the first two days, and indeed such a change would scarcely be possible,
considering the shortness of the stalks. The flowers are markedly protogynous.
The stamens are crowded together in large numbers, and their closed anthers,
grouped in the middle of the flower, resemble the grains of a head of maize. Above
the anthers rises a sheaf of styles bearing mature stigmas. Insects, especially hive-
and humble-bees, are attracted at this stage of floral development by the honey
which is secreted by small club-shaped nectaries interspersed amongst the sepals
and stamens. On entering a flower they rub against the sheaf of stigmas, even if
they have not actually used it as an alighting-place, and, in the event of their
bodies having been besmeared with the pollen of older flowers, a cross with some
plant which may be either of the same or of another species ensues. When two
days have elapsed, the aspect of affairs is altogether changed. The peduncle has
become considerably longer, and the flower nods slightly when darkness sets in; the
inner stamens are no longer stiff but curve outwards, whilst those anthers which
are nearest to the styles have undergone dehiscence and offer their pollen for
dispersion. The sepals, which are concave towards the middle of the flower, have
elongated somewhat to protect the pollen. Insects now come in quest of pollen as
well as honey, and are certain to get dusted with a quantity of it which they may
then transport to other flowers. When a flower closes in the evening, pollen from
the anthers of the reflexed stamens is invariably affixed to the inner surface of the
superincumbent sepals. At this stage, too, pollen is liable to be shaken out of the
anthers of the longest stamens, and this falls, in the case of a nodding flower, on to
the central stigmas of the fascicle of styles. Two days later, again, the condition of
the flower is as follows:—The stalk is from ten to twenty times as long as it was,
and the flower is nutant in the daytime as well as by night. The stamens have all
relaxed from their rigidity; the filaments are curved outwards, and the anthers are
open. The sepals have more than doubled their original length, and the pollen
affixed to their inner surfaces has consequently been raised to the level of the
stigmas. In addition, the form of the three inner sepals has changed; the concave
inner face is now convex, and the external surface is coneave. The result of these
changes is that the stigmas at the periphery of the fascicle now receive their share
from the elongated sepals, which are appressed to them and yield up to their
receptive tissue the pollen sticking to their inner surfaces.

390 AUTOGAMY.

The processes which lead to autogamy in the Water Avens (Geum rivale), the
Raspberry (Rubus Ideus) and some other Rosacew allied to these are even more
complicated than those above described. Thus, for example, the flowers of Gewm
rivale, on the day that they open, face laterally and have their stalks horizontal;
the filaments are short, and the anthers are all closed, while the stigmas which
project in a tuft 2 mm. beyond the anthers are already mature. At this stage
insects may occasion cross-fertilization, but autogamy is not yet possible. Subse-
quently, the filaments lengthen and the anthers of the longest stamens open and
come into contact with some of the stigmas at the periphery of the bundle of styles.
The pedicel is now curved and the flower nods; consequently, the pollen which falls
from the anthers above, when they shrivel, is forthwith received by the outer stigmas
of the fascicle of styles, that is to say, by those of the outer stigmas which appertain
to the upper half of the flower. The pollen which falls from the anthers of the
under half of the flower when they dry up, is caught, on the other hand, by the
petals on that side of the flower, and is afterwards transferred, by means of an
elongation of these petals, to the stigmas of the adjacent reflexed styles. A couple of
days later the pedicel is curved into a semicircle, and the flower hangs down with
its mouth towards the ground. By this time the anthers of the shorter stamens
are open; the whole flower has become loosened, and the fascicle of styles resembles
a sheaf of corn. All the styles, including those in the middle, become twisted and
reflexed to the extent necessary to bring the stigmas underneath the most recently
opened anthers, and when these anthers shrivel and the pollen is forced out, it falls
upon the central stigmas, which hitherto have not been furnished with any. Thus,
in this case we have (1) the inflection of the pedicels, (2) the elongation of the petals,
(3) the elongation of the stamens, and (4) the inflection of the styles—all co-operating
towards the same end, namely, that in the event of no insects visiting a flower all
the stigmas may receive pollen from the anthers developed in the flower itself.

The foregoing descriptions, though extremely brief and cursory, give a general
idea of the many kinds of contrivances whereby autogamy, as well as heterogamy,
is promoted in hermaphrodite flowers. It is evident from them that any mechan-
ism which leads to autogamy has full scope for its operation only if cross-pollina-
tion has not previously been effected. Again and again we have found that certain
processes only take place in the event of a flower being unvisited by insects through
whose agency eross-fertilization would have been brought about. In this connection
we have also the remarkable phenomenon that many flowers adapted to cross-
fertilization by insects do not open at all when there is no chance of their being
visited by the agents in question. In the mountainous districts of the temperate
zones it often happens that rainy weather sets in just at the time when the flowers
are about to open, and that it lasts for weeks. Humble- and hive-bees, butterflies,
and flies retire to their hiding-places, and for a considerable time cease to pay any
visits to flowers. The growth of the plants is not, however, arrested during this
period, and even in the flowers themselves development quietly progresses if the

AUTOGAMY IN CLEISTOGAMIC FLOWERS, 391

temperature be not too low. The stigmatie tissue becomes receptive; the anthers
attain to maturity, dehisce and liberate their pollen notwithstanding that no ray of
sunshine penetrates the clouds and that rain falls continuously. In such cireum-
stances the mouth of the flower is not opened; autogamy takes place in the closed
flower, and all the adjustments evolved with the object of ensuring cross-fertilization
are ineffectual. This is the case, for instance, in the following:—Alsine rubra,
Anagallis phenicea, Arabis cerulea, Azalea procumbens, Calandrinia compressa,
Centunculus minimus, Drosera longifolia, Gagea lutea, Gentiana campestris, G.
glacialis, G. prostrata, Hypecoum pendulum, Hypericum humifusum, Lepidium
sativum, Montia fontana, Oxalis corniculata, O. stricta, Polycarpon tetraphyllum,
Portulaca oleracea, Sagina saxatilis, Silene noctiflora, Sisyrinchiwm anceps, Sper-
gula arvensis, Stellera Passerina, Veronica alpina, V. bellidioides and V. Chame-
drys—plants which grow in widely different habitats, but which all have the com-
mon property that their flowers open for but a short period, if at all. In plants
with long-lived flowers it is of not uncommon occurrence for autogamy to be
accomplished during a spell of wet weather, and for the petals to open subsequently
all the same, and so afford the possibility of the remains of the pollen being carried
away by insects. This phenomenon has often been observed, for example, in
Rhododendron hirsutum, the Bog-bean (Menyanthes trifoliata), and the Greater
Dodder (Cuscuta Europea).

There is also the case of such plants as Alisma natans, Illecebrum vertieillatum,
Limosella aquatica, Peplis Portula and Subularia aquatica, which live in pools or
on the banks of ponds where the level of the water is variable. If the buds of
these plants are submerged at the time when they are about to open, they do not
unfold, and autogamy takes place in the closed flowers under water. It must be
observed that the water does not penetrate into the air-filled interior of the flowers,
so that we have here the curious phenomenon that the transference of pollen to the
stigma, though accomplished under water, is yet a case of pollination in the medium
of the air.

An allied phenomenon is exhibited by some of the Knotweeds (Polygonum
Hydropiper, P. minus, and P. mite). Isolated plants of any of these species, in
which all the flowering branches are exposed to the sunshine, and are both visible
and accessible to insects, unfold all their flowers; but, if hundreds of one species are
crowded close together, only a limited number of the flowers open their perianths.
The flowers growing on the upright branches alone of such crowded plants unclose,
and receive insects’ visits, whilst those which grow on the under, procumbent
branches, and are consequently concealed and not easily reached by insects, remain
shut. Nevertheless autogamy is effected with obvious success in these also.

Plants of the kind just alluded to form a transition to those which normally
produce two kinds of flowers, viz.: some which open and are adapted to cross-
fertilization through insect-agency, and some which remain closed and exhibit
autogamy with great regularity. The latter have received the name of cleistogamic
(x\ewros=that can be closed, yduos, marriage) flowers, and amongst them may be dis-

392 AUTOGAMY.

tinguished a series of very wonderful forms. A common characteristie of them all
is the stunted development or complete abortion of petals which would otherwise
attract insects by their scent, colour, or honey. The only function of the petals is that
of an envelope under cover of which ovules and stigmas, anthers and pollen, attain
maturity and are able to enter into combination with one another. In many cases
there is no trace of a corolla to be seen; green sepals alone are developed into a
floral envelope, and they are kept fast elosed and cover the stamens and pistil in
the form of a hollow cone. Thus, for instance, Aremonia agrimonioides, a plant
growing abundantly in the forests of Carniola, has cleistogamous flowers about a
millimetre in diameter, in which stamens and sepals spring from the edge of the
excavated disc, whilst petals are entirely absent. In other cases, though petals
exist, they remain small and of a greenish-white tint. Precisely those parts of the
corolla which in open flowers are most conspicuous in form and coloration are here
abortive. Thus, in the cleistogamous flowers of several species of Violet, the
spurred petal, which in the open flower is the most striking, is scarcely recognizable;
its lamina is oval in outline, and is rolled into a hollow cone eovering the anthers
and stigma. The anthers in most cleistogamous flowers are so situated that when
the pollen is ripe and issues from the loculi it comes immediately into contact with
the stigma. Sometimes, it is true, there is a tiny interval between the pollen
adherent to the anther-lobes and the stigma, but in that case tubes are put forth by
the pollen-cells in the direction of the stigma, and these tubes lay themselves upon
the papillee on the stigmatic surface and thence pursue their way to the ovules. In
the cleistogamous flowers of the Henbit Dead-nettle (Lamium amplexicaule) it has
even been observed that the anthers do not open, but that, nevertheless, pollen-tubes
emerge from the pollen-cells, perforate the walls of the anther and grow in the
direction of the stigma until they reach it. Ifa cleistogamous flower of this kind
is examined after autogamy has been accomplished within it, one might at first
sight think the anthers and stigmas were adnate to one another, so firm is the union
of the pollen-tubes with the stigma.

As has been already said, all species of plants which produce cleistogamous
flowers also develop other open ones. For the most part these latter possess very
striking forms, scents, and colours, and are adapted to receive the visits of insects
and to undergo cross-fertilization through their agency. It is interesting to note,
however, that these open flowers possess none of the contrivances for effecting
autogamy in the event of a dearth of insects. From these observations we are
justified in supposing that we have here a sort of division of labour, inasmuch as
the functions, usually discharged by one form of hermaphrodite flower alone, are
here divided between two kinds of flower—both also hermaphrodite —viz., cross-
fertilization is assigned to those that open, self-fertilization to those that remain
closed.

Amongst Grasses, Rushes, Scirpuses, and other plants of the kind, which produce
dust-like pollen in their hermaphrodite flowers, only a few species are known to
possess cleistogamous flowers. The oldest established example is that of Oryza

AUTOGAMY IN CLEISTOGAMIC FLOWERS. 393

clandestina, a widely-distributed bog-grass allied to the Rice-plant. The panicles
of this Oryza include chiefly flowers which remain closed and are adapted to
autogamy; they develop only on their very highest branches a few flowers which
open and may be cross-pollinated by the agency of the wind. On the other hand,
the number of species possessing cleistogamous flowers to be found amongst plants
with adhesive pollen, and liable to be crossed by insect agency, is very large.
Numbers of tropical and sub-tropical Asclepiadace», Malpighiacez, Papilionaces, and
Orchidacex afford instructive examples of this phenomenon. The splendid colours
of the open flowers in these plants attract insects, and if the flowers are visited
eross-pollination is rendered inevitable by the various kinds of apparatus for
pressing, sprinkling, or shooting the pollen upon the insects with which the flowers
are furnished; but if in spite of allurements no insects arrive, the stigmas are not
besmeared with pollen at all, and these great open flowers wither without forming
fruit. It then comes to the turn of the cleistogamous flowers. They are developed
in the axils of special leaves as small, greenish, bud-like structures, which are
destitute of means for alluring insects, but are none the less sure on this account to
produce ripe fruit and fertile seeds. There is, besides, in temperate zones, no lack
of plants in which the same phenomenon may be observed. A host of Bell-flowers,
Rock-roses, Balsams, Polygalacew, Oxalidacew, and Serophulariacee (e.g. Cam-
panula, Specularia, Helianthemum, Impatiens, Polygala, Oxalis, Linaria) and, in
particular, the Violas of the Vominiwm and Dischidium sections, exhibit the same
difference in the functions assigned to their two kinds of flowers. The beautiful
Viola mirabilis has scented flowers stored with honey, which unfold great violet
petals in the spring. If these blossoms are visited by hive- or humble-bees they
are cross-fertilized; but many are not thus visited, and their fate is then to wither
without effecting that process of autogamy which has been described (p. 387) as
taking place in the species of Violet belonging to the Melanium section. In the
summer, however, special branches of the same individual plant bring forth small
green flower-buds which do not open, but nevertheless produce soon afterwards
large ripe capsules full of seeds. This phenomenon, in apparent contradiction to
the ordinary idea of the result of the flowering process, did not escape the attention
of the Botanists of the eighteenth century, and they named this species of Violet, in
which the majority of the large open blossoms fail to produce fruit whilst the closed
bud-like flowers are invariably productive, Viola mirabilis, or the Wonderful Violet.

In Viola mirabilis and in all its allied species, called “caulescent” in the
language of descriptive Botany, the cleistogamous flowers are developed on special
shoots, and these shoots are either erect or else prostrate in long zigzags. This is
also the case in several species of the Wood-sorrel genus (Oxalis) and in Aremonia
agrimonioides. A few Papilionaces (e.g. Vicia amphicarpa) and Crucifere (e.g.
Cardamine chenopodiifolia) are known too, whose cleistogamous flowers spring
from underground runners or stalks, whilst the open flowers are borne upon aérial
shoots. In several Violets of the kind called by descriptive Botanists “acaulescent”,
such as Viola collina and V. sepincola, the cleistogamous flowers develop likewise

394 AUTOGAMY.

underground, their stalks springing from special shoots of the rootstock. In all
these cases the two kinds of flowers are always borne on the same plant, though on
different branch systems; there are, however, also instances, such as the Yellow
Balsam (Impatiens Noli-tangere), where the open flowers are developed on different
individuals from those which produce the closed ones. To be accurate we should
say that the statement in each case expresses the general rule for the plants in
question, for instances of transition are by no means uncommon. Thus, for example,
individual plants of the Yellow Balsam do oceur in which open flowers with large
corollas, half-open flowers with stunted corollas, and small cleistogamous flowers
stand side by side; and, again, on the zigzag runners of the Sand Violet (Viola
arenaria) flowers with large expanded petals have often been seen growing in
company with the cleistogamous flowers. The same remark applies as regards the
time at which cleistogamous flowers make their appearance. In the majority of
cases they are not developed until the open flowers have withered and disappeared,
but in Cardamine chenopodiifolia it has been observed that the subterranean
cleistogamous flowers are produced earlier than those which are borne on above-
ground stems and unfold their petals to the air.

In former times it was asserted that plants exist which never bear any but
cleistogamous flowers. Thus the Toad-rush (Juncus bufonius) was stated to
produce cleistogamous flowers only. Later investigations have, however, established
the fact that this plant possesses two kinds of flowers—viz. terminal flowers with
three stamens which are cleistogamous, and lateral flowers with six stamens which
open, like those of other Rushes, under the warmth of the noonday sun. It was
also supposed that the African species of Salvia, to which the name of Salvia
cleistogama was given, produced cleistogamous flowers only, but after repeated
sowings plants have been obtained with flowers which opened. Anyone who has
only seen the Yellow Balsam growing on the heaps of detritus brought down by
the mountain-streams in the upland valleys of the Tyrol might think that this
plant also was an instance of a species producing cleistogamous flowers only; for in
those localities open flowers are not found on this species. But if seeds from these
cleistogamous flowers are sown in good vegetable mould, in a partially shaded spot
in a garden, a few individuals with large open yellow flowers spring up, as a general
rule, even after a single sowing. There is a species of Violet named Viola sepincola
which grows deep in the shade of the woods clothing the hills at the foot of the
Solstein chain in the Innthal district. I saw it there for the first time about the
middle of May, and it was then covered with an abundance of ripe fruit. In follow-
ing years I looked for flowers of this plant early in the spring, as soon as the snow
had melted, but found that not a single individual had developed open flowers with
expanded petals on erect above-ground stalks. On the other hand, there were a
number of cleistogamous flowers concealed under the fallen leaves and partially
buried in the earth, so that it looked very much as if the species produced no other
kind of blossom. But plants subsequently reared in a part of my garden which was
exposed to the sun’s rays during some hours of each day developed, in the next

AUTOGAMY IN CLEISTOGAMIC FLOWERS. 395

year but one after their being sown, in addition to cleistogamous flowers, beautiful
scented blossoms of a violet colour which were borne on erect stalks and in due time
unfolded their petals.

This result throws some light on the nature of the stimulus which causes the
formation of the flowers in question. No open, aérial flowers were produced by
Viola sepincola so long as it grew in the cool shade of a dense wood, but when
transferred to open ground, accessible to sunlight, such flowers were developed.
One can hardly err in ascribing to the sun’s rays a very important influence in
stimulating plants to the inception of flowering shoots, especially such as bear
blossoms possessing bright-coloured petals. Indirectly, however, this advantage
accrues to the plants in question that, living as they do in the deep shade, where no
bees would, in any ease, visit them, even if they had open flowers, they can confine
their constructive energy to the inception and development of cleistogamous flowers
and save themselves the trouble of producing open flowers adapted to cross-pollina-
tion (but useless in the place in question). If the spot where the Violet grows becomes
exposed to the sunlight through the trees shading it bemg blown down or felled,
humble- and hive-bees make their appearance in search of honey, and, buzzing from
flower to flower, cross one with another. In such circumstances the open, sweet-
scented Violet blossoms are in request, and the same plant-individual, which for
years in the dark shade has developed none but cleistogamous flowers, is now stimu-
lated by the sun’s rays into producing flowers with expanded petals.

A similar instance is afforded by the Henbit Dead-nettle (Lamium amplexi-
caule), which grows on cultivated ground—in kitchen-gardens, vineyards, and
amongst crops. This plant bears two kinds of flowers, viz. some with purple
corollas 15 mm. in length, which keep the entrance leading to their honey wide
open, and, secondly, cleistogamous flowers with abortive corollas and small green
ealices, which remain closed. As is the case with many other annual weeds, Dead-
nettle plants which have germinated late in the season maintain their vitality
through the winter and into the following spring, and accordingly they may be
seen at all seasons flourishing, fresh and green, in situations such as are mentioned
above. Flowers, too, are initiated and developed by them at all seasons of the year,
but it is interesting to note that only in the warm summer, when flower-seeking
insects are about, are the beautiful purple corollas of this plant to be seen; in the
late autumn and early spring, when it is cool, and there are no flower-seeking
insects, this Dead-nettle is able to do without the luxury of corollas, which are the
means of alluring insects, and as a fact only cleistogamous flowers make their
appearance at those seasons. It must not, of course, be imagined that the plant
exercises an intelligent discretion of its own when it abandons the development of
corollas. The connection between this effect and the aforesaid conditions is indirect,
and we must conceive that the nature of the stimulus which results in the inception
of flower-buds is different, when a plant is subject to the influence of the short days
and low temperature of late autumn and early spring, from what it is under the
conditions prevailing on warm summer days.

396 AUTOGAMY.

Amongst the contrivances mentioned in the last chapter as being adapted to
bring about eross-fertilization at the commencement of a flower's period of bloom,
was the production of heterostyled flowers (see pp. 302 and 312). It was pointed
out (p. 316) that in heterostyled plants the very first, or last (as the case may be). .
of all the flowers of a partieular speeies are, in consequence of the diehogamy which
prevails, fated to be erossed with flowers of another species, or, in other words, to
undergo hybridization, and that, according to experience, this erossing is often
effective. Considering the results obtained in the cases of other plants with herma-
phrodite flowers, one would expect to meet with some provision for the timely fulfil-
ment of autogamy in heterostyled species as well, i.e. that in the event of no insects
visiting a plant of the kind, the stigmas should at the proper moment be dusted
with pollen from the anthers in the same flower. This expectation has been, in
fact, confirmed; all the investigations directed to this question having resulted in
showing that a process of autogamy takes place also in heterostyled flowers, but is
always confined to one only of the forms which together constitute the species. In
one section of the heterostyled species, including, for example, those which belong
to the genera Gentiana, Menyanthes, and Thesiwm, the short-styled flowers are
adapted to autogamy, whilst in others, such as the heterostyled species of Mertensia
and Pulmonaria, autogamy takes place in the long-styled flowers. In Primula
longiflora and P. minima it is the short-styled flowers which have their stigmas
dusted with pollen from their own anthers, whilst in Primula Auricula, and P.
glutinosa it is the long-styled flowers which thus accomplish self-fertilization. All
these variations are exactly adjusted with reference to the other arrangements for
promoting autogamy in the flowers in which they are exhibited.

One contrivance which deserves mention here is the disparity in the size and
conspicuousness of the floral envelopes in the two forms of flowers of the same
species. In Primula longiflora and P. minima the long-style 1 flowers, and in
Primula Auricula and P. glutinosa the short-styled flowers have a larger and
more striking limb to their corollas than the other forms in each case. It may he
taken to be a general rule that the flowers adapted to eross-fertilization, in which
no autogamy takes place, are larger than those in which the accomplishment of
autogamy is assured. This phenomenon has been explained by the circumstance
that flowers destined to be crossed with others require to be more plentifully
equipped with the means of attracting insects than those which are certain to
undergo fertilization even if no insects visit them.

The means whereby autogamy is achieved in species with heterostyled flowers
are in the main the same as they are where the flowers are not heterostyled. In
some cases the stamens, or the petals with pollen affixed to their surfaces, elongate
sufficiently to enable the stigmas to come into contact with them: in others the same
result is attained by an inclination or an inflection of filaments or sty!e; in a third
series the stigma is dragged through the ring of anthers when the corolla falls off,
or the petals by opening and closing effect the transference of the pollen from the
anthers to the stigma; and lastly, in some instances, the pedicels undergo elongation

AUTOGAMY IN HETEROSTYLED FLOWERS. 397

and infleetion, which result in bringing the stigma underneath the anthers, so that
when the latter shrivel their pollen must fall upon the receptive tissue. Of the
host of observations relating to this matter, we can here only select a few to serve
as examples, and the most suitable for our purpose will be the Primulas, to which
reference has already been frequently made, viz. Primula Awrieula, P. glutinosa,
P. longiflora, and P. minima.

The corolla in the short-styled flowers of Primula Awrieula has a comparatively
large expanded limb, the surface of which is slightly concave; the five stamens are
adnate to the contracted throat of the corolla, where the tube passes into the
limb, and the anthers form, at that part of the flower, a ring through the middle of
which insects must penetrate in order to enter the floral interior. The style is short,
and the spherical stigma at the top of it stands at a level corresponding to only a
third of the length of the corolla-tube. At the time when the dehiscence of the
anthers takes place, the flowers are in a nodding or horizontal position. In these
circumstances no pollen can reach the stigma, and, unless visited by insects, the
flower remains unpollinated until it fades, nor does the fall of the corolla operate as
a means of conveying pollen from its own anthers to the receptive tissue. It is quite
different with the long-styled flowers of the species in question. The limb of the
corolla is rather smaller, and is hollowed into the shape of a basin; the five stamens
are adnate to the lowest third of the tube, and their anthers stand at the same height
as does the stigma in a short-styled flower. The style is long, and the stigma may
be seen in the middle of the flower’s throat. In other respects there is no difference
worth mentioning between the two forms. The stigmas of the long-styled flowers
are liable to be dusted with pollen brought by insects from the anthers stationed in
the throats of short-styled flowers. Whether this occurs or not, the receptive tissue
under any circumstances gets covered with pollen when the corolla becomes detached
and falls off, for the stigma is then dragged through the ring of anthers in the
corolla-tube, and is certain to remove some of the pollen which still adheres in more
or less abundance to them.

Altogether different is the process of autogamy as manifested in Primula longi-
flora. In this case the corolla of a long-styled flower has a shorter tube and larger
limb than that of a short-styled flower. The anthers are situated in the throat just
behind the mouth of the corolla-tube. The style is long and projects far beyond the
throat, whilst the stigma is held considerably above, that is to say, in front of the
ring of anthers. The flowers are either horizontal or else ascend obliquely, and
neither of these positions admits of pollen being deposited by the anthers upon the
stigma. As in this species the corolla does not drop but persists even when withered,
no autogamy takes place in the long-styled flowers when the plant is growing wild.
On the other hand, every insect which enters the flower must necessarily touch the
stigma, stationed where it is in front of the passage, and cross-fertilization then
ensues. The short-styled flowers have a longer tube and smaller limb to the corolla.
Their anthers, unlike those of many other Primulas, are situated in the throat close
beneath the corolla-limb in the same position as in the long-styled flowers; but the

398 AUTOGAMY.

style does not project outside the throat, and its stigma rests only just above the
tips of the anthers. Under these conditions eross-pollination is as likely to be
brought about through insect-agency as it is in the case of the long-styled flowers;
but in addition autogamy takes place towards the end of the period of bloom. The
manner in which the latter is effected is as follows:—During the period of the
flower's bloom the corolla-tube grows some millimetres in length until finally the
ring of anthers, which are adnate to the throat of the corolla, is brought up to the
same level as the stigma. The stigma then stands in the centre of the ring and
receives an abundant supply of pollen from the adjacent anthers.

In Primula minima (see figs. 288! and 288°, p. 302) the heterostyled flowers
are erect and maintain this position unaltered till the corolla withers. The limb of
the corolla in the long-styled form (see fig. 288') is larger than it is in the short-
styled form. The anthers in the long-styled flower are inserted on the lower part
of the tube; the style projects above the ring of anthers and the stigma rests some-
where in the uppermost third of the tube. On entering a flower an insect would
first come against the stigma, and would then probably dust it with foreign pollen.
Autogamy scarcely ever takes place. In the wild state of the plant the corolla
withers without falling off; only in rare instances does it happen that the corolla
becomes detached from the receptacle, and is carried away by the wind. On such
an occasion the stigma might touch the ring of anthers and get covered with pollen.
Self-fertilization is, on the other hand, all the more carefully ensured in the short-
styled flowers. Here the anthers are attached to the highest third of the corolla-
tube, and the stigma capping the short style rests below the ring of anthers. When
the flower’s period of bloom is nearly at an end both the corolla-tube and the anthers
begin to wither and contract, with the result that the pollen falls from the anthers
down the tube, and is caught upon the stigma.

Thus, autogamy is effected in the long-styled flowers of Primula Aurieula and
P. glutinosa by the stigma being dragged through the ring of anthers as the corolla
falls off, in the short-styled flowers of Primula longiflora by the elongation of the
corolla-tube and elevation of the anthers to the level of the stigma, and in the short-
styled flowers of Primula minima by the anthers shrivelling and letting their
pollen fall. The fact of the occurrence amongst Primulas alone of three kinds of
contrivance for promoting autogamy gives us some idea of the immense variety
which prevails in this respect amongst heterostyled plants in general. The impos-
sibility of entering here into the further details of this subject is the less to be
regretted, seeing that to a great extent such an account would involve a repetition
of facts which have already been stated.

The number of species possessing heterostyled flowers is far larger than was
formerly supposed. The list of such species known at the present day includes
members of the following families: Boraginacex, Caprifoliacee, Caryophyllacew,
Colehicaceze, Crassulacex, Ericaceze, Gentianacex, Globulariacex, Iridacex, Linacez,
Lythracex, Onagracex, Oxalidacese, Papaveraceee, Plantaginacex, Plumbaginacee,
Polygonacex, Primulacex, Rubiacez, Santalaces, Solanace®, and Valerianacex, and

RELATIVE PREVALENCE OF AUTOGAMY. 399

it is probable that more thorough investigation will result in the addition of many
more instances, especially amongst tropical plants. In most cases the species of one
such as Linum

genus produce only two forms of flowers; but there are also genera
and Oxalis—in which some of the species develop long-, mid-, and short-styled
flowers, others long- and short-styled forms, and others again none but flowers
with styles of equal length. The determination of the point as to whether hetero-
stylism exists or not in a particular case is, in many species, attended with some
ditheulty, owing to the stamen-filaments increasing in length during the period of
the flower’s bloom in both the long-styled and the short-styled flowers—a eireum-
stance which greatly complicates the relations subsisting between the two forms in
respect of the lengths of their different parts. There is also some danger of mis-
taking for heterostyled species a class of forms which do not in reality come under
that category. In the species alluded to, a proportion of the individual plants
produce apparently hermaphrodite flowers, with ovaries, styles, and stigmas which
ean be clearly identified as such, but which nevertheless are not capable of under-
going fertilization.

The results of the investigations into the subject of autogamy recorded in this
chapter may be summed up as follows. In plants whose flowers are hermaphrodite,
but neither cleistogamous nor heterostyled, both eross- and self-fertilization occur in
one and the same flower at different epochs; in plants with cleistogamous flowers a
division of labour is established between two kinds of hermaphrodite flowers, of
which the one form opens and is adapted to heterogamy, whilst the other remains
closed and ean only result in autogamy; and, lastly, in heterostyled plants, each
species includes two or three different forms of individual, varying in respect of the
structure of the flowers, which in the one case aim at cross-fertilization, and in
another especially at autogamy.

In view of the detailed consideration which the methods for promoting autogamy
in various plants has received in the foregoing pages, it may not be without interest
to allude here briefly to the relative prevalence of this mode of pollination in certain
Floras. During the passage of the present edition of this work through the press,
a notable addition to our knowledge of Floral Biology has been made by E. Loew
(Bliitenbiologische Floristik), in the form of a treatise wherein are summarized the
vast number of observations upon flowers and their relations to insects, &e., so far
as the Floras of Europe and Greenland are concerned, that have been published in
one place and another during the last ten years. This tabulating of observations
has enabled the author to make many interesting comparisons between the Floras
of various regions, and, supported by statistics, to exhibit the relative prevalence of
types adapted to this or that method of pollination. Though many of the results
do but confirm views already the common property of Biologists, they have an
altogether special value from the manner in which they have been obtained.

As regards autogamy, it appears from statistics that it shows an increase in high
Alpine forms as compared with plants from a lower level. The accompanying

400 AUTOGAMY.

table, taken from Loew, contrasts alpine and sub-alpine plants in regard to the
relative prevalence of autogamy:—

(I.) Of 130 entomophilous plants in sub-alpine regions—
35 species=26°97% are rarely or never autogamous.
86 species =6671% are autogamous as well as heterogamous.
9 species= 69% are invariably or usually autogamous.

99:9%

(II.) Of 133 entomophilous plants in high alpine regions—
35 species = 26°3% are rarely or never autogamous.
78 species =58°6% are autogamous as well as heterogamous.
20 species=15'0% are invariably or usually autogamous.

99:9%

Thus we see that 20 high alpine species show pronounced autogamy as compared
with 9 sub-alpine forms.
In the mountain Flora of Scandinavia the prevalence of autogamy is even more
marked.
(IIL) Of 74 species from the Dovrefjeld—
12 species= 162% are rarely or never autogamous.

40 species =54:0% are autogamous as well as heterogamous,
22 species =29'7% are usually autogamous.

99-9%

As compared with the high alpine plants (table II.) we note a diminution of 10°/,
in those which are always heterogamous, and an increase in those usually auto-

gamous of some 15°/,.
In plants whose distribution is restricted to the Arctic regions, the number of

autogamous plants is in the majority.

(IV.) Of 45 species of purely Arctic plants—
0 species= 0°0% are almost exclusively heterogamous.
14 species =31°1% are autogamous as well as heterogamous.
26 species =57'8% are usually autogamous.
5 species=11'1% are doubtful.

100%

Precisely what factors in their environment have led to this increased preval-
ence of autogamy in high alpine and far northern species is at present not certainly
determined. A lack or comparative rarity of insect-visitors on the one hand, or
unfavourable climatic conditions on the other, might either of them well lead to
such a condition. Regarding the alleged paucity of insects in the Alps, one so well
qualified to speak as Hermann Müller says':—‘I have not been able to convince
myself that alpine flowers are, on the whole, less frequently visited and crossed by
insects than are those of the plain”. Nor does Loew, with the statistics before him,
dissent from Miiller’s opinion. So also with regard to the northern types, concern-
ing which the view is widely spread that their preponderatihg autogamy 1s connected

1 Alpenblumex, p. 547

FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS. 401

with the paucity of insects. Loew is of the opinion that the insects there are
adequate for the work they have to do, 7.e. are suflieiently numerous for the main-
tenance of the species of plants which depend upon their visits.

Putting aside the visits, and proceeding to consider the elimatie conditions, we
are on much surer ground. Both on the mountains and in the far north the period
of vegetation is a short one, and the shortness of the summer, combined with the
broken character of the weather, which is common to the Alps and Arctic regions
during that period, can hardly fail to promote autogamy amongst the plants grow-
ing in those regions. Such as have flowers that can pollinate themselves spontane-
ously will be more sure of ripening their seeds before the brief summer ends than
will such the flowers of which must wait for insects. In the foregoing pages
several instances have been described in which autogamy is promoted by the closing
of the flowers. By these movements the pollen is mechanically transferred to the
stigmas. It may well be that by the considerable increase which must accrue in
these closing movements, owing to the frequency of unfavourable weather in alpine
and arctic regions, a further condition favouring autogamy is obtained.

FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

Pollination, or the dusting of the stigma with pollen, is only the prelude to
the phenomenon known as Fertilization. It is important to distinguish clearly
between these two events, especially as the term “fertilization” is frequently used
by authors when they really mean “ pollination” —indeed, this substitution is almost
inevitable in many cases, the custom being what it is. Fertilization can only occur
in Phanerogams after previous pollination, though pollination does not invariably
connote a subsequent fertilization. Thus, cases are known in which flowers, polli-
nated by insects at the proper time, do not produce fruit, and others in which the
pollen of the same flower falls upon the stigmas with a like failure of result. In
other words, both eross-pollination and autogamy may be without result.

It must be explained, to prevent misunderstanding, that the older accounts of
this lack of result attending pollination should be received with caution. Formerly,
judgment was passed rather hastily as to the results of pollination in hermaphro-
dite flowers, as it seemed obvious that the sexual elements must, unavoidably, come
together. If no production of fruit took place in a really hermaphrodite flower, it
was assumed that pollination was without result, and no precautions were taken to
demonstrate that pollination had actually occurred. Thus it happened that certain
plants were regarded as sterile, although this sterility had only been observed upon
isolated specimens growing in gardens. In many cases the flowers of the plants in
question were strongly protogynous, i.e. at the time when the stigmas should have
been pollinated there was no pollen, there being no plants growing near with
flowers in a more advanced stage. Similarly, such flowers cannot be autogamous,
as the two sets of organs are never at maturity simultaneously. They are marked

out for cross-pollination. When for any reason this does not take place, fertilization
Vou. II. 76

402 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS,

and fruiting obviously cannot oceur. It is instances of this kind that are adduced
by the older botanical writers to prove that the hermaphrodite flowers of certain
species are infertile.

Plants have also been regarded as sterile from the fact that the particular
insects necessary for the transfer of their pollen were absent from the locality in
which the observations were made. Thus, Paederota Ageria, a plant not infre-
quently found in rocky crannies in the Southern Alps, and cultivated in large quan-
tity in the Innsbruck Botanie Garden, was always found to be sterile in the last-
mentioned locality, although it flowered profusely. The flowers of the plant require
insects to pollinate them, as the relations of the parts are such that autogamy can-
not occur. Since the particular insects which visit it in its own habitat are absent
from the Botanie Garden, the plant is infertile from lack of pollination. In its own
home in the Southern Tyrol and Krain, where these insects are present, it ripens
an abundance of fruits. The same is the case with several introduced plants which
have become partially wild. The Sweet Flag (Acorus Calamus), truly indigenous
to Eastern Asia, has spadices of densely-crowded, hermaphrodite flowers. The indi-
vidual flowers are’ strongly protogynous, and when the anthers open, the stigmas
of the same flower are already faded. Autogamy is consequently excluded. The
opening of the flowers is from below upwards, and when the anthers of the lowest
flowers are discharging their pollen the stigmas of the uppermost flowers are still
capable of pollination. Could the pollen pass from the lower to the upper flowers,
geitonogamy would take place, but this is only possible through the agency of
insects, as the pollen is adhesive. In Europe, where the plant is not originally
indigenous, this never happens, as the insects which visit it are absent; consequently,
with us, Acorus is always sterile. But further east, where it is indigenous, its
flowers are pollinated by insects, and it produces its fruit in spikes of red berries.
The Day Lily (Hemerocallis fulva) has ephemeral flowers which open in the morning
in summer-time between 6 and 7 o’clock, and close between 8 and 9 in the evening.
Its flowers are protogynous for a very short time. For half an hour before the
opening of the flower the mature stigma projects from the tip of the perianth.
Simultaneously with the folding back of the perianth, the anthers liberate their
adhesive pollen. The style being longer than the stamens, its stigma is not auto-
matically pollinated. For pollination insect visits are necessary. Honey is secreted
at the base of the tube of the perianth, which is 2 em. long. The entrance to this
honey is so narrow that only a very delicate proboscis can gain access. Beetles,
flies, bees, and other short-tongued insects cannot get it, nor would they be of any
use for pollination if they could. The whole flower seems adapted for the visits of
some large butterfly with a long, thin proboscis, but curiously enough the flowers of
Hemerocallis fulva are never visited by butterflies in Europe. As autogamy is
excluded, the flowers remain unpollinated, and are sterile. Neither in gardens,
where it is much cultivated, nor in its semi-wild state does the Day Lily ever fruit
with us. It is more than probable that Hemerocallis is visited, in Northern Asia
and Japan, where it is truly indigenous, by some butterfly absent from Europe.

POLLEN ON THE STIGMA, 403

It has been already mentioned (p. 156) that the flowers of the American Yuccas
are pollinated by small moths, unknown in Europe, and that these flowers set no
fruit with us. Also, that several species of Catchfly, indigenous to the Southern
and Eastern Alps, though robbed of their honey by humble-bees, are but seldom
pollinated and fruitful (p. 239).

Lastly, many cultivated plants, depending on insects for fertilization, flower in
gardens earlier or later than in their wild surroundings. In nature, their period of
flowering coincides with the time of flying of certain insects; in gardens—even
when the insects in question occur—the flowers may be too early or too late for the
insect season. From what has been said above, it will appear that sterility in many
cases is only apparent, and is due merely to the lack of the normal and necessary
conditions for bringing about pollination.

In other cases it may happen that although the stigmas are pollinated, the pollen
cells are abortive and incapable of producing pollen-tubes. This condition of the
pollen obtains most frequently in gardens amongst plants on rich, well-manured
soil, artificially-produced hybrids, and plants whose stamens are partly converted
into petals. At the same time it must not be supposed that by any means all plants
which show a “doubling” produce bad pollen; for instance, many double Roses pro-
duce pollen which is used by gardeners for artificial pollination with good results.
Still, in the majority of such plants abortive pollen is the rule, pollen which is non-
effective on the stigma.

In nature, especially in places where many plants flower at the same time, as on
the borders of a wood, in meadows and heaths, it is unavoidable that the pollen of
various species should be deposited on one and the same stigma. Insects certainly
show a preference for a single species for considerable periods, particularly when
this species is flowering in quantity on a confined space; still, anyone who closely
observes insects visiting flowers can easily convince himself that the flowers visited
are changed from time to time. A bee which has just dusted itself with pollen in
the flower of a Winter Aconite (Zranthis) will fly across to visit a bush of Salia
daphnoides, and as it passes a plant of Daphne Mezerewm it will suck its honey; a
moment later it will swoop down to the flowers of Crocus vernus in the meadow
near by, and then fly on to the Sweet Violet (Viola odorata). On the stigma of the
last-mentioned plant will be found the pollen of all or several of the just-visited
flowers, on the Crocus that of the Willow, and so on. The case is similar with
wind-pollinated flowers. I have found the pollen of the Spruce Fir (Abies excelsa)
and of Dog's Mercury (Mercwrialis perennis), both brought by the wind on to the
stigmas of the Herb Paris (Paris quadrifolia); and on another occasion the stigmas
of Gagea lutea were so thickly dusted with the pollen of Alnus viridis that there
would have been no room for any pollen more.

That the pollen of the Willow will fertilize the Crocus, that of Dog’s Mereury
the Herb Paris, or that of the Alder the Gagea is « priori improbable. Only such
changes take place in the pollen as always oecur when it is placed on a moist
substratum; all further stages in its development are arrested. The commencing

404 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

pollen-tubes, sometimes found, though in some cases they penetrate the tissues of
the stigma, do not fertilize the ovules. It is another question whether or no this
“foreign” pollen is entirely without effect, whether it does not possibly influence the
stigmatic tissue so that less foreign pollen, arriving later on the same stigma and
developing pollen-tubes, is affected. But this subject can only be dealt with later
on; here it suffices to state that all pollen falling on a stigma is not necessarily
suitable, and that the stigma has, in a manner of speaking, to make a selection.

It is very difficult to say what conditions come into play in this choice of pollen.
Experimental inquiry into this matter has not been wanting, but its results tell us
little as to the fundamental processes at work. By it we ascertain little more than
whether this or that artificial pollination leads to a production of seeds or not.
Thus in one ease no seed will be formed, in another a few, and in a third case an
abundant crop. The sources of error in this class of experiment are considerable,
nor do the results by any means always harmonize. Thus, in experiments of my
own as to the fertility of certain Catchflies when pollinated from allied forms, no
result would be obtained in one year, whilst in the following year their repetition led
to the production of a certain number of seeds. Other observers have had the same
experience; and it would seem that whatever care be exercised, absolute reliance
cannot be placed on the result—especially where it is a negative one. Caution must
be used, therefore, in generalizing from such experiments, especially in cases where
their number is limited. In the main, the general results are very instructive, and
must not remain unnoticed here in so far as they relate to the connection between
fertilization and the origin of new species.

These results may be shortly summarized as follows. When the pollen of one
species is placed on the stigma of another species, pollen-tubes capable of fertilizing
the ovules are developed only when the two species belong to the same genus or to
the same natural family of plants. Families and genera are conceptions devised by
Botanists, and although their limitations are to some extent arbitrary or dependent
on the personal equation of individual observers, in the main there is little differ-
ence of opinion as to these limitations in the case, at any rate, of families. How far
new discoveries may lead to a revision of their present limits must remain un-
decided, but, of families as at present laid down, we may say that crossings of pollen
between species of two different families (orders) is without result, whilst between
species of two different genera very rarely is seed produced.

The crossing of species of the same genus results, in most cases, in fertilization,
and eventually in the production of hybrids. It is certainly remarkable, in this
connection, that external similarity between the two species crossed has little bear-
ing on the result or absence of result. One of the commonest of naturally-produced
hybrids is one which owes its origin to the union of Primula glutinosa with
Primula minima, two species very dissimilar in the form of their foliage and
flowers. On the other hand, hybrids of the very similar Cowslip and Bardfield
Oxlip (Primula officinalis [veris] and Primula elatior) are but rarely met with in
nature, whilst artificial pollinations between them only occasionally lead to any result.

RESULTS OF VARIOUS CROSSINGS. 405

If ripe pollen from the male flowers of a plant be placed on the mature stigmas
of female flowers of the same species, the result may be regarded as certain. This
holds good equally for moncecious and dicecious plants, and for such also as have
apparently hermaphrodite flowers in which one or other set of sexual organs is more or
less abortive, so that the flowers in question are to all intents and purposes unisexual.

It has been shown that for plants with true, non-heterostyled, hermaphrodite
flowers, a transfer of ripe pollen from the anthers of one flower to the mature
stigma of another, belonging to the same species, constantly leads to fertilization. In
those cases only in which the stamens are of unequal lengths is pollination attended
with unequal results, according as the pollen has been taken from the longer or
shorter stamens.

The behaviour of plants with hermapbrodite heterostyled flowers is peculiar.
Pollen from the anthers of a short-styled flower applied to the stigma of a long-
styled flower, or from a long-styled flower applied to the stigma of a short-styled
flower, gives the best result. The other possible combinations, &.e. pollen from long-
styled or short-styled flowers applied to the stigmas of the same class of flower give
indifferent results, and frequently none at all. Experiments have shown in the case
of the Loosestrife (Lythrum Salicaria), which, as we have seen (p. 303), possesses
long-, mid-, and short-styled flowers, that crossings between stamens and styles of
the same length (“legitimate unions”) are fruitful, whilst all other crossings (“illegiti-
mate unions”) are either quite sterile or followed by only a sparing production of seed.

It has been demonstrated that the pollen-cells of heterostyled flowers vary both
in size and colour according to the length of stamen (or height of anther or corolla)
producing them. Thus, in the Loosestrife, the dry pollen-cells of the long stamens
are green, and 30-38 long and 20-26 » broad; those of stamens of the middle length
are yellow and 23-26 » long and 13-16 x broad; those of the short stamens are also
yellow, but 20-25 » long and 11-13 » broad (x = yy millimetre). In the Cowslip
(Primula officinalis [ =veris]) the pollen-cells, produced by anthers at the mouth of
the corolla-tube (and destined for a long style), have a diameter of 30 x, those arising
from anthers low down the tube (and destined for a short style), a diameter of only
20. The explanation offered by Delpino of this difference in size—that, other
things being equal, pollen-tubes which have to traverse a greater distance to reach
the ovules require a more ample supply of reserve-materials than those which have
less far to penetrate—sounds plausible, but the problem is probably a rather more
complex one than appears at first sight. As a general result of experiments upon
heterostyled plants we may say that the most copious production of good seed
results from a pollination of stigmas with pollen from stamens of similar height.

As to the result of awtogamy (self-pollination) in ordinary hermaphrodite
flowers, it would appear, in all cases where the stamens are of unequal heights,
that the pollen has a dissimilar effect according as it comes from a longer or shorter
stamen. If pollen, which would not unaided reach the stigma of the same flower, be
artificially transferred to that stigma, the product is usually very small. If, however,
pollen which would ultimately reach the stigma of the same flower be artificially

406 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

transferred thither a good erop of seed results. Artifieially produced autogamy in
hermaphrodite flowers, in which the stamens are all of one length, is generally
productive, nor does it appear to matter whether the pollen used for pollination be
taken from the first stamen to open or the last. The number of species in which
artificial autogamy is unfruitful is extremely small. Crambe tataria, Draba repens,
Lilium bulbiferum, Lysimachia nummularia, and a few Orchids and Papilionaces
may serve as examples, though even in these cases it is quite possible that some
source of error, such as was mentioned at the commencement of this chapter, has
been overlooked.

We may now proceed to discuss what is known as the prepotency of foreign
pollen over own pollen. The term “foreign” is used of pollen upon a stigma which
has been brought from another flower of the same or of some other species; “own”
pollen, on the other hand, is applied to such as has originated in one of the anthers
of the same flower. These terms are employed for the sake of brevity. If one
examines a flower of Corydalis early in the morning of the day on which that flower
will become accessible to insects, one finds that the anthers have already dehisced,
and that the stigma is covered with own pollen. The stigma, lying between the two
spoon-shaped petals, is regularly embedded in pollen. But as yet the stigma is
immature and unreceptive, so that the absence of any interaction between pollen
and stigma at this stage is intelligible. When insects come in due course, a portion
of this pollen will be removed (ef. p. 266). Should the insects have visited Corydalis-
flowers previously, they will leave some of the foreign pollen with which they are
dusted upon the stigma at the moment when they remove some of the own pollen.
The stigma is now in contact with both own and foreign pollen, nor will additional
insect-visits materially alter this state of affairs. In due time the stigma becomes
receptive and exerts a selective action upon the pollen. Though the process, as it
takes place here, cannot be followed step by step, still we are justified in assuming,
on the results of many experiments of artificial pollination, that the foreign pollen
receives the preference. It has been shown for Corydalis cava that the flowers are
absolutely barren to their own pollen, only slightly fertile to pollen from another
flower on the same plant, and only thoroughly fertile when impregnated with pollen
from a different plant. For other species, however, e.g. Corydalis capnoides, fabacea,
and ochroleuca, it has been shown that the plants are fertile to their own pollen, so
that if no insect-visitors come, the flowers do not remain sterile.

These results show how fallacious it would be to make the condition obtaining
in Corydalis cava the basis of any far-reaching generalization, such as that auto-
gamy is prevented, and without result. In point of fact, autogamy is highly pro-
ductive in most species of Corydalis, and occurs, in such plants as are unvisited by
insects, in the closed flower in a manner recalling that form of autogamy known as
cleistogamy (cf. p. 391). That foreign pollen is prepotent in Corydalis capnoides,
fabacea, ochroleuca, &e., when both foreign and own pollen are present on the stigma
together, is neither asserted nor denied, though, in view of all the circumstances, it
seems probable.

PREPOTENCY OF POLLEN. 407

In agreement with Corydalis stand numerous species of Fumaria, and a great
number of Papilionacez, especially those whose flowers possess a piston-apparatus
(ef. p. 260). Pisum and Ervum, Lotus and Melilotus, the various species of Tri-
Jolium, almost all of them, when unvisited by insects, ripen seed, only a few species
here and there being infertile when dependent upon their own resources. Thus we
may say that when the stigma has to choose between own and foreign pollen, the
latter probably gets the preference, though, when own pollen alone is present, it is

_ adequate for fertility.

A similar condition obtains amongst the Scabiouses (Scabiosa) also. Their
flowers are hermaphrodite and protandrous, and united into heads. At the time
when the anthers dehisce, the pollen remains hanging to the stigmas, although these
are not as yet actually receptive. For the time being, this pollen is without effect-
By the visits of insects a portion of this pollen is removed and replaced by foreign
pollen, which is ultimately, on the maturing of the stigmas, probably preferred to
the own pollen. In the absence of insects, however, the flowers are undoubtedly
fertile to their own pollen.

Likewise, in many Labiates (e.g. Leonwrus heterophyllus) and Scrophulariaceze
(e.g. Linaria littoralis and minor), has essentially the same state of affairs been
shown to exist. One more instance only need be described, that of a Catchfly (Silene
noctijlora). This plant opens its flowers at about seven in the evening. If, however,
the flowers be opened artificially a little earlier, at about six p.m., it is found that
all the anthers have already dehisced, and that the delicate stigmatic papille are
already dusted with the pollen from the five short stamens. Thus, already in the
bud, autogamy has taken place in a manner not unlike cleistogamy. As the flowers
open in spite of this, it can only be on the chance of crepuscular or nocturnal moths
visiting them and bringing foreign pollen. The flowers of this Catchfly are not very
eagerly sought after by insects, still now and again a Plusia or other owlet moth
may be seen flitting from flower to flower, sucking honey and bringing and taking
pollen. Thus, again, a selection of pollen by the stigma probably occurs with
preference for the foreign; otherwise, why need these flowers open at all since the
stigmas are already coated in the bud with own pollen? In the absence of insects
the own pollen will be potent and lead to seed-production. In wet, cold weather
also, when the flowers do not open at all, the ovules ripen into seeds, no doubt
impregnated by their own pollen. In all the cases enumerated the behaviour is
essentially the same, in the early stages of flowering the opportunity is given for
eross-pollination by insects, but, wanting this, autogamy or self-pollination ensues.

We may now pass on to speak of the germination of the pollen-grain upon the
stigma and of the development of the pollen-tube. The pollen is at this stage
influenced by the receptive stigma. There would appear to be a taking up of fluid
matter by the grain, though its exact nature has not been accurately determined.
Since, however, pollen-grains germinate readily in a 3-per-cent sugar-solution, it is
extremely probable that sugar is an important component of this stigmatic fluid.

The first demonstrable stage in the production of the pollen-tube is the pushing

408 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

out of the delicate inner coat of the grain in the form of a tube through the thin
places in the extine. The structure and distribution of these thin spots has been
already described (p. 102); it need only be added that a tube may be pushed out
at each or any of them. When pollen is artificially cultivated in a prepared sugar-
solution several tubes arise simultaneously from different spots, but, in nature, on
the stigma, the production of a single tube is the rule. The tube which contains the
whole of the contents of the pollen-grain (spermatoplasm) forsakes the extine, which
remains behind as a dead shell. Very soon after its appearance through one of
these holes in the extine, the pollen-tube comes to have a considerable diameter, j
often approaching that of the grain in size. The tube now elongates, growing always
at the expense of the stigma. Its mode of growth is similar to that of a fungal
hypha, and its relation to the stigmatic tissues resembles that of the hypha of a
parasitic fungus to its host. Like the parasite, it is able to penetrate the subjacent
tissue and to make its way through it for long distances.

This penetration by the pollen-tube is certainly amongst the most remarkable
properties of flowering plants. The object of these wanderings is to reach and
fertilize the ovules contained—in Angiosperms—in the closed chamber of the ovary.
Whether the stigma be sessile upon the ovary or situated upon a style, the distance
to be traversed is considerable, and, in a very large number of cases, the way leads
through closed tissues. As the pollen-tubes travel as a rule by definite rows of cells
or tracks, we may assume that these latter are in some way specialized for their
conduction; still it is very puzzling to understand exactly in what manner these
cells become thus qualified. In all likelihood the pollen-tubes are attracted by
certain substances secreted by the tissues, which they have to traverse in order to
reach the ovules. Of these sugar seems to be the most important, and by a continuous
secretion of this (and possibly other substances), the tubes are led on to the ovules.
Casual allusion has already been made to the fact that the motile spermatozoids of
Cryptogams swim through the water to the archegonia (amphigonia) in response to
a somewhat similar stimulus (p. 68).

Investigations into the course followed by the pollen-tubes in passing from the
stigma to the ovules show that it varies in different cases. Simplest, and perhaps
typical of what was formerly supposed to be the route universally followed, is the
case of the Martagon Lily (Lilium Martagon, ef. fig. 313"). If the columnar style
of this plant be cut longitudinally one sees that it is penetrated by a canal which
narrows below towards the ovary, but widens out into a funnel at the stigma, where
it opens by a tri-radiate slit. The lips of this aperture bear numerous papill»; to
these the pollen-grains become attached and here commence to form their tubes.
The tips of the pollen-tubes curve down into the funnel and grow along the cells
which line the style-canal (fig. 3131). Passing down this canal, which is at this
time more or less mucilaginous, the pollen-tubes are led ultimately to the cavity of
the ovary in which are contained the ovules.

Very different is the mode of travelling of the tubes in Grasses, of which Avena
elatior (fig. 3132) may be taken as type. Upon the spherical ovary of this plant

THE COURSE OF THE POLLEN-TUBE. 409

two delicate feathery stigmas are inserted (ef. fig. 231, p. 139). The shaft of each
of these stigmas consists of elongated, succulent, colourless cells, whilst the barbs of
the feather are extremely delicate and filamentous in character, and have the upper
extremities of the cells of which they are composed continued as little papillee (fig.
3132). Neither in the main axis nor in the branches of the stigma are canals present.
The cells fit edge to edge, and the pollen-tubes must bore a way for themselves in
order to traverse the tissues in this case. The pollen-grains are attached to the

Fig. 313.—Development of Pollen-tubes.

1 Longitudinal section of the stigma and upper portion of the style of Zilium Martagon. The pollen-grains present on
the stigmatic papille are sending their tubes down the mucilaginous cells of the style-canal (after Dodel-Port); x110.
2 Portion of the feathery stigma of Avena elatior. Pollen-grains are attached to the papille, and their tubes may be seen
boring in between the cells of the stigmatic branches; x 170.

papille, and as the little pollen-tubes are produced, these latter bend round so as
to grow down along the inner face of the papilla. To do this they often execute
very complicated curves, or they may grow spirally round the papille. Having
reached the angle at the base of a papilla, they bore themselves a passage between
the superficial cells and grow henceforward down to the ovary in an intercellular
channel of their own making.

In the Grasses not only is no pre-existing canal present, but the cells between

410 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

which the pollen-tube penetrates show no demonstrable difference from their neigh-
bours. In this respect the Grasses differ from the very large number of plants
which, although they do not possess an open style-canal as in Liliwm Martagon,
have a loose axial string of mucilaginous tissue in their styles through which the
pollen-tubes readily penetrate. Examples of this condition are the Solanacew and
Scrophulariaceze. In other cases the conducting tissue is not differentiated from its
surroundings, so that the whole of the substance of the style and stigma serves for
the conduction of the pollen-tubes, as in Cistus, Helianthemum, and Orchids.

A curious condition prevailing in the Cactuses has been observed in the fre-
quently mentioned Cereus. Here, although a narrow style-canal is present, the
pollen-tubes prefer to make their way to the ovary embedded in the tissue surround-
ing the canal. From this it would appear that it is of advantage for the pollen-
tubes to travel thus inclosed by other tissues.

Different again is the course followed by the pollen-tubes in the Malvacez and
in many Caryophyllacex. The stigmas here are in some degree like those of
Grasses. As there, so here, the superficial cells are produced into long, thin-walled
papille; to these papille the pollen-grains become attached by the agency of insects.
The pollen-tube as it develops from the grain at once perforates the wall of a
stigmatic papilla and continues its growth in the cell-cavity. The course now fol-
lowed is remarkable. In the Corn Cockle (Agrostemma Githago) the pollen-tube
often zigzags from one side of the cavity of the stigmatic papilla to the other, not
infrequently taking first of all the wrong direction and bending up towards the tip
of the papilla, and then bending completely round again. Having reached the base
of the papilla, the tube bores through into the conducting tissue in the interior of
the style, but in its further course down to the ovary grows solely between the cells,
not in them. It sometimes happens that more than one tube arises from a single
pollen-grain; the accessory ones, however, are for purposes of firmer attachment,
and though they occasionally enter a stigmatic papilla do not continue their growth
down the tissue of the style. One functional pollen-tube only is produced from
each pollen-grain. In the Malvacez (e.g. Malva sylvestris) the pollen-tube entirely
fills a stigmatic papilla, broadening out at the base. Ultimately the contents of the
tube escape from their membrane and travel down the style in an elongated mass,
destitute of wall, like the plasmodium of a Myxomycete.

Whatever be the manner of its travelling, whether with or without a wall
of its own, the aim of the protoplasm of the pollen-grain is to reach one of the
ovules in the ovary. Having entered the cavity of the ovary, a pollen-tube
shapes a course for an ovule. The particular portion of the ovule aimed at—in
the vast majority of flowering plants—is the micropyle (cf. vol. i. p. 644), the
little receptive spot at which the coats of the ovule are discontinuous, and at
which access to the embryo-sac (wherein is contained the egg-cell) can be gained.
Only comparatively rarely is the micropyle situated immediately below the point
at which the pollen-tube must enter the ovary, as represented, for instance, in
fig. 208°, p. 74. Sometimes the micropyle is directed towards the side wall of

THE COURSE OF THE POLLEN-TUBE. 411

the ovary, sometimes towards the eentral column, as in the Star of Bethlehem
(Ornithogalum, figs. 315 %*5); whilst frequently the ovule is inverted so that the
micropyle faces the base of the ovary (ef. fig. 211°, p. 79). Since, in the majority
of plants, several ovules are contained in a single ovary and each is fertilized by a
separate pollen-tube, we find a number of tubes traversing the style, and, on their
entering the cavity of the ovary, diverging to the several ovules. One would
expect now to find this portion of the route to be followed by the pollen-tubes well

Fig. 314.—The course of the pollen-tubes in a Rock-rose (Helianthemum marifolium).

1A single flower, natural size. 2A flower, stripped of its sepals and petals, showing stigma and style and ovary in longitudinal
section; the pollen-tubes are seen passing down the style to the ovary and there going one to each ovule (the tubes are
indicated erroneously as going direct to the micropyles; actually they follow a more devious course, first down the inside
wall of the ovary and then up to the micropyles); x22. %Stigma and upper portion of style in longitudinal section; shows
pollen-grains attached to the stigmatic papille and tubes penetrating the tissues; x 55. 4# A dry pollen-grain; x 300. 5A
moistened pollen-grain developing its tube; x 300. 6 An ovule—which in this plant is of rather unusual form, the
micropyle being at the end of the ovule distant from the point of attachment; x50.

indicated, either mechanically as by furrows and grooves, or by lines of secretory
and nutrient cells leading to the micropyle. This, however, seems to be very rarely
the case. As a rule such obvious guiding mechanisms are wanting. The pollen-
tubes creep along the inner wall of the ovary to the places where the ovules are
borne and then turn up and enter the micropyles, one pollen-tube to each ovule.
The adjacent figure 314° shows for a Rock-rose (Helianthemum) the whole course
of the tubes from the stigma to the micropyles. As the tubes enter the cavity of
the ovary they diverge and pass one to each ovule. A slight error, however, has
crept into the figure in question in that the tubes are represented as passing direct

412 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

to the micropyles. In point of fact they follow a more roundabout course, creeping
along the ovary wall, and then up the individual ovules to the mieropyle.

It has been stated above that the pollen-tube enters the ovule at the micropyle
in the vast majority of flowering plants. But this is not universally the case, as
recent investigations have proved. In several of the trees belonging to the group
of the Amentacez the pollen-tube follows an altogether different course. This
was first established for the case of
Casuarina, a curious switch-plant
indigenous to Australia and certain
parts of Eastern Asia. A small por-
tion of a branch of this tree is shown
in fig. 69° (vol. i. p. 299). Casuarina
is wind-pollinated, the flowers being
unisexual, though both male and
female flowers are borne on the same
individual. The pollen-grains ger-
minate in due course on the stigma,
and their tubes traverse the tissues of
the style. The tubes do not, however,
enter the cavity of the ovary, but con-
tinue their growth immersed in the
tissues of the ovary. They thus make
their way to the points of insertion
of the ovules, where they enter them,
and at once travel to the base or
chalaza. From the base of the ovule
the pollen-tube penetrates towards

the apex of the ovule, reaching the
egg-cell from below, not from above

Fig. 314 4.—Chalazogamic fertilization in the Hornbeam
Corre Babies) as in cases in which the pollen-tube

The drawing shows a longitudinal section of an ovule almost fill- = -
ing the cavity of the ovary. The micropyle (m) and the two entered the ov ule by the mıcropy. le.

integuments are shown above the apex of the nucellus (in This t e of fertilization ha
whose cells the nuclei are indicated). Within the nucellus yP ert = s been

three embryo-sacs are represented; a pollen-tube (p.t.), pass- termed chalazogamie in eontradistine-
ing down into the substance of the ovule from the placenta, A 2
follows the course of the raphe and at the base of the nucel. t10n to the more usual micropylar or

lus (chalaza) bends sharply round and enters one of the . tl A . t ] t ]
embryo-sacs; its tip penetrates to the egg-cell at the apex porogamic me 10d. Qui e lately a

MF Beaty Much enlarged (rom a drawing ty renewed examination of many common

trees belonging to the Amentaceous
group has shown that in several of them also fertilization is chalazogamic. This is
the case in the Hazel (Corylus) and Hornbeam (Carpinus, fig. 314 4), belonging to
the Corylacez, as also in the Birch (Betula) and Alder (Alnus, fig. 3148), belonging
to the Betulacez. In the Hazel and Hornbeam the pollen-tube, after reaching the
‘base of the ovule, passes straight up to the egg-cell in the embryo-sae (ef. fig. 3144,

pt.) in a manner similar to Casuarina, but in the Birch and Alder its course is

CHALAZOGAMIC FERTILIZATION. 413

not so direct. Here it passes by the embryo-sac on one side and then turns sharply
down again, reaching the egg-cell from the same direction as it would have done
had it entered by the micropyle (ef. fig. 314.8, p.t.). It is interesting to note that
in many nearly allied Amentacex, as in the Cupuliferee, which includes the Oak
(Quercus), Beech (Fagus), and Chestnut (Castanea), fertilization is by the micropyle.

The following table indicates the method of fertilization as at present known in
the various families comprehended in the group

Amentaceze:— J

AMENTACE. A
Mode of fertilization,
1. Betulacex.
otula R Ge
zu | ene ess «. Chalazogamic. P
Alnus
2. Corylacez.
Hazel (Corylus :
run) R ! Chalazogamic.
Hornbeam (Carpinus) §
Hop Hornbeam (Ostrya) ... Not ascertained.
3. Cupuliferze.
Oak (Quercus)
Beech (Fagus) Porogamic.
Chestnut (Castanea)
4. Juglandacee.
Walnut (Juglans) ... ... Porogamic. -
Carya, Ptero-carya, &. ... Not ascertained. SE
5. Myricacex. Zu
Sweet Gale (Myrica) --- Porogamic. Fig. 314 B.—Chalazogamic fertilization in the
6. Casuarinex Alder (Alnus glutinosa). Diagrammatic.
Casuarina... O22 SO Chalazogamic. The drawing shows one half of a longitudinal
7. Salicines. section of the ovary. The wallof the ovary
7. Sa ee : is thick, and has a hardened middle layer
Willow (Sahix) ! ER Porogamic. (shaded dark). At the topis the base of the
Poplar (Populus) 5 = style, from which the pollen-tube (p.t.) can
be traced passing straight on through the
R substance of the ovary to the ovule. Enter-
Many experiments have been made from ing the ovule by its point of attachment to
5 5 5 = ee the placenta the pollen-tube bends sharply
tıme to time with a view to explaining the upwards (at the chalaza) into the nucellus.
phenomena attendant on the wandering of the MEIDEN NE EAN TEL OT
on the inner side, and when below the micro-
pollen-tube from the stigma to the mieropyle. It Buena EBEN AOL ST Ne
2 embryo-sac. e vascular supply 0: ne
has been shown that the pollen-tube is extremely ovules, which forms acolumn in the placen-
ehe = ofa ta, is shaded dark. Considerably enlarged
sensitive to various external conditions, and that (rom a drawing by M. F. Ewart),

by appropriately varying these the direction

followed by the tube in its growth may be controlled. Pollen-tubes are especially
sensitive towards sugar-solutions, and bend out of their course towards the sugar.
They also tend to grow away from the air, and show a preference for spaces satu-
rated with aqueous vapour to such as are less humid. Of all the conditions which
affect a pollen-tube, most conspicuous is the attraction which sugar exerts upon it.
Various portions of the pistil exert a similar chemical stimulus on pollen-tubes, very
marked being the action of the micropyle in this respect. A few of the experiments
demonstrating this attractive property of stigma and ovules may be briefly
deseribed. If a fresh mature stigma be cut off and laid on a plate of gelatine, and

414 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

the gelatine in its immediate neighbourhood be dusted over with pollen-grains of
the same plant, in the course of a few hours, as the pollen-tubes are developed, it
will be found that they converge upon the stigma in an unmistakable manner.
Pollen-tubes, even at so considerable a distance from the stigma as seventy times
their own diameter, have been observed to be influenced in this way. Similar
results obtain when sections of a style are employed instead of a stigma, but the
attraction is not so strong. Isolated ovules laid on the gelatine exert a very marked
attraction upon pollen-tubes. In one case as many as forty pollen-tubes were
counted converging upon the micropyle of an ovule of Scilla patula. Ripe ovules
ready to be fertilized exert the strongest attraction, though younger and as yet
immature ovules are not without influence.

Noteworthy is the fact that an ovule is found to attract not only pollen-tubes
from pollen of the same species, but of others far removed from it in point of
affinity. Thus the pollen-tubes of Scilla patula (a Monoeotyledon) were found to
be attracted by the ovules of Diervilla rosea and Ranunculus acer (Dicotyledons),
tubes of Primula sinensis by the ovules of Antirrhinum majus and Digitalis
grandiflora, those of Hesperis matronalis by ovules of Lonicera Periclymenum,
&c. In these experiments these strange pollen-tubes were not only attracted
towards the micropyle, but actually in a few cases penetrated it. Still, no suggestion
is made that anything of the nature of fertilization could be accomplished by these
foreign pollen-tubes.

Nor is this attraction limited to pollen-tubes. The delicate hyphe of several
mould-fungi are similarly attracted, as also, when the surface on which the ovule
rested was moistened, was that common micro-organism of decomposition, Bacterium
Termo.

Thus it appears that substances are present in the stigma, style, and ovules,
which exert a chemical attraction upon pollen-tubes, gradually leading them to the
micropyle. Though it has not been possible to determine in all cases what these
substances are, it is extremely probable that they are of a sugary nature. In the
case of plants with chalazogamic fertilization, in which the pollen-tube, as we have
seen, never enters the cavity of the ovary, it would be of interest to ascertain if the
micropyle is destitute of attraction for pollen-tubes.

As stated, the attraction exerted by a given ovule or portion of a pistil is not
limited to pollen-tubes of the same species, but seems common to pollen-tubes in
general, and indeed to fungal hyphe and the like. Thus it happens that instances
are recorded in which fungal spores fell on the stigma, and germinating there, sent
their hyphz down the style to the ovary like pollen-tubes. And so with foreign
pollen. Though it is often stated that the pollination of the stigmas of a plant A
with pollen from B (a plant not allied to A) is without result, what is actually indi-
cated is that no seed has been ripened by the pistil thus pollinated. Experiment
has shown that, just as the pollen-tubes of one plant may be attracted towards the
micropyle of an ovule of a plant of entirely different family, so pollen will germin-
ate on the stigma of a similarly remote plant and form tubes which penetrate

FERTILIZATION, 415

considerable distances down the style, though they perish eventually. Still even
should these foreign pollen-tubes actually get access to the micropyle, a fertilization
of the egg-cell by the foreign spermatoplasm would be impossible, owing to the
inability of the sexual protoplasm to combine outside a very narrow range of
affinity. We have already seen that many plants can be fertilized either by pollen
from another flower of the same species, or, wanting this, by their own pollen.

Fig. 315.—Fertilization.

1 Longitudinal section through the ovule of Ephedra (a Gymnosperm); x3. 2 Apical portion of a longitudinal section of the
ovule of Ephedra, showing the pollen-grains in the micropyle producing their pollen-tubes; x100. % Longitudinal section
through the ovary of Ornithogalum nutans; x 2. 4 Transverse section of the same ovary; x 3. 5 Longitudinal section
through stigma, style, and upper portion of ovary of Ornithogalum showing a pollen-grain on the stigma with its pollen-
tube passing down the style-canal to the micropyle of an ovule; x 3. § Longitudinal section through an ovule of
Urnithogalum. The funicle or stalk of the ovule is seen to the left, the ovule proper to the right. In the latter there is a
large central space, the embryo-sac which contains certain small cells; towards the apex two together of which one is the
egg-cell and the other a synergida, at the base two antipodal cells are represented. Around the embryo-sac is a layer of
nucellar tissue one cell thick, whilst below, this tissue is more bulky (contents dotted), Around the nucellus are the
integuments. A pollen-tube has grown down the micropyle and perforated the apex of the embryo-sac. It is represented
in contact with the egg-cell and one synergida. The other synergida is not shown; x100. (Partly after Strasburger.)

Both categories of pollen-grains are competent to develop tubes and to fertilize the
ovules. Under these circumstances it would be very interesting to know what
exactly happens when pollen-grains of both these categories are present on one and
the same stigma; whether (as is probable) both develop pollen-tubes, whether both

416 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS,

sets of tubes reach the ovary, or whether one set receives a check of some sort. In
fact we want to know whether foreign pollen is prepotent over own pollen (where
both are competent to fertilize), and if so how the prepoteney is accomplished. This
and a host of similar problems await solution.

Passing on now to the union of spermatoplasm and ooplasm it is first of all
necessary to describe the structure of the ovule in some detail. The egg-cell which
has to be fertilized forms but a small portion of the ovule. It is produced in
Flowering Plants within a large cell prominently developed and termed the Embryo-
sac. This embryo-sac is one of the cells of the central portion of the ovule known
as the Nucellus, and this cell as the time of maturation of the ovule approaches
grows much in size, in part at the expense of its neighbours. Ultimately the
embryo-sae occupies a large portion of the nucellus, being still inclosed by a layer
of small nucellar cells. Outside this are the integuments. They are not completely
closed, but at one spot an opening (the micropyle) is left, the entrance by which
the pollen-tube gains access to the embryo-sae. The general relations of the embryo-
sac to the other portions of the ovule are shown in fig. 315°, a longitudinal section
of the ovule of Ornithogalum. In fig. 316 three stages of the embryo-sac of Mono-
tropa are shown just at the time of fertilization. At an earlier stage the embryo-
sac is a uni-nucleate cell, and before the arrival of the pollen-tube at the micropyle
its contents divide up into a number of small cells, which, though devoid of cell-
membranes, are readily distinguishable from one another. At the apical or micro-
pylar end three of these cells are situated. The two uppermost, side by side, are
known as the synergide, whilst close below them and slightly to one side (cf. fig.
316) is the egg-cell, destined to be fertilized. These three cells constitute the “egg-
apparatus”. At the other extremity of the embryo-sac, .e. at the base, three cells
are present which are known as the antipodal cells. These, soon after their forma-
tion, develop walls around themselves and appear to play no part in subsequent
phenomena. Besides these, there are two nuclei (the so-called polar nuclei) lying
in the protoplasm of the embryo-sac, one close above the antipodals, the other just
below the egg-apparatus (fig. 8161). These two approach one another at about the
moment of fertilization and fuse (figs. 316° and 316°) about midway between egg-
apparatus and antipodals. They give rise ultimately to the food-material which
nourishes the young fertilized egg-cell during its early stages of development.

The egg-cell and its attendant synergide contain each a well-marked nucleus
and vacuoles. In the egg-cell the vacuole is above the nucleus (fig. 316°), in the
synergid the vacuoles are below the nuclei (fig. 316°). The nucleus of the egg-
cell is often very large. The structure and changes of cell-nuclei have already been
briefly reviewed at vol. 1. p. 581.

Meanwhile, in the pollen-tube changes have also taken place. Actually in the
pollen-cell before the pollen-tube is produced two nuclei are present. Though both
of these enter the tube one is quite sterile and soon atrophies. The other, however,
surrounded by a small portion of protoplasm, but destitute of wall, constitutes the
male sexual cell. It is carried, embedded in the general protoplasm of the pollen-

FERTILIZATION IN ANGIOSPERMS. 417

tube, near the tip, and so is gradually brought down to the embryo-sac. Usually
this male cell divides into two, but there is no evidence to show that more than one
of the daughter-cells thus produced takes an actual part in fertilization. When the
tip of the pollen-tube reaches the micropyle (as in fig. 315°, though the contained
male cells are not shown), the male sexual cells are well up to the end of the tube.
The pollen-tube forces its way down the micropyle, and perforates the apex of the
embryo-sac. The tip of the tube is now opened, and a male sexual cell passes out,
and, traversing the synergids, enters the egg-cell. The synergid® seem to promote
this transfer of the male cell to the egg,
though the precise part played by them
is not fully understood. With the pas-
sage of the male cell the synergide col-
lapse and shrivel; their part is played.
The anterior of the two male cells
of the pollen-tube enters the egg-cell,
the other one being possibly of the
nature of a reserve in case of accident.
Occasionally, it also enters, and has been
observed in the egg, though probably
this is an accidental circumstance. After
the entrance of the male cell its nucleus
approaches the female (egg-) nucleus
and fuses with it. This fusion con-
stitutes the act of fertilization. Though
this nuclear fusion is the most charac-
teristic feature of fertilization it may
well be that the other elements which
enter the egg-cell with the male nucleus

Fig. 316.—Embryo-sac of Monotropa.

Three stages are shown just preceding fertilization, in the
order 1,2, 8. In each of them we see the group of antipodal

likewise fuse with the protoplasm of
the egg. So far, observations have not
absolutely determined the fate of these
less conspicuous elements. On the
other hand, it is possible that these
subordinate elements serve in large part

cells at the base, and the egg-apparatus at the apex. 1 and
2 show the two synergidz side by side and the egg-cell ad-
jacent to them. Inthe synergid# are on the left, seen
through one another, both their nuclei showing; the egg-
cell on the right. The process of fusion of the so-called
polar nuclei is shown in the figs.; in 1 they are not yet
detached from their respective groups, in 2 they have ap-
proached one another, in ® they are in process of fusion.

merely as food-material for the egg. As yet the time has not arrived to speak

decisively on these points.

The fertilized egg-cell, which we may now term the embryonic cell, soon gives
indication of the change which it has undergone. It secretes a cell-wall around

itself.

Had it not been fertilized the egg-cell would have remained naked and

inactive, and ultimately would have perished.

In the account of fertilization of the Angiosperm just given, the main facts have
been related; and although from time to time fresh observations come to light, it is
hardly probable that the main outlines as given above will be overthrown. That a

Vow. II.

17

418 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

fuller knowledge of the details will be obtained is exceedingly probable, in view of
the active state of research into these processes.

In the Gymnosperms, the group of Flowering Plants with exposed ovules,
though the essential facts of fertilization—the fusion of the male sexual cell with
the female sexual cell (egg)— are the same as in the Angiosperms, just described,
in many subordinate points they exhibit marked differences. The male flowers of
Gymnosperms produce stamens with anthers in which pollen-grains are developed
much as in Angiosperms. The arrangements, however, associated with the produc-
tion of ovules are simpler than in the Angiosperms, and recall to some extent the
characters presented by certain Ferns. In the Ferns and other Cryptogams it will
be remembered that fertilization is under water, whilst in Phanerogams this is
accomplished through the medium of the air (cf. p. 71). The spermatozoids of the
Cryptogams reach the egg-cell in the oogonium or archegonium by swimming; they
are naked protoplasmic masses, and need no enveloping and protective cell-wall. It
is otherwise in the Phanerogams, where aérial fertilization obtains. Here a mem-
brane around the spermatoplasm is of great value; it serves to protect the contents
of the pollen-grain during its journey through the air, and afterwards, in connection
with the pollen-tube, is of the utmost value in conveying the male sexual cell to the
egg. Notwithstanding the resemblance presented by the female flowers of many
Gymnosperms to certain Cryptogams, they agree with the Angiosperms in the fact
that the male cell is brought to the egg-cell by means of a pollen-tube. In this
point all Gymnosperms agree, 2.e. the Cycads, Conifers, and Gnetacez.

The ovules of Gymnosperms show the grosser characters of those of Angiosperms.
In fig. 3357 is shown a scale from a female flower (cone) of the Seotch Pine (Pinus
sylvestris). Right and left at its base are the ovules, two in number. Each ovule
exhibits a central nucellus and a conspicuous integument surrounding it, leaving a
wide, funnel-shaped micropyle giving access to the tip of the nucellus (cf. also fig.
2085, p. 74, representing an ovule of Cycas). Within the nucellus a large cell
becomes marked out, as in Angiosperms; this is the embryo-sac. The embryo-sae
becomes filled with an extensive tissue, the endosperm, and produces at its apical
end (towards the mieropyle) a number of egg-cells. These vary in number from
2-15 in various Gymnosperms, but in any case they are all assembled together
beneath the micropyle. Associated with each egg-cell is a neck, recalling that
structure in the archegonium (or amphigonium) of Ferns (ef. p. 67). Fig. 315°
shows the tip of a gymnospermie ovule in section, considerably enlarged. Note
the funnel-shaped mieropyle (with germinating pollen-grains in it) and two large,
oval egg-cells in the endosperm below. The slight shading above the tips of the
two egg-cells indicates the necks. The contents of the egg-cells in this figure have
already given rise to several cells, as in the stage represented fertilization has just
occurred. The cells here shown in Ephedra (fig. 315°), or in most other Gymno-
sperms a limited number of cells (often four) cut off at the base of each egg-cell,
develop into little embryos, of which, however, ultimately one only survives for each

FERTILIZATION IN GYMNOSPERMS. 419

seed. A characteristic feature, occurring shortly before fertilization, is the eutting-
off of a small cell from the summit of the egg-cell. This little bi-convex cell (shown
at the tip of the right-hand egg in fig. 315°) is known as the “ventral canal-cell”.
A similar cell is cut off in the Ferns, &e., and lies at the base of the neck of the
archegonium just above the egg-cell. It is afterwards absorbed.

From a comparison of the structures in the ovule of a Gymnosperm with those
arising on the Fern-prothallium, or Moss-plant, it seems probable that the egg-cell,
with its neck in the former, corresponds to the archegonium of the latter, though
the archegonium in the Gymnosperm is somewhat reduced when compared with the
exposed archegonium of Ferns and Mosses.

The number of egg-cells (=archegonia) produced in the ovule of a Gymnosperm
is various. In the Spruce Fir and Pine there are from 3 to 5, in the Cypress and
Juniper 5 to 15. In the Firs and Pines the egg-cells are well isolated from one
another by layers of endosperm, in which they are embedded; in Cypresses and
Junipers the egg-cells are all in immediate contact, forming a rosette-like cluster
at the top of the endosperm under the micropyle. The tissue in which they lie
embedded, the endosperm, is in Gymnosperms pretty extensive, and being well-
stocked with food-materials, forms, after fertilization, a nutritive bed for the young
developing embryos, and is ultimately absorbed by them.

In the Angiosperms, on the other hand, the ovules are not exposed on open
scales, as in Gymnosperms, but inclosed in definite chambers, the ovaries. Pollen is
brought to the stigma (not to the micropyle, as in Gymnosperms), and fertilization
is accomplished by the development of pollen-tubes, which penetrate the tissues of
the style to the ovules. In Gymnosperms there are no ovaries or styles or stigmas.
Pollen is brought by the wind direct to the micropyle of the ovules. Various
arrangements exist for bringing the pollen-grains into the micropyle and for hold-
ing them there. Just at the time when pollen is liberated from the male flowers
the micropyle is opened wide, and its lining cells are rendered sticky by a mucila-
ginous secretion, so that the pollen brought by the wind sticks to it. This mucilage
often projects as a little droplet from the micropyle, and in it the pollen-grains are
caught; as this drop gradually dries up and contracts the pollen-grains are sucked
into the micropyle, so that the grains come to lie right on the tip of the nucellus of
the ovule, from which point they germinate, putting out their tubes (ef. fig. 315).
These drops of mucilage can be well seen in early spring on the exposed ovules of
the Yew-tree (Taxus baccata). This plant is dicecious, and on the female plants the
tips of the ovules project from a few scale-like wrappings, which envelop the base
of each ovule (ef. figs. 336° and 336°). At the time when the male flowers are
intrusting their pollen-grains to the wind (usually in March) one may see the
female plants, on a sunny morning sparkling in the sunshine as it were with dew-
drops. These “dew-drops” are in reality droplets of mucilage, excreted from the
micropyles of the ovules, awaiting the chance deposition by the wind of pollen-
grains. By and by they dry up and the entangled grains are sucked into the
micropyle. In Gymnosperms it is the micropyle, not the stigma, which is pollinated.

420 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

After the entrance of the pollen-grains into its mouth the micropyle con-
tracts somewhat, so that the pollen is, so to speak, imprisoned. In Gymnosperms
the active development of pollen-tubes only occurs some considerable time after
pollination. In the Pine the pollen-grains put out short tubes soon after pollina-
tion, but these tubes remain dormant from the spring in which pollination takes
place through the summer, autumn, and winter, and only continue their growth
after the lapse of about a year. Meanwhile changes take place within the ovule
leading to the production of the archegonia with mature egg-cells. Actual fertili-
zation occurs about thirteen months after pollination.

The contents of the pollen-cell, before it leaves the anther (Pines and Firs), or
shortly after its reception in the mieropyle (Taxus and Cupressus), divides several
times, a number of small cells being cut off at one side of the grain and their
substance being separated from the rest of the contents of the grain by cell-mem-
branes. Of these small cells one is the male sexual cell, and ultimately effects ferti-
lization. The big cell (known as the “vegetative cell”) produces the pollen-tube.
The male sexual cell (“generative cell”), becoming free from its attachments
(membranes), passes into the pollen-tube, where it divides into two cells. Ulti-
mately one of these cells fertilizes an egg-cell (the other not being required). In the
Juniper, where one pollen-tube fertilizes more than one archegonium, both these
generative cells—and possibly others, the result of their further division—would
appear to be utilized. The generative cells are carried along with the tube near
its growing tip—much as in Angiosperms. Bit by jbit the pollen-tube penetrates
deeper into the substance of the ovule which forms the floor of the micropyle.
Ultimately the tube reaches the neck of an archegonium, and pushes in between
the neck-cells, carrying the male cells to the mature egg-cell. In the Cypress
and Juniper, where several egg-cells are clustered close together, the tip of the
tube widens out, sending a little branch to each of the egg-cells (archegonia),
every one of which it is competent to fertilize. In the Pine, Firs, and other
Gymnosperms, distinct tubes from separate pollen-grains penetrate to the several
archegonia.

Fertilization happens much as in Angiosperms (described on p. 417); the male
cell enters the egg-cell, and the male nucleus fuses with the female nucleus.
Probably the other elements of the male cell are also taken up by the egg-cell.
Indeed, the whole process of pollen-tube development and fertilization is exceed-
ingly similar to these events as described in the Angiosperms. A chief point of
difference consists in the absence of distinct cell-walls between the cells which arise
in the pollen-grain of the last-named group.

The development of the embryo from the fertilized egg-cell is different in Angio-
sperms and Gymnosperms. In Angiosperms the egg-cell, after surrounding itself
with a cell-wall, becomes partly attached to the apex of the embryo-sae. It divides
by a transverse wall into two cells, one directed towards the micropyle, the other
towards the base (chalazal end) of the embryo-sac. The upper (i.e. micropylar) of

THE EMBRYO OF ANGIOSPERMS. 421

these two cells stretehes, and is repeatedly segmented; thus a string of cells is
formed, known as the suspensor, bearing at its lower extremity the embryo-cell,
which gives rise to the greater portion of the young plant. The suspensor, by its
elongation, brings the embryo-cell well down into the cavity of the embryo-sac,
where it is embedded in the substance of the endosperm which has meanwhile
developed. The nutrition of the young plant is thus assured during its early
stages. In many Parasites and in Orchids the full-grown embryo shows but little
differentiation, and is little more than a mass of cells exhibiting no distinction of
stem and leaf-structures; but in the great majority of Angiosperms it soon shows a
differentiation into parts—into a little root at one end and a stem at the other, with
the rudiments of leaves (cf. vol. i. p. 599, figs. 1411 and 141°). These leaves, the
cotyledons, are a conspicuous feature of the embryo, and in several plants they are
coloured green by a precocious development of chlorophyll in their tissues (e.g.
Styphnolobium japonicum). In a large number of plants, as, for instance, the
Apple and Oak, Bean and Pea, garden Nasturtium (Tropeolum) and Water
Chestnut (Trapa, ef. vol. i. p. 607, figs. 144425 4%), the cotyledons become much
enlarged and succulent, and take up large quantities of food - material, which
remains stored up in them as reserve-material for the further development of the
young plant at germination. When this happens the cotyledons usually come to fill
the whole cavity of the seed right up to the integument (testa). In the majority
of plants, however, the cotyledons remain small and thin, and do not take up the
whole reserve of food-material which envelops the embryo. Under these circum-
stances the embryo is provided with a special reserve-tissue, destined for its con-
sumption when it is separated from the mother-plant. This tissue is analogous to
the yoll of a bird’s egg, and consists of a tissue of cells filled with fat, starch- and
proteid-granules. This food-tissue is variously known as endosperm, albumen, &e.,
but the terminology associated with it does not reflect great credit upon the
Botanists who are responsible for the introduction of the various terms.

The starting-point for this reserve-tissue consists of the nucleus which arises
in the embryo-sac from the fusion of the so-called polar nuclei (represented in
figs. 316 %®, and described on p. 416). Around these nuclei a certain amount
of protoplasm collects, and after their fusion into the so-called definitive nucleus
(fig. 316°), a very active cell-division sets in, which results in the formation of a
parenchymatous tissue which occupies the embryo-sac and becomes filled with food-
materials (fat, starch, and proteids). This tissue is the already-mentioned reserve-
tissue of the seed or endosperm. Most frequently, as we have stated, the embryo
enters on a resting period embedded in or adjacent to this reserve, and absorbs it
at germination. In other cases, as in the Bean, Oak, &c., as mentioned, the
cotyledons of the embryo forthwith take up all this food, so that when the resting-
stage comes on, the greatly swollen embryo fills the whole cavity of the seed. This
former class of seed is spoken of as albwminous, the latter as ex-albuminous. There
is just this difference between albuminous and ex-albuminous seeds: in the former
the embryo only takes up the food-material at germination, in the latter, relatively

422 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

early, before the seed enters on its resting-stage. The ultimate fate of the food-
material is the same in both cases, 7.¢. to nourish the young plant.

The relations of the embryo to its reserve-tissue are very various. In many
plants, e.g. Pimpernel, Wood Sorrel, Snapdragon, and Strawberry-tree (Anagallis,
Oxalis Acetosella, Antirrhinum majus, Arbutus Unedo, ef. TIPE Sh (abc PTs B20);
the straight embryo lies embedded in its reserve-tissue. The same relations obtain
in the Rue (Ruta graveolens, cf. figs. 317! and 317 ?), the embryo here being slightly
bent; whilst in Phytolacca decandra (fig. 317"), on the other hand, the embryo is
outside its reserve-tissue, and curved around it like a horse-shoe. In Sapindaces

and Chenopodiacez the embryo is spirally twisted. In the Grasses it is laterally
placed to its reserve-tissue (cf. vol. i. p. 599, figs. 141% and 141 +4), and the manner
in which it utilizes its reserve has been already fully described in vol. i. p. 604.

1

4

Fig. 317.—Seeds with a Reserve-tissue.

1 Ruta graveolens, the intact seed. 2 Longitudinal section of the same. % Ozalis Acetosella, intact seed. + Longitudinal
section of the same. 5 Anagallis phoenicea, intact seed. 6 Longitudinal section of the same. 7 Arbutus Unedo, intact
seed. ® Longitudinal section of the same. 9% Antirrhinum majus, intact seed. 1° Longitudinal section of the same.
11 Longitudinal section of seed of Phytolacca decandra. (After Baillon.)

Both the embryo and its reserve-tissue increase at the expense of the tissue
immediately external to the embryo-sac; and in the ripe seed very slight traces of
this tissue are to be found. Only in relatively few seeds is food stored in this
peripheral tissue (7.e. in the tissue of the nucellus between the integument and
embryo-sac). Under these circumstances this nucellar tissue assumes very much
the character of the more usual reserve-tissue (endosperm) which is formed within
the embryo-sac. Its cells become filled with fat, starch, and proteids, which serve
later on as food-material for the young plant. Reserve-tissue when stored within
the embryo-sae is termed endosperm; this, which arises external to the embryo-sac
is, in contradistinction, termed perisperm.

It is worthy of note that a formation of reserve-tissue does not take place in
ovules which are not fertilized. The act of fertilization obviously exerts an influence
not limited to the embryo. One may compare this influence to the impulse gene-
rated when a stone is thrown into still water. Just as waves travel in ever-
widening circles from the centre of disturbance, so it is with the changes in the ovule:
first, changes are noticeable in the egg-cell, then successively in the embryo-sac,

SECONDARY EFFECTS OF FERTILIZATION. 423

integuments, in the carpels, and, finally, in the flowering axis which bears the whole
of the structures concerned. These changes, which become manifest in the form of
growth, are executed on a definite plan in every plant, and depend on the peculiar
constitution of the protoplasm. The aim of these growth-changes is not difficult
to determine. The new organism which has arisen from fertilization must be
adequately provided for the future; it is detached sooner or later from its parent-

Fig. 318.—Seeds with winged and hairy appendages.

1 Dehiscent fruit of Eriodendron; the seeds embedded in a hairy investment are visible between the valves. * Dehiscent fruit
of Gossypium herbaceum; the mass of seeds is contained in a hairy investment protruding from the valves. * Seed of Aspen
(Populus tremula) with silky appendage. 4 The same seed stripped of its silk. 5 Winged seed of Lepigonum marginatum.
% Longitudinal section of the winged seed of Vochysia. 7 Winged seed of Cinchona. 8 Longitudinal section of this seed.
9 Winged seed of Cedrela Toona. 10 Longitudinal section of same. 48 magnified. (Partly after Baillon.)

plant, and has to establish itself in a new place. The embryo requires special
equipment for its journey and for its start in life; it requires a means of dispersal
and protection against attacks from animals so long as it remains attached to the
parent-plant, it requires also protection against unfavourable climatic conditions.
These various equipments are provided by peculiar changes in the integument,
carpels, and receptacle, changes which are initiated at fertilization.

424 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

The integuments of the ovule are altered into the seed-coat, which often exhibits
a differentiation into two layers. The inner layer takes the form of a delicate,
colourless membrane which is rarely hardened, or of a mucilaginous, readily-swelling
layer. The outer seed-coat or testa shows, however, a great variety of form. It
usually consists of several layers of cells, the successive layers of which are frequently
very differently fashioned. Sometimes they are soft and membraneous, sometimes
rigid and parchment-like, woody or horny, whilst in other cases they may be succu-
lent and fleshy, or converted into a mucilaginous, sticky envelope. The outmost
layer of the testa is usually brown, gray, and black, more rarely yellow, white, or red
in colour. The significance of the various slimy layers, which on moistening become
sticky, of the little pits and furrows, warts, spines, and the like in promoting the
firm anchoring of the seed on its germinating bed has already been fully pointed

Fig. 319.—Salia polarıs with opened fruits showing masses of hairy seeds escaping.

out (cf. vol. i. pp. 614-620). Many seeds, in order that they may be distributed by
the wind, develop from the outmost layer of the testa wing-like appendages, as,
for instance, in the seeds of the Caryophyllaceous Lepigonum marginatum (see
fig. 318°), in those of the Cinchona-tree (Cinchona, figs. 3187 and 318°), in the
tropical Vochysia (fig. 318°) and Cedrela (figs. 318° and 3187), and many others.
This just-mentioned Vochysia-seed is also characterized by the curious wrapping
of the cotyledons upon one another (fig. 318°). Often, again, for the same purpose,
the superficial cells of the testa grow out, forming a plume or plexus of silky or
cottony hairs, as in the Indian species of Cotton-plant (Gossypium herbaceum,
fig. 318°), and in the cotton-produeing Hriodendron (fig. 318’). In the seeds
of the Oleander (Neriwm Oleander) the hairs at the apex are longer than those
at the base, whilst in the Willow-herb (Epilobiwm) a delicate tuft of long silky
hairs is developed at the apex only.

In a considerable number of plants there is developed from the base of the seed,
or from its funicle, a curious and special structure, which by the time the seed is ripe
envelops the seed like a mantle. This structure is known as the Aril. These arils

ACCESSORY STRUCTURES OF THE SEED. 425

show very various characters, just as the testa itself may do. In the Willow (Salia,
fig. 319) and Poplar (Populus, figs. 318° and 318 *) it consists of long, delicate silky
hairs; in many Passifloraceze, Sapindacew, and Celastrinee—amongst others, in the
well-known Spindle-tree (Hwonymus), it forms a fleshy, succulent investment, often
coloured bright red or orange, whilst in the Myristicacez it forms a curious, laciniated
sheath. In the Nutmeg (Myristica moschata) the seed proper constitutes the
nutmeg of commerce, whilst the mace is the aril which grows around this seed.
When these accessory structures of the seed are only developed locally as little
ridges or bumps at the base of the seed, or on the funicle, they are known as
caruncles. A well-marked, fleshy cock’s-comb-like caruncle is formed on the seeds
of the Celandine (Chelidoniwm majus). When the swelling is limited to the point
of attachment of the seed to its funicle, one speaks of a hilar caruncle, as is seen in
the Pansy (ef. figs. 320!
and 320°). The spot
where the seed is at-
tached to its stalk is
known as the hilwm, and
is readily seen, even
when distinguished by
no special swelling or
caruncle, on a detached
seed. It is usually a
well-defined area, col-

oured differently from —
the rest of the testa, Fig. 320.—Seeds with caruncles and hilar scars.
sometimes projecting, 1 Seed of Viola tricolor. 2 The same in longitudinal section. 3 Seed of Ricinus com-

Ei li htl munis. 4 The same in longitudinal section. 5 Seed of Physostigma venenosum.
sometimes S 1g y exca- 6 Seed of Anamirta Cocculus. 7 The same in longitudinal section. (After Baillon.)

vated, and not infre-

quently having the form of a well-marked groove (see fig. 320°). At the place
where separation has occurred there is a kind of scar, the hilar scar (sometimes
called the omphalodium). The spot occupied by the micropyle is often recogniz-
able on the ripe seed, and may be termed the micropylar scar. It usually appears
as a little hole or pin-point depression bordered by peculiar tissue. In curved (cam-
pylotropous) seeds, the micropylar and hilar scars are seen near together, but not so
close as to be inseparable (figs. 320° and 320°; in 320° the point indicates the posi-
tion of the micropylar, the excavation that of the hilar sear). In the Castor-oil plant
(Ricinus communis, figs. 320° and 320), the lips of the micropyle undergo con-
siderable growth, forming a little cushion or micropylar caruncle, very conspicuous
at the top of the seed.

Corresponding to the externally visible hilar and micropylar scars is a curious
internal structure of this portion of the seed-coat. This will be more intelligible
when it is explained that in many cases the water needed by the resting embryo
for its further development can only be absorbed at these spots. The tissue here,

426 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

indeed, serves as a mechanism for supplying the embryo with moisture from the
germinating bed. For its successful operation it is necessary that the seed should
be favourably situated upon the soil, in other words, that these portions of tissue
which conduct water to the embryo should be in contact with the damp earth.
Such a position is promoted by the fact that in cases of the kind under discussion
the seed is so formed and its centre of gravity so adjusted that in falling the hilar
scar generally comes to lie underneath. The tissue here is more or less porous and
provided with lacunz, so that water can be taken up and transmitted to the
embryo. Not infrequently
it consists of loose stellate
cells, and water is absorbed
from the environment as
by a sponge and placed at
? the service of the deeper-
lying regions of the seed,
especially the embryo.

In those seeds, on the
other hand, in which water
is not absorbed at definite
spots but over the whole
surface, there exist scat-
tered over the surface be-
tween the thickened imper-
vious cells, which form the
greater portion of the in-
vestment, special strings of
cells or minute canals which
at the proper time are per-
meable and serve for the
taking up of water. Thus,
for instance, in the hard,

Fig. 321.1 Branch of Mezereon (Daphne Mezereum) with berries. 2 Fruiting f
branch of the Lime (Tilia) with downy hairs investing the nut-like fruits. round, black seeds of the

8 Longitudinal section through a fruit of the Lime, 1 and 2 natural size. D
ren Indian Shot (Canna), the

testa, consisting as it does
of an outer layer of thick-walled palisade-cells with several layers of transversely-
stretched stony cells beneath, constitutes an exceedingly strong protection for the
embryo. But over the whole surface of the seed are distributed tiny depressions,
at the base of each of which a stomate opens. Each of these stomates leads into
a canal of minute proportions traversing the layers of the testa and adequate for
taking up water at germination.
Intimately connected with the developing seeds is the structure in which they
are contained, and in which they were originally fertilized. This is known at the
time of fertilization as the pistil or ovary, and later, when the seeds are ripe, as the

STRUCTURE OF THE FRUIT. 427

pericarp, seed-capsule, or case. Asa rule this structure is known to Botanists as
the frwit, though this designation is open to criticism. In the broad sense the fruit
in Phanerogams should include everything which undergoes alteration after fertili-
zation either in the flower or flowering axis. All these changes take place in the
parts in question for the purpose of promoting the interests of the embryo, and
properly equipping it when the time comes for its severance from the parent plant,
consequently the whole of the structures which participate in this object should be
regarded as the fruit. From this point of view the seed-case or pericarp (derived

from the pistil) constitutes only a portion of the fruit. Since, however, the seed-
1

Fig. 322.—Indehiscent fruits and schizocarps.

1 Drupaceous Nut of Fumaria. 2 The same in longitudinal section. 3 Indehiscent fruit of Callitriche. 4 The same in longi-
tudinal section. 5 Schizocarp of Feniculum aromaticum. $ Schizocarp of Petroselinum sativum. 7 Schizocarp of Carum
carvi, Allthe figs. enlarged. (After Baillon.)

case in a very large number of cases approximates to and essentially constitutes the
whole fruit, we will not press our quarrel with the deseriptive botanists to the point
of pedantry, but having made our protest fall into line with the usual terminology.

Types of Fruit—When the seed-case derived from the pistil becomes altogether
fleshy and succulent, the fruit is termed a Berry. From inferior pistils arise inferior
berries. From superior pistils superior berries. The berries of the Bitter-sweet
(Solanum Dulcamara), of the Deadly Nightshade (Atropa Belladonna), of the
Barberry (Berberis vulgaris), and of the Vine (Vitis vinifera) are superior; those
of the Mistletoe (Visewm album), and of the Gooseberry (Ribes Grossularia) are
inferior. The berry of the Mezereon (Daphne Mezerewm) is also superior, but is

428 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS,

peculiar in that the flesh is contributed not only by the pericarp proper (fruit-wall),
but also by the outmost layer of the seed-coat. It is the inner layer of the seed-
coat which here gives rise to the stone.

When the outer part of the pericarp is fleshy, and the inner part which imme-
diately invests tbe seeds stony, the fruit is called a Drupe or stone-fruit. The

Fig. 323.—Winged Fruits.

1 Cluster of fruits of the Ash (Fraxinus excelsior). 2 A single fruit artificially opened. % Seed of Fraxinus excelsior. 4 The
same seed in longitudinal section. 5 Fruit of Banisteria. $ Fruit of Angelica sylvestris, 7 Fruit of Ailanthus glandulosa,
the central, seed-containing portion seen in section. (Partly after Baillon.)

majority of drupes, e.g. the Sloe (Prunus spinosa), and Cherry (Prunus aviwm),
contain only a single stone and seed. That of the Buckthorn (Rhamnus) contains
two stones, each of which contains a seed, whilst that of the Elder (Sambucus
nigra), usually described as a berry, isin reality a drupe containing from 2-4 stones
each with one seed.

In a very large number of fruits the pericarp is entirely dry. These dry fruits

INDEHISCENT FRUITS. 429

may be distinguished into Indehiscent frwits, Schizocarps, and dry Dehiscent frwits.
The indehiscent fruit never opens spontaneously. When ripe it comes away with
the inclosed seed and is concerned in the dispersal and establishment of this seed.
The indehiscent fruit is termed a Nut when it arises from a pistil constituted
of more than one carpel, as in the Lime (Tilia, figs. 321° and 321°), an Achene when
produced from a monocarpellary pistil. When the contained seed is entirely fused
with the lining of the fruit-wall, as in Grasses (ef. vol. i. p. 599, fig. 141°), the fruit

Fig. 324.—Flowering branch of Banksia serrata with thick-walled dehiscent capsules. (After Baillon.)

is termed a Caryopsis. Sometimes the wall of the nut consists of an outer more
fleshy layer, and an inner harder layer after the manner of a drupe. Such a fruit,
as in the Fumitory (Fumaria, figs. 3221 and 322°), is known as a drupaceous nut.
As a rule the nut is uni-loculate and contains but a single seed; and this notwith-
standing the terms of our definition, according to which a nut is the product of a
multi-carpellary ovary. Actually in development all the chambers but one (which
contains the ripe seed) atrophy. Only rarely are nuts multilocular, as in the Water-
star (Callitriche, figs. 322° and 322°) which has a 4-chambered nut and forms a
transition to the schizocarp.

The Schizocarp may be regarded as consisting of a number of Achenes united
together. Two or more carpels, each containing a seed, remain joined together during

430 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

ripening, and only later, when the seed is ripe, do they separate from one another,
as though the original fruit had been eut into its component parts by a sharp knife.
Each of these components (known as Mericarps) remains indehiscent like an achene,
and is distributed with its contained seed. As a type of these schizocarps the
Mallow (Malva) may be taken. In the Umbelliferee the two mericarps into which
the schizocarp splits remain for a long time suspended from the tips of a forked
prolongation of the axis, as in the fruits of the Caroway (Carum carvi, fig. 322"),
Parsley (Petroselimum, fig. 322°), and Fennel (Feniculum, fig. 322°).

As already mentioned, the pericarp of many indehiseent fruits assists in the
dispersal and establishment of the inclosed seeds. This may happen in two ways.
The surface of the fruit may bear hairs, curved bristles, or hooked spines which
become attached to the coats of animals; or wings, plumes, &e. may be produced,
allowing the fruit to be readily borne away even by the gentlest of breezes. Such
winged fruits are termed Samaras, and many forms of them are distinguished by
the descriptive botanist. To these remarkable fruits, however, we shall return in
detail later on when dealing with the dispersal of plants; it will suffice here to indi-
cate briefly a few forms. The fruits of the Ash (Fraxinus excelsior) are shown in figs.
3231234) The pericarp of each consists actually of two carpels joined together; it is
continued into a well-marked membraneous wing. Fig. 3237 represents the samara
of the Tree of Heaven (Ailanthus glandulosa) which is continued below and above
the seed-containing portion into a thin, spirally-twisted wing. In the fruit of the
Umbelliferous Angelica sylvestris (fig. 323°) each half (mericarp) shows a sinuous
wing-like fringe on either side, whilst in Banisteria (fig. 323°) there projects from
the back of each component a membraneous continuation resembling a butterfly’s
wing.

Dry dehiscent fruits are also known as Capsules. When ripe their pericarp,
which is quite dry, opens and liberates the seeds in a variety of ways. The empty
capsule remains, as a rule, on the parent plant, or comes away in pieces (valves) at
the time of dehiscence. In neither case, however, has the pericarp any further con-
cern with the seeds after these are once liberated. These capsules are the commonest
class of fruit, and as their structure is characteristic of many genera, their various
modifications have received distinctive names. When the pericarp arises from a
single carpel, and at ripening opens along one side, along the so-called ventral
sutwre, whilst the opposite side (the dorsal sutwre) is unsplit, or but partially, one
speaks of the fruit as a Follicle. As a rule several follicles are collected together
in a elnster at the end of the flower-stalk, as, for instance, in Monkshood (Aconitum)
and in the Star Anise (Illieiwm anisatwm, ef. fig. 3251); more rarely are they
solitary, as in certain species of Larkspur (Delphinium). In the Proteacew, also,
a single follicle arises from each flower, and in the Australian “Wooden Pear”
(Xylomelum pyriforme, fig. 325°), belonging to this order, the huge and extraordi-
narily thickened follicle splits completely down the ventral and halfway down the
dorsal suture. In Banksia, also, of which a head with fruits is shown in fig. 324,
the follicles are very hard and woody.

VARIOUS DEHISCENT FRUITS, 431

Fig. 325.—Various Capsular Fruits.

1 Follicles of Illicium anisatum. 2 Follicle of Xylomelum pyriforme. * Pods of Lotus corniculatus. 4 Pod of Cassia angus-
tifolia. Capsule of Aristolochia. ® Capsule of Ruta. 7 Capsule of Viola. 8 Capsule of Oxalis. 9 Capsule of Antirrhinum.
10 Capsule of Cinchona. 11, 12 Capsules of Anagallis. 13, 14 Capsules of Eucalyptus. 15, 16 Siliquas of Brassica.
§, 10, 1) enlarged; the rest natural size. (After Baillon.)

432 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

Like the follicle, the Legume or Pod arises from a single carpel, but on ripening
it splits down both sutures completely to the base into two valves, which at the
moment of dehiscence become rolled up spiraily. This type of fruit is extremely
common in the Leguminose. As examples may be mentioned Lotus corniculatus
(fig. 325°) and the Senna (Cassia angustifolia, fig. 325 *).

Dry dehiscent fruits, the product of two or more carpels, are termed capsules in
the restricted sense. We may distinguish several types of capsules; (1) such as split
into valves from the apex, as in the Birthwort (Aristolochia, fig. 325°), Rue (Ruta,
fig. 325°) and Violet (Viola, fig. 325”); (2) such as open by means of teeth restricted
to the apex, as in Caryophyllaces; (3) such as split longitudinally down the side-
walls, the actual cavities of the fruit opening, as in the Wood Sorrel (Oxalis,
fig. 325°); (4) such as produce several large apertures by the folding back of teeth,
as in the Snapdragon (Antirrkinum, fig. 325°); and (5) such as form numerous

Fig. 326.—Achenes provided with a plume or pappus.

1 Fruit of Valerian (Valeriana officinalis). 2 The same in longitudinal section. 3 Fruit of the Artichoke (Cynara Scolymus).
(After Baillon.)

small pores by the shrivelling of restricted areas, as in the Poppy (Papaver). The
capsules of the Cinchona-tree (Cinchona, fig. 3251°) split into two valves, which
remain attached at the apex, separating at the base only; whilst many capsules
dehisce transversely, a lid being removed, as in the Pimpernel (Anagallis, figs. 325 "
and 325?) and Eucalyptus (figs. 3251 and 32514).

A special form of capsule, known as the Siliqua, is characteristic of most
Crucifers. It is usually described as consisting of two carpels, the exposed walls of
which come away, leaving a framework (the replwm) to which the seeds are attached.
Stretched upon this framework is the membrane which formed the (“false”) parti-
tion of the ovary. This class of fruit is well shown in Honesty (Zwnaria) and in
the Cabbage (Brassica oleracea, figs. 325! and 3257). According to the termi-
nology given at p. 75 (4), the two valves which come away correspond to the two
outer non-ovule-bearing carpels, whilst the ribs which remain are the two inner
ovuliferous carpels.

Though, in a great number of Angiosperms, the various floral-leaves disarticulate
and fall away after pollination and fertilization, this is not universally the case; in
a considerable number some of them remain behind, undergo various changes, and
form an outside investment or appendage to the fruit which plays an important
part in the dispersal or preservation of the seeds. The same is true of the bracts

ACCESSORY STRUCTURES OF FRUITS. 433

and bracteoles, the leafy structures which are present in the immediate vieinity of
the flowers, though not actually included in them. We may distinguish, perhaps,
amongst these accessory structures of the fruit, between such as arise from portions
of the perianth on the one hand, and such as are formed from bracts and bracteoles
on the other. The enumeration of these structures here, however, must be distinctly
limited to a few of the more commonly occurring.

A curious form of fruit obtains in the Mulberry (Morus). The female flowers

Fig. 327.—The Hornbeam (Carpinus Betulus) in fruit.

in this tree are arranged in little catkin-like clusters. Each flower consists of an
ovary inclosed in an inconspicuous four-leaved perianth. From each ovary a tiny
nut arises; but the ripe fruit resembles a succulent berry rather than a collection of
nuts. This is due to the fact that after fertilization, whilst the ovaries are developing
into nuts, their perianths become distended and fleshy, altogether concealing the
ovaries. Without a knowledge of the mode of development, the perianth might now
be readily mistaken for the true fruit-wall (pericarp), and the nut for the seed
In several species of Trefoil (e.g. Trifoliwm agrariwm, badiwm, spadiceum) the
papilionaceous corolla is yellow. After fertilization this turns brown, dries up and
forms a flying-arrangement for the small fruit within (ef. figs. 442 > % % 5),

lt very frequently happens that the Calyx is retained as an accessory to the
Vou. IL 78

434 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

fruit. In the Winter Cherry (Physalis Alkekengi), a solanaceous plant often eulti-
vated in gardens, the calyx, originally small and green, becomes much inflated
during ripening and forms a bright red bladder inclosing the actual berry; in the
Henbane (Hyoscyamus), belonging to the same family, the calyx tightly incloses
the capsular fruit, its periphery forming a characteristic funnel around the top. In
Labiate the calyx persists as a short tube, or as a bell or pitcher, at the base of
which the actual fruit is found. In the Water Chestnut (Trapa natans, cf. vol. i.
p. 607, fig. 144°) the four segments of the calyx become hardened and persist as four
spines arranged cross-wise around the fruit. In many Valerians, Composites, and
Scabiouses, the calyx persists, growing, as the fruit ripens, into a radiating crown

Fig. 328.—Fruits with persistent receptacies.

a The Carolina Allspice (Calycanthus). 2 Longitudinal section of the same. % Fruit of Agrimonia. 4 Longitudinal section of
the same. (After Baillon.)

of bristles or feathery hairs. This crown, known as a Pappus, serves the achene as

a parachute (cf. figs. 326123 and fig. 447).

Amongst the Amentacez, trees whose flowers are for the most part destitute of
perianth, the bracts and bract-like scales associated with the flowers often play a
prominent part in the fruit. In the Grasses also the same feature is noticeable.
In these latter the actual grain is very frequently closely enwrapped by one of the
glumes, so tightly indeed, that they easily escape observation, as in Barley, Oats,
and many others. The greatest variety of fruit-investment is met with in the
Cupuliferse and allied Amentaceze, which include the Hornbeam, Hop-hornbeam,
Beech, Hazel, and several other well-known trees. The actual fruit in all these is
a nut, but inclosed in a peculiar involuere-like sheath (the ewpule) derived from
bract-like scales external to the flowers. In the Oak (Quercus) the eupule is cup-
like (figs. 3291 and 329°); in the Beech (Fagus) it completely envelops the paired
triangular nuts, and is spiny outside, at ripening it bursts into four valves like a
capsule; in the Chestnut (Castanea) it is extremely prickly, and, as in the Beech,
bursts into valves (fig. 3394); in the Hazel (Corylus) it forms a laciniated, leathery
envelope to the nuts (fig. 235, p. 147), whilst in the Hornbeam (Carpinus, fig. 327)

ACCESSORY STRUCTURES OF FRUITS. 435

it has the form of a three-lobed open scale, to the base of which the ribbed nut is
attached. Finally, in the Hop-hornbeam (Ostrya, fig. 437°) it forms a loose papery
envelope.

The Receptacle of the flower is not infrequently a conspicuous feature in con-
nection with the fruit. This is well shown in the Carolina Allspice, in Roses, and
in Pomacex. In the Carolina Allspice (Calycanthus, figs. 328! and 328 *) an exca-
vated pitcher-like receptacle, invested on the outside with scales, incloses the achenes;
in the Rose there is a similar inclosure, here smooth and fleshy, and bearing a five-
leaved calyx above, this constitutes the hip. In the Apple, Pear, Quince, and other
Pomacex, the receptacle forms an extremely succulent mass, in which the actual
fruit is imbedded, and
with which it is entirely
fused (e.g. Quince, Cy-
donia, fig. 330°). In
the Strawberry (Fra-
garia), on the other
hand, the fleshy recep-
tacle is convex, and
bears the little achenes
scattered over its sur-
face. Not always, how-
ever, is the receptacle
fleshy; thus, in the
Agrimony (Agrimonia

Fig. 329.—Fruits with Cupules

1 Quercus pedunculata. 2 Quercus sessiliflora.

Eupatoria, figs. 328%
and 328) it forms a dry and woody inclosure for the one or two achenes, and is
provided with numerous stiff hooked bristles on its periphery.

Much less frequently does the flower-stalk (pedicel) take a share in the fruit
formation. This is so, however, in Anacardiacex, in some Rhamnacex, and in a few
other groups. Thus, for instance, in the tree which produces Cashew-nuts (Ana-
cardium occidentale, fig. 3301), the upper portion of the pedicel swells up into a
fleshy pear-like structure; on its summit is perched the kidney-shaped nut with its
inclosed seed. In Hovenia dulcis (allied to the Buckthorn) a similar arrangement
prevails, the flower-stalks are swollen, and contain a sweet red pulp appreciated by
the Chinese and Japanese. To these instances may be added the Fig (Ficus, ef.
figs. 240" and 240, p. 157), in which the whole receptacle of the inflorescence is
excavated, urn-wise, and becomes very succulent on ripening. The little grains inside,
commonly taken for seeds, are in reality the actual fruits or nuts, each of which
contains a seed. Asa final instance may be mentioned the polygonaceous Brunnichia
africana from west tropical Africa; in this case the flower-stalk becomes winged
down either side, from its point of insertion up to the nut at its apex. It thus serves
as a distributing organ for the fruit.

In many plants whose flowers are clustered very close together it often happens

436 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

that the fruits of the several flowers as they increase in size become more or less
fused together; or the axis which bears them, or other associated parts, become fleshy
forming a succulent matrix for the individual fruits. Such a mass of fruits is termed
a collective fruit. ‘Good examples of this are the Mulberry (Morus), the Pine-apple
Ananassa sativa), Piperacere, e.g. Betel Pepper (Piper Betle, fig. 3311); and Arto-
carpe, eg. the Bread-fruit (Artocarpus incisa, fig. 332) and Jack-fruit (Artocarpus
integrifolia). With these collective fruits may be contrasted the clustered crowded

Fig. 330.—Fruits in whose structure the receptacle and pedicel take a share,

1 Longitudinal section of the fruit of the Cashew-nut Tree (Anacardium occidentale). 2 Longitudinal section through a Quince
(Cydonia). (After Baillon.)

carpels produced from single flowers (aggregate fruits), such as the Raspberry
(Rubus Ideus), Calycanthus, Rose, &e., already described, also many Anonaceze, as,
for instance, the West-Indian Sour-sop (Anona mwricata, fig. 331%), the Sweet-sop
(Anona squamosza, figs. 331? and 331°) and Custard-apple (Anona reticulata). The
terminology that has grown up around the types of fruit described in this paragraph
is extremely confusing and slovenly. We propose to call the compound fruit arising
from a number of crowded flowers a collective fruit, that from the carpels of a single
flower an aggregate fruit. An altogether peculiar fruit is that of the Lotus Lily
(Nelumbium speciosum, cf. figs. 333 and 334). Here the receptacle is enlarged into
a huge top-shaped structure in the middle of the flower (fig. 3341); the upper surface
of this top is like a honey-comb, and in each “ cell”, a carpel is sunk as in a socket

THE EMBRYO IN GYMNOSPERMS. 437

(fig. 334°). When the fruit is ripe and dry, these carpels form hard, woody achenes
which rattle in their loose sockets like teeth in the jawbone of a skull.

Our descriptions of the fruit and its various forms and modifications relate, so far,
solely to the Angiosperms. In the Gymnosperms, however, several essential differ-
ences are to be noted. The account of their methods of fertilization (pp. 418-420)
was left at that stage at which the male sexual cell had fused with the egg-cell.

The nucleus of the fertilized egg now moves down to the base (away from the

Fig. 331.—Collective and Aggregate fruits.

1 Collective fruit of Betel Pepper (Piper Betle). 2 Aggregate fruit of Sweet-sop (Anona squamosa) formed by fusion of the
carpels of a single flower. 3 Transverse section of the same. + Longitudinal section of the aggregate fruit of the Sour-sop
(Anona muricata) produced in the same way. (After Baillon.)

micropyle) of the egg-cell and divides several times, each product of its division
becoming enveloped in protoplasm and ultimately in a cell-wall. In the Gnetacez
which many Botanists regard as more nearly allied to the Angiosperms than either
of the other two families of Gymnosperms (Conifere and Cycadacez), there arise
in this way from 2-8 daughter-nuclei around each of which protoplasm aggregates,
and a cell-membrane is formed (cf. fig. 315%, p. 415). Between each of these cells
there is no connection: each grows out into a tube which penetrates the wall of the
egg-cell and pushes its way down into the reserve-food (endosperm) below. From
the tip of the tube a small cell, the embryonal cell, is eut off and from this cell by
further division and growth an embryo is produced, which is nourished by the food-
material. Of the many embryos which are inaugurated, one only comes to maturity,
and is found in the ripe seed.

38 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS,

In the Silver Fir, Spruce Fir, Pine, and other Conifers, comprised under the
family Abietines, the nucleus of the egg-cell divides into four at the base of the
egg-cell, and here four little cells are produced, arranged like a rosette at that end.
Each of these is divided into three stories, and the four cells forming the middle
story elongate, diverge, and grow down into the endosperm, carrying the little
embryonal cells at their tips. The four cells of the upper story remain attached to
the residue of the egg-cell, and serve as a fulcrum for the elongating tubes—the
suspensors. As in the Gnetacez, the embryonal cells become modified into embryos,

Fig. 332. —Branch of the Bread-fruit Tree (Artocarpus incisa) showing a male inflorescence (sausage-shaped, to the right), a
female inflorescence (globular, near the apex) and a collective fruit (to the left), (After Baillon.)

but ultimately only one of them prevails, and, growing at the expense of the food-
material, is a conspicuous object in the ripe seed (fig. 335°). A portion of the
endosperm remains as a mantle around the embryo, and is only absorbed at ger-
mination.

In the Juniper, Arbor Vite (Thuja), Cypress, and other Conifers belonging to
the family Cupressinex, each egg-cell, after fertilization, gives rise to but a single
embryo (though there are exceptions to this rule). Otherwise the events are not
very different from those occurring in the Abietinex.

The Integument of the ovule in Gymnosperms forms the seed-envelope (or testa),
as in Angiosperms. The Micropyle becomes closed up, and the whole testa very
hard. In the Pines, Firs, &e. (Abietinez), the mieropyle points away from the free
margin of the open scale which bears the ovules (fig. 3357), ü.e. towards the axis of

THE SEEDS OF GYMNOSPERMS. 439

the cone; in the Cypress and other Cupressinew, on the other hand, towards the
free margin of the scale (figs. 337° 4°), and away from the axis of the cone.
In several species, as in the Stone Pine (Pinus Pinea) and the Arolla Pine

(Pinus Cembra), the seed-coat attains a thickness of 14 to 2 millimetres, so that

the seed resembles a nut in appearance. Both these species, indeed, serve as an

LA
i BR

Fig. 333.—The Lotus Lily (Nelumbium speciosum). (From a photograph.)

article of diet, being eaten like nuts. The seeds of Pines and Fir-trees are provided
with a one-sided wing (cf. figs. 335% %°) which plays an important part in their
dispersal by wind. In the Maidenhair Tree (Gingko biloba) the integument of the
seed becomes succulent and coloured a bright orange, so that the seed in a way
resembles a drupe (cf. fig. 3377). In Cycas revoluta, also, the integument becomes
red and fleshy (ef. fig. 208°, p. 74)

f=)

440 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

The ovules of both Abietinese and Cupressine are inserted upon scales of vary-
ing form, the insertion of which on the axis of the cone may be broad or narrow (ef.
figs. 38575 ° and 337% 4°), These scales form an important constituent of the ripe
cone, and are known as the ovuliferous scales. In not a few cases, as in the Silver
Fir (Abies pectinata, figs. 3354%%4) and Larch (Laria, figs. 335° and 3371), there
exists a second scale, the bract scale, beneath each ovuliferous scale, and subtending
the same. In the Pine, also, both scales are present, though in the ripe cone there
are no signs of the bract-scales at the exterior owing to the fact that they become
entirely overgrown and embedded between the big ovuliferous scales.

In the Abietiner the scales of the cones are inserted in a continuous spiral (ef.
fig. 3351, and vol. i. p. 403, fig. 101), whilst in Cupressinez the scales are inserted in
whorls of 2 or 3 scales each (cf. figs. 336%7 and 337 %5). In both, the margins of

Fig. 334.—The Lotus Lily (Nelumbium speciosum).

1 Flower from which the perianth-leaves have been removed; expanded receptacle in centre. 2 Longitudinal section through
the top-shaped enlargement of the receptacle, showing three carpels embedded in their sockets. (After Baillon.)

the seales overlap, and the seeds are ripened in the slit-like chinks between them
(ef. 336° and 337°). The whole assemblage of scales constitutes an aggregate fruit,
and is known as a cone. The scales may be hard and woody, when we have a
woody cone (335! and 337 "%5); or they may be succulent, giving a fleshy cone.
In such fleshy cones very few of the whorls are succulent, the central axis is very
short, and the whole structure has much the appearance of a berry, as in the
Juniper (Juniperus communis, figs. 8367 and 336°).

The section of Gymnosperms known as the Taxinez do not produce cones.
Their seeds arise alone or in pairs at the ends of special short branches, or upon the
surface of small fruit-seales. The plum-like seeds of the Maidenhair Tree (Gingko
biloba) are arranged in pairs at the ends of axes which resemble cherry-stalks (see
fig. 3377). The seeds of the Yew (Taxus baccata) occur at the tips of little scale-
bearing shoots, and when ripe are almost completely enveloped in a sweet, fleshy,
crimson tissue (see figs. 336b%°). This fleshy inclosure, which arises as a circular
cushion from the place of insertion of the ovule, is not of the nature of a carpel, it

THE FRUITS OF GYMNOSPERMS. 441

is an aril. In Podocarpus, also, is developed a peculiar structure of the same
kind.

In Cyeads the seeds are borne upon carpels arranged in cones, and have a
woody integument. In some cases they correspond in position to metamorphosed
lobes of a carpel (cf. fig. 2087, p. 74), and have the outer layer of their integument
developed as a succulent coat. In the Gnetacex, the seed at maturity is inclosed

| inne

aa!

Fig. 335.—Fruit and Seed of Conifers,

ı Cone of the Silver Fir (Abies pectinata). 2 Bract scale and ovuliferous scale of the same seen from the outside (the bract
scale is pointed). % Ovuliferous scale of same seen from above, showing the two winged seeds, and the bract scale behind.
4 Longitudinal section of bract and ovuliferous scales, showing a seed inserted upon the latter. 5 A winged seed of the
same. © Longitudinal section of the seed. 7 Ovuliferous scale of the Scotch Pine (Pinus sylvestris) seen from above; it
bears two ovules. ® Single ovuliferous scale of Larch (Lariz europea) showing two ovules on its surface and bract scale
(with bristle) below it. 9 Longitudinal section of the ovuliferous scale of the Larch. 1 nat. size; the other figs. enlarged.

in a fleshy “perianth” in Ephedra; in Welwitschia cone-like collective fruits are
produced; finally, in Gnetum leaf-structures around the seed unite to form cup-
like receptacles for the seeds.

From the brief observations on the manner of fructification of Gymnosperms, it
will be seen that their methods are very various, and that, in all cases, they differ
from those of Angiosperms. They agree in the common object of producing a

442 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS,

vigorous embryo, and in providing it with adequate safeguards against unfavour-
able external conditions, and with means of dispersal, when the time comes for the
seed to be detached from the parent plant and to take up an independent existence.

Whilst still attached to the parent plant, the embryo needs protection against
the ravages of animals, and against wnfavowrable climatic conditions. Means of
protection against the former are provided sometimes on the seed-coat, in other
cases on the wall of the ovary; or they may be on other structures associated with
the flower, or upon the flowering axis itself. These defensive arrangements fall
into several groups. First of all, there are thorns, prickles, and spinous bristles, met

Fig. 336.—Fruits and Seeds of Conifere.

1 Branch of Yew (Taxus baccata) with ripe seeds, each inclosed in its aril. * Tip of ovule of same projecting from between
the scales of the little fertile shoot. % Longitudinal section of the same. 4 Young seed of the same only partly inclosed
in its aril. 5 Longitudinal section of the ripe seed of the same, showing the aril. ® Branch of the Arbor Vite (Thuja
orientalis) showing female flowers and ripe, burst cones. 7 Branch of Juniper (Juniperus communis) showing berry-like
cones. 8 Longitudinal section of one of these cones. 9 Female flower of Juniper. 1,% and? nat. size; the other figs. enlarged.

with especially on the ovary and immediate envelopes of the fruit. The capsule of
the Thorn-apple (Datura Stramonium), that of the Anatto (Bixa Orellana, see fig.
338), the long 3-valved fruits of Schrankia (see fig. 339°), the pods of the Russian
Liquorice Plant (Glycyrrhiza echinata), the persistent calyx of a steppe-plant,
Arnebia cornuta, and the cupule of the Chestnut (Castanea vulgaris, see fig. 339 *)
may serve as examples. Several Pines, of which the North American Pinus
serotina is a type, have cones the scales of which are produced into sharp spines
(see fig. 337°), so that the seeds are inaccessible to animals till such time as
the scales separate and the winged seeds are committed to the wind. Of interest
in this connection are certain Crucifers (Tetractiwm quadricorne, Matthiola
bicornis, M. tricuspidata, fig. 339*) in which, at the end of the fruit just below the
scar of the style, 2,3, or 4 stiff spines are formed, which make these fruits unaccept-

PROTECTION OF RIPENING SEEDS AGAINST ANIMALS. 443

able morsels for animals. A less common condition, and one deserving of special
mention, occurs in several Mimosas belonging to the immediate alliance of the
Sensitive Plant (e.g. Mimosa pudica, M. polycarpa, M. hispidula); of these the
last-named may serve as type (see fig. 3391). The pods here are densely crowded
together, and their dorsal and ventral sutures form a strong framework bearing a
double row of short spines. These spines hinder all animals from interfering with

Fig. 337.—Coniferous Fruits and Seeds.

1 Branch of the Larch (Lariz Europea) with ripe cone. ? Branch of Pinus serotina with ripe cone. 3 Female flower
of the Cypress. + Longitudinal section of thesame. 5 Ripe cone of the Cypress (Cupressus sempervirens). $ Single carpel
of the Cypress with numerous ovules. 7 Branch of Gingko biloba with unripe fruit. 1, 2,5,7 natural size. The other
figures enlarged.

the fruits. As the seeds ripen, the valves fall away from their spiny framework,
and are, with their contained seeds, dispersed by the wind. As a rule, the valves
break up at this time into one-seeded segments (fig. 339"), and being very light in
proportion to their area, are carried considerable distances.

In the instances just enumerated the protection is provided only up to the time
that the seeds are ripe. With the severance of the seeds from the parent plant the
protective function of the spines is at an end. The spinose investment as a rule
remains upon the plant, and only rarely, as in the winged fruit of Centrolobiwm
robustum (see fig. 339°), does the thorny ovary wall (pericarp) become detached
with its contained seed. Under these circumstances the spines may play a further

444 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

part, either by serving as a mechanism of dispersal, or by fixing the seed in the
germinating bed.

In the case of plants with succulent fleshy fruits, the seeds of which are dis-
tributed by birds, it would be extremely disadvantageous for the fruits to be
provided with spines or prickles when ripe. In point of fact, when such structures
are present they often disarticulate and fall away as the fruits ripen, so that birds
may have unhindered access to them. The fruits of the leguminous Mucuna
pruriens are clad during
their ripening period with
a felt-work of serrated
bristles, which contain an
irritating fluid. These
bristles cause an intoler-
able itching, or even an
eruption of the skin, and,
so long as they remain on
the fruit, effectively guard
it from animals. But as
the seeds ripen, and the
fruit becomes pulpy, these
bristles fall away (so it is
stated), and animals are
no longer repulsed, but
devour the pulp, and so
disperse the seeds.

The well-known Hips
of Roses which ripen in
the autumn, do not fall

away from the plant, but
remain attached. The

Fig. 338.—Protection of ripening seeds against animals.

The Anatto plant (Bixa Orellana) with flowers and fruit. Three of the fruits have

opened showing the seeds. (After Baillon.) seeds Eas contained un

hard and tiny nut-like
fruits, which are inclosed in the fleshy and excavated receptacle. They are
destined to be distributed by blackbirds, jackdaws, and other birds, which devour
the hips for the nutriment contained in the fleshy investment; the little nuts, how-
ever, pass out undigested in the droppings in some place more or less distant from
the Rose-bush. Whilst these birds, attracted by the coloured fruits, are welcome
guests, the case is quite the reverse as regards mice and other little rodents; they
gnaw the nuts, and devour their contents, the seeds. But the Rose-hips are well-
protected against these animals. The stems and branches, up which they must climb
to reach the fruits, are provided with sharp prickles with downwardly-directed
points, which give complete immunity against these animals. I have repeatedly,
in the late autumn, when the mice desert the fields and take up their winter-

PROTECTION OF RIPENING SEEDS AGAINST ANIMALS. 445

quarters in the abode of man, strewed the ground in my garden with Rose-hips of
an evening. Invariably, next morning, I found that they had been gnawed and
demolished by mice, whilst those remaining in situ on the plants were untouched.
The fruits of several dwarf Palms are similarly defended against the attacks of
animals, by zones of spines upon the stem, prickles upon the floral investments, &e.
The berries of several shrubby Solanacew (e.g. Solanwm sodomewm, and S.
sisymbriifolium) gain a like protection, as do those of the Blackberry, from
numerous prickles which clothe the stem and even the fruit-stalk and calyx. In

Fig. 339.— Protection of ripening seeds against the attack of animals.

1 Mimosa hispidula. 2 Schrankia. 3 Matthiola tricuspidata. 4 Castanea vulgaris. 5 Centrolobiwm robustum.

several members of the Gorse genus, Ulex Gallii, mieranthus, and nanus, the pods
are borne upon branches which bristle with spines. The spines project beyond the
pods, and their sharp points being directed downwards, mice are prevented from
climbing up and working havoc.

Other animals besides these rodents, such as caterpillars, snails, earwigs, centi-
pedes, and the like, have to be warded off. Some caterpillars find the green ovaries
acceptable as food, others the seeds themselves. Still, as we have seen, it is of
direct advantage to several Caryophyllaceze, Leguminoss®, and species of Yueca,
that a portion of the seeds should fall to the lot of insect-larve (cf. pp. 153-161).
It may be repeated here that prickles and spines, the points of which are directed
upwards, serve to protect the foliage against browsing animals (cf. vol. i. p. 432).
In the above-mentioned case of the Gorse, the spines towards the tips of the

446 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

branches keep browsing animals away, whilst those inserted lower down, which are
directed earthwards, prevent mice from climbing up the plant.

A peculiar protective contrivance has been observed on the calyx of several
Labiates, e.g. Thymus, Calamintha, Ballota. The corolla falls away after fertiliza-
tion, but the calyx persists, forming a sheathing envelope for the 4 nutlets. For the
better protection of these nutlets the mouth of this cup-like envelope is closed by
the development of a crown of hairs, which is impenetrable to small, seed-devouring
animals, A further use of these envelopes in seed-dispersal will be alluded to in
another place.

In other cases fruits are protected against unwelcome guests, not by spiny
structures, but by the elongation of their stalks during ripening, rendering them
inaccessible. Thus it would be a difficult feat for a mouse to reach the pendent
pods of the Pea (Piswm), or those of the Vetches (Vicia dumetorum, V. pisiformis,
V. sylvatica). Should by any chance a pod be accessible to these animals, by some
other route, it is as good as lost, as the nutritious seeds of these plants are much
sought after by them. Cherries also, on their long stalks, no doubt derive consider-
able immunity from earwigs, centipedes, &e., as those which fall to the ground
are speedily attacked and devoured.

In the case of seeds whose dispersal depends on the attraction of animals by
sweet, fleshy pericarps, these tissues are the reverse of appetizing before they are
ripe; not until the seeds are ready to be separated from the parent plant do fruits
of this kind become attractive. It is only necessary to cite as instances unripe
Cherries, Plums, Apples, and Grapes. It was stated on a previous occasion (vol. 1.
p. 462), when dealing with chemical changes occurring in plant-tissues, that the
fleshy parts of fruits are rendered disagreeable to animals before they are ripe by
the presence of bitter or poisonous glucosides, &e. Later on these substances are
altered, perhaps under the influence of the acids, which are present in large quanti-
ties in unripe fruits, and their place taken by sugars and other harmless materials:
thus, what is at first unattractive, and even repulsive, becomes, on ripening, a
nutritious food, much sought after by animals, which, at the same time, uncon-
sciously disperse the contained seeds. In this connection the Walnut (Juglans
vegia) is very instructive. Until the seed contained in the “nut” (here really the
stone of a drupaceous fruit) is ripe, the latter is surrounded by a fleshy investment
rich in tannin. It is not known at this stage that the “nuts” are ever interfered
with by nut-crackers or other animals. But on the ripening of the seed the fleshy
envelope splits, and the “nut” becomes accessible.

In other cases it is not by acids or bitter stuffs that the seeds are protected, but
by strong-scented resinous or sticky substances, which are contained in the cells
and passages of the fruit. Thus, in the scales of the cone of the Arolla Pine (Pinus
Cembra) quantities of resin are present until the seeds are ripe. If the cones be
cut with a knife this resin escapes, and can only be removed from the blade with -
the utmost difficulty. Were a nut-cracker to peck the scales at this stage to
obtain the young seeds, its beak would get all besmirched with the resin. It

PROTECTION OF SEEDS AGAINST WEATHER. 447

is easy to observe at Zermatt and Arolla in the Pennine Alps, where this Pine
grows, that the nut-crackers attack only the fully-ripened side of even almost ripe
cones. As the cone ripens the seeds become easily accessible, but with their manner
of dispersal we shall deal in a later section of this work. Here we are concerned
only with the fact that many ovaries and fruit-envelopes render their contents
undesirable to animals by sticky secretions or disagreeable scents. The pods of
several Leguminos, e.g. species of Adenocarpus (A. decorticans, A. Hispanicus,
&e.), are invested both on their flat sides and round the edge with short-stalked,
sticky, brown glands, which are to be regarded as a protective arrangement for the
young pod. The same obtains in the Hemp (Cannabis sativa), though here it is
not the ovary but the scales immediately about it which are sticky and strongly
odorous. So also in the Hop (Humulus Lupulus), the fruits are invested in scales
bearing glands which play a like part. Even the ubiquitous sparrow leaves the
fruits of these two plants alone during the period of ripening.

Of not less importance to the young embryo is protection against injurious
climatic influences. Among these, undue moisture and dryness are the chief; and
it is to be expected that due provision against them should be made on behalf of the
young plant whilst it remains on the parent. Seeds contained in berries, drupes,
and indehiscent fruits, as well as those which, produced in capsules, are dispersed
at the moment of fruit-dehiscence, hardly come under consideration here, as the
opportunities for hurt by weather are relatively small. But in the case of dehiscent
fruits which open by means of valves, teeth, or pores, and in which the seeds are
retained for some time after the opening of the fruit before they are scattered,
provision must be made against the entrance of rain into the cavity of the fruit,
which might injure the seeds. This class of danger is averted by the fact that the
various valves, teeth, &e., which guard the apertures of the fruits, are very hygro-
scopic and close in humid weather; or, what is equivalent to this, they only open in
dry weather, especially under the influence of drying winds. To make this remark-
able contrivance intelligible we must briefly describe the arrangements for seed-
dispersal obtaining in capsules of the kind. Capsules opening by valves, teeth, &e.,
are usually inserted on long stalks, or, if sessile, the axis from which they arise
possesses considerable length. These stalks are fairly stiff, and oscillating to and
fro in gusts of wind the contained seeds are shaken out, usually as the capsule
springs back after the blast. In the case, for instance, of the beaker-like capsules
of the Nottingham Catchfly (Silene nutans, fig. 340°) the seeds cannot fall out
of their own accord, the opening being directed upwards; but as soon as the wind
sets the long stalk in vibration they are jerked out. For this mode of scattering
of the seeds it is essential that the apertures of the fruit should be directed
upwards. Indeed, in the great majority of cases of this class, this is their position.
In this Catchfly at the time of flowering the flower-stalks are pendent (see figs.
238 and 239, pp. 154 and 155), but, as the fruit ripens, the fruit-stalk becomes
erect; the same thing is well shown in the Martagon Lily. On the other hand,
when the fruit-stalk bends down after flowering, as in the Bellflower (Campanula,

448 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS,

fig. 3401) and in the Winter Green (Pyrola, fig. 340°), the holes and slits are not
formed at the apex of the fruit, which is directed downwards, but at its base, close
to the insertion of the stalk. This position of the apertures would render the
inside of the capsule liable to wetting from rain, &c., and the contained seeds to
injury therefrom, were it not for the fact the openings are closed when this danger
threatens. The wall of the capsule is very hygroscopic, and the slits and valves
quickly close in damp weather. In fig. 340 several examples of this opening and

Fig. 340.—Protection of seeds against wet.

1 Capsules of Campanula rapunculoides in dry, Y in wet weather. 2 Capsule of Lychnis diurna in dry, ? in wet weather.
3 Capsules of Linaria Macedonica in dry, * in wet weather. 4 Capsules of Cerastium macrocarpum in dry, # in wet
weather. * Capsules of Silene nutans in dry, 5 in wet weather. 6 Capsules of Pyrola chlorantha in dry, % in wet weather.
7 Capsules of Gymnadenia Conopsea in dry, 7’ in wet weather. ® Capsule of Pinguicula vulgaris in dry, * in wet weather.

closing are represented. In the already mentioned capsule of the Catchfly (fig. 340°)
the aperture at the summit is guarded by a number of divergent teeth; the same
is true in the case of those of various species of Toadflax (e.g. Linaria Macedonica,
fig. 340°). In Cerastium macrocarpum (fig. 340 *) the opening is directed laterally,
and in the Campion (Lychnis diwrna, fig. 340°) the capsule is erect with revolute
teeth. In the Bellflower (e.g. Campanula rapunculoides, fig. 340+) small, cireum-
scribed portions of the wall near the base fold back as valves, giving rise to as
many apertures; in the Winter Greens (e.g. Pyrola chlorantha, fig. 340°) a number

PROTECTION OF SEEDS AGAINST WEATHER. 449

of slits arise near the base, while in the Butterwort (Pinguieula vulgaris, fig. 340°)
the fruit splits into two valves. How all these capsules behave is shown in the por-
tion of the illustration with the shaded background (figs. 340" to 340°). Closure
is so complete that the entrance of moisture into the capsules is impossible, and
the seeds have absolute immunity from premature wetting. Even in the case of
capsules with lateral slits, where there is a possibility of moisture entering, the
same arrangement prevails, as is well illustrated in the Fragrant Orchis (Gymna-
denia Conopsea, cf. figs. 3407 and 3407).

Of capsules with openings directed downwards there are but few, and in these
the dispersal of the seeds is not accomplished quite in the same manner as in those
just described. In the Funkias (Funkia ovata, Sieboldi, subcordata, &e.) the pendent
capsules open by three valves at their depressed tips, and concurrently some of the
seeds are shot out into the air—often to some little distance. Those which remain in
the capsule after the sudden opening are not, as one might expect, deposited in a
heap on the ground close by, but, being attached to the valves by delicate strings,
and having a flattened form, offer considerable surface to the wind, which ultimately
loosens them and bears them far away. The fact should be emphasized that in
many cases fruits only open under the influence of dry winds, and that the same
wind which promotes their dehiscence at the same moment scatters the seeds. This.
is very well shown by the Scotch Pine (Pinus sylvestris). Its cones only separate
their scales in the afternoon when the air is driest and a wind is blowing. When
the conditions for this are favourable one hears quite a series of noises in the tree-
top, caused by the separating of the scales, and at the same time the winged seeds
go spinning through the air. The scales protect the seeds in this case against
wetting, and indeed against other dangers as well. It should be remembered that
any protective arrangement is but rarely directed solely against one particular
source of danger. An envelope may protect the embryo at one time against the
wet, at another against excessive desiccation; sometimes the same envelope may
also ward off attacks from undesired guests of the animal world.

Developments on fruits whose chief function is the protection of the seeds
against desiccation are, on the whole, scarce. In certain portions of Australia the
whole vegetation enters upon a sort of summer sleep; during this period no rain
falls and the surface of the earth is hardly ever wetted with dew; such a dryness
of the air and of the soil prevails that plants are compelled to suspend operations
for a while. It has been already explained how the foliage is protected against
drying up (ef. vol. i. p. 296); but the embryo also, which has arisen within the ovule
during the period of vegetative activity, has to be preserved during this period.
This is achieved by the massive development of the ovary wall, which in this
respect exceeds anything met with in the Floras of other regions of the globe. The
seeds of the Wooden Pear (Xylomelum pyriforme, see fig. 325° p. 431) are inclosed
in a strong pericarp, the wall of which attains a diameter of 2 centimetres, and can
resist the greatest dryness for very long periods. So also is it with the seeds of the

Australian species of Banksia and Eucalyptus (see figs. 324 and 325 '% 14 pp. 429
Vou. IL 79

450 FERTILIZATION AND FORMATION OF FRUIT IN PHANEROGAMS.

and 431), the walls of their capsules being exceedingly thick and strong. In not a
few Steppe-plants the seeds within are protected by the nature of the inclosing
pericarp during the hot, rainless summer season. Remarkable amongst them are
the big Umbelliferous genera Prangos and Cachrys, the schizocarps of which are
protected by a thick spongy wall not unlike elder-pith in nature. Preserved within
these walls against desiccation, the embryo secures this further advantage, that from
the relative largeness and lightness of the fruits they are readily dispersed by the
wind over the Steppe.

In dry, dehiscent fruits protection against unfavourable climatic conditions is
extended only so long as the seeds remain attached to the parent plant; in achenes,
nuts, and schizocarps it lasts longer, however. For in the latter classes of fruit the
pericarp accompanies the seed after severance, protecting and aiding it during its
passage, and often assisting it at germination. All those developments of the seed-
coat, met with in the cases in which the seeds themselves are liberated, are replaced,
in these non-dehiscent fruits, by the pericarp or other associated portion—calyx,
bracts, and the like. These structures are fashioned so as at once to preserve the
seed on its journey, be it by air or water, and to attach it to its germinating-bed
by various irregularities of surface—pits, furrows, warts, or even sticky excretions.
Further, it is important that arrangements be provided so that the young plant
should have access to water at certain spots on the fruit wall, and that on germi-
nation it should be able to push out its young rootlet without undue effort, as, for
instance, in the Water-chestnut and Bulrush (cf. vol. i. p. 607, figs. 144% #1 12, 18),

The stage of development at which the embryo is detached from the parent
plant is not the same in all cases. In the Maidenhair Tree (Gingko biloba) the
embryo is but slightly differentiated at the time when the plum-like seed falls. The
egg-cell has been already fertilized, and the enveloping tissues of the seed have
matured, but the differentiation of the embryo is postponed till after the seed has
fallen. So, too, in Orchids and in many parasitic and saprophytic plants, such as
Cuscuta, Orobanche, Monotropa, and Balanophoree, the embryo, at the moment of
severance of the seed, is of the most rudimentary character. But in the majority
of Phanerogams the embryo shows a differentiation into plumule, and radicle, and
cotyledons. In Ceratophyllum the plumule has already slightly elongated and
exhibits a number of little leaves, and in Nelwmbium the leaves show a differentia-
tion into blade and petiole. In the Mangrove Tree (Rhizophora Mangle, see fig.
3411) the embryo attains to a very considerable degree of development. whilst still
attached to the parent plant. Its root penetrates the wall of the ovary (fig. 341?)
and ultimately attains a length of 30-50 em. and a thickness of 1-5 em. and a
weight of some 80 grams. Finally, the young plant breaks away from its sucker-
like cotyledon and falls into the mud below, where it speedily unfolds a pair of
green foliage-leaves (cf. vol. i. p. 604). Thus, in the Mangrove Tree, it is not the
seed but the embryo which is detached from the parent plant. Comparing the
Gingko to an oviparous animal, the Mangrove might be regarded as viviparous.

The envelopes which surround the embryo at the moment of detachment vary

DIMENSIONS OF SEEDS. 451

enormously from plant to plant. The seed of the terrestrial Orchid Gymnadenia

Fig. 341.—Mangrove Tree (Rhizophora Mangle).

1 Branch with flowers and fruits (reduced). 2 Single fruit, the apex of which is being penetrated by the radicle of the embryo.
(After Baillon.)

Conopsea measures 1 mm, in length and weighs ‘008 gram: that of the Cocoa-nut
Palm 11—14 em. and weighs 800-1100 grams. The Wind Bent-grass (Apera spica-

452 FRUITS REPLACED BY OFFSHOOTS.

venti) has a grain 1'2 mm. long, '3 mm. broad, and weighs ‘05 grm.; the fruit of the
Seychelles Palm (Lodoicea Sechellarwm) measures 32 em. by 18-25 em. by 22 em.,
and weighs 4200-4800 grams. The largest fruits are produced by the Cueurbitacex;
in a suitable soil Gourds attain a diameter of half a metre, whilst fruits of the
Melon-pumpkin (Cucurbita maxima) have a greatest diameter of over a metre, and
a weight of 75 to 100 kilograms. The fruits of the Bottle-gourd (Lagenaria) attain
under favourable circumstances a diameter of 30 cm. and a length of a metre and

a half.

3. CHANGE IN REPRODUCTIVE METHODS.

Fruits replaced by Offshoots.—Parthenogenesis.—Heteromorphism and Alternation of Generations.

FRUITS REPLACED BY OFFSHOOTS.

By Annual Plants are understood such as germinate, grow, and conclude their
flowering and fruiting within the limits of a single year, and after the ripening of
their seeds die away. The activity of these plants is concentrated on the production
of a large amount of seed; it is worthy of note that autogamy is frequently met
with amongst them, followed by good results. They produce just so many foliage-
leaves as are necessary to provide the materials for their flowers and fruits, and
reserve-substances for their seeds. With the production of seed, the leaves, stems,
and roots perish without forming vegetative buds or offshoots, so that these plants
are represented for several months by their seed only. Their rejuvenescence can
only oecur under favourable climatic conditions where an unimpeded germination
is allowed these seeds, and when no interference in the process of development is
imposed by men or animals. If the weather be unfavourable in the situations
where the plants have established themselves, if the summer be a cold one, so that
fruit cannot be ripened, they do not perish at the end of the first year, but prolong
their existence till another year by means of offshoots, becoming, for the time being,
perennial plants. We may put it, in a manner of speaking, that when the danger
of extinction threatens, fruit-production is replaced by offshoots; instead of fruits,
tubers, buds, or other shoots are produced, and not infrequently these structures
arise in the position usually occupied by fruits. Among the Crassulacez there are
several annual species (Sedum annuum, glaueum, &e.) which normally die away so
soon as their seeds have ripened and been dispersed. But when it happens from any
cause—as by the premature on-coming of winter—that these processes are interfered
with, little rosettes of leaves arise from the base of the stem in close proximity to
the root; these are detached, and, as offshoots, continue the life of the plant into
another season. Similar phenomena are observed in many other herbs whose
flowers or fruit are destroyed by frost. Indeed by experiment these statements
can be readily verified. Members of various families (Poa annua, Senecio nebro-

FRUITS REPLACED BY OFFSHOOTS. 453

densis, S. vulgaris, Ajuga Chamepitys, Herniaria glabra, Viola tricolor, Cardamine
hirsuta, Medicago lupulina), normally annual, are transformed into perennial plants
when grown in my alpine experimental garden on the Blaser in Tyrol (Gschnitzthal),
at a height of 2200 metres, there being insufficient warmth there for them to produce
good seed.

Interference with fruit-production due, in inhospitable situations, to an un-
favourable climate, can be artificially brought about by the removal of the flowers
from a plant as they appear. Annual plants pruned in this way produce shoots
and offshoots which would otherwise have remained undeveloped. These remain
living till next year, and if the same treatment be continued indefinitely, a plant,
otherwise annual or biennial, becomes perennial. Upon this fact depends the
gardening feat of producing little Mignonette trees. Normally the seeds of this
plant germinate in a sandy and humous soil, and the plants arising perish in the
autumn after flowering and ripening their fruit; but if the inflorescences be care-
fully pinched off, the stem doesn’t die down but produces lateral shoots with the
object of developing new flowers. If these flowers be removed year after year,
gradually a little tree is formed, with woody stem and branches; and if ultimately
it be left alone will cover itself with hundreds of sweet-scented flower-spikes.
That a much increased production of leafy shoots and offshoots can be stimulated
in perennial plants by this kind of pruning has long been known; by its aid many
modes of propagation, as practised in horticulture and agriculture upon cultivated
plants, are obtained.

It sometimes happens in nature that a failure of flowers is due to the plants
being overshaded. That is to say, many plants growing in shady places either
do not produce flowers or their flower-buds do not open and cannot ripen fruit.
Such plants produce offshoots from the lower portion of their stem in the form
of leafy shoots, runners, &e., if they are able to do so, and this in a very marked
degree; in other words, the more flowering and fruit-production is hindered by
shading, the more is a development of offshoots promoted. The Willow-herb
(Epilobium amgustifoliwm) develops its beautiful flowers only in sunny situations,
accessible to hive- and humble-bees. The more intense the sunlight, the more
vividly are the flowers coloured. Should trees grow up and densely overshadow
the Willow-herbs, the flower-buds atrophy before opening and fall away from the
axis as small withered structures. Whilst the richly-flowering plants form only
short offshoots, these shaded plants produce long, subterranean runners, which seek
to penetrate to a distance, out of the circle of shade.

Another remarkable phenomenon in the growth of perennial plants, which
flower and fruit copiously under favourable elimatie conditions, is that in inhos-
pitable situations, where this is restricted, they propagate themselves very
readily by means of offshoots. A Composite, Nardosmia frigida, allied to the
Butter-bur, is widely distributed over the Aretie regions. Only towards its
southern limits does it produce flower and fruit; further north flowers are never
met with upon it, but, instead, it propagates itself far and wide by means of

454 FRUITS REPLACED BY OFFSHOOTS.

offshoots. Similar in its behaviour is another Composite, the alpine Adenostyles
Cacalie. It blossoms and fruits in sub-alpine forests even up to the tree limit, but
in high alpine regions, above 2200 metres in altitude, it never flowers, but forms
offshoots, and in this way fills little depressions on alpine slopes with its vigorous
foliage. The terrestrial form of Polygonum amphibium occurs in a little bog
close to my country house in the Gschnitzthal in the Tyrol at a height of 1200
metres. For twenty-eight years I have examined this bog every year without ever
finding a ripe fruit upon these plants. But it propagates itself with rare luxuriance
by means of offshoots and forms a broad girdle around the bog. These plants,
Nardosmia frigida, Adenostyles Cacalie, and Polygonum amphibiwm, grown in
a more favourable climate, produce good seed, but their vegetative methods of
propagation are so restricted that one might almost suppose them to be different
species of plants.

Instances in which flowers are replaced by offshoots or bulbils in the inflores
cence may be mentioned in connection with the above. Polygonum viviparum
and bulbiferum, Saxifraga cernua, nivalis, and stellaris, Juneus alpinus and
supinus, and the Grasses Aira alpina, Festuca alpina and rupicaprina, Poa
alpina and cenisia occur, it is true, with normally developed flowers and fruits,
but in alpine, and especially in arctic regions, where these plants have their head-
quarters, one very frequently finds purely vegetative buds or bulbils, which become
detached from the parent plant and give rise to new individuals, in place of flowers
and fruit. In the Polygonums mentioned little bulbils replace a portion of the
flowers. Saxifraga cernua usually produces a single terminal flower at the end of
its inflorescence, the lateral flowers being replaced by little tufts of bud-like offshoots
on short stalks (see fig. 342*)> These buds, when they fall off, are either still closed
(fig. 342°), or their thick, fleshy, outer scales are already parted, exposing a little
green foliage-leaf. On the ground they soon produce roots and grow into new
plants (see figs. 342° and 3427). In Sawifraga nivalis little shoots are formed in
place of flowers, each bearing a tuft-like rosette of minute leaves (fig. 342'). These
rosettes are readily separable, and producing roots from their abbreviated axes,
give rise to new plants. So also in the Juncuses and Grasses mentioned, little
shoots replace the fruits and come away from the inflorescence. These shoots are
produced in Poa alpina (see fig. 342°) and in most of the other Grasses mentioned,
in the following manner. The axis of each spikelet, after producing several glumes
at its base, forms green leaves above—as it were a grass-plant in miniature (see figs.
342° and 3421°). Later, these disarticulate, take root, and grow into new plants.
More rarely do shoots arise laterally on the axis, in the axils of subtending scales;
when this is the case they fall away in the usual manner. The earlier Botanists
termed all such Grasses, and indeed all plants which produce bulbils in their inflor-
escences, viviparous, the idea being, that in all of them the seeds germinated
precociously whilst still attached to the parent. This view was probably suggested
by the common experience of agriculturalists that Rye, Oats, and other cereals
sometimes “sprout”, 7.¢. that when the spikes are continually wetted by rain about

FRUITS REPLACED BY OFFSHOOTS. 455

the time of harvest, and the haulm laid flat on the ground, the embryos begin to
develop whilst the grain is still in the ear. This premature germination, however,
is quite independent of the parent plant, which has given up all its food-materials,
and is already dead; the grains, held between the glumes mechanically, are no
longer in vital connection with the plant which gave them origin. Their germina-
tion between the damp husks is similar to what would occur between pieces of
moist blotting-paper. But in these so-called “ viviparous plants” the phenomenon

Fig. 342.—Bulbils replacing flowers and fruits.

1 Saxifraga nivalis with rosettes of little green leaves instead of flowers (natural size). ? Two of these rosettes, enlarged; one
of these has become detached from its stalk. 3 Saxifraga cernua (natural size). 4A cluster of bulbils of this plant.
5, 6,7 Bulbils of same in various stages of development. ® Poa alpina with bulbils replacing its flowers (natural size).
9 A portion of the inflorescence (enlarged). 1° A miniature grass-plant developed between the glumes of a spikelet of Poa
alpina (enlarged).
is quite different from this “sprouting” of cereals. In them no flowers or seeds are
formed, consequently there can be no germination of seeds still united to the parent
plant. The detached structures, formerly regarded as germinated seedlings, are in
reality little, leafy shoots which have been produced instead of flowers and fruits.
The plants which we have just been discussing are essentially forms living in
high alpine and arctic regions, that is to say, in regions in which they have but
some two to four brief months in the year in which to complete their vital

processes. In the majority of plants growing under such inhospitable conditions.

456 FRUITS REPLACED BY OFFSHOOTS.

the flowers for the following summer are already developed in miniature the pre-
ceding autumn, so that on the melting of the snow and the termination of winter
the flowers can be at once expanded. When such plants can avail themselves of the
warmth of the whole summer they are able to ripen fruit and seed. But it is other-
wise with those which produce their flowers on a leafy axis, and which must first
form an under-structure on which they can be produced; with these, before
flowers can be unfolded, a considerable interval of time must elapse. Their blossom-
ing is delayed, and the ripening of their seed takes place quite at the end of the
period of vegetation. There is thus always the danger of early frosts or of the
winter-covering of snow intervening before the seeds can be ripened and dispersed.
It is in just such plants that preservation and propagation are ensured by a
development of bulbils; these structures are more speedily produced than seeds,
nor do they require so much warmth; further, they are not so liable to injury
from premature advent of winter as are developing fruits. The above-mentioned
Polygonums, Saxifrages, Rushes, and Grasses are amongst those which flower
relatively late, and are liable, in unfavourable seasons, to a destruction of their
seeds. The very frequent substitution in them of vegetative for sexual reproduction
would seem to be undoubtedly correlated with this liability of seed to fail. And in
not a few steppe-plants the substitution of offshoots for flowers is probably con-
nected with the fact that with them, also, the season is not always long enough for
the formation of stem, flowers, and fruit.

It has been previously pointed out that a great many aquatic plants, with
roots fixed in the mud and stems and foliage floating in the water, raise their
flowers above the surface and avail themselves of the wind and of fiying insects
for pollination and fertilization. For such plants fluctuations in the level of water
must be of considerable moment, and it may well be that if the surface is raised
for any length of time, flowering and fruiting are hampered, and, in many cases,
rendered impossible. Many marsh and water plants possess, indeed, the capacity
of stretching to the surface, the stem continually elongating as the level is raised,
until the flowers can be expanded above the surface. But this growth in length
has its limits, and it not infrequently happens that, even after an extraordinary
elongation of stem and flower-stalk, the surface of the water is not attained. And
these flowers in most cases cannot be fertilized under water; if already formed, the
flower-buds do not open, but atrophy and fall off without producing fruits. In the
little meres of the Black Forest, Littorella lacustris, a plant allied to the Plantain,
grows; but it only flowers and fruits in very dry years, when the expanse of water
is much contracted and the bottom is in large part laid bare. But this is not very
often; ten years may pass without the conditions favourable to the flowering and
fruiting of Littorella obtaining. During the whole of this time the plant must
remain barren were it not for the fact that off-shoots, which take root in the mud,
are produced instead of fruits. Thus it is able to maintain and propagate itself.
Several Pondweeds and Water-erowfoots (Potamogeton and Ranuneulus) behave

FRUITS REPLACED BY OFFSHOOTS. 457

like Littorella, and it would appear that the capacity to propagate by offshoots, so
common in aquatic plants, is connected with the impediment to flowering so often
presented by a high water-level. Cymodocea antaretica, a submerged aquatic
plant, which grows in great luxuriance on some parts of the coast of Australia,
flowers so rarely that its peculiarly formed bulbils were for a long time regarded
as its flowers. Nor has every Botanist seen the flowers and fruits of the Duckweed
(Lemna); whilst the renowned American Water-weed, Llodea canadensis, which
has been such an obstacle to navigation in canals, &e., but seldom flowers, and owes
its very remarkable propagation and distribution, not to fruits, but to a quick and
plentiful production of offshoots.

A dearth of water, also, like a too ample supply, can render fertilization im-
possible and promote the propagation and distribution of some plants by offshoots
toa remarkable degree. In Ferns and Mosses the spermatozoids reach the arche-
gonia, swimming in the water which accumulates on or about the sexual generation
of these plants (cf. pp. 65 and 68). In the great majority of cases, it is rain and
dew which provide the capillary water which invests the plants, and in which the
spermatozoids swim. And other conditions in the life of Ferns and Mosses besides
fertilization depend on an adequate supply of water; their existence depends on a
certain definite amount and on a certain annual duration of atmospheric precipita-
tion. Mosses, and particularly Ferns, have but a restricted distribution in dry
localities; or they may be entirely wanting. In humid regions, on the other hand,
they attain to a luxuriant growth. The contrast in this respect is striking enough
for illustration. Elvend Kuh, a mountain in the interior of Persia, rises to a height
of some 3750 metres, and is the culminating point of a considerable plateau. The
rainy season is limited to a period of two months, and a rich and well-marked
steppe-flora covers the ground. Ferns are absent from an area some 5000 square
kilometres in extent, whilst Mosses are only represented by a few species which pro-
pagate by means of thallidia, rarely maturing spore-capsules. In the hill country of
the West Indies, particularly the Blue Mountains of Jamaica, the vapour condenses
every morning, and in the course of the afternoon is precipitated as rain. Here are
found some 500 Ferns, and large numbers of Mosses and Liverworts. The level
or sloping ground, rocks, the forest floor and decaying tree-trunks, all are covered
with Ferns of every shape and size; there are groves of Tree-ferns, the trunks of
trees are invested right up to the crown with delicate, green fronds, whilst tiny
representatives of the Filmy Ferns (Hymenophyllacee) have actually taken up
their abode on the foliage-leaves themselves. Within a distance of a hundred
paces the plant-collector can find fifty different sorts of Ferns, and as many
Mosses.

And between the extremes we have described there are regions with an inter-
mediate climate, of such a character, that although the fertilization of Ferns and
Mosses is not perpetually prevented, still wet years are rare, and several years may
elapse without the conditions being favourable for it. Such a region is the Hun-
garian plains, the fields and woods of which produce only two species of Ferns and

458 FRUITS REPLACED BY OFFSHOOTS.

some dozen Mosses. The latter have almost entirely ceased developing fruits,
and propagate themselves for the most part by thallidia, since these can be pro-
duced much more simply, and their production is independent of enduring drought.

Certain Ferns must be mentioned in this connection, on the prothallia of which
offshoots arise instead of normal, sexually produced embryos. It is true that
they form archegonia, but they are abortive, and propagation is asexual. The
little Fern-plant arises not from the archegonium but from the tissue in its im-
mediate neighbourhood; the archegonia remain closed, are not fertilized, turn
brown, and die. This substitution may be observed in Aspidium falcatum, in a
crested variety of Nephrodiwm Filiz-mas, and in the variegated form of Pteris
Cretica, frequently cultivated in greenhouses. On the prothallia of normal forms
of Nephrodium Filix-mas, and on those of wild plants of Pteris Cretica, fertiliza-
tion takes place in the usual way, so that it is possible that the substitution of
offshoots for fruits is a result of the conditions of cultivation. To what causes
exactly the phenomenon in question may be due, is, however, unknown.

As factors in promoting a substitution of offshoots for fruits amongst the
Mosses, other climatic conditions exert considerable influence. But it would lead
us too far were we to treat of all these in detail; only a few of the fifty or so
examples from the European Moss-flora can be mentioned here. Leucodon sciwr-
oides, a Moss which rarely fruits in Northern Europe, produces instead numerous
leafy shoots (brood-bodies) which, becoming detached, readily root on a moist
substratum (see figs. 196° and 1967, p. 23). Campylopus fragilis, again, scarcely
ever produces fruits in the Alps; it forms readily separable lateral branches, the
leaves of which are carried away by the wind. Any of these leaves falling on a
moist spot develops green filaments, upon which little buds arise, originating
new leafy Moss-stems (see fig. 196", p. 23). The case of Barbula fragilis and
Timmia Norvegica, growing in the Alps, is similar to that of Campylopus. Of
several Mosses the fruits have never been seen; such are Dicranodontium aris-
tatum, Barbula papillosa, Grimmia torquata, Bryum coneinnatum, and B.
Reyeri. They are able to maintain themselves in spite of this by vegetative propa-
gation.

In addition to the cases already enumerated, in which climatic conditions,
excess or lack of water, &c., promote vegetative as opposed to sexual reproduction,
numerous others are known in which peculiarities in the structure of the flowers
cause the ovaries to abort, or make it necessary that a formation of offshoots
should be initiated if the plants are to be maintained. In this connection certain
hybrid Fuller’s Thistles and Mulleins (Cirsiwm and Verbascwm) must be noted.
The plants in question are hybrids, that is to say, they are produced by crossing of
different species. They flower early in the summer, and have ample time to
ripen seed before the on-coming of winter, but in a number of these hybrids, owing
to variations in the structure of the flowers and of the pollen, few or no seeds
are ripened. On the other hand, just these very plants form aérial buds and
subterranean offshoots very freely. Cirsium purpurewm, a hybrid between

FRUITS REPLACED BY OFFSHOOTS, 459

Cirsium heterophyllum and spinosissimum, and Cirsiwm affine, a hybrid between
C. heterophyllum and C. oleraceum, are very abundant in many Alpine valleys,
and one may find more examples of these hybrids than of their parents in many
a meadow. Several of the Fuller's Thistle hybrids, the parents of which are
biennial, become perennial by a production of lateral shoots from the leaf-axils at
the base of the stem. Here also, as with climatic conditions, we find vegetative
propagation replacing fruit-production.

There are also many species, of which it cannot be definitely asserted that
they have arisen by hybridization in recent times, which fruit but seldom even
when the climatic conditions are in every way favourable for this kind of repro-
duction. According to agriculturists, there are many kinds of Potato which flower
only occasionally but do not ripen fruit, although the flowers and pollen-grains
appear quite normal. It is just these Potatoes which are characterized by their
rich production of tubers, fruit-formation being in them replaced by vegetative
propagation.

That plants, with double flowers, the ovaries of which, under the influence of
little insects (Phytopus), have undergone a deep-reaching transformation, should
ripen no fruits is to be expected and has long been known, as also is the fact that
these plants produce buds and offshoots freely. Of special note in this connection
is a Bitter-eress (Cardamine uliginosa) often met with in damp meadows in the
neighbourhood of Vienna, Salzburg, and Ried, growing wild with double flowers.
On most of the plants, the fruits of which are abortive, those curious leaf-buds,
represented in fig. 2004, p. 41, are to be found.

Again, with many species of plants, it may come to pass that the insects which
should accomplish their pollination are now no longer prevalent in the region
where the plants grow, or indeed have entirely deserted them. This category of
plants obviously includes only such forms as are destitute of arrangements for
promoting autogamy, in the case of eross-pollination not taking place. In a very
considerable number of these plants, flowers and fruits are replaced by offshoots—
offshoots of the most varied kinds, including aérial and subterranean tubers,
bulbils, green leafy shoots, and, in rare cases, little bud-like structures, from each
of which a thick, fleshy root arises in such a manner that the greater part of the
offshoot consists of a root. ;

As all these varieties of offshoots will be dealt with in a later chapter devoted
to the distribution of such structures by wind, animals, and special mechanisms, it
must suffice to speak here of a very few cases. Growing in sunny spots, the
yellow flowers of the Lesser Celandine (Ranunculus Ficaria) are occasionally
visited by little pollen-eating beetles, by flies and bees; under these circumstances
heads of fruit are ripened here and there from the flowers. But in shady places,
beneath bushes, and on the dark forest floor, these insect-visits are much rarer,
and almost all the flowers fail to ripen fruit. These shaded plants, however,
develop little bulbous bodies in the axils of their upper foliage-leaves, which
become detached on the withering of the shoot and give rise to new plants (see

460 FRUITS REPLACED BY OFFSHOOTS.

fig. 343°). Those which ripen fruit, on the other hand, form no offshoots, or only
very few. In the Coral-root (Dentaria bulbifera, see figs. 344 %%5) a similar state
of affairs prevails. Pollination is accomplished only by insect-agency, and where
insects fail no fruits are ripened. The plant grows sometimes near the sunny
border of young Beech-plantations where insects are plentiful, and also in the
forest of older growth in whose dusky glades bees and flies, humble-bees and
butterflies are rarely met with. Those which grow in the better lighted, younger

Fig. 343.—Flowers and fruits replaced by tubers and bud-like offshoots.

1 Gagea Persica. 2 Lycopodium Selago. % Ranunculus Ficaria. 4 Bud-like offshoot from the leaf-axil of Gagea Persica.
5 Bud-like offshoot of Lycopodium Selago. ® Tuber-like offshoot of Ranunculus Ficaria. 1, 2, ® nat. size; 4, 5, 6 enlarged.

portion of the wood ripen their cruciferous capsules, but the others, in the deep
gloom, are free of insects and blossom in vain. Their ovaries for the most part
abort and fall away, and only occasionally do their fruits come to maturity (ef. fig.
3447). But in proportion as fruit-production is arrested, vegetative propagation
by bulbils is promoted; large bulb-like buds are formed in the leaf-axils, which
disarticulate as summer advances and the shoot begins to fade; they are detached
by the wind as it sways the stems, and falling on the moist floor of the forest take
root (fig 3444) and give rise to subterranean rhizomes (fig. 344°). Some plants

FRUITS REPLACED BY OFFSHOOTS, 461

oeeur in these shady spots which bear no flowers at all, and depend entirely on a
production of these offshoots (ef. fig 344°).

There are two forms of Orange Lily indigenous to Europe. One (Liliwm
croceum), occurring especially in the Pyrenees and South of France, almost always
ripens fruits and forms no bulbils in its leaf-axils. The other (Liliwm bulbiferum),

Fig. 344.—Flowers and fruits replaced by bulbils. The Coral-root (Dentaria bulbifera).

1 Inflorescence. 2% Leafy shoot on which two fruits have ripened; bulbils in the axils of some of the leaves. * Leafy shoot
whose inflorescence has atrophied; bulbils in the axils of all the leaves. 4 Detached bulbils forming roots. 5 Rhizome
of Dentaria bulbifera.

found in the valleys of the Central and Northern Alps, hardly ever fruits, but is
characterized by the bulbils it produces in the axils of its leaves; bulbils which
disarticulate in autumn and are scattered by the wind. But there is no difference
noticeable in the structure of the flowers in these two Orange Lilies, and it is
difficult to explain their difference in mode of propagation, save on the assumption

462 FRUITS REPLACED BY OFFSHOOTS.

that in the regions where Liliwm bulbiferwm grows those insects are wanting
which should convey its pollen from flower to flower. As the Orange Lily possesses
no arrangements for autogamy, no fruits are formed in the absence of inseet-visits.
It appears that this plant has lost the capacity for autogamy; at any rate if a stigma
be pollinated with pollen from the same flower, on plants in a garden, no result
follows. On the other hand, offshoots in the form of numerous bulbils are pro-
duced by Lilium bulbiferum, by means of which it is propagated and dispersed.
In several valleys of the Central Alps it does not flower at all, and thus obviously
depends entirely upon its bulbils for propagation.

Gagea Persica (fig. 3431) a member of the Liliacee, repeats several of the
peculiarities met with in the Orange Lilies. The stem of this little bulbous plant
terminates in a flower which, in the absence of insect-visits, withers without
setting fruit. Little buds arise in the axils of its filamentous foliage-leaves. With
the atrophy of its fruits these grow into little bulbils (fig. 343%); but if fruit be
formed these buds for the most part atrophy. Nor must we omit to mention the
ally of this plant, Gagea Bohemica, belonging to the flora of Central Europe.
From its speeifie name, Bohemica, it might be supposed that it is solely met with
in Bohemia; this is not so, it was first discovered there, but is distributed widely
over Persia, Asia Minor, Southern Russia, and the Balkan Peninsula. Further west
Gagea Bohemica occurs rather sparingly, in Bohemia and in the neighbourhood of
Magdeburg—these occasional occurrences being no doubt a last lingering remnant
of a Steppe-flora which at some former period extended to the Harz Mountains.
We shall later have opportunity of explaining how this Steppe-flora has retreated
eastwards and been replaced by other communities of plants; here we may mention
that this retreat of the Steppe-flora was accompanied by a retreat of the Steppe-
fauna. The Steppe-antelope, Steppe-marmot, Steppe-porcupine, rat-hare, &e., which
existed in those times in Central Germany, have long forsaken this region, and we
have good grounds for assuming that the insects of that period have also migrated.
It is certainly remarkable that this Steppe-plant, Gagea Bohemica, the flowers of
which are adapted to insect-pollination, and in which autogamy does not occur,
should never ripen its fruit and seeds in these scattered localities of Bohemia and
Germany. One can hardly help supposing that this abortion of fruits is due to
the absence of those Steppe-inseets which were formerly, in all probability,
distributed also over Bohemia and Germany. Whatever be the explanation, it is a
fact that these isolated western representatives have never been known to ripen
fruit and seed. But instead, at the bases of the leaves, bulbils are formed which
fall away and root, maintaining and propagating the species.

Equally instructive is the case of one of the Chickweeds, Stellaria bulbosa, now
confined to a restricted area in Carniola and Croatia. It flourishes there in the deep,
black humus of the forest floor, preferably on the banks of little water-courses,
forming here and there dense, luxuriant masses. Its flowers unfold quite early in
the spring; and although they are fairly conspicuous, standing up white from the
green background, they are rarely visited by insects. The few flies which come to

PARTHENOGENESIS, 463

them seem to be undesired guests; they promote no pollination, and fruits are not
ripened. I have sought vainly for fruits in the neighbourhood of Laibach in Carniola
where Stellaria bulbosa is very abundant; there were thousands of faded flowers,
but never a fruit with ripened seeds. Its filamentous subterranean stems, on the
other hand, bear innumerable white buds; and if one digs up a handful of the
black woodland mould, it simply teems with these offshoots. The little streams in
spate after a thunderstorm often wash away some of the humus from their banks,
exposing and carrying away these little buds in the whirl of waters. Ultimately
they are left somewhere, high and dry; and if the conditions are favourable, take
root and establish themselves in these new localities. In this manner, at the
present time, is Stellaria bulbosa propagated and distributed. We cannot suppose
things have always been thus; we are driven to the conclusion that in this case,
also, the plant, much restricted as to its distribution, is a fragment of a vanished
flora. In the Karst district of Carniola and Croatia such fragments are not infre-
quent, and when one puts all the facts together one may well conclude that this
flora has retreated or been driven back in a south-easterly direction at a period not
very remote from our own. Accompanying these changes there may well have
been changes in the distribution of the insect-fauna, and those insects which
formerly visited the now rare Stellaria bulbosa of the Karst, and were of great
importance to it, may have migrated eastwards or indeed have become extinct.

PARTHENOGENESIS.

At the commencement of the Nineteenth Century the attention of Botanists was
directed to a certain aquatic plant, widely distributed in the Old World from
Treland to China, and from Finland to Northern Africa, and occurring very
commonly on the Baltic littoral and its islands. This plant was Chara erinita, one
of the Characez, which flourishes in brackish water near the sea, and here and
there in salty, stagnant inland lakes. In whatever ditch or pool it takes up its
abode it occurs in large quantities, and forms, like many of its allies, extensive and
luxuriant masses. It is an annual plant, dying off in the autumn. Next spring
young plants arise from the oogonia which have passed the winter on the muddy
bottom—and so from year to year. Chara erinita is dicecious, that is to say, some
plants bear oogonia only, others antheridia (cf. p. 62). Whilst in the generality
of dicecious Characeze the male and female plants grow in one another's immediate
vicinity, in Chara erinita such a distribution is extremely rare. Hitherto, male
plants have only been found at Courthezon, near Avignon, in the South of France;
near Gurjew on the Caspian Sea; and at Salzburg, near Hermannstadt, in Sieben-
biirgen (Hungary). I have myself found plants bearing antheridia in some little
salty pools near Soroksar, south of Buda-Pesth in Hungary. In the North of
Germany on the shores of the Baltic, where Chara crinita is very abundant, a
male plant has never been found. Nor have Botanists been wanting in their
endeavours to find such, should any occur in this region. The Dassower See near

464 PARTHENOGENESIS.

Lübeck, the neighbourhood of Warnemünde near Rostock, the two Jasmunder Bod-
dens (inland branches of the sea), on the island of Rügen, and the Wanger Wieck
near Stralsund, where Chara erinita is exceedingly plentiful, have been repeatedly
searched for male plants but in vain. And the female plants also have been
examined in case, perchance, an occasional antheridium might oecur upon them, as
in the moncecious species of Chara. Thus we may take it as established that in
the Baltic region no antheridia and consequently no spermatozoids are developed.
Nor was the attempt successful to explain the matter on the supposition that at
the time of fruiting spermatozoids were brought by water-birds from Hungary, the
Caspian, or the South of France. In the Baltic the egg-cells of Chara crinita
remain unfertilized in their oogonia; the latter fall off in autumn and, without
stimulus from any spermatozoid, germinate in the spring. We have here an
instance of what Zoologists have termed Parthenogenesis. It has been demonstrated
with certainty that new individuals arise from unfertilized eggs in the Spruce-gall
Aphis (Chermes), in plant-lice (Aphis), and in many bees, wasps, &e. Also, in the
Silk-worm Moth and in Solenobia, larvee arise from unfertilized eggs and these
pupz give rise only to females. This is of interest in that from the unfertilized
oogonia of Chara erinita only individuals with oogonia arise.

Cases similar to Chara crinita are thought to exist in several plants found in
water or on moist substratums. In the genus Syzygites (now included in Sporo-
dinia), a mould-like Fungus belonging to the Mucorini (cf. p. 54), the protoplasm
in the conjugating branches forms the starting-point of new individuals without.
any actual fusion or conjugation taking place. So also in the Saprolegniacese it
often happens that the egg-cells in the oogonia form new plants without being
fertilized; probably renewed investigations will bring to light similar relations in
many Peronosporez, Siphonacee, &e.

Amongst the Mosses parthenogenesis does not seem to be so very rare. In
them, as in Characex, fertilization is accomplished by means of water; the plants
are wetted by rain and dew, and this moisture is held by capillarity in the chinks,
&e., between the leaves. The fertilizing spermatozoids travel some distance, swim-
ming through the water to reach the archegonia. This distance is not very great
in many forms, and these ripen their fruits freely. But there are several species
in which only male plants occur in one locality and female plants in another—
it may be hundreds of miles away. Such species are Paludella squarrosa, which
oceurs in North Tyrol with antheridia, and in Bohemia with archegonia only;
Grimmia Hartmanni, found in the Alps with antheridia, and in the Carpathians
with archegonia. Neckera Besseri, Aulacomnion turgidum, Bryum alpinum and
B. Duvalii, Didymodon ruber, Barbula recurvifolia, Amphoridium Mougeotii,
Mnium insigne, Pterogonium gracile, Hypnum rugosum, and Thuidiwm abie-
tinum are further examples of which we cannot treat here in detail. As it is
impossible for the archegonium of a Moss in the Carpathians to be fertilized by
a spermatozoid from an antheridial plant in the Alps, and as fruits are ripened
nevertheless, though not very abundantly in truth, it may well be that these are

PARTHENOGENESIS. 465

eases of parthenogenesis, cases, that is, of egg-cells which continue their develop-
ment unfertilized.

Amongst Flowering Plants, also, cases are known in which ovules sometimes,
without ever being fertilized, form embryos which grow up into healthy plants.
An instructive example is the ease of Gnaphalium alpinum (= Antennarva
alpina), a perennial Composite nearly allied to both the common Cat’s-foot
(Gnaphalium dioieum) and Gnaphalium carpaticum of the Alps and Car-
pathians. This plant occurs in Scandinavia from Telemarken to Havosund (59°
52’ to 71° north. lat.), and in Russia from Finland to the Kola Peninsula, also
in Arctic Siberia, in Arctic America, in Labrador, Melville Peninsula and the
whole Arctie Archipelago, in Greenland between the parallels 60° and 72° north
lat., finally in Iceland. Thus it is distributed in a zone surrounding the North
Pole, some 12° in breadth. It is absent from the mountains of Central and
Southern Europe, and is not known to exist, for certain, on the mountains of
Central Asia. In these northern latitudes Gnaphalium alpinwm is exceedingly
common, occurring abundantly in innumerable localities. But it is a remarkable
fact that neither in Arctic America nor in Arctic Asia has a plant producing
pollen ever been found. In the Scandinavian Flora once, in the year 1842, a
pollen-bearing plant was alleged to have been discovered; but this has been dis-
eredited. A large number of Botanists, thoroughly familiar with the Scandinavian
Flora, are unanimous in saying that they have never seen stamen-bearing flowers,
and that ovaries only occur. I have myself obtained plants of Gnaphaliwm
alpinum from the Dovrefjeld in Norway, and have flowered them in my garden.
Every flower produced an ovary but no pollen, so that the possibility of pollination
was excluded. A number of achenes ripened containing good seeds, and these,
carefully cultivated, produced plants, in all respects similar to the parent form.
When these young plants flowered the same phenomena occurred. ‘Thus, one has
good grounds for asserting that Gnaphaliwm alpinum, throughout the wide area
of its distribution, is propagated parthenogenetically, and that its reproduction is
not hindered by the absence of pollen-bearing plants.

Another plant, of which it has been long known that embryos arise in its
unfertilized ovules, is a species of Dog’s Mercury (Mercwrialis annua, see fig. 345),
one of the Euphorbiacez, widely distributed in fields and gardens, in hedge-backs
and waste places, throughout Central Europe. Some individuals of this species
produce staminal flowers only (fig. 3451), others, female flowers only (fig. 345 ?).
Its dust-like pollen is conveyed to the stigmas by currents of air, and the ovaries
of the female flowers ripen seeds freely as the outcome of fertilization. But
female plants have often been cultivated in pots by themselves, with the result
that they also ripened seed, though smaller in amount than when there is access
to pollen, as is the case with plants growing freely in the open. These results
were much canvassed, and discredit thrown upon them by many. It was urged
that the dust-like pollen might have come from afar, in the air, and have entered

the conservatory in which the experiments were conducted; and again it was
Vor. II. 80

466 PARTHENOGENESIS.

pomted out that many female plants of Merewrialis annua bear here and there
a male flower alongside the female ones. For the refutation of these objections
fresh experiments were necessary in which every precaution should be exercised
to eliminate sources of error. Such expeiiments should be conducted in some
district in which for miles around the plant did not grow wild, so that the possi-
bility of casual introduction of pollen might be excluded. Fulfilling this require-
ment is the Central Tyrol, from which both the annual and perennial species
of Dog’s Mereury are absent. Accordingly I repeated in my upland garden in
the Tyrolese Gschnitzthal the cultural experiments originally carried out in 1833
by Ramisch at Prague. Every precaution was taken to avoid sources of error;

= RE TG
SSS Se =
FE SEY,
Ly, DE A ——u

aa
SEN
A/B
nn =
SF NER

Fig. 345.—The Annual Dog's Mercury (Mercurialis annua).

1 With male flowers 2 With female flowers.

and in particular were all plants destroyed which showed a tendency to produce
male flowers, and the utmost vigilance kept lest an isolated male or hermaphrodite
flower should make its appearance anywhere. At the time when the stigmas
were ready to be pollinated there were no pollen-grains of this plant anywhere
in the neighbourhood for miles around, so that the possibility of such a pollination
was excluded. Nevertheless the ovaries set and fruit was ripened, and from the
seeds young plants arose.

Another plant, also belonging to the Euphorbiaces, in which embryos arise
in unfertilized ovules, is Calebogyne ilicifolia. It was introduced into Europe
from the bush of Eastern Australia in 1829, and is now in general cultivation
as a hot-house plant in Botanic Gardens. The first specimen introduced bore only
female flowers, and all the plants which have been raised from this specimen, and
distributed over Europe, resemble it in this respect. Plants of Calebogyne with
male flowers are unknown in European conservatories. The possibility of such

PARTHENOGENESIS. 467

occurring on the female plants (ef. p. 300) has not been ignored, but they have
never been detected on the plants used for observations; consequently its own
pollen has never had access to the stigmas of the plants in question. In spite
of this, ripe seed has been obtained and new plants raised from it, which, in their
turn, bore only female flowers. Nor do these new plants differ in any way from
the plant originally introduced; this observation is of importance, as it might be
suggested that they were hybrids, that the pollen of some other euphorbiaceous
plant had reached the stigma, there produced pollen-tubes and fertilized the ovules
of Calebogyne. But this is not so, otherwise the offspring would give some indica-
tion of such origin. And the plant itself gives indication that it is not fertilized
by any pollen. If a plant of Celebogyne be kept apart where no pollen has access
to it, it can be noticed that its stigmatic lobes remain quite fresh for a long time,
even till the ovary begins to swell. Only later do they fade, when the seeds are
well advanced. This observation is of value since in ordinary cases the stigmas
fade very soon after pollination, and it is only unpollinated stigmas which retain
their freshness (cf. p. 285). In view of these oft-confirmed results, from which
all possible source of error has been eliminated, we may conclude that the ovules
of Celebogyne ilieifolia are able to produce embryos without the co-operation of
the male protoplasm.

We may now consider whether the instances just described can be regarded
as cases of true fruit-formation. As the essence of fruit-formation is a union
of ooplasm and spermatoplasm, or in other words, fruit-production must be pre-
ceded by fertilization, and as this condition is not fulfilled, these structures are
not true fruits. In the absence of fertilization, we must regard these reproductive
bodies as brood-bodies, or a special form of offshoot. As has been previously
mentioned (p. 44), brood-bodies can arise from any portion of a thallus, from any
portion of the stem, and from leaves of the most various kind. A brood-body
can originate from the protoplast of a cell of a Lichen-thallus or of a Moss-leaf,
from one in the root of an Ash-tree or in the stem of an Orange Lily, on the
margin of an Orchid-leaf, or over the midrib of a Begonia-leaf; why not also
from the protoplast in the oogonium of Chara erinita, or in the archegonium
of a Moss, and in the ovules of Gnaphalium alpinum, Merewrialis annua, and
Celebogyne ilicifolia? Experience shows that in the great majority of cases,
both in the Cryptogams and in the Phanerogams, the young commencements of
the fruits abort if the ooplasm be denied the spermatoplasm which should fertilize
it; but it also shows in unmistakable manner that in a few plants the ooplasm
does not die even in the absence of fertilization.

Without entering upon profitless speculations belonging to the domain of
Nature-philosophy, we may discuss the question of the possible reasons for the
curious behaviour of the “fruits” in these cases. And first of all it may be '
observed that all the plants exhibiting the phenomenon of parthenogenesis are
dicecious. For such plants a crossing with other individuals is alone possible.
But what occurs should a crossing in such plants be impeded from any cause? It

468 PARTHENOGENESIS.

seems contrary to the economy of plants that the egg-cell, produced at great expense
of energy, and in a sense the eulmination of a plant’s activity, should wither away
unproductive. Plants with hermaphrodite flowers can, if denied crossing, resort
to autogamy. But this is of course impossible with dicecious plants; instead of
autogamy the formation of embryos in unfertilized oogonia and ovules is a
possibility open to them, whereby their outlay of material and energy shall not
be wasted. Diceeious plants, which are likewise annuals, are especially liable
to the danger of extinction in the absence of pollen and consequent fruit-pro-
duction; for them the death of the individual may connote the disappearance of
the species. Against such possibilities many precautions exist amongst plants,
notably the formation of offshoots or brood-bodies; the leafy shoots arising from
these structures preserve the plant from such a contingency. In the same way
we may regard the formation of brood-bodies in the ovules of dicecious plants
as a means contrived to prevent the extinction of the species. The fact that
brood-bodies are formed in the ovules of not a few dicecious plants to which
pollen has not ready access, supports this view. There has been a specimen
of the Californian bush, Obione halimifolia (an Atriplex, Chenopodiacee), for
many years in the Vienna Botanic Garden. This plant is dicecious; the Vienna
plant bears only female flowers, and pollen is not accessible within hundreds
of miles. Its stigmas remain unpollinated, and its ovules unfertilized. But as
the autumn draws in, the ovaries of this plant begin to swell, and the perianth
which ensheaths the ovary expands, and what appear to be fruits are formed.
But these fruits are what we call “deaf”; no signs of an embryo are to be found
within. Thus, in this plant, no brood-body has been produced; it is impossible
to say whether or no, at some former period, this plant ripened brood-bodies in
its unfertilized ovules. Why the male plants of Chara erinita are absent from
the Baltic, and those of Gnaphalium alpinwm from the Arctic regions, are puzzles
as yet unanswered. In Chara erinita it is only on the coast-regions that male
plants are wanting; inland, male and female plants grow side by side. Possibly,
climatic conditions and the vicissitudes to which our existing Flora has formerly
been subject have brought this about, but we lack the data for continuing the
discussion further.

If, in the plants enumerated, parthenogenesis be but a special case of offshoot
formation, it is a matter of indifference which cells within the ovule are the
starting-points for the brood-bodies. In Calebogyne, in addition to the egg-cell,
other cells belonging to the wall of the embryo-sac are concerned in the production
of brood-bodies. Cells quite outside the embryo-sac can also initiate these off-
shoots; in which case they project as little papille into the cavity of the embryo-
sac, where they continue their development. In this way several embryos may
arise side by side, a condition which has been termed Polyembryony. This phe-
nomenon occasionally takes place in the ovules of hermaphrodite flowers, in which
a normal pollination and passage of pollen-tubes to the micropyle occur. This
is the case in certain Liliaceze, polyembryony having been observed in species of

HETEROMORPHISM AND ALTERNATION OF GENERATIONS. 469

Funkia and Allium, in both of which normal fertilization takes place. It is
interesting to note that in the case of Alliwm odorum recent investigations show
that the accessory embryos arise actually from the antipodal cells (ef. pp. 416,
417), i.e. from cells at the base of the embryo-sae which, in ordinary cases, simply
atrophy. Usually one embryo only arises from this source, but occasionally all
three antipodal cells develop into embryos. The ultimate fate of the embryo
arising (by fertilization) from the egg-cell and of those arising from the antipodal
cells has not been ascertained.

A peculiarity of parthenogenesis consists in the fact that the brood-bodies
arising in the ovules assume the form of embryos, not distinguishable from
embryos resulting from fertilization of an egg-cell. Little tubers or buds produced
in the ovary in places of ovules, as in Amaryllis and Crinwm (ef. p. 44), partake of
the nature of branches of the plant producing them; but the offshoots which arise
within ovules are not branches but young plants, provided with root, stem, and leaves,
and they are nourished by a special tissue which cannot be interpreted as a portion
of the axis of the young plant. These offshoots arising within the ovule possess
a new and independent axis, and herein exhibit an essential difference from the
offshoots described in the last chapter. Why these offshoots in the ovules always
assume the guise of embryos is a problem which we shall not solve, perhaps, until
we have more knowledge as to the essential differences in property between the
protoplasm of the ovule and that of other plant-organs,

HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

A sight of the sea-anemones and ever-varying polyps and corals, viewed through
the blue-green waters of a shallow bay, at first suggests a kaleidoscopic assemblage
of blossoming plants. At a distance the crowns of expanded tentacles resemble
red and purple Asters or the flowers of Mesembryanthemums; the skeletons of
these organisms are not unlike, in their ramification, the branching of some tufted
plant. The corals and polyps, like plants, are denied free movement, and like red
and other seaweeds, are attached to their stony substratum. Very appropriate
then, in view of their characteristic appearance, is the name of Zoophytes which
Zoologists gave to these animals.

And in their internal structure and mode of life they present certain remarkable
points of resemblance to plants. In many species the single individuals which are
joined together into a colony behave quite like the organs of a body, or the mem-
bers of a single organism which discharge different functions. There is a division
of labour amongst the individuals or polyps of the colony. One branch of the
colony is concerned in the acquiring of nutrition, another in reproduction, yet they
have a common digestive cavity, so that the juices obtained by one portion may be
shared by others which cannot take them up from the environment for themselves.
To this differentiation amongst equivalent members we may apply the term Hetero-

470 HETEROMORPHISM AND ALTERNATION OF GENERATIONS,

morphism; it will be seen in the sequel that Heteromorphism is a condition of
wide occurrence amongst plants.

Zoophytes propagate themselves in two ways. They may produce buds which
grow into new individuals, just as buds arise on the branches of a tree and grow
into new branches; and, like the latter, the products of these buds remain attached
to the part of the colony producing them, so that ultimately the extent of the
colony is considerably augmented. In many Zoophytes, especially in the Polypo-
medusz, certain branches of the non-sexual polyp-form assume the form of cups
or capsule-like structures in which buds arise which grow into disc-like, free-
swimming medusz, with a crown of tentacles. These medus® contain sexual
organs, and from each of their fertilized eggs an embryo arises which becomes
attached to the sea-bottom, and grows either into a non-sexual polyp or into a group
of sexual medusee. In the last-named event the pear-shaped embryo, after swim-
ming about for a while, becomes attached by its pointed end. On its body arise a
number of ring-like furrows, which gradually deepen until the cone-shaped embryo
is segmented into a number of transverse dises. Ultimately the cone disarticulates
and the discs swim away as medus&®. These medusz are sexual persons, and from
the fertilized egg-cells, either sexual or non-sexual generations may arise. This
alternation of sexual and non-sexual persons is known as Alternation of Generations.

Thus within the limits of the Zoophytes we see displayed two entirely distinct
things. First, heteromorphism, which gives us equivalent polyps on the same
colony, variously modified for the discharge of different functions; secondly,
alternation of generations, in which medusa-forms (sexual persons) arise by a process
of budding from polyp-forms (asexual persons), and give rise, by a sexual process,
to fresh polyps. Alternation of generations is an alternation of sexual and asexual
individuals, the one giving rise to the other.

Both these phenomena are widely manifested amongst plants. The plant-body
amongst the Flowering Plants may be regarded as an assemblage of shoots. Each
shoot or branch-system consists of a series of members, of which the upper and
younger ones are developed with the assistance and co-operation of the lower and
older. These shoots are all united together, and the tissue which unites them,
with its conducting-tubes and air-lacunz, may be regarded as an organ common
to them all. From the fact that the several shoot-members have the capacity
of independent existence, when separated from one another, they have been re-
garded as individuals and termed “ Anaphytes” (cf. p. 6). Shoots, united together
into a plant-body, possess a common household, and division of labour is manifest
amongst them. The Anaphytes of the foliage region serve especially for the
preparation of food-stufts, those of the flowering region for the production of
sexual cells and fruits. Shoots of the latter kind are termed flowers, of the former
foliage-shoots. Shoots arise from buds, and these may be similarly distinguished
into flower-buds and foliage-buds. Those which arise from foliage-buds remain,
for the most part, attached to the plant-body, appearing as branches of the same;
those, on the other hand, which arise from flower-buds ultimately disarticulate,

HETEROMORPHISM. 471

leaving a scar. Thus we see the shoots of a plant-body are variously modified,
and we may speak of a heteromorphism in this connection analogous to that
existing amongst the polyps of a coral.

It not infrequently happens, amongst purely foliage-shoots, that the lateral
shoots (or anaphytes) bear foliage quite unlike that borne by the shoot that gives
them origin. In many perennial shrubs and trees a long series of asexual shoots
arises, of which the lowest and highest are so different, that one might easily
suppose them to belong to different species of plants; or that a gardener had
grafted a bud of another species upon the plant. The shoots of young Ivy plants
(Hedera Helix), whether creeping on the soil of the forest-floor, or climbing up
the trunks of trees or steep rock-faces, bear shortly-lobed, white-veined, dull-
looking leaves, and produce a large number of attachment-roots which hold the
shoot to the substratum. The shoots of an old plant, however, developed high
up on the tree crown, or over the top of the wall, bear bright shining, heart-
shaped leaves without conspicuous veins, nor do they produce roots at all. It
is this latter class of shoots alone which bring forth flowers; the creeping shoots
never do so (cf. vol. i. p. 709).

This contrast between the appearance of the shoots of a young plant and those
produced in later years is much more marked in the Aspen (Populus tremula).
The foliage-leaves of the first year’s shoots are triangular, cordate at the base,
and only shortly stalked, they are also hairy on the under surface; those arising
on the shoots of a thirty-year-old Aspen are circular in outline, smooth on both sides,
and provided with long petioles. Similar is the case of many Willows, Oaks, and
Myrtaces; in the last-named family the Australian Hucalyptus globulus is worthy
of mention. The leaves on its first year’s shoot are sessile and cordate at the base,
whilst on the grown tree they are stalked and curved like a boomerang. Very
marked, again, are the differences in the character of the foliage-leaves on the
successive shoots of the Junipers (e.g. Juniperus excelsa, japonica, pheenicea,
chinensis, and Sabina). The leaves on the younger branches (for the first ten
years about) are acicular, stiff and spreading; those on the shoots of later years
are short, scale-like, and closely imbricating. Worthy of note in this connection
is the contrast of long and short branches seen in many Conifers, e.g. the Larch
(Lariz). Though the actual leaves are not dissimilar, their insertion is, and the
length of the shoots producing them. Whilst the short branches do not attain
a greater length than 1 centimetre, the long branches reach to 15 or 25 em.;
to this contrast is due in large degree the altogether peculiar physiognomy of the
Larch-tree, as shown in fig. 354 (cf. also, fig. 3371, p. 443).

The fruit-trees in our orchards are some years covered with blossom, and,
with a propitious summer, they are weighed down with fruit in the autumn.
Such “bumper” years are generally followed by a series of lean years, in which
little fruit is ripened, or flowers are hardly produced at all. The same thing
is observed in forest trees. There is a saying that Firs and Larches only form
their cones in plenty once in seven years. This is so far right in that a good

472 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

fruiting year is followed, in these trees, by several sparing ones; so much so that
it suggests that the trees are exhausted by the heavy produetion and require
time in which to recover, and, by the formation of non-flowering shoots with
green foliage, to manufacture and lay by stores of food-material. So also in

Fig. 346.—Alternation of Generations in Ferns.

1A Fern-prothallium seen from the under side; archegonia are present amongst the rhizoids and towards the sinus at the top,
antheridia on the margin below. 2 Longitudinal section of an archegonium showing the egg-cell (shaded) in its ventral
portion. The canal leading to the egg occupies the neck-portion. 3 Longitudinal section of an antheridium showing the
spermatozoids coiled up within. 4 Antheridium discharging its spermatozoids. 5 Commencement of the asexual genera-
tion. The first simple frond of the young fern-plant (sporophyte) is held aloft, whilst a root descends into the ground.
The young fern-plant is still attached to the prothallium. & Complete sporophyte of the Wall-rue Spleenwort (Asplenium
Ruta-muraria) with its fronds showing sori. 7 Under surface of a pinnule of the sporophyte of the Wall-rue Spleenwort
(Asplenium Ruta-muraria) showing the linear aggregations of sporangia (sori), with lateral indusia. ®A young prothallium
arising from a spore; the spore is below. ® natural size; 1 x 8; 2, 3, and 4 x 350; °x 6; 7 x 3; § x 240.

many low herbs. Now and then the Orchids in the meadows flower in immense
profusion, and we say it is a good “Orchid year”; then follow years in which,
in the same localities, hardly an orchid-flower is to be found.

ALTERNATION OF GENERATIONS, 47:

BET SEEN NE DEREN TEE

Na

Fig. 347.—Tree-ferns (Alsophila) in Ceylon (drawn from nature by Ransonnet).

474 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

The impulse to the production of flowering-shoots cannot entirely depend
on the prevailing climatie conditions of the year in which the flowering takes
place. For in the autumn of the previous year the bud is already laid down,
and one can tell by dissecting it whether it will form a flowering or a foliage-
shoot. In associating climatic conditions with flower-production, it is the summer
of the year previous to flowering which must be taken into account. ‘This is
well illustrated by the seasons of the years 1893 and 1894. The summer of 1893
was, as is well known, remarkable for its warmth and long-continued sunshine.
This was followed in 1894 (to take an example to hand) by the flowering of many
plants in Kew Gardens which are hardly ever known to flower there in the open,
under ordinary circumstances. Of these it will
be sufficient to mention two Gymnosperms,
Ephedra and the Maidenhair tree (Gingko biloba).

It is easy to observe the fact that in a big
tree, of which one side is in the full sun whilst
the other is shaded, the shady side produces
foliage-shoots for the most part, whilst the sunny
side blossoms freely. Nor can one resist the
conclusion that it is the sunshine which stimu-
lates the flowermg. The same thing is shown
by plants, which, growing in dense forest shade,
remain without flowers from year to year: but
as soon as the trees about them are felled, and
the light gains entrance, form flower-buds, and
ultimately blossoms and fruits. The advantages

accruing to the plant by this change in its sur-
Fig. 348.—Rhipidopteris peltata showing sterile roundings have already been indicated on pp. 394
as a eee ra59 ; but what immediate influence the sun-
light has on the building capacity of the plant,

and how it is that the tissue which, in the shade forms a foliage-bud should in the

sunshine form a flowering shoot, must for the present remain unanswered.

And now, as regards Alternation of Generations. The relations between the
sexual and asexual generations are very various in different portions of the vege-
table kingdom. In some groups of plants the two generations are obvious and
distinct, in others it is very difficult to draw the line between them. In the Ferns,
Horsetails, and Vascular Cryptogams generally, the two generations are quite
distinct and easily recognizable. In the Ferns the generation which bears the
sexual organs (=sexual generation or oophyte) takes the form of a small, expanded
plate of cells, from the under side of which delicate hair-like rhizoids are developed
which penetrate the soil (see fig. 1891, p. 11, and fig. 3467). This plate-like
structure is usually known as the prothallium; it is either heart-shaped or ribbon-
like and lobed, attaining a length of from '5 to 1 centimetre. The sexual organs

ALTERNATION OF GENERATIONS. 475

are borne on the under surface of the prothallium; the antheridia as little hair-
like structures distributed over the surface (fig. 346 °), the archegonia, flask-like in
form, and having the expanded ventral portion sunk in the substance of the pro-
thallium and the neck projecting (see fig. 346°). In the majority of Ferns both
sorts of sexual organ occur on the same prothallium, the archegonia on the central
parts and in the region of the notch or sinus, the antheridia towards the margin
and on the lobes. Fertilization is brought about by the escape of spirally twisted

Fig. 349.—Platycerium aleicorne (drawn from nature by Selleny).

spermatozoids from the antheridia (fig. 346*), which enter the neck of the arche-
gonium, one of them fusing with the egg-cell contained in the ventral portion of
that organ (fig. 3467). We may regard the fertilized archegonium as the fruit. It
does not become detached from the prothallium, but the fertilized egg-cell develops
in situ into the next (or asexual) generation, which differs altogether from the
sexual one. The egg-cell divides into several cells, one of which gives rise to the
young stem, another to the first frond, a third to the primary root, whilst a fourth
forms a sucker or “foot”, which maintains communication for some time with the
tissues of the prothallium (ef. fig. 346°). Soon after the first simple frond is expanded,
a second is formed, and the young fern-plant is now able to continue its development
independent of the prothallium. The prothallium now dies away, and in its place

476 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

we have the young fern-plant with its fronds (ef. fig. 346°). The fern-plant bears
no sexual organs, and must be regarded as the asexual generation (or sporophyte).
Its first fronds provide the necessary food-materials for the production of new
fronds, which arise in increasing numbers from the stem-apex; as a rule the stem
remains short, or it may be elongated horizontally as a rhizome, or, in the Tree
Ferns (cf. fig. 347), it develops into an erect caudex bearing a tuft of green fronds at
its apex. In addition to their purely assimilating function, the fronds are concerned
in the propagation of the plant, and produce quantities of spore-cases (or sporangia)
containing spores. These sporangia arise in clusters, known as sori, and are usually
situated on the under sides of the fronds (see figs. 346 ® and 346, and fig. 189, p. 11).
In the majority of Ferns these two functions—assimilation and spore-production—
are performed by one and the same frond, and there is no especial difference in
structure between the assimilating and spore-producing portions. But in the
so-called “ Flowering Fern”, or Royal Fern (Osmunda regalis), these two portions
of the frond stand out in marked contrast; the topmost pinnules of the frond are
entirely covered with sporangia, and light brown in colour, whilst the lower portions
are bright green, and quite destitute of sporangia. In the Hard Fern (Blechnum
Spicant) and Parsley Fern (Allosorus erispus) there is a distinction between the
sterile and fertile fronds, the pinnules of fronds which bear sporangia being much
narrower than those of purely assimilating fronds. In Rhipidopteris peltata, again,
the fertile fronds are disc-like, whilst the assimilating fronds are branched and
filamentous (see fig. 348); in Platycerium aleicorne the fertile fronds are branched
like a reindeer horn, whilst the sterile ones form great green discs in close contact
with the bark of the tree on which it grows, and remind one of huge prothallia
(see fig. 349). As soon as the spores are mature they are discharged from the
sporangia and scattered by the wind. Falling on moist earth, on the bark of a
tree, or in a rocky cleft, they germinate, producing prothallia, upon which the
sexual organs are borne (cf. fig. 346°). Thus in the Fern, two stages are well shown
in the life-cycle, (1) the prothallium, the sexual generation or oophyte, and (2) the
fern-plant, the asexual generation (or sporophyte), which bears spores, these in turn
give rise to the first generation again.

In the Horsetails (Equisetace®), which have been figured and referred to at
p. 14, a similar alternation of generations occurs. The fern itself is the asexual
generation, and bears cones of sporangium-producing scales. From the contained
spores prothallia are formed. In several species of Horsetail (e.g. Hquisetum
sylvaticum, tig. 1907, p. 14) one and the same shoot bears the organs of assimilation
and spore-production; whilst in other species (e.g. Equisetwm arvense) these functions
are relegated to distinct shoots; ze. shoots formed in spring, which terminate in
cones (fig. 190%, p. 14), and others formed later, which bear numerous green assimi-
lating branches, but no cones (fig. 1901, p. 14).

In the group of the Lycopodin® very interesting conditions prevail. In the
so-called Club Mosses (Lycopodiacez) the plant is much branched, and in a great
many species of Lycopodium (e.g. Lycopodium annotinum, tig. 378) the shoots end

ALTERNATION OF GENERATIONS. 477

in cones of closely-fitting scales, each of which bears a sporangium. The spores in
Lycopodium are all alike, and on germination form prothallia, which bear antheridia
and archegonia. It is interesting to note in passing that we have only become
acquainted with these prothallia in recent years, and for the most part in exotic
species. The prothallia of a limited number of European species, however, have
been seen. Included in the Lycopodine is the genus Selaginella (ef. fig. 111},
vol. i. p. 421), resembling Lycopodiwm in its moss-like habit, but differing from it
in that two sorts of spores are produced. These spores, known as macrospores and

Fig. 350.— Alternatior. of Generations in Mosses.

1A spore germinating. 2A moss-protonema. * Protonema giving rise to a bud from which will arise a leafy moss-shoot
4 Longitudinal section of tip of a male shoot of a moss-plant; antheridia are present between the scales, 5 Tip of a female
shoot with archegonia; two of them have much enlarged due to the swelling of the young sporogoniums within. © Leafy
female shoot of a moss-plant with fully developed sporogonium at its tip. Spores arise asexually in the terminal capsule.
1, 2, 3 x 350-400; 4x 15; 5 x 80; 6x5.
microspores, arise in different sporangia in the same cone, in many cases. The
macrospores are relatively large, and are contained four in a sporangium; the
microspores are small, and a large number of them is present in a sporangium.
The prothallia resulting from their germination are of two kinds; the macrospore
gives rise to a female prothallium which bears archegonia; the microspore to a
much reduced male prothallium bearing a single antheridium. The sexual genera-
tion— which in the Fern consists of one structwre, the prothallium—here consists of
two structwres, the male and female prothallia. After fertilization the archegonium
gives rise to a new, asexual Selaginella plant.
This differentiation amongst the spores in Selaginella (in consequence of which
the plant is termed heterosporous, in contradistinction to Ferns, and Lycopodiwm,

478 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

which, having one sort of spore only, are termed homosporous) is of interest, since
it leads on to the condition prevailing in Flowering Plants. In these the alternation
of generations is not obvious, no recognizable and detached sexual generations being
seen. But on certain shoots of flowering plants (7.2. in the flowers) sporangium-
bearing leaves are borne; these are the stamens and carpels respectively. The
sporangium borne by the stamen is the pollen-sac, and the contained pollen-grains
are the microspores. The microspore or pollen-grain, when it germinates on the
stigma (or in the mieropyle, in Conifers, ef. p. 418) forms a pollen-tube, which
contains the male fertilizing element, corresponding to a spermatozoid. Of course
the conditions of fertilization in the Flowering Plant are altogether different from
those obtaining in the Vascular Crytogams, and motile swimming spermatozoids
are no longer produced. The sporangium borne by the carpel, on the other hand, is
the ovule, and the embryo-sae contained within the ovule is regarded as the macro-
spore. As a rule but one macrospore is met with, but in certain Amentace (e.g.
Carpinus, see fig. 3144, p. 412) more embryo-sacs (macrospores) than one are present.
In the Flowering Plant the macrospore is not shed from its sporangium (ovule), but
germinates in situ, forming an egg-apparatus (ef. fig. 316 and p. 417), and certain
other cells, which ultimately form the endosperm. These structures are regarded
respectively as corresponding to the archegonium and female prothallium of such a
heterosporous Vascular Cryptogam as Selaginella. If the contents of the embryo-sae
in Gymnosperms (see p. 415) and in Angiosperms (see p. 417), respectively, are com-
pared with the female prothallium of Selaginella or other heterosporous Vascular
Cryptogam, it will be seen that the Gymnosperm shows the greater agreement.
In it the archegonia are still quite recognizable as such, though these now take
part in quite a different type of fertilization. In all Flowering Plants (Gymnosperms
and Angiosperms) as opposed to the Vascular Cryptogams, the microspores produce
pollen-tubes in the vicinity of the ovules, and these penetrate to the embryo-sac
(macrospore) and fertilize the egg-cell. Consequently the counterpart of the arche-
gonium is not exposed, as it is in Vascular Cryptogams, in which a free-swimming
spermatozoid has to gain entrance.

Thus we see that in Flowering Plants the female prothallium or sexual genera-
tion is hidden away in the embryo-sac, and is never an independent structure.
This fact is correlated with the different manner of fertilization which obtains in
Flowering Plants as compared with Vascular Cryptogams.

In the Mosses the sexual organs are formed at the tips of little leafy shoots;
tertilization is much as in Ferns, and from the fertilized egg a new (asexual)
generation arises. This generation, known in Mosses as the sporogonium, consists
of a stalk (the seta) terminating in a spore-capsule above. The sporogonium
develops within the archegonium on the sexual generation of the Moss. The base
of the seta penetrates some distance into the fertile Moss-shoot, and is in this
way able to absorb nourishment. As the sporogonium elongates, the archegonial
wall stretches with it up to a certain point, then it breaks across transversely and
the upper portion is raised up on the capsule as a sort of hood or extinguisher (the

ALTERNATION OF GENERATIONS IN MOSSES. 479

calyptra, see figs. 350° and 350°). Ultimately this hood is thrown off and the
capsule, within which quantities of spores are produced, opens. The spores are
readily distributed by the wind shaking the capsule on its stalk. It should be
noted that in Mosses this asexual generation (the sporogonium) never becomes
independent of the sexual Moss-plant; the base of its stalk always remains embedded
in the tissues of the sexual generation. In the Ferns, on the other hand, the

Fig. 351.—Alternation of Generations in Mosses. Various forms of sporogonium, which as the asexual generation
have been produced at the tips of leafy shoots.

1 Splachnum luteum. * An unripe capsule of the same. % A ripe and open capsule of the same. 4 Splachnum vasculosum.
5 Longitudinal section of a ripe capsule of this Moss. $Splachnum ampullaceum. 7 An unripe capsule. 3A ripe
capsule of the same. 9% and 10 Schistostega osmundacea. 11 A ripe capsule of the same. 1, *, 6, 1° natural size: 2, 8 x 2;
7,8,9x 10; 11x15; 5 x 100.

asexual generation (=the Fern-plant), though at first drawing nutriment from the

prothallium (ef. p. 475) by its “foot”, soon becomes quite independent, the prothal-

lium dying away. The form of the sporogonium is very varied in different groups
of Mosses. In fig. 351 are shown the sporogonia of a number of Mosses, including
species of Splachnum (S. luteum, 8. vasculosum, and 8. ampullacewm), a rare form
occurring on the exerements of cattle, reindeer, &e., that of the already-mentioned
Luminous Moss (Schistostega osmundacea, cf. vol. i. p. 385); and in fig. 191, p. 16

480 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

those of Polytrichum, Bryum, Hylocomium, Andrewa, and Sphagnum. The spores
of the asexual generation germinate on a moist substratum, giving rise to a tubular
filament which becomes segmented, and gives rise to a considerable growth of simple
character, known as the protonema (see fig. 350°). Certain rows of cells of the
protonema are colourless and penetrate the ground as rhizoids, the others are
extended on the soil and are bright green in colour. After a while bud-like
structures arise here
and there upon the
protonema (see fig.
350°); these de-
velop into leafy
Moss-shoots, upon
which the sexual
organs are borne—
usually in little
clusters. Thus, in
Mosses, the sexual
generation has two
stages; the proto-
nema and the leafy
Moss-plant. From
the latter arises the
asexual generation
or sporogonium. In
many of the Liver-
worts the sexual
generation is much
simpler, consisting
of a thallus, in
which the arche-
gonia and anther-

Fig. 352.— Asexual and sexual reproduction in Saprolegniaces.

1 Formation of asexual zoospores in Achlya. 2% Oogonia with antheridia and fertilizing ° 1: =
tubes. 3 Fruit. All figures x 300. (After Sachs.) idia are sunk. How-

ever, a great variety
is met with amongst them, but the main relations of the sexual and asexual genera-
tions are much as in Mosses.

It will be noted that in Mosses the sexual generation is much more complex a
structure than the corresponding structure (the prothallium) in Ferns. The asexual
generation, on the other hand, in Mosses is never independent, whilst in Ferns it
becomes so quite soon and attains, in the latter group, to much greater structural
complexity than in the Mosses.

Amongst the large assemblage of simple plants which together constitute the
class Thallophyta we find in some forms an incipient alternation of generations on
the lines already described for Mosses, Ferns, &e.; in others there is no suggestion of

ALTERNATION OF GENERATIONS IN ALGE. 481

such alternation; and in others again (such forms are numerous), an alternation
oceurs, but of a character quite different from that of higher plants.

First we will mention such as show an alternation of generations not unlike
that of the Fern. It will be remembered that in the Fern there is a simple pro-
thallium upon which the sexual organs arise, and from the fertilized egg-cell a new
generation, of considerable dimensions, is developed which produces asexual spores,
these in turn giving rise to prothallia. In the group of the Red Seaweeds or
Floride® (cf. pp. 61, 62, and
figs. 2047 and 204°, p. 53), the
seaweed plant is the sexual
generation and bears the rudi-
mentary fruits with tricho-
gynes and the male spermatia.
After fertilization, a consider-
able growth is initiated, which
results in a mass of spores
being abstricted, these spores
being in many cases inclosed
in a sort of capsule, which
develops concurrently with the

spores. This capsular struc-
ture with its spores we may
interpret as a very simple
asexual generation comparable
to the sporogonium of a Moss
or to a Fern-plant with its
spores. Of course this asexual
generation is very ill-marked

in the Red Seaweed, and it

is difficult to quite draw the P : : ‘ j
fs 2 1 Mycelium producing asexual spores in stalked sporangia. 2A single sporan-
line between it and the sexual gium in section. 3 Formation of a zygospore. 1 x 40; 2 x 260; 8 x 180.

Fig. 353.—Asexual and sexual reproduction in the Mucorini.

generation of which it forms
a continuation. It has this in common with Mosses and Ferns; that from a single
process of fertilization a numerous progeny of spores is begotten—spores which
on germinating give rise to sexual plants again.

The brown Wrack, Fucus, is an example of a Thallophyte in which alternation
of generations is not known to take place. In this seaweed every generation is a
sexual generation, and the fertilized egg-cells, so far as is known, give rise—not to
spores—but to new sexual generations. Its life-history is deseribed and figured on
pp- 51, 52.

And now we come to a type of alternation of generations, prevalent amongst
green Algze and some families of Fungi, which seems to be quite distinct from the

rhythmic alternation which obtains in the Mosses, Ferns, &c. The oft-mentioned
Vou. IL 81

482 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

tubular Alga, Vaucheria sessilis (belonging to the family of the Siphonace») will
serve as an admirable example of what we mean. This plant reproduces sexually
(ef. pp. 57, 58, and figs. 204° and 204° p. 53) by means of oogonia and antheridia of
simple character; it also propagates itself by means of large asexual zoospores
which it liberates from the tips of its tubular filaments (ef. vol. i. pp. 23, 24, and
Plate L, figs. a-d). But these two classes of reproduction do not oceur simul-
taneously upon one and the same plant; but rather, so it was till lately supposed,
upon generations which alternated with one another either regularly or irregularly.
Sometimes the Vaucheria-plant arising from a zoospore bore sexual organs, and
from the fertilized egg-cell arose a non-sexual plant which gave rise to zoospores
again; or a series of asexual generations followed one another, the series being
terminated by a sexual generation, the fertilized egg-cells of which entered on a
resting stage.

The meaning of this supposed alternation of generations in Vaucheria has
recently been cleared up by Klebs in a series of very interesting culture-experi-
ments. Without describing these in detail we may briefly indicate some of Klebs’s
results. If a number of young Vaucheria-plants be cultivated, three possibilities
are open; the plants may produce sexual organs; they may be reproduced asexually
by zoospores; or, finally, they may remain perfectly sterile. Klebs found that by
appropriate treatment of plants, he could bring about any of these possibilities at
will. Young plants placed in a 2-4 per cent sugar solution, and kept in the light at
a temperature not falling below 3° C., invariably produced sexual organs in the
course of some ten days. Other plants, which had been grown in a dilute nutrient
solution of food-salts in the light for a short time, were removed to water and placed
in the dark. These plants soon gave rise to enormous quantities of zoospores; in time
these zoospores germinated, and the resulting plants in their turn produced fresh
zoospores, and soon. The third condition, that of sterility, was obtained by keeping
plants in strong sugar solution (10 per cent), and also by other methods. More than
this, the same plants were caused to alter their mode of reproduction by varying
the conditions; in this way it was possible to cause them at one time to produce
zoospores and at another sexual organs. This brief summary is sufficient to show
that a given Vaucheria-plant has no inherent tendency to reproduce asexually in
preference to sexually, or conversely; and that its manner of reproduction (or its
abstention from reproduction) depends on the conditions which prevail outside the
plant. Thus,in Vaucheria, no true alternation of generations prevails in the sense
in which it does in Mosses and Ferns, and every generation is potentially both a
sexual and an asexual generation. It is the external conditions which call forth
the one or the other.

In a great many other Thallophytes the same is no doubt true, though exact
experiments have yet to be performed on the majority of them. We know it to
be so in Botrydiwm and in the Water-net (Hydrodictyon) and in others. The
Water-net (figured on p. 24) propagates asexually by the contents of its cells
breaking up into very numerous (7000-20,000) swarm-spores (thallidia) which

HETEROMORPHISM AND ALTERNATION OF GENERATIONS. 48°

Fig. 354.—Larch-trees (Larix europea).

454 HETEROMORPHISM AND ALTERNATION OF GENERATIONS.

do not forthwith escape, but swim about for a while within the wall of the
cell in which they originate. Then they join together into a tiny net which
escapes, ultimately growing to its full size (ef vol. i. p. 36). In sexual repro-
duction a much larger number (30,000-100,000) of small motile bodies (gametes)
escape and conjugate in pairs. Klebs has found here also that either of these
methods can be produced at will by altering the conditions under which the plant
grows.

Among the Fungi the Saprolegniacee show well-marked sexual and asexual
methods of propagation. These are mould-like forms which attack fish and other
aquatic animals upon which they are parasitic. Purely asexual reproduction occurs
by means of zoospores which are liberated from long, club-shaped sporangia (fig.
352"); whilst sexual reproduction (which may occur upon the same plant) takes
place by spherical oogonia arising upon certain branches and antheridia as small
lateral twigs below them (fig. 352°). The latter perforate the oogonium-wall with
their “fertilizing tubes” (cf. the allied Pythiwm, p. 56), but curiously enough there
is no real fertilization. Nothing has been observed to pass from the fertilizing-
tubes to the egg-cells, and we must regard the process of fertilization here as
obsolete. The egg-cells, though unfertilized, put on cell-walls (fig. 352°) and ger-
minate, as one might say, parthenogenetically.

In the Moulds of the family Mucorini the mycelium establishes itself upon an
organic substratum and produces, at one time, long-stalked sporangia (figs. 3537
and 353°), and at another short sac-like outgrowths which arise in pairs near one
another and conjugate, forming a zygospore (fig. 353°). Whether this or that
method of reproduction prevails in these Fungi depends, most probably, on external
conditions; indeed examples from amongst the Fungi could be adduced in which
careful experiment has determined that this is the case.

In conclusion we may inquire how is it that alternation of generations is so
widely distributed amongst plants, whilst in the animal kingdom it is of relatively
rare occurrence. We obtain an answer to this question when we consider what
are the distinguishing characters of those animals in which alternation of
generations takes place. The corals, polyps, and other animals exhibiting alterna-
tion are in great part sessile organisms, attached to their substratum. But when a
fixed organism propagates itself and distributes its kind, it must commit portions
of itself to the winds or to currents of water, if new regions are to be occupied; a
condition applying equally to plants and animals. Or, as an alternative, sexually-
produced progeny may be liberated from the mother-organism and take up new
positions. But sexual reproduction amongst fixed organisms requires rather special
arrangements, and even with their aid is not invariably certain. Interference with
fertilization may connote the extinction of the species; consequently a propagation
by asexual means is of great importance for such organisms. By a definite alter-
nation of the two methods, by a single act of fertilizing leading to an organism
capable of multiplying itself almost indefinitely by asexual spores, a numerous
progeny is ensured even from a single sexual union. Take the case of the Fern-

ALTERNATION OF GENERATIONS. 485

prothallium; from one fertilized archegonium arises a Fern-plant with many fronds
and capable of producing millions of spores. Thus the species, whilst retaining to
itself such advantages as may be inherent in the sexual process, is likewise able
to diffuse itself in large numbers over an extended area by means of its numerous
asexually-produced spores.

Allusion has been made to the advantages inherent in the sexual process.
The investigation of their precise nature will be one of the main problems reserved
for the second part of this volume. That a production of flowers and a ripening of
seed is not absolutely essential for the maintenance and distribution of plants,
seems not improbable—judging from the considerable number of plants which do
well and flourish without them.

THE HISTORY OF SPECIES.

1. THE NATURE OF SPECIES.

Definition of Species—Specific Constitution of Protoplasm.

DEFINITION OF SPECIES.

The history of plant species is founded on the history of individual plants
given in the first section of this volume, more particularly on the results afforded
by investigation into the processes of reproduetion and propagation. It deals with
the description of the species from its origin to its end, and also takes cognizance of
the replacing of extinct species by new ones. The execution of this task is less easy
than the representation of the life-history of the individual which can be deduced
from direct observation and experience. It being possible to follow the course of
even long-lived individuals, beginning with the origin of the embryo and following
it through all its life’s stages, the meaning of certain vital processes as, for example,
the pollination of the stigmas and the germination of the seeds can be understood.
The origin of most of our present species, however, which have arisen without the
aid of man, is shrouded in mystery; it occurred in long past ages and we are
obliged to fall back on conjectures which, however intelligent and however they
may be supported by carefully weighed considerations, are still only conjectures
after all. For purposes of direct observation we have only the fossil remains of
earlier times and the species which are living at the present day. By comparing
these with one another, and by inferring the nature of extinct forms from that of
living species, we are able to construct a chain of conclusions which after all may be
regarded as the best available substitute for a history of species.

The most important foundations for these conclusions are afforded by the
knowledge of the relations of living species to their environment, especially the
recognition of those causes which bring about permanent changes of form, for this
alone can elucidate the question of the origin of new species. Before discussing
these important questions the nature of species must be described and we must
understand exactly what is meant by a species.

The definition of a species was first introduced into science by Linnzus, and
the Latin word “species” owes its origin in this sense to the great master of
Botany. Linnzeus laid down that each species consists of similar individuals which
are related together by their origin, and which are the unaltered descendants of
a common ancestor or pair of ancestors. It does not affect the value of the

THE SPECIFIC CONSTITUTION OF PROTOPLASM, 487

definition that Linnzeus considered these ancestors to be creations of the “infinitum
ens”; but it is very important that he recognized existing organisms as the
continuation, the rejuvenated portions of one and the same living being, so that
the species is not a figment of the human mind, but is something which actually
has an objective existence.

Moreover, to decide which individuals are similar, i.e. of the same species, we
take note of characters apparent to our senses, especially of the form and structure
of the plant-body. Each species has its special features or characteristics, and all
individuals possessing these specific marks are said to belong to the same species.
Specific characteristics are hereditary, and are transmitted unaltered to the
descendants. There are, however, some plant characteristics which are not
inherited, but which may appear or not according as the individual develops in
this or that place, and these must be regarded as the expression of certain external
conditions which have an influence on plant-organization. They form the founda-
tion for the existence of the variety, according to Linneus. The individuals of
each species may vary, but the variations are not handed down to posterity; they
change according to position and other external influences. Systematic Botanists
since the time of Linnzeus have therefore to consider two kinds of distinguishing
marks or characteristics: (1) those which are inconstant and not inherited; and
(2) those which are constant under widely different external conditions and are
hereditary. The latter determine the species, the former the variety. Each species
may exhibit several varieties at one time, but its specific characteristics remain
unaltered. If the specific marks should have undergone any alteration in the
descendants, these will form a new species, or rather the appearance of an in-
dividual furnished with new specific marks forms the starting-point for a new
species.

The relations of outward form and structure relied on by systematic Botanists
in the identification of plant species depend of course on the plan of construction of
the protoplasm of the species in question, and again only the specific constitution of
the protoplasm determines this constructive plan. Before we can arrive at a
correct idea of the nature of species, therefore, it is above all things necessary to
obtain as clear a picture as possible of the relations of the protoplasm to the
external visible form.

THE SPECIFIC CONSTITUTION OF PROTOPLASM.

Mention has previously been made of the remarkable fact that the species of
a genus differing from one another in outward appearance also differ in respect
of the scents secreted by them. Many Roses have different scents (Rosa alpina,
arvensis, cinnamomea, Gallica, Indica, Nasterana, pomifera, rubiginosa, sepiwm,
&e.), and a blind man could distinguish each species by the scent of its flowers.
This is also true of species the foliage, stem, and roots of which emit odorous
substances. By rubbing the foliage of different species of Thyme in one’s fingers

+58 THE SPECIFIC CONSTITUTION OF PROTOPLASM.

(Thymus Chamedrys, montanus, vulgaris, Zygis, &e.), each will give off a peculiar
scent; and when the roots or root-stocks of different Valerians (Valeriana celtica,
dioica, elongata, officinalis, Phu, saxatilis, &e.), or of different species of the Asara-
bacca genus (Asarum Canadense, Ewropeum, &e.) are dug up, though they all
smell of valerianie acid or spikenard, each species has in addition a distinetive
odour of its own. The edible Fungi (Polyporus confluens, frondosus, ovinus, &e.),
Garlies (Allium ascalonicum, Cepa, Porrum, sativum, Schenoprasum, &e.),
various Currants (Ribes alpinum, petreum, rubrum, &e.), and the Strawberries
(Fragaria collina, elatior, grandiflora, vesca, &e.) all demonstrate most decisively
that our olfactory nerves can distinguish between the different species of some
genera. It might also be pointed out that it is no infrequent oecurrence for one
species of a genus to be poisonous to man while another is harmless, e.g. species
of the Star-Anise genus (Illievum amisatum and religiosum), and of the fungal
genus Lactarius (Lactarius deliciosus and torminosus). It is familiar to naturalists
how precisely herbivorous animals can distinguish between different species of
plants. The caterpillar of the Oleander Hawk-moth (Sphinw Nerii) lives exclu-
sively on the Oleander (Neriwm Oleander), that of a small Mediterranean butterfly,
Thais Hypermnestra, only on the Birthwort (Aristolochia Clematitis), that of
the small Tortoise-shell Butterfly (Vanessa Urtice) only on the leaves of the large
Stinging Nettle, and that of Libythea Celtis only on the foliage of the Nettle-tree
(Celtis australis). Each caterpillar can at once distinguish the only species which
suits it from numerous other similar ones. A friend of mine once found the
caterpillar of a butterfly he did not know high up on the Gletscherstock in the
Stubai, Tyrol, which he took into the valley with him intending to feed it until
it became a chrysalis in order to obtain the butterfly. In the valley he placed it
on about a hundred different plants in the hope that it would settle on one or
other and use it as food. But it would not touch one of them, although caterpillars
apparently suffer from voracious appetites. My friend now determined to revisit
the spot where he had found the caterpillar and to set it at liberty there. When
he did so it at once crawled as quickly as possible to a certain plant (Cardamine
alpina) and attacked it with great eagerness. Later he discovered it to be the
caterpillar of Pieris Callidice, which only feeds on the small Alpine Bitter-cress
(Cardamine alpina). Generalizing from these instances, many more of which
might be given, we are justified in assuming that the aromatic substances, alka-
loids, acids, &e., which are manufactured in the plant metabolism are quite definite
for each particular species. But it is equally obvious that a specific protoplasm is
necessary for the manufacture of specific substances, or, in other words, that each
plant-species with a certain definite form possesses also a definitely constituted
protoplasm of its own.

The behaviour of different species with regard to temperature is especially
worthy of note among the many observations which support this view. It is well
known that seeds of various species which closely resemble one another in outward
appearance differ greatly in the temperature they require for germination. Seeds

RESISTANCE TO COLD. 489

of one species are content with a low temperature, while those of another require
much greater heat, although the eye can distinguish no difference in the structure
of their coat, in their manner of storing reserve food, or in the structure of their
embryos. The same may be said of the freezing of plants. Many Californian and
Mexican Pines (Pinus) are very like those of Northern and Central Europe, and
yet the one will be frozen to death as soon as the temperature sinks below freezing
point, while the other can sustain winter temperatures of —20° ©. without injury.
There seems to be no reason why the South European Junipers, Juniperus Oxycedrus
and phenicea, which are apparently of the same structure as the similar species
Juniperus nana and Sabina, should not flourish equally well on our mountain
heights in the Central Alps, where the latter cover whole mountain peaks and send
their roots into ground which is covered with snow eight months every year, and
is frozen hard for months together. The common Ivy (Hedera Helix) grows in
Central Europe without any protection from the fairly severe cold of winter; the S.
European Ivy, Hedera poetarwm, which is very similar to the common species, but
can be distinguished from it by several external characteristics, requires a protecting
roof in the gardens of Central Europe if it is to survive the winter unkilled by the
frost. The same is true of two closely allied species of Marigold, viz. Calendula
arvensis and fulgida, the former growing in Central, the latter in Southern
Europe. In 1874 I sowed seeds of Calendula arvensis from the Rhine district
side by side in the same garden-bed with seeds of Calendula fulgida, which had
been gathered in Sicily. Very luxuriant plants which flowered in profusion grew
up from both kinds of seeds. The first-frost in that year in the place where the
experiment was made occurred on October 25th. Calendula arvensis was not
injured; its foliage was fresh and green, and remained in this condition during the
following days, although, until November 2nd, the temperature fell every night
from —1'5° to —2'5° C., and in the morning the stem, leaves, and flowers were
studded with hoar-frost. Calendula fulgida, on the other hand, was destroyed by
the frost on the night of the 24th-25th October. Its leaves and stems withered and
turned brown, and exhibited all the symptoms observable in death by freezing. In
1864 I found a Cytisus on the rocky shores of the Adriatic Sea at Rovigno, which
closely resembled the wide-spread Cytisus nigricans of Central Europe, but which
had certain distinguishing features. I named it Cytisus australis. Some of its
seeds were collected, and from them strong young seedlings were obtained in the
following year. These were planted in the Botanie Garden at Innsbruck with
some seedlings of Cytisus nigricans of the same age from the Danube valley, near
Mautern, in Lower Austria. Both grew under identical external conditions, and
appeared to be equally vigorous. But during the winter the plants of the Cytisus
from the shores of the Adriatic were killed by the frost, while those of the Cytisus
from the Danube valley remained healthy and strong. The experiment was repeated
with the two plants in the following year. Young plants were again raised from
seed, but this time those from the Adriatic coast were protected against the cold,
and in this manner they survived the winter without harm. Two years later both

490 THE SPECIFIC CONSTITUTION OF PROTOPLASM.

the species of Cytisus developed flowers and fruits almost simultaneously under
the same external conditions, and it was noticed that the same real, if insignificant,
deviations were present in the external characteristics which had been present in
the parents. This different behaviour of plants which, on account of their form,
are described by the Botanist as distinct species, although closely allied, can indeed
only be explained by assuming that the protoplasm, though having on the whole a
similar constitution, is somewhat different in each species.

As a further confirmation of the assumption that the protoplasm of each species
possesses properties which are lacking in that of others, we may take the case of
the behaviour of pollen-cells in fertilization. If two kinds of pollen-cells are
brought to the stigmas of a plant, 7.e. pollen-cells of two different species, it usually
happens that the one will fertilize the ovules with its pollen-tubes, while the other
will be without effect. And yet the conditions are the same in both cases, and the
difference in behaviour must therefore depend upon some difference in the proto-
plasm of the pollen-cells. Protoplasts which swim about as swarm-spores in the
same drop of water, exposed to exactly the same condition of light, heat, pressure,
&e., display a different behaviour if they belong to a different species. Those of
one species will always twist to the right, those of another always to the left, some
seek the light, others shun it for the darkest places. But since the protoplasm
behaves differently under the influence of the same ray of light, the same tempera-
ture, and the same pressure, the cause must be sought for in the tiny mass of proto-
plasm of which each swarm-spore is composed.

The little amcebe which proceed from the spores of Myxomycetes are protoplasts
without a cell-wall; they live on dead parts of plants, where they feed, grow, divide,
and multiply. When the right time comes these amcebz fuse together to form a
body known as a plasmodium, which is ultimately converted into a mass of
sporangia (cf. vol. i. p. 572). Although the little amoebe of different species cannot
be distinguished from one another, and the plasmodia look like masses of formless
protoplasm which only differ sometimes in colour, the resultant sporangial forms
exhibit a remarkable variety of forms. From the plasmodium of Stemonitis
fusca there arises a network of dark brown threads which is penetrated by and
borne on a central axis like the shaft of a feather (see figs. 3551 and 355°); from
that of Spwmaria alba is formed a white slimy mass resembling the “cuckoo-spit ”
of the Cicadellidz and enveloping stem and leaves just in the same way (see fig. 355°);
from the plasmodium of Dictydiwm cernwum there arises a globe-like lattice-work,
with strong longitudinal ribs and delicate cross-bars, which is carried on a hooked
stalk (see figs. 3554 and 355°); from the formless plasmodium of Crateriwm
minutum arise stalked cups of a gray colour (see figs. 355° and 3557); from that
of Arcyria punicea short stalked conical bodies not unlike Strawberries (see figs.
3555 %10); the plasmodium of Lycogala epidendrum, which penetrates the wood
of dead tree-trunks, forms balls of the colour of red-lead, about a centimetre in
diameter (see fig. 355"), and out of the plasmodium of Leocarpus fragilis, which
spreads over dead branches and twigs, proceed stalked egg-shaped sporangia, with

DIFFERENCES AMONGST FUNGI. 491

little brown coats (see fig. 355"). And all these peculiar forms arise under similar
external conditions from apparently similar slimy and formless masses of proto-
plasm.

The same thing occurs in the Mushroom and Toadstool Fungi (Hymeno-
mycetes) which develop in the mould of the forest ground and on the dead bark
of tree-trunks. The mycelium is a network of white threads and strands, and
neither the form of the colourless elongated cells composing the network nor

Fig. 355.—Myxomycetes.

1 A group of sporangia of Stemonitis fusca. 2A single sporangium; x 6. % Dendritic mass of sporangia of Spumaria alba on
a Grass leaf. 4Sporangium of Dietydium cernuum; x 25. 5A group of sporangia of the same. 6 and? Sporangia of
Craterium minutum; ® x 25. 8% Sporangia of Arcyria punicea. % Asingle sporangium; x 10. 1° Part of the net-like
capillitium of the same; x160. 1 Fructification of Lycogala epidendrum on a piece of wood. 12 Leocarpus fragilis; a
plasmodium on the right; several sporangia on the left.

the protoplasm within the cells afford any indication by which we can judge
the species to which the mycelium belongs. But how different are the fructi-
fications proceeding from these apparently identical mycelia. In a part of the
forest ground not twenty paces across there grow large specimens of Boletus
edulis with chestnut-brown hemispherical caps; a little distance off a group of
Chantarelles (Cantharellus cibarius), with yellow colour like yolk of egg, close
by the Fly-agarie (Agaricus muscarius or Amanita muscaria), with snow-
white stipe and crimson cap (pileus) spotted with white, and near at hand, from

492 THE SPECIFIC CONSTITUTION OF PROTOPLASM.

a mycelium which has penetrated the bark and wood of a Beech-tree, grows
the horse-shoe-shaped ashen-gray Polyporus fomentarius (cf. the accompanying
Plate XIV., showing these Fungi amid their natural surroundings).

The fruits resulting from the conjugation of the unicellular Desmids are
minute balls of protoplasm, and although they may originate from very different
species, outwardly there is not the slightest distinction between them. But as
soon as these small balls of protoplasm begin to develop, the greatest variety
of cell-forms is the result. Each is fashioned after the form of the parent in-
dividuals which produced the fruit by conjugating. One cell will be half-

3

Fig. 356.—Desmidiex.

1 Micrasterias papillifera. 2 Micrasterias morsa. 3 Cosmarium polygonum. 4 Xanthidiwm aculeatum. 5 Staurastrum
Jurcatum. 6% Euastrum oblongum. 7 Penium Brebissonü. 8 Closterium Lunula. *? Xanthidium octocorne. 10 Staur-
astrum alternans (two views). 11 Cosmarium tetraophthalmum, 12 Aptogonum Desmidium. All the figures magnified
about 200 times.

moon-shaped, another cylindrical, a third angular and table-shaped, others again
stellate and with manifold projections; some have a smooth surface, while the
cell-wall of others is beset with spines or studded as if with pearls. The figures
above, representing twelve different species of these Desmids, will give some idea
of the multiplicity of their forms. And all these varieties spring from apparently
identical masses of protoplasm, and develop side by side in the same drop of water,
under the same illumination, the same temperature, and, generally speaking, under
exactly the same external conditions and stimuli.

All these observations and results seem to indicate that the hypothesis as
to a specific constitution of the protoplasm in each species is almost a necessary
assumption. The word “constitution” has been purposely used instead of “com-
position”, which might be taken to mean essensially the same thing were we

THE SPECIFIC CONSTITUTION OF PROTOPLASM. 493

dealing merely with a chemical compound. Nothing would be more natural
than a comparison with inanimate things whose outwardly perceptible features
are the expression of a definite chemical composition, é.e. of a certain grouping
of molecules and atoms which can be represented by a certain formula. But
although this comparison is allowable in general, yet there is an essential difference
between mineral and plant species. No formula can be given for the protoplasm
of a species of plant, and the structure of a protoplast cannot be compared with
that of a erystal. Each protoplast represents an organism which contains very
many chemical compounds. It is able to renew them when required, and to
modify their grouping as dictated by external stimuli. With these displacements
there must of course be a temporary alteration of structure, ö.e. of the grouping
in the formed part of the protoplasm. But all these displacements and alter-
ations take place in each species according to the same plan. The same chemical
compounds, the same aromatie bodies, the same acids and the same alkaloids, &e.,
can alone be demonstrated. The recently-formed parts agree with those already
present, and merely fill up the places previously assigned to them. This unalter-
able law of form which governs the working of the protoplasm in each species is,
therefore, dependent on some structure of the protoplasm which is beyond the
perception of our senses, and it is this which is termed the specific constitution of
the protoplasm.

In the above-mentioned Desmids, which afford such especially instructive
examples, and in numerous other unicellular plants where all the formative
processes are carried on within a single protoplast, it is easy to see the connection
between the outward appearance and the specific constitution of the protoplasm.
It is more difficult in species where there is greater division of labour, a division
into manifold cell-forms and a gradual succession of different members. One
might compare the processes occurring in them with similar processes in mineral
species, which, with the same chemical composition present a great difference
in their outward form and appearance. Carbonate of lime, which forms the
mineral species calcite, appears in four kinds of erystal-forms, but they all belong
to the same system, and can be derived from one another. In the same way
the varied cell-forms and tissues, as well as the cotyledons, foliage, and floral-
leaves, which arise from the same plant in regular succession, are to be regarded
as members of the same system, succeeding one another in definite rule, although
the specific constitution of the protoplasm in the particular species undergoes
no change.

At one time the idea was prevalent that there are two kinds of protoplasm,
idioplasm and cytoplasm. To the former was assigned the formative activity,
while the latter was regarded as merely a nutritive plasm or medium. Subse-
quently it was shown that in every protoplast there is a more definite part, termed
the nucleus, which dominates the whole, especially in the building and renewal
of the cell-wall, while it also takes a leading part in cell-division and multiplica-
tion. Thus the assumption that all formative processes are carried on through

494 THE SPECIFIC CONSTITUTION OF PROTOPLASM.

the cell-nucleus was held to be correct. The fact of the constaney of species
from generation to generation was therefore referred, especially, to the specific
constitution of the cell-nucleus. Since the nucleus plays such an important part
in the process of fertilization, which precedes the inception of the new individual
in sexual reproduction, the hypothesis was put forward that the constancy of
form in the offspring, or, in other words, the transmission of form, depends upon
the specifie constitution of the nuclei taking part in this process. Nor would
this hypothesis be open to objection had not recent investigations shown it to
be extremely probable that portions of the male cell other than the nucleus assist
at this process. If, as it appears, more than the mere nucleus passes over from
the pollen-tube at fertilization (cf. p. 417), how can we certainly allege that (to
take a definite case) all the properties which the young plant inherits from its
male parent are transmitted through the medium of the nucleus? If it be true
that a certain portion of the cell-protoplasm takes part in this act, it must be
proved that it plays only a subordinate part in the process (e.g. a nutritive function)
before we can attribute to the nucleus the part of sole carrier of transmitted
properties.

To the proposition that new individuals with the unaltered properties and
characteristics of the species can only spring from the protoplasm of this nucleus,
we cannot assent. Thousands of plant-species reproduce asexually in unaltered
form by spores and other offshoots. As already stated so often, every young cell
of a plant may be the starting-point of an offshoot or brood-body, and so may
lead to the beginning of a new individual; and an individual produced in this
way bears all the characteristics of the parent plant which produced the offshoot.
It might even be asserted that the features of the species are more certainly
inherited in the case of reproduction by offshoots and brood-bodies than in sexual
reproduction, and in a subsequent chapter it will be shown that it is sexual repro-
duction alone which affords the possibility of posterity with altered characteristics.

The view that the part surrounding the nucleus of a protoplast, the cell-proto-
plasm or cytoplasm, has no formative importance is not borne out by the evidence
of investigations into the origin of the so-called galls, which we shall discuss in
detail later, nor by our knowledge of hybrids. On the contrary, hybridization
causes not only an alteration of form in the new individual arising from the
germ-nucleus, but also an alteration in the form of the tissue in the region of
the ovule exclusively influenced by the cytoplasm, so that the effect of hybridi-
zation can be recognized even in the fruit which arises from the ovary. Every
influence on the cell-nucleus must be transmitted through the cytoplasm. But
it would be much more difficult to imagine that the cytoplasm remains quite
indifferent to this transference than that it also experiences a change identical
with or similar to that undergone by the cell-nucleus. Fortified by these con-
siderations, we may then assume (1) that all protoplasts which we know are able
to form the starting-points of new individuals have the capacity of transmitting
the external form of the species unaltered to the offspring, and (2) not only a part

DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE. 495

but the whole of the protoplasm of any species possesses the specific constitution of
that species.

It is of the greatest importance not only for the existence of the species, but
also for the origin of new species, that the protoplasm, by reason of its specific
constitution, should always take the same form. New species can only arise from
those already in existence. This is equivalent to saying that the protoplasm of
an existing species must undergo alterations in its constitution. Living protoplasm
with new specific constitution must be produced from what already exists. How
such a fundamental alteration is effected can only be guessed at by roundabout
methods. One has to be content, as in so many other instances, with the results
of experiment and experience, and with ascertaining, above everything, what in-
fluences are capable of altering the outward form of a whole or part of a plant
either temporarily or permanently.

2.—ALTERATION IN THE FORM OF SPECIES.

Dependence of Plant Form on Soil and Climate.—Influence of Mutilation on the Form of Plants.—
Alteration of Form by Parasitic Fungi.—Alteration of Form under the Influence of Gall-
producing Insects.—Origin of New Forms by Crossing.

DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

The little town of Kitzbühel, in the North-east Tyrol, has a very remarkable
position. On the north rises the Wilde or Vordere Kaiser, a limestone chain of
mountains with steep, pale, furrowed sides, and on the south the Rettenstein group,
a chain of dark slate mountains whose slopes are clothed far up with a green
covering. The contrast presented by the landscape in its main features is also to
be seen in the vegetation of these two mountain chains. On the limestone may be
seen patches of turf composed of low stiff Sedges, Saxifrages whose formal rosettes
and cushions overgrow the ledges and steps of the rugged limestone, the yellow-
flowered Auricula, the Rock-rose-flowered Rhododendron, and white-flowered Cinque-
foil adorning the gullies, dark groups of Mountain Pines bordered with bushes of
Alpine Rose; and opposed to these, on the slate mountains, are carpets of thick turf
composed of the Mat-grass sprinkled with Bell-flowers, Arnica montana and other
Composites, groups of Alpine Alder and bushes of the rust-coloured Alpine Rose—
these are contrasts in the plant-covering which would strike even a cursory observer,
and would lead a naturalist to ask what could have been the cause. No wonder that
the enthusiastic Botanist, Franz Unger, was fascinated by this remarkable pheno-
menon in the vegetable world. In his thirtieth year, furnished with a comprehensive
scientific training, he came as a doctor to Kitzbühel, and with youthful ardour
he used every hour of leisure from his professional duties in the investigation

496 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

of the geological, climatic, and botanical conditions of his new locality, devoting
his fullest attention to the relations between the plants and the rocks forming their
substratum. The result of this study was his work, published in 1836, On the
Influence of Soil on the Distribution of Plants as shown in the Vegetation of
the North-east Tyrol, which marked an epoch in questions of this sort. The ter-
minology introduced in the book found rapid entrance into the Botanical works
of the time. Unger divided the plants of the district according to their occurrence
on one or other of the substratums—in which lime and silica respectively pre-
dominated—into (1) those which grow and flourish on limestone only; (2) those
which prefer limestone, but which will grow on other soils; (3) those which grow
and flourish on silica only; and (4) those which, whilst preferring silica, will grow
on other soils. He tabulated his results in such a way as to show clearly how
certain species grew on the limestone and others on the silica-containing rock.
Naturally these facts elicited a number of speculations. If the species Gentiana
Clusii, Hutchinsia alpina, and Juncus monanthos growing on the limestone soil
are replaced on the slaty soil by the similar (but yet distinct) species, Gentiana
acaulis (excisa), Hutchinsia brevicaulis, and Juncus trifidus, we are justified in
assuming that the difference in form is due to the influence of the substratum, ü.e.
to the influence of the chief materials in the rock—limestone and silica. But it
has yet to be ascertained and proved, if possible by experiment, how this influence
works; whether limestone and silica, respectively, introduce certain compounds into
a plant, thus altering its outward appearance, or whether the difference is due
rather to the fact that each plant-species requires so much lime or so much
silica, and that when this is lacking in the soil the outward form becomes changed;
or again, whether, after all, the physical properties of the substratum, its porosity,
capacity for retaining water, and its specific heat, have not more influence on the
form of plants than its chemical constitution.

Unger and his followers, amongst whom I enroll myself, thought they would
obtain an answer to these questions by comparing the chemical composition of the
plant-ash with that of the soil in which the plants were grown. But the results of
careful investigations were anything but satisfactory. Both the substances named,
the presence of which was supposed to be of special importance, could be demon-
strated in most of the soils examined. Labrador felspar, hornblende, and other
minerals in crystalline slate yield as much lime in the upper soil as is required
by plants demanding or preferring limestone (classes 1 and 2, above), whilst the
Limestones, which almost all contain clay, have silica enough for the needs of
plants which demand or prefer silica (classes 3 and 4, above). Moreover, it was
shown that plants have the power of obtaining materials which are valuable to
them even when these occur around their roots in hardly appreciable quantity, so
that they actually become accumulators of certain materials, and in this way
a substance of which there are only minute traces in the underlying rock may
be relatively abundant in the superficial layers of soil impregnated with the dead
plant-remains (cf. vol. i. pp. 70 and 259).

INFLUENCE OF THE SUBSTRATUM. 497

Under these circumstances it is a matter of indifference whether 10 per cent
or only traces of lime or silica can be demonstrated in the soil, and the hypothesis
that plant-species which grow on limestone fail to grow on slate because they
are not able to supply their need of caleium, or that the plants growing on slate
cannot flourish on limestone mountains because they cannot obtain the necessary
amount of silica, must be abandoned, as well as the assumption that these substances
when absorbed as food serve as a stimulus to change of form.

I strongly supported this latter hypothesis at the time, and thought I should be
able to strengthen and confirm it by eareful eultural experiments. Seeds of several
species which demand lime were sown in soil containing hardly perceptible quanti-
ties of lime, and the seedlings were watered with water devoid of calcium; in
another place seeds of species demanding a silica-containing substratum were placed
in soil which contained much limestone, and the seedlings were watered with lime-
water. At first it seemed as if an alteration of form had actually taken place in
some individuals. But this was a mistake, or rather, the alteration only consisted
in the greater or less luxuriance of the foliage, lengthening or shortening of the
stem, abundant or scanty development of flowers and the like. But no actual
change of form which would be retained by their descendants could be obtained.
The species of plants accustomed to lime, grown on a soil devoid of lime, presented
a miserable appearance, with scanty flowers which ripened only a few seeds,
whilst the silica~-demanding species grown on lime-containing soil soon withered
and died without flowering at all. The change of form, indeed the actual inter-
change I had anticipated between the closely allied species which grow on the
two rocky substrata in a state of nature, did not occur at all.

If we still take the case of siliceous and calcareous plants, and regard the soil
as the source of free inorganic substances which influence the plants, we are
forced to assume that greater quantities of one substance will be injurious to one
or other of them. The absorbent cells have the capacity of choosing between the
substances at their disposal, but this capacity has a definite limit in every species.
The cells can absorb as much as they require from a very weak solution of
common salt, soda, gypsum, calcium bicarbonate, &e., but a concentrated solution
of these salts may injure and destroy their structure and function. If it
is allowed to act for any length of time on the cells whose function is to absorb
inorganic nutriment, the death of the whole plant will inevitably result. If the
Moss which grows on blocks of granite is watered with a saturated solution of
gypsum; if the soil into which our Meadow-grasses send their roots is watered
with a saturated solution of common salt; or if the humus in which the plants of an
upland moor grow is mixed with sodium carbonate or caleium bicarbonate, the plants
invariably perish, and the same mineral substances, which in a very weak solution
are needful, or at any rate harmless, become poisonous when the solutions are
concentrated. The fact that one species of plant prefers this and another that
mineral substance (see vol. i. p. 73), however, renders it probable that the injurious

effect of materials in large quantity in the soil varies, that a large quantity of
Vou. II. 82

498 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

common salt would be injurious to one species, and an abundance of sodium or
potassium salts to another. From the present standpoint of our knowledge
concerning the absorption of inorganic materials by plants, therefore, Unger’s
classification, especially the expressions silica-demanding and silica-preferring, is no
longer suitable, and it would be more to the purpose to speak of plants which are
injured by lime, potash, We.

The difference in the vegetation on the closely adjoining limestone and slate
mountains met with in so many places in the Als, and so well seen in the neigh-
bourhood of Kitzbiihel, where the climatic influences on the two ranges are identical,
can be accounted for most satisfactorily in the following way. Plant-species which
demand or prefer a siliceous soil are absent from limestone mountains wherever
their roots would be exposed to more free lime than is beneficial; if present they
would be weakened, and thus vanquished in the struggle with their fellows, to
whom the larger quantity of lime is harmless, and they would eventually perish.
These plants flourish luxuriantly, however, on slate mountains, because there the
soil does not contain an injurious amount of lime. The absence of species, demand-
ing or preferring lime, from slate mountains can be explained in the same way.
When seeds are brought thither by the wind from the neighbouring limestone
mountains and germination commences, their further development is visibly
retarded; they dwindle wherever there is not much lime, and are overgrown
and suppressed by the siliceous species which flourish there so luxuriantly. The
brown or black mass formed by the decomposition of dead plant residues, known as
humus, plays a very important part in the contrasting vegetation on limestone and
slate mountains. To obtain a true idea of its significance it must first be pointed
out that three distinct stages can be distinguished in the development of a
continuous and intricate plant-covering. To the first stage belong the plants
which settle down on the bare earth content with a substratum wholly devoid of
humus; in the course of time they conquer the most barren rock, the barest
boulders, and the dreariest shifting sands. The species of this group belong chiefly
to the Lichens, Mosses, Grasses, Pinks, Crucifers, House-leeks, Saxifrages, and
Composites, whose spores, seeds, and fruits are exceptionally well adapted for wind
distribution, and can be transferred with ease to the steepest slopes and the most
uncompromising crags. The second stage includes plants which require a moderate
amount of soil mixed with humus; they establish themselves on the ground pre-
pared by the first settlers, wresting it from them and taking possession, and then
suppressing and overgrowing them entirely. These plants belong to very different
families, whose distribution and establishment are effected in very many ways to
be described subsequently. The third stage of development consists of plants for
which the abundant humus stored up successively by the plants of the second stage
is absolutely indispensable. Bog-moss, Lycopodiums, Sedges, and Heaths form the
chief part of this stage. In the course of years the amount of inorganic materials
in the soil which supports the plants of the third stage continuously diminishes.
Plants which require a large quantity of inorganic salts languish, and are, moreover,

INFLUENCE OF THE SUBSTRATUM. 499

overecome by saprophytes which find a suitable habitat there and flourish in
abundance. The decayed portions of Saprophytes contain relatively little inorganic
material. No trace of lime (in particular) is to be found in their ash. In this way
a superficial layer of humus is formed which actually excludes a large number of
plants. The next deeper layer may contain a considerable quantity of inorganic
salts, but they are valueless to plants rooted in the upper (humus) layer, as they
cannot penetrate it. It has been shown by experiment that pure humus possesses
the power of holding back materials which are soluble in water. It possesses this
property to such an extent that if salt solutions are filtered through a layer of
humus the water which escapes below is almost pure. It is therefore impossible
for inorganic substances from the deeper layers of the soil, much less from the
underlying rock, to reach the surface layer of humus in solution by diffusion; and
if some mineral ingredients are not introduced by irrigation or flooding, the upper
layer of soil consists of pure humus on which only saprophytic plants can flourish.

The formation of such layers of humus occurs much more easily and quickly on
slate mountains than on limestone, because in the former the rock and the products
of its decomposition retain water much better, and a uniform saturation promotes
the development of humus, and also because on slaty soil the second stage of the
development of the plant-covering consists of plants which require very few inor-
ganie food-substances, and accordingly very few inorganic materials are yielded
by the humus, which originates at the cost of the decaying portions of these plants.
But a thick stratum of pure humus may also arise in course of time on lime-
stone mountains. Only the soil must be uniformly moist in that spot, and
neither sand nor mud must be deposited on it. If these conditions are fulfilled a
deep humus will gradually spread itself over limestone rocks and débris in the
third stage of development, the superficial layer of which will contain no trace
of lime, but will afford an excellent soil for silica-loving plants (7.e. for those to
which lime is injurious). The isolated occurrence of so-called siliceous or slate-
plants on limestone mountains, even in the middle of a patch of plants which are
characteristic of a limestone soil, may be naturally explained in this fashion.

The water which moistens the rock and soaks the soil has, apart from its
mechanical action, the important function of opening up mineral substances and
of forming solutions from which the absorbent plant-cells may take their choice.
The atmospheric water which penetrates into the earth from above is especially
valuable as a solvent on account of the carbonic acid gas it contains. It is
immeasurably more valuable to every part of the soil which is riddled by the
roots of living plants than the soil-water, so poor in carbonic acid, which collects on
impervious strata of the soil and soaks upwards through the superficial layers.

The power of the soil to retain water depends mainly on the extent of breaking
up undergone by the rock whose disintegration has formed the soil and upon the
amount of clay which has arisen from this disintegration. But the amount of
humus which in course of time has mixed with the disintegration and the decom-
position products of the underlying rock is also an important factor, and thus very

500 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE,

complex conditions arise which render the estimation of the soil’s capacity for
retaining water very difficult. If permeable sandy soil, poor in humus, is deprived
of ground water and is dependent for its moisture solely on the atmosphere, the
plants growing in it will be retarded in their development if rain and dew are
absent for any length of time, and their outward appearance will be altered by this
restriction of growth. Annual plants subjected to a lack of moisture in the soil
just at the time when their growth should be at its maximum, show best how far
these alterations will go. The stem-structures remain short, the foliage-leaves
shrink to their smallest extent, and no lateral shoots are developed. Only a few,
or perhaps only one, of the flower-buds mature; it is small, opens comparatively
very early, and the whole plant has a dwarfed aspect. Annual plants of the Poppy
(Papaver Rheas, somniferum), Pheasant’s Eye (Adonis estivalis, flammea), Corn-
cockle(A grostemma Githago), Cornflower(Centawrea Cyanus),and common Groundsel
(Senecio vulgaris) grown on a dry soil differ from plants grown in the same place,
but in a damp year, to such an extent in the size of all their parts that at first sight
they might be mistaken for other species. A clay soil which retains water is less
exposed to danger of too great dryness, but if it is not mixed with humus, and
therefore loosened, it has the disadvantage that the water it contains cannot take
up the inorganic foods quickly enough and in sufficient quantity for the require-
ments of the plants. This drawback explains the surprising fact that plants grown
on heavy wet clay soils have a dwarfed appearance exactly like plants growing on
dry sandy soil. In regions liable to flooding by streams and rivers where not
infrequently sandy and clay soils, in all degrees of porosity and admixed with
humus in all possible proportions, are to be met with within a few yards of one
another, certain species of plants are to be found growing near together in all imagin-
able degrees of size, e.g. Aster Tripolium, Bidens cernua and tripartita, Polygonum
lapathifolium, Rumex maritimus, Veronica Anagallis. In places where the
seedlings cannot find enough free mineral foods, in spite of the abundant moisture
in the soil, the stem rises to some 3-8 em.; in places which favour the absorption of
food, to some 50-80 em. We will describe only one species, Veronica Anagallis,
more in detail. Plants of this species are found with stems 3-5 em. high and 0:5
mm. thick, with foliage-leaves 6-12 mm. long and 5-6 mm. broad when fully
developed. The number of flowers in one inflorescence is about 4-5, the calyx and
ripe capsular fruit measure 3 mm. in length. Contrasting with these are plants
with stem 30-50 em. high and 7-8 mm. thick, whose fully-formed leaves are 80 mm.
long and 35 mm. broad. There are 40-50 flowers in each inflorescence, and the
calyx and ripe capsule measure 4-5 mm. in length. Generally speaking these
plants are about ten times as large as the others. If the soils which give rise to
such surprising differences in size are examined it will be noticed that the dwarfed
specimens are rooted in a heavy soil devoid of humus, while the large luxuriant
plants flourish in a clay soil which is mixed with plenty of humus, and is
therefore very open. Obviously the plants could not obtain from the heavy clay
soil what they required for the structure of a vigorous plant, even although the

INFLUENCE OF THE MEDIUM. 501

ground was well moistened and warmed; but this they could obtain in abundance
from the saturated clay soil containing the humus.

It has been already stated that the ground water is less favourable for vegetation
than rain and dew on account of its paucity of carbonic acid. But the moistening
of the ground by water which wells up from below brings other evils in its train.
By this means the soil is over-saturated for a long time, a condition which the roots
of most land-plants will not tolerate. When it remains stationary for a long while
potassium and sodium salts, and, under certain conditions, humous acids pass into it
from the wet earth in quantities anything but advantageous to the plants. Vege-
tation, therefore, exhibits a scanty growth in places where the ground water
influences the stratum of soil penetrated by roots, and it usually consists of
comparatively few species.

In low-lying regions, where the ground water rises to the surface, we have the
formation of lakes and ponds with variable water-level. Sometimes the plants
growing in such places are quite submerged, while at other times their stem
and leaves are above water. Land plants do not take kindly to this. Most of them
cannot survive very long immersion; they become suffocated, die, and decompose
under water in a few days. Only a few species have the remarkable power of
growing equally well below or above water, and these are, of course, extremely
interesting on account of their form. Im accordance with the great contrast
presented by the external conditions of life to which these species are temporarily
exposed we have a fundamental change both in their outward appearance and in
the internal structure of their several organs. In order that the stem and leaves
should be held in the best position by the flowing water, the mechanical tissue in
submerged varieties of these species is much reduced (see vol. 1. pp. 424 and 665)
They are also devoid of the contrivances which usually regulate transpiration, since
no evaporation occurs under water. Stems grown under water consequently appear
limp and flaccid when taken out of it; their leaves, when compared with those
growing in the air, are much weaker and more delicate. They have no gloss, but
are brighter green in colour, and in the air they collapse and dry up in a very
short time. A vertical section through the leaf shows that the number of cells
between the upper and lower epidermis is much reduced, and that the cells are
shortened in a direction perpendicular to the leaf surface. The foliage-leaves of
Veronica Beccabunga, when grown under water, are hardly one-third as thick as
those grown in the air, and between the upper and lower epidermis there are only
4-5 layers of short cells, while in corresponding leaves of aérial plants there are
10-12 cell-layers and a distinct division into palisade and spongy parenchyma (see
vol. i. p. 279). The shape of the leaf is also much changed under water. In
Veronica Beccabunga the difference in aérial and submerged leaves is very slight,
consisting only in the shortening of the petiole and in the marginal teeth becoming
less marked. In Veronica Anagallis, likewise, the alteration in shape is incon-
siderable, but in many others it is very noticeable, and we shall return to it when
speaking of the influence of light.

502 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

Plants rooted in the mud of a river-bed, the stems and leaves of which are
surrounded by rapidly-flowing water, must possess corresponding strength if
they are not to be torn. In comparing two plants of the same species, the one
growing in the still water of a deep lake, the other in a rapidly-flowing stream,
it will be noticed that the walls of the superficial cells of the latter have become
strongly thickened, and that strong bundles of bast-fibres have developed in the
cortex of the stem, while in the former only the weakest traces of bast-fibres
can be seen. The extraordinary length of stem, petiole, and leaf-blade is also
very surprising in plants which grow in rapid water. The Pondweed Potamogeton
fluitans, the Rushes Juncus lamprocarpus and swpimus, the Grasses Agrostis
stolonifera and Glyceria fluitans are very instructive examples. A plant of
the last-named Grass growing on damp soil on the edge of a stream over the
water had linear, bluntly-pointed leaves, whose sheaths were on the average 15 cm.
long, the blades 23 em. long and 85 mm. broad. After this plant had been sub-
merged under rapidly-flowing water in the following year, leaves unfolded, which
tapered gradually to a point, with a sheath having a mean length of 47 em., and
blades 73 cm. long but only 5 mm. broad. The blades produced in running
water were three times as long and actually rather narrower than in the air.
There was no difference in the number of strands traversing the blade, but they
were nearer to one another than in the aérial leaves. The Arrow-head (Sagittaria
sagittifolia), which usually grows on the muddy bottom of shallow lakes, raising
its leaves above the still water, has gained its name from the likeness of its
leaf-blade to an arrow. If it is planted in the bed of a rapid stream so that
the leaves during their development are exposed to a vigorous current, the
leaf-blade is almost entirely suppressed. What still remains has the form of a
spade, but not infrequently all trace of lamina is wanting. The petiole, however,
lengthens to 70 cm., and forms a limp, flat, pale-green ribbon 1-2 em. broad,
which might easily be mistaken at first sight for the leaf of Vallisneria.

Another remarkable change which is effected by submerging growing plants
is the non-development of the epidermal structures called hairs, so that the leaves
and stems of submerged plants always appear smooth. The suppression of haır-
structures is very noticeable in the aquatie variety of Polygonum amphibiwm.
In aérial plants of this species the leaves have short petioles, are lanceolate in
shape, and are covered thickly with short hairs, which are rough to the touch:
while the aquatic plants have long-stalked, broadly-linear leaves completely smooth
on both sides.

The humidity of the atmosphere has a marked effect on the form of land
plants. Transpiration, which is so deeply concerned in all the vital processes,
is carried on very slowly in air which is almost or quite saturated with water-
vapour. If plants of a species which usually grows in dry air come into a humid
atmosphere, they must be furnished with means for aiding evaporation. On
the other hand, plants which grow in dry air must be protected against excessive
transpiration. The aids and protective measures were so minutely described

INFLUENCE OF TEMPERATURE. 503

in vol i. pp. 284 and 307, that it is needless to repeat them here; but it should
be noted that the capacity of plants to construct their tissue as need requires,
either for aiding transpiration or for proteetion against excessive evaporation,
is very limited. It must also be pointed out that it is very difhicult to distinguish
clearly between the direct effect of the humidity of the air and the effects of
other influences. Heat and light, as well as the amount of moisture in the soil,
are intimately connected with the humidity of the air, but the relations are
difficult to estimate. To a certain extent they are interchangeable, and therefore,
in most instances, it is impossible to say which external influence is the cause of
any particular alteration in the tissue concerned in transpiration. For the answer
to the chief question, whether it is possible for a change in the conditions of
life to cause an alteration of form in the sense of an adaptation, it is really a
matter of indifference which influence causes the visible effect. Only here, as in
so many other cases, matters are simplified if a certain partiality is permitted in
experiments for solving these difficult questions, and if the interwoven influences
of soil and climate are treated separately.

The effect of heat on growing plants was discussed at vol. i. p. 523. It only
remains to say here that the formation of starch and other reserve-foods, as
well as the formation of sugar in fruits, is largely connected with heat. Fruits
of the same species which ripen under a higher temperature differ greatly in the
amount of sugar they contain from those ripening at a lower temperature. It is
generally accepted that the size also of the stem, foliage, flowers, and fruit is
influenced by heat. The changes which occur when plants in flower, after being
for some time in a very warm room are transferred into a cooler room, the
other conditions remaining the same, are in particular now recognized. When a
large-flowered bulbous plant, e.g. the Belladonna Lily (Amaryllis Belladonna),
is transferred to a cold greenhouse after opening its first flowers in a warm one,
the flowers it here develops at a lower temperature are almost a third smaller
than those produced in the warm house. But when the first flowers open in
the cold, and the later ones in a warm atmosphere, the former remain small
and the latter are larger in size. It is important to emphasize this circumstance
in order that the phenomenon here exhibited may not be mistaken for another,
in case we should be led to think that the flowers of a plant which first unfold
are larger than those which succeed them even when there has not been the
slightest alteration in the conditions of light, heat, humidity, &e.

It is particularly instructive, when examining the effect of heat on the form
of a species, to compare plants grown in water of different temperatures but
under conditions otherwise similar. In mountainous districts the springs on the
same mountain slope have a different temperature according to their elevation,
and yet the same species of plants may be found growing in springs at the foot
and high up on the mountain. Let us take as examples plants of Cardamine
amara, Myosotis palustris, Pedicularis palustris, and Veronica Beccabunga.
These species grow at the foot of the Patscherkofel, near Innsbruck, in the bed

504 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

of streams with a mean temperature of 10:2 ° C., but they also flourish in a stream
above the tree-line, at a height of 1921 metres above the sea-level, known as the
“Kreuzbrunnen”. Comparing plants of the same species growing under the
influence of these different temperatures, the following differences are to be noted:—
Plants of Veronica Beccabunga growing in spring water at a temperature of
102° C. were 20-50 em. high, and displayed 4-6 internodes between the bottom
in which they were rooted and the level of the first inflorescences. The internodes
of the stem were 60-120 mm. long and 5 mm. thick; the leaves springing from
the middle of the plant were 40-60 mm. long, 20-25 mm. broad, and each of the
flower racemes had 12-16 flowers. Plants growing in the spring water at a
temperature of 42° C. were 10-15 em. high with 4-6 internodes between the
ground and the level of the first inflorescences. The internodes were 15-30 mm.
long and 10-12 mm. thick, and each inflorescence had 12-16 flowers. Cardamine
amara, Myosotis palustris, and Pedicularis palustris behaved similarly. There
seemed to be no alteration in the form of the leaves and flowers; the corollas
assumed a rather deeper tint in the Kreuzbrunnen; Myosotis palustris, which
was 20 em. high at the foot of the Patscherkofel, was 4-5 em. high in the Kreuz-
brunnen, and closely resembled the Hritrichium nanum of the Southern Alps
in the deep blue of its corollas. Cardamine amara, in the same cold spring, in
addition to the shortening of its internodes and diminution of its foliage-leaves,
displayed a red colour on the outside of its white petals which was not present
in plants at lower levels.

The powerful influence of light on the development of plants was discussed at
vol. i. p. 371. The question now before us is how far bright and subdued light are
able to alter the size, form, and colour of plants. The following is a general review
of what has been ascertained in the matter from experiments and direct observa-
tion of nature. When plants of a species develop in subdued light they always
have higher stems and longer leaves than when grown in bright light, provided,
of course, that the conditions of moisture and temperature have been as far as
possible identical. This difference is especially noticeable in comparing two plants
of a species, one of which has developed in the dim light of a greenhouse in the
short days of winter, the other in an unshaded place in the open country during
the summer when the light lasts for 16-17 hours every day. The former has a
lank thin stem, delicate yellowish-green leaves, and either none of its flowers
unfold or else they have a weak appearance and their corollas are pale and flaccid.
The illuminated plant has, on the other hand, a compact vigorous stem, dark green
leaves, and unfolds a multitude of bright-hued flowers. One only of the large
number of experiments which have been performed for the purpose of determining
this matter definitely will be mentioned here—one indeed which shows how far
the form of the flowers also may be affected. Seeds of a biennial Saxifrage,
Saxifraga controversa, which were sown in several flower-pots filled with similar
soil, produced numerous young plants. A pot with six of these young plants
was taken in the autumn into the hot-house; another, likewise containing

INFLUENCE OF LIGHT. 505

six young plants, passed the winter under a thick coat of snow in the open.
At the beginning of December the six plants in the hot-house sent up from
the centre of their small leaf-rosettes slender stalks 10 em. high, whose upper
internodes were 22 mm. long and 1 mm. thick. The stem-leaves were yellowish,
entire, elongated, 6-7 mm. long and 2 mm. broad; ealyx-tube 4 mm. long, 13 mm.
broad; calyx-teeth 2 mm. long, 15 mm. broad; petals 35 mm. long, 2 mm.
broad; stamens 1 mm. long. It was noted that lateral axes only developed in
the axils of the upper stem-leaves, and that the buds of the lateral shoots in the
lower leaf-axils atrophied. In the following May strong stems 6 em. high were
sent up from the leaf-rosettes of the plants which had wintered under the deep
snow in the open; their upper internodes were 12 mm. long and 2 mm. thick.
The stem-leaves were somewhat broadened in front with dentate margin, red in
colour, 5 mm. long and 3 mm. broad. The measurements of the parts of the
flowers were:—Calyx-tube, 2 mm. long, and 2 mm. broad; calyx-teeth, 1°5 mm.
long, 1 mm. broad; petals, 23 mm. long, and 2 mm. broad; stamens, 1 mm. long.
From the axils of the stem-leaves flower-bearing shoots developed, which, like the
parts of the main stem exposed to the sun, were coloured red. Here then the
alterations which certainly are due to the various light influences consist not only
in the lengthening and shortening of the stem- and foliage-leaves, but the flowers
are correspondingly changed. The petals of the flowers which opened at the New
Year when the days were shortest were not only relatively but actually narrower
than those which belonged to flowers which opened in the early summer when the
days were longest.

It has already been stated that the elongation of the leaves and the division of
the leaf-lamina into long narrow segments in submerged leaves is associated with
the diminution undergone by the light in passing through the water (see vol. i.

_ p. 665). The elongation of submerged leaves is very well seen in the water Star-
wort (Callitriche) and Mare’s-tail (Hippuris). In the latter the linear submerged
leaves are thirty times as long as they are broad, while the length of the aérial
leaves is only 7-9 times their width. In Roripa amphibia the leaves which
develop under water are deeply cleft compared with those produced in the air.
The aérial leaves of this Crucifer are linear-lanceolate, about ten times as long as
broad, with finely toothed margin. Under water the leaves have an elliptical
shape, are 2-3 times as long as broad, and the lamina is cleft almost down to the
midrib in narrow segments 2-3 em. long, like a comb or feather. The aérial
leaves of the whorled Waterwort (Zlatine Alsinastrum) are grouped in whorls of
three. They have an ovate shape, and their margins are finely notched. Each is
traversed by 3-5 veins. The leaves developed under water are divided almost
their whole length into 3-4 narrow linear segments, and each whorl looks as if it
were composed of twelve leaves. Each segment is smooth round the edge, and
traversed only by one central vein. The difference between the aérial and sub-
merged leaves of the white-flowered Crowfoots (belonging to the Batrachiwm
section of the genus Ranunculus) is even more surprising. Plants of these Crow-

506 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

foots which have developed on muddy but not inundated ground display three-
or five-cleft leaves whose segments are light green in colour, shiny, and almost
fleshy, and spread out flat. When these plants are grown under water the leaves
appear quite different; they become divided into numerous thread-like or hair-
shaped segments which have a dark-green colour, and the polished surface has
entirely disappeared.

The shade afforded by stones, loose earth, undergrowth, and neighbouring
bushes and shrubs acts on growing stems, foliage-leaves, and flowers just in the
same way as the light-subduing layer of water. In a place near my country house
which was formerly used for storing wood and dry twigs, but which had remained
unused for a long time, the Creeping Thistle (Oirsvwm arvense) had established itself
and formed an intricate growth. The crowded stems attained a height of 80 em.
at the time of flowering and fruit ripening. In the winter of 1885 wood was
again stored there in piles 150 cm. high. When, early in the following summer,
the new shoots of the Thistle began to spring up they were obliged to content
themselves with growing through the dark chinks between the blocks of wood.
Many were thus forced to bend and twist, and finally came against some insur-
mountable obstacle so that they dwindled in the crevices of the wood-stack without
ever reaching the light. Others again which were able to find a fairly straight
road through the crevices grew up until they reached the surface of the wood-heap,
they then continued to grow 50 em. higher and unfolded large foliage-leaves on
this upper portion. They also developed branches with flower-heads, and from
a distance it looked as if a group of Thistles had grown on the top of the wood-
stack. The stems had attained a height of 2 metres. The lower internodes were
twice as long as usual, the foliage-leaves which sprang from the stalk inside the
dark crevices were small, yellowish green, and the buds in their axils did not
develop. The Cow-berry (Vaceinium Vitis-Idea) behaves similarly when its
shoots are obliged to grow up to the light through dead tree-trunks. Shoots which
force their way in the dark between the bark and the wood of the trunk may
reach the height of a metre, while neighbouring ones, springing directly from the
soil of the forest are only 15 em. high. The shoots inside the bark have a reddish
colour, and they bear small pale scales instead of dark-green foliage-leaves.

From the creeping stems of the White Clover (Trifoliwm repens) spring erect
petioles terminating in three leaflets, and an erect angular stem bearing a flower-
head. In sunny places, especially where no neighbouring plants cast a shade, the
petioles reach a length of 8 cm., and the stem of 10 cm. But if dense bushes
overshade the Clover, the petiole and stem elongate until the leaflets and capitulum
they bear reach the light. Under these conditions petioles 28 em. long have been
found, and stems attaining a height of 55 cm. An extraordinary elongation also
oceurs in the radical leaves of the Dandelion (Taraxacum officinale) in places
where high Grasses and thick bushes shade the moist soil. In the open the leaves
reach a length of 20 em., but in the shade they become twice or three times as
long. The lower part of the leaf lengthens most, the free end is comparatively

INFLUENCE OF LIGHT. 507

very little altered, and in the central portion the only change is that the lobes and
teeth become shorter and less clearly marked.

In order to ascertain the effect of covering plants with earth, numerous bulbs
of a species of Tulip (Tulipa Gesneriana) were planted at the same depth in one
garden bed, and in another some corms of the Spring Crocus (Crocus vernus).
Earth was heaped over these bulbs and corms in successive heights of 5, 10, 15, 20,
25, 30, 35, 40, 45, and 50 em. Naturally the leaf-tips and flower-buds were first
seen in the places where the bulbs were only covered with 5 em. of soil; in both
beds the development was delayed—in the other cases in proportion to the height
of the soil above the bulbs. Some flower-buds of the Crocus appeared above the
20 em. of soil, one of the Tulip above the 30 em. Numerous leaf-tips of the
Crocus appeared above the 35 em., and a few of the Tulip above the 40 em. of soil.
The perianth-tube, the peduncle and the foliage-leaves were almost twice as long as
those which had developed under only 5 em. of soil. The flowers were smaller, and
unfolded just above the soil; the leaves were narrower and pale yellow in colour
as far up as they were covered with the soil. Neither the Crocus nor the Tulip
raised their leaves higher than 40 em. Apparently the reserve-materials stored in
the corm and bulb-scales were not sufficient for a further elongation. The stems
and leaves of the Crocus and Tulip thus exhibit alterations similar to those
observed in the sprouts of Potato-tubers in a dark cellar.

We should expect that if moisture and lack of light produce elongation of
shoots and yarious alterations in leaves, a brilliant illumination would have the
opposite effect on growing plants. This is indeed the fact. Plants which have been
for a year in the shade and have been placed at the beginning of their development
in the following year in the sun display shorter internodes and firmer leaves; they
blossom more abundantly, the flowers are of a deeper hue, and in many cases a
covering of hairs is formed over the green portions. It is not necessary to mention
how far transpiration, which is much more active in the sun than in the shade, is
concerned in this; these alterations are certainly produced in the end by sunlight.

The effect of brilliant illumination is best seen by comparing plants grown from
similar seeds at different elevations, but under identical conditions in other respects.
The results obtained in my experimental garden near the summit of the Blaser in
the Tyrol, at a height of 2195 m., during the years 1875-1880 illustrate this very
fully, and I will briefly recount them here. The seeds of some annual plants were
sown in September. The beds were covered with a layer of snow a metre thick
throughout the winter. The germination of the seeds took place in the following
year soon after the snow melted between the 10th and 25th June. The seedlings
therefore developed during the time when the sun was highest and the days longest,
and the young plants were exposed to a temperature not lower but rather higher
than that enjoyed by plants from similar seeds which began to develop in the
experimental beds of the Vienna Botanic Garden in March, when the daylight
lasted about 12 hours. The seedlings of several species (e.g. Gilea tricolor, Hyos-
ecyamus albus, Plantago Psyllium, Silene Gallica, Trifoliwm incarnatum) were

508 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

killed by the isolated frosts which occurred in each of the six years of the experi-
ment, not only in the last week of June, but during July and August; but others
(e.g. Agrostemma Githago, Centawrea Cyanus, Iberis amara, Lepidium sativum,
Satureja hortensis, Senecio vulgaris, Turgenia latifolia, Veronica polita, Viola
arvensis) only underwent a short temporary stoppage of growth from this cause,
and opened their flowers at the end of August and beginning of September. In
the plants of some species (e.g. Senecio vulgaris, Veronica polita, Viola arvensis)
ripe seeds capable of germinating were formed in September. The flowering speci-
mens, in comparison with those which had grown during the short days of the
spring exposed to numerous night-frosts in the Vienna gardens, displayed extremely
shortened internodes. The number of internodes was also lessened, or rather,
fewer were developed. For example, where 10 internodes developed in an experi-
mental plant in Vienna, in the Alpine garden a corresponding plant would only
have 5-6. The same was true of the development of the flowers. While in a plant
of Viola arvensis in Vienna the axillary buds of the first six foliage-leaves were
suppressed and flowers were not produced until the seventh and eighth leaves,
flowers grew from the third and fourth axillary buds in the same species of plant
grown in the Alpine experimental garden. The number of flowers on a plant was
less, the petals were smaller on the average, and, generally speaking, the annual
plants in the Alpine garden had the same appearance as those grown in the plain
on dry, sandy soil described on p. 500. It has already been stated on p. 453 that
some of the species which are annuals in the valley and on the plain do not die
in the autumn in the Alpine garden, but remain alive through the winter and in
the following year develop new shoots from the stem.

To deseribe the alterations undergone by biennial species in Alpine regions we
will take Libanotis montana (an Umbellifer) as an example. Its stem in the
Alpine garden was 16-24 em. high and developed 5 internodes which were 2-5 em.
long. From the axils of the 5 green stem-leaves sprang lateral shoots which did
not branch but terminated in a single umbel, so that the plant only bore 5 umbels
altogether. The plants grown from similar seeds in the Vienna Botanic Garden
exhibited a stem more than a metre high with 10 internodes each 10-20 em. long.
No lateral shoots were produced from the axils of the lower stem-leaves. Those
from the axils of the middle and upper leaves were branched and bore several
umbels. On an average a plant had about 20 umbels altogether.

Over 300 species of perennial plants were grown in the Alpine experimental
garden. Only 32 of them blossomed, however. Those whose flowers usually pre-
cede the foliage-leaves were in full blossom at the beginning of July, the others,
which had to develop a leafy stem before their flowers appeared at the top or
in the axils of the leaves of this stem, did not flower until the end of August and
beginning of September. Three species of the latter kind will be more particularly
treated of here; one species whose stem bears only a single leaf and is terminated
by a single flower (Parnassia palustris), one whose stem is beset with decussate
leaves and terminates in a loose inflorescence composed of small cymes (Lychnis

INFLUENCE OF ELEVATION. 509

Viscaria), and a third whose stem bears alternate leaves and whose flowers are
grouped in capitula (Pyrethrum corymbosum).

The Grass of Parnassus (Parnassia palustris) from the Alpine garden, when
compared with plants grown in the experimental beds of the Vienna Botanie
Garden, showed the following measurements:—

Vienna Botanic Garden. Experimental Garden on the Blaser.

Dimensions of leaf............... 3°3 cm, long, 2:4 em. broad. 1:0 em. long, 0°6 em. broad.

Height of stem ..................- 20-27 cm. | 5-9 cm.
Diameter of flower ............... | 2'8-3'4 cm. | 1'8-2°0 cm.

In the Alpine regions, therefore, the plant was only } or } as high and the leaves
only 4-4 as large as in Vienna, whilst the flowers in the Alpine region had a much
smaller diameter than in Vienna.

Comparing the hermaphrodite plants of Lychnis Viscaria in the experimental
garden of the Blaser with those of the same species at Vienna, we obtain the
following:—

Vienna Botanic Garden. | Experimental Garden on the Blaser.
|

Height of the stem, includin er

the axis of the ren | ten ae SSS AU UE
Dimensions of lower leaves ...... 80 mm. long, 4 mm. broad. | 50 mm. long, 3 mm. broad.
ÜNHOTESCENCE Ferne ee cee cecceswcecs oes 80 ,, BT en 5 GOR; BRAUNE, ns
ee nn ld, es 65 ,, = 13°5 ,, en DIE 5
Lamina of petals.................... Uwe 54 Busen > Be ” 6:82, =
Clawrof petals.c-...--s0-c-..cccs= +00" | 8 mm. long. 7 mm. long.

Plants from the Alpine garden, therefore, when compared with those from the
Vienna Botanie Garden, exhibit smaller measurements of stem, leaves, and flowers.
The following points were also noted: the number of internodes in plants from
the Vienna Garden was 9, of which 5 were on the axis of the inflorescence; each
cyme consisted of 3-5 flowers, and the whole inflorescence bore 33-40 flowers.
Plants from the Alpine Garden had only 6-7 internodes, of which 3 belonged to
the inflorescence; the cymes composing the inflorescence were only occasionally
3-flowered; in most of them only the central flower developed, the two lateral ones
being suppressed. The whole inflorescence included only 5-11 flowers.

Plants of Pyrethrum corymbosum, from the Alpine Garden, compared with
those from the Vienna Botanic Garden (all raised from one batch of seeds) showed
the following differences:—

Vienna Botanic Garden. Experimental Garden on the Blaser. |
|
Height of the stem................ 950 mm. | 250 mm. |
Dimensions of leaves, ............ 170 mm. long, 50 mm. broad. | 45-50 mm. long, 20 mm. broad.

Diameter of the capitulum,.... 26 mm. 20 mm.
Bay-ioreta,..., ser. 8 mm. long, 4 mm. broad. | 7 mm. long, 3 mm. broad.

510 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

In this case, again, plants from the Alpine Garden, when compared with those
of the Vienna Botanic Garden, had smaller stems, leaves, and flowers. The lobes
of the foliage-leaves from the middle of the stem of plants from the Alpine Garden
were pinnate, and the pinne were either entire or beset with two small teeth
on each side, near the apex. The stem had ten foliage-leaves, the four uppermost
of which were much reduced and served as scale-leaves for the lateral shoots
arising from their axils. These lateral axes were not branched, and each bore
only a single capitulum. There were five capitula altogether. On plants from
the Vienna Botanic Garden the lobes of the foliage-leaves from the middle of
the stem were more divided, and the pinn® were beset on each side near the
top with 3-5 teeth. The stem bore 25-27 foliage-leaves, of which the 6-8 upper
ones were much reduced in size, and functioned as scale-leaves for the lateral
shoots in their axils. These lateral shoots were branched, and each branch
terminated in a capitular inflorescence. The total number of capitula was 20-30.

From these examples it will be seen that all the parts of plants grown in
the Alpine experimental garden were much hindered in their growth. The
foliage- and floral-leaves were smaller, the stems shorter, the number of internodes,
foliage-leaves, inflorescences, and flowers was diminished. The flowers were
relatively nearer the earth, and this was due not only to the diminished number
and length of the internodes of the stem, but principally to the fact that the
flowers sprang from the axils of the lower stem-leaves.

Plants growing in Alpine regions derive a great advantage from these altera-
tions, which are chiefly produced during their development by the influence of
the long and bright daylight of June, July, and August. If these plants had
to produce the same under-structure as their fellows in the Vienna Botanic
Garden, 2015 metres lower down, much time would be lost, and the earliest
flowers would hardly open before October, at a time when the winter snow is
already beginning to fall. But since the number of internodes is restricted, and
flowers are developed from the lower stories, it is possible for the plants to blossom
at the end of August and beginning of September, and perhaps to ripen their
fruits—one of the chief aims of the plant’s existence. To this modification in
their mode of development is also due in part the repeatedly-mentioned fact
that many alpine plants blossom earlier than those in lower regions. But in
order to avoid misunderstanding, it must be expressly stated that in not one of
the thirty-two perennial, nor in the biennial and annual species which blossomed
in the Alpine experimental garden, was the early flowering hereditary; con-
sequently these plants must be carefully distinguished from the so-called asyn-
gamic species, which will be spoken of in one of the last chapters in this book.

The relation of light to the colouring matters of plants has been repeatedly
the subject of careful investigation. All observers agree that the amount of the
pigment known as anthocyanin increases and diminishes with the stronger or
weaker sunlight enjoyed by the parts of the plant in question, and that the
yellow colouring matter of flowers holds a similar relation. Chlorophyll, however,

COLOUR AT DIFFERENT ELEVATIONS. 511

is actually destroyed by bright light in plants which are not properly screened,
and the green tissue is then blanched and assumes a yellow tint. Since the
intensity of the sun’s rays increases with the elevation in mountain districts
(see vol. i. p. 525), we should expect that this effect of light would be shown
particularly well in plants of high elevation. And this is certainly the case.
The flowers of species grown in the Alpine garden on the Blaser at a height
of 2195 metres above the sea exhibited, as a rule, brilliant floral tints, and some
were decidedly darker than the flowers grown in the Vienna Botanic Garden.
Agrostemma Githago, Campanula pusilla, Dianthus inodorus (sylvestris), Gypso-
phila repens, Lotus corniculatus, Saponaria ocymoides, Satureja hortensis,
Taraxacum officinale, Vicia Cracca, and Vicia sepiwm are good examples of this.
Several species, which produced pure white petals in the Vienna gardens, e.g.
Libanotis montana, had petals coloured reddish-violet by anthocyanin on their
under sides in the Alpine garden. The glumes of all the Grasses which were
green, or only just tinged with violet at a low level became a dark brownish-
violet in the Alpine garden. The abundant formation of anthocyanin in the
green tissue of the foliage-leaves and sepals, and in the stem, was particularly
apparent. The leaves of the Stonecrops, Sedwm acre, album, and sexangulare
became purple-red, those of Dracocephalum Ruyschianum and Leucanthemum
vulgare violet, those of Lychnis Viscaria and Satureja hortensis a brownish-
red, and the foliage-leaves of Bergenia crassifolia and Potentilla Tiroliensis,
even in August, had the scarlet-red colour which they usually assume in sunny
spots in the valley in late autumn. I must not omit to mention that, according
to some of my zoological friends, many animals, especially spiders and snails, which
have been transferred from the plains to the mountain-heights, assume a darker
tint in alpine regions.

A considerable number of plant species, especially those which grow in the
valley in shaded or half-shaded places, as, for example, Arabis procurrens, Digitalis
ochroleuca, Gewm urbanum, Orobus vernus, Valeriana Phu, and V. simplicifolia,
Viola cucullata, developed more or less yellowish leaves in the Alpine garden,
where they were exposed to the full sunlight. It was mentioned in vol. i. p. 393,
that the Flax (Linum usitatissimwm), which flourishes in mountain valleys
at a height of 1500 metres, where its chlorophyl! is uninjured, nevertheless
turns yellow in the Alpine garden at a height of 2195 metres.

From this general review of the modifications in plant-form obtained by
culture-experiments, a series of important conclusions may naturally be drawn.
In the first place we must point out that two kinds of characters are to be observed
in plants, those which are the result of certain conditions and properties of soil
and climate, and those which appear independently of these external influences.
This distinction is so important that we shall illustrate it by two examples.
The white Water-lily, Nymphea alba, develops scale-leaves of ovate or lanceolate
shape with no separation into petiole and lamina. The foliage-leaves, however,

512 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE.

have a rounded petiole and a dise-shaped lamina. These characters are always
present whether the seed which produced the plant germinates in a deep lake
or in the mud of a marshy meadow. In the marshy meadow the scale-leaves
remain short, and the walls of their epidermal cells thicken in a remarkable
way; the petioles of the aérial foliage-leaves become about a span long, and, in
order to increase their resistance to bending, a strong layer of bast arises, the
thickness of these bast-layers amounting to 0.17 mm. The walls of the epidermal
cells are thickened, 5-9 layers of collenchymatous cells are formed under the
epidermis with walls ‘007 mm. thick, and the air-spaces in the centre of the leaf-
stalk are much narrowed. But if this species of Water-lily grows under water,
the scale-leaves elongate into long and flaccid ribbons, and the petioles of the
foliage-leaves continue to grow until their blades are raised to the surface of the
water. According to its depth they attain a length of 30, 40, 50-100 cm.
Resistance to bending is but little required by the petioles, which are surrounded
by water, and the bast is therefore only slightly developed. The strings of
bast which traverse the leaf-stalk are only 0:11 mm. thick, the walls of the
epidermal cells are only half as thick as in the aérial leaves, only 3-5 layers of
collenchyma are developed below the epidermis and the air-spaces in the centre
of the leaf-stalk have a diameter of over half a millimetre. These petioles are
consequently flexible, and cannot support the leaf-blade if taken out of the water.
The general form of the scale- and foliage-leaves, the segmentation of the latter
into petiole and blade, the configuration of the blade and the distribution of
the bundles in it are all the result of internal forces due to the specific constitution
of the protoplasm; but the thickness of the epidermal cells, the strength of the
mechanical tissue, and the length of the leaf-stalk, are determined by the depth
of the water-covering. The same thing is seen in the flowers; their structure
depends upon the specific constitution of the protoplasm, but the size of the
petals is determined by the temperature of the water.

The Meadow-grass Poa annua has a rapid growth; its haulms and leaf-sheaths
are round, the leaf-lamina is traversed by seven strands, the lower branches of the
inflorescence are single or paired but never whorled, and the spikelets of the
panicle are much compressed and egg-shaped in outline. These characters are
unalterable and are observed in Poa annua under all conditions. But when the
haulms growing in the gardens in the plain project beyond the short upmost leaf
the spikelets become 6-7-flowered, and have a pale green colour. When the plants
become perennial in alpine regions the haulms bend towards the ground and remain
so short that they do not reach above the highest foliage-leaf; the spikelets
develop only 3-4 flowers, and their glumes are dark violet on the surface and
brownish-yellow at the edge; thus these modifications are in relation to peculiarities
of situation (in the plain and alpine regions) as effect to cause, and are to be
ascribed to the influences of heat, light, and moisture, which act in various ways
according to the situation.

These alterations are always to the advantage of the plant. They make the

ARE THESE CHANGES IN FORM PERMANENT? 513

individual more resistant, support and proteet its organs, and render it possible
for the separate parts to perform their work in spite of the necessarily altered
conditions. They seem to have the task of keeping the plant alive under very
different vital conditions, of promoting growth and the formation of offshoots
and fruit with the smallest possible expenditure, and they may therefore be
regarded as adaptations to the particular conditions of soil and climate.

The capacity for adaptation is of course founded in the specifie constitution of
the protoplasm, and is very different in different species. One species may adapt
itself by appropriate alterations to the influence of bright light, submersion under
water, a dry atmosphere, &e., while another cannot do so. If the protoplasm of the
Flax (Linum usitatissimum) could manufacture as much anthocyanin in its green
tissue as the Summer Savory (Satureja hortensis) it would blossom and ripen its
fruits in alpine regions as this plant does, and would not suecumb to the effect of
the strong light. If the protoplasm of the Common Bent-grass (Agrostis vulgaris)
were able to continue its constructive activity under water it would not perish as
soon as it is submerged, but would maintain itself like the stoloniferous species
(Agrostis stolonifera) by green stalks and leaves adapted to an aquatic habitat.
In short, the adaptability of each species is restricted within definite limits which
depend upon the specific constitution of the protoplasm and cannot be overstepped.

It is a matter of great import in the history of species whether modifications
in form effected by change of soil and climate are transmitted to the descendants,
and whether they can be inherited. This of course can only be ascertained by
experiments, and by experiments in which all possible sources of error have been
eliminated. This last remark is made advisedly, for: the sources of error in such
experiments are very numerous. I will briefly indicate two which interfered with
some experiments I carried out in the years 1863 and 1864. It is not enough to
be careful that the seeds sown in the prepared experimental beds are all from the
same plant; care must also be taken to see that they are not the result of a hybrid
eross-fertilization. Some seeds taken in 1863 from a plant of Dianthus alpinus
growing in the Botanic Garden at Innsbruck, and sown in different soil in two
experimental beds, produced plants in soil free from lime, which, in their external
appearance, agreed with Dianthus deltoides. It seemed as if Dianthus alpinus, a
lover of limestone rock, had become transformed into Dianthus deltoides when
grown without lime. The seeds of the plant so like Dianthus deltoides were again
sown in soil without lime, but the resulting plants no longer resembled this species;
they showed themselves to be constant in their characteristics. The whole
experiment with Dianthus alpinus was then repeated, but this time the plants
on the clay soil without lime did not change, and I was obliged to conclude that
the plant I had regarded as a stage in the transformation of Dianthus alpinus
into Dianthus deltoides was a hybrid of these two species. In order to be certain
about this a crossing between the two species was effected artificially. From the
resulting seed plants were actually grown which were exactly like those I had

regarded as transformations, and there was no longer any doubt that some of the
VoL. II. 83

514 THE INFLUENCE OF MUTILATION ON THE FORM OF PLANTS.

stigmas of the Dianthus alpinus which had yielded the seeds for the first experi-
ment had been pollinated by insects with the pollen of Dianthus deltoides.

Mistakes often arise also from the fact that the young stages of many plants
are very different from the fully-grown specimens. Young Birches grown from the
seeds of Betula verrucosa bear leaves which are simply serrated, thickly covered
with hairs, and soft to the touch. They are deceptively like the leaves of adult
plants of Betula alba or pubescens. The leaves of the adult Betula verrucosa have
quite a different form; they are doubly serrated, smooth, and harsh to the touch.
These latter are the only form of leaf described in Botanical books for Betula
verrucosa. Anyone sowing the seeds from a grown tree, and watching them grow
up, with leaves of a different shape and surface, might easily think an actual
fundamental change had occurred, and might be tempted to regard the transforma-
tion as the direct effect of a change in external influences.

It is perhaps superfluous to state that due regard was paid to these possible
sources of error in the later series of cultural experiments, carried out during six
years in the Alpine garden on the Blaser (2195 metres), and for comparison in my
Villa Marilaun in the high-lying Tyrolese Gschnitzthal (1215 metres), in the
Botanic Garden at Innsbruck (569 metres), and in the Botanic Garden of the Vienna
University (180 metres); in no instance was any permanent or hereditary modifi-
cation in form or colour observed.

Seeds of a plant grown in the valley when sown in the Alpine region produced
plants which exhibited the modifications described above. They were also mani-
fested by the descendants of these plants but only as long as they grew im the same
place as their parents. As soon as the seeds formed in the Alpine region were
again sown in the beds of the Innsbruck or Vienna Botanic Gardens the plants
raised from them immediately resumed the form and colour usual to that position.
The modifications of form and colour produced by change of soil and climate are
therefore not retained in the descendants; the characteristics which appear as the
expression of these changes are not permanent, and the individuals are to be there-
fore regarded as varieties, of which Linnzus says in his Philosophia Botanica:
“ Varietates tot sunt, quot differentes plante ex ejusdem speciei semine sunt pro-
ducts. Varietas est Planta mutata a caussa accidentali: Climate, Solo, Calore,
Ventis, &c., reducitur itaque in Solo mutato.”

THE INFLUENCE OF MUTILATION ON THE FORM OF PLANTS.

When Birches and Firs grow up side by side in a wood-clearing, the crowns
of the Birches will overtop the Firs in some twenty years’ time, and this will
seriously interfere with the growth of the latter. With every blast of wind the
whip-like branches of the Birch strike against the upper shoots of the Firs, so
that these gradually wither and die off. A lateral branch of a Fir tree altering
its direction of growth and replacing the dead leader will, in its turn, soon be
scourged to death. The top of the Fir is permanently mutilated, and the injury

THE INFLUENCE OF MUTILATION ON THE FORM OF PLANTS. old

can be recognized years after by the flattened form of the erown, so different
from the usual appearance, when the offending Birches have perhaps long dis-
appeared. Many other trees wage the same war with one another, the result
in each case being the mutilation and alteration of the form of the summit of
one of the trees. The Maple, for example, is either put quite hors de combat by
the long thorny branches of a neighbouring Gleditschia (Gleditschia triacamthos)
or else the crown becomes lop-sided owing to the destruction of the branches
on the side facing the Gleditschia.

The way in which the appearance of Firs, Larches, Beeches, and Ling is
altered by the attacks of ruminants, especially goats, was described in vol. i.
p- 445, and we may add here that Pines and Junipers are mutilated in the same
manner. The consequence is that lateral branches, which would not otherwise
develop, grow out in the following year from the base of the twigs which have
been bitten off Apparently no other alteration takes place in these plants.
But when huge boughs are broken off close to the ground by storms and the weight
of snow, when the tree-trunks of the forest are sacrificed to the wood-cutter’s
hatchet, and the stems of seedling trees and shrubs in the meadow to the mower’s
scythe, when all the young shoots are frozen by a night’s frost in spring, or when
all the leaves are devoured by caterpillars and the branches are left bare as in
winter—then the consequences are much more serious. In these cases new shoots
make their appearance either from “eyes” in the stem or from the reserve-buds
of the branches and twigs, or by buds produced by the roots below the ground.
The leaves of these shoots, or suckers, as they are called, differ very much from
those of the branches which have been broken, eaten, cut, or frozen off. The
leaves from the crown of the Aspen (Populus tremula) are stiff and smooth in
their adult condition; the circular blade is borne on a long petiole, and its margin
is coarsely notched and undulated. The lateral veins traversing the blade are
lost in a network near the edge in which no strong curved ribs occur. The leaves
of a sucker from the base of a mutilated stem, or from the root, are soft and
thickly covered on both sides with downy hairs; the heart-shaped blade is borne
on a short stalk, and the margin is beset with numerous upwardly-directed notched
teeth. The lateral veins of the blade merge near the edge of the leaf into a
network, in which strong curved ribs are plainly visible. The leaves from the
crown of the Oak (Quercus pedunculata) are deeply lobed and furnished with
two so-called auricles at the base; those of the suckers are quite entire or very
slightly lobed, with no auricles at the base. The leaves of the sucker of the
common Beech (Fagus sylvatica) are more or less plainly serrated at the edge,
while those of the topmost branches of the tree are quite entire. In the Black
Mulberry (Morus nigra), and in the Paper Mulberry (Broussonetia papyrifera),
the leaves of the sucker have a sinuous margin and are more or less deeply lobed,
but those of the tree-top are heart-shaped with notched margins and no lobes.
The leaves of the sucker of the Birch (Betula verrucosa) are simply serrated,
with velvety hairs; those on the crown of the tree are doubly serrated and

516 THE INFLUENCE OF MUTILATION ON THE FORM OF PLANTS.

smooth. The leaves on the suckers of the Round-eared Willow (Salix awrita)
are broadly ovate, fairly smooth, and the veins in the blade form a wide-meshed
reticulum; the leaves on non-mutilated branches are widened in the upper third,
strongly wrinkled, and covered with grey hairs, whilst the reticulum of the veins
is narrow-meshed. In Saliw rosmarinifolia, the leaves of the suckers are twice
or three times as broad as those of the normal branches, and they are smooth,
while those of ordinary branches are covered with silky hairs, and gleam like
silver. Hundreds of trees and shrubs might be mentioned in which there is a
distinct difference between the foliage of the suckers and of the normal branches
of the crown. But these few examples will suffice, and we will only mention
the Norway Maple (Acer platanoides), because the difference in the foliage-leaves
can be seen from the illustrations in vol. i. The leaves of the summit (see vol. i.
fig. 106, p. 416, and fig. 109, p. 419) are borne on long petioles, the blade is 5-7
lobed, and the lobes are short and beset with several pointed, tapering teeth.
The leaves of the suckers in this same Norway Maple are short-stalked, the blade
is slightly 3-lobed, and each lobe is triangular and without the elongated pointed
teeth. They exactly resemble the first foliage-leaves shown in vol. i. p. 9, fig. 1°.
This is also true of the leaves on the suckers of other woody plants. The shoots
developed from reserve buds, “eyes”, and the like, repeat to a certain extent the
beginning of the leafy stem, so that the phenomenon is only an exhibition of the
usual metamorphosis of the foliage-leaves. The difference between the older and
younger, 7.¢. lower and upper foliage-leaves, only seems strange because the two
kinds of leaf-forms are not usually seen simultaneously on one and the same
plant. By the time the crown of a tree has developed, the first (oldest) leaves
which adorned the young sapling have long disappeared. Many descriptive
Botanists, as a rule, only consider the foliage-leaves of the fully-grown trees
and bushes; some of them have hardly ever seen the first leaves of the commonest
trees, and when they do happen to come across them they regard them as an
extraordinary phenomenon, declare the shoots bearing them to be “bud variations ”,
and draw bold and bewildering hypotheses from their appearance. This alteration
in form, however, has nothing to do with the formation of varieties, nor is it
dependent either upon the influence of the soil or upon the effect of climate.
Moreover, the form of leaf characteristic of the sucker is not possessed by the
secondary shoots which arise from the suckers; these are adorned with the same
foliage which occurs on the topmost branches of the tree.

Alterations in the seale-leaves as well as in the foliage are brought about by
mutilation of the branches. When the upper portions of Willow boughs with
their foliage-buds are cut off, leaving the lower portions with the buds of the
flower-catkins on them, the small pale scales at the base of the catkins change
into green foliage-leaves; the axis bearing these leaves elongates, and the catkins
then form the termination of a leafy shoot. Many Willows, e.g. Salia cinerea
and S. grandifolia, by this metamorphosis assume a very unusual appearance.
In the following year the branches bearing the flower-catkins, if they are

THE INFLUENCE OF MUTILATION ON THE FORM OF PLANTS. nly

not mutilated afresh, will again put out short catkin-stalks with small pale
scales.

Mutilation of herbaceous plants is caused by herbivorous animals, viz. insects
and mammals, and on a large scale by man when he mows the meadows and
euts the crops and makes other necessary invasions on the natural vegetation in
the interests of husbandry. The alterations caused by these inutilations of the
foliage-leaf region are in the main the same as in woody plants. From the
remaining stumps of the stem lateral shoots arise whose first leaves are like the
first leaves of the seedling. Usually they are less divided and have fewer hairs
than the leaves on shoots of normal plants, and on this account they have a very
different character. In the floral region the effects of mutilation are twofold—
first the peduncles or the lateral axes which are terminated by inflorescences
elongate, and then the flowers become smaller. For example, when a vigorous
stalk of the Ox-eye Daisy (Chrysanthemum Leucanthemum) bearing a capitulum
is cut off close to the ground, long lank lateral stems develop from the axils of the
lowest remaining leaves, each one ending in a capitulum. The main stem is now
seen to be branched at its base, which is never the case in normal plants. If about
half the stalk of the common Foxglove is cut off in the spring long flower-racemes
will arise from the axils of the leaves just below the cut, but the flowers will be
only half as large as those which would have developed on the uncut main stem.
The stem of Althea pallida rises a metre above the ground if its development is
not hindered, and forms fascicles of short-stalked flowers in the axils of the upper
leaves. If the stem is broken off lateral axes develop from the axils of the
remaining leaves, and bear little long-stalked flowers. Particularly good examples
are furnished by the annual weeds Delphinium Ajacis, Nigella arvensis, Stellera
Passerina, and the like, which grow up amongst cereals. Their main stems are
broken off when the corn is cut, and they then develop comparatively long
branches with small flowers from the remaining stumps. If only single flower-
buds, and not the whole inflorescences, are removed from a herbaceous plant whose
main stem terminates in a long raceme, so that each flower is cut away in turn
from below upwards just before it opens, the rachis of the raceme elongates
enormously and flower-buds are developed at its end which would certainly not
have unfolded had there been no mutilation. In the Red Foxglove, for example,
the rachis of the raceme which has been damaged in this way will grow to twice
its ordinary length, and twice as many flowers will be developed. The last and
highest flowers in such racemes, however, are only half the size of those which
arise on normal racemes.

We must now consider certain perennial meadow plants which when mown
down are stimulated by the mutilation to develop flower-stalks in the same year,
which would, in the normal course of things, not have flowered till the year follow-
ing. In Alpine valleys it is a very common thing for the flowers of the spring
plants Anemone vernalis, Geranium sylvaticwm, Gentiana verna, Polygonum
Bistorta, Primula elatior and P. farinosa, Trollius Ewropeus, &e., to appear in

518 ALTERATION OF FORM BY PARASITIC FUNGI.

the autumn in meadows which have been mown in the spring. The flowers appear-
ing under these eircumstances are remarkable for their small size. Their diameter
is at least a third smaller than that of the spring flowers. In conclusion we may
refer to the gardener’s artifice which has already been described (p. 453) of pro-
ducing perennial plants with wocdy stems from an annual Mignonette plant by
mutilation. We might also mention the dwarf shrubs and trees produced by
combined mutilation and grafting, especially the strange-looking little Ivy trees
obtained by grafting a flowering branch of Ivy on an erect stem a span high, and
the dwarf Conifers so much in favour with the Japanese.

Gardeners and deseriptive Botanists have frequently determined and described
mutilated plants as other species, hybrids, or varieties. They are neither the one
nor the other. The peculiar appearance of the altered members resulting from
mutilation is exactly determined beforehand in each species; it is due to the specific
constitution of the species, and thus is part of its being. It is not produced by the
external influences which lead to the formation of varieties, but is brought about
by inherent necessity quite independent of the influences of climate and soil.

ALTERATION OF FORM BY PARASITIC FUNGI.

A considerable number of the trees and shrubs of Central and Southern Europe
bear bristling, much-branched structures on some of their boughs which, from a
distance, look like large birds’ nests or brooms, and which have been popularly
termed “witches’ brooms”. They are the outward and visible signs of a disease
from which the plants in question suffer, and, as their name testifies, their origin
was thought to be connected with witches. Traditionally witches have the power
of “wishing” harm to mankind, animals, and plants; and superstitious people, at
the sight of these peculiar pathological structures on the trees, may have started
the idea that the disease was caused by witches that they might have brooms
ready at hand for their midnight ride on the Brocken. Other plant diseases have
been ascribed to unusual conditions of weather, especially to long-continued rain
or great drought. It is not long since the discovery was made that most of the
diseases attacking trees, shrubs, and herbs are caused by Fungi, and that atmos-
pherie conditions are only concerned in the matter in so far as they hinder or
favour the establishment and development of these parasites.

All the Fungi in question are parasites. They penetrate into the tissues of the
host-plant and sooner or later cause the death of the affected part, and frequently
of the entire host-plant. The living protoplasm in the cells and tissues of the host
which is influenced by the parasite undergoes fundamental changes in its com-
position. Some of the cells are drained, their living protoplasm being consumed,
so to speak, and these cells are obviously marked for destruction. Others are not
killed, but changed. The metamorphosis occurs, in the first place, in the consti-
tution of the living protoplasts which have not yet completed their development,
the change much resembling that known as fermentation in fluid substances

TYPES OF FUNGAL GALLS. 519

(ef. vol. i. p. 508). In fermentation the chemical eomposition of the fluid is
altered, its chemical compounds are shaken, decomposed, and split up and new
compounds are formed by the action of the living Yeast cells. The same thing
happens here in the interior of the living plant in its turgid, meristematic tissue—
that is to say, in a group of protoplasts which still have the power of growing
at the expense of materials supplied them, of increasing in size, and of multiplying
by division. But these cells no longer behave as—in the absence of the parasite—
they would have done. Profoundly modified under the influence of the parasite,
but yet not killed, these cells, by their continued division, form tissues and organs
of new and unusual form; in other words, that part of the host which is invaded
but not killed by the parasite will continue to grow and increase in size, and in
consequence of the change which its protoplasm has experienced will assume a
ditferent outward form.

These altered tissue-bodies produced by parasitic Fungi are called gall-structures.
They are usually characterized by an excessive growth known as hypertrophy, as
well as by their altered shape. The hypertrophy is without doubt caused by a
stimulus proceeding from the parasite. We may conclude that the significance
of the increased growth lies in the abundant supply of nourishment thus placed
at the disposal of the parasite, since the large quantity of food-material brought
for the excessive development of the hypertrophied growth connotes a large supply
for consumption by the parasite. In many cases, however, the hypertrophied tissue
merely forms a wall protecting the host against the further depredations of the
intruder. It then contains no nourishment for the use of the parasite, being built
up chiefly of corky cells, which the latter cannot consume or destroy. Such a tissue
might be compared to the so-called callus which grows up in plants in parts de-
prived of epidermis after an injury, or in other wounds, and gradually covers them
over with a protective layer.

The formation of the gall is often restricted to only a small portion of the
afflicted plant; in other cases whole leaves and branches, and sometimes even ex-
tensive shoots, become modified in shape. To get a general idea of the four types
of hypertrophied growths it will be best to take them one after the other in the
order mentioned, commencing with the simplest.

The simplest of these galls consist of a few degenerate and metamorphosed cells
in the centre of an extensive and unaltered tissue. They are produced chiefly by
parasites of the genera Rozella, Synchytriwm, Exobasidiwm, and Gymnosporan-
gium. Rozella septigena, one of the Chytridiee, develops swarm-spores which
attack the various species of the fungal genus Saprolegnia. They settle on the
tubular branches of the Saprolegnia at a place where it was just about to divide
and to produce swarm-spores of its own. In consequence of the invasion of the
parasite this does not take place, but the tubular cells which would have formed a
Saprolegnia-sporangium divide instead into short barrel-shaped cells, each of which
becomes a sporangium of Rozella septigena. In addition to this the infected cells
develop lateral outpushings which swell up spherically, and each contains a resting-

520 ALTERATION OF FORM BY PARASITIC FUNGI.

spore of the parasite. Parasitic species of Synchytriwm cause a vesicular enlarge-
ment of single cells of the epidermis in the leaves of phanerogamie host-plants.
The not uncommon species Synchytriwm Anemones and 8. Taraxaci produce only
a slight overarching, and the enlargement of the cells is hardly more than four
times, often only twice the usual size. But, by the influence of Synchytrium
Myosotidis, hypertrophied epidermal cells rise up from the leaves of the Forget-
me-not (Myosotis) in the form of comparatively large, club-shaped, bottle-like, or
egg-shaped bladders of golden or reddish yellow colour, and each contains the
parasite, or rather its spores. The parts of the leaf attacked by Synchytrium
Myosotidis are also much thickened, the palisade cells and the air-containing
lacunze of the spongy parenchyma (cf. vol. i. p. 279) disappear, and the tissue
consists entirely of large similarly-shaped cells which fit close to one another,
leaving no spaces between. Im the gall caused by Synchytriwm pilificum on
Potentilla Tormentilla the much-enlarged cells in which the parasite settles are
overgrown by the adjoining hypertrophied cells, some of which rise up in the form
of hairs, and the whole new structure resembles a hairy wart.

A curious gall is produced by Hxobasidiwm Rhododendri on a sharply-defined
portion of the folvage-leaves of the Alpine Rose (Rhododendron hirsutum and
ferrugineum). A spherical spongy body rises from a restricted portion of the
leaf, usually from the under side of the somewhat projecting midrib, sometimes
only as large as a pea, sometimes as big as a cherry, and occasionally even attaining
the dimensions of a small apple. It is yellow, but rosy-cheeked like an apple on
the side turned to the sunlight, and it reminds one of this fruit by its succulent
tissue and sweet taste. Indeed, these galls are sometimes called “Alpine Rose-
apples”. Their surface is covered with a bloom which is caused by the numerous
spores developed there and does not consist of wax like the bloom on an apple
rind. The neck joining the gall to the leaf is not more than 1-2 mm. across, and,
what is still more remarkable, except for this sharply-defined place of connection
the infected leaf is unaltered.

Galls produced by the Gymnosporangia on the leaves of the Mountain Ash,
Pear-tree, Rock-medlar, and other Pomez exhibit strange forms. One of them,
caused by Gymnosporangium conicum, on the foliage of the Rock-medlar (Aronia
rotundifolia), is represented in fig. 357°. It resembles a tubercle furnished with
horns projecting from the lower surface of the leaf. Microscopie examination
shows that the knob consists of the strangely metamorphosed spongy parenchyma
of the leaf. The intercellular spaces which normally contain air are quite filled
with the mycelial threads, and in the projecting portion of the tubercle, which
is very hard and almost cartilaginous, tubes are inserted which terminate blindly
below, where the spores of the parasite are developed, whilst above they are open
and fringed, thus allowing the spores to escape. These tubes look like horns to
the naked eye. Usually several galls occur together on the same leaf. They are
conspicuous at some distance on account of their colour. The chlorophyll is
destroyed wherever the mycelium of the parasite extends and a reddish-yellow

FUNGUS-GALLS ON STEMS. 521

colour takes its place, so that orange spots appear on the surface of the foliage,
contrasting vividly with the green of the unaltered portions of the leaf.

Galls rising from sharply defined parts of the stem are comparatively rare.
One of the most remarkable is produced on the stems of a Laurel (Lawrus
Canariensis) by the parasitie Exobasidium Lauri. When it appears above the
bark it looks like an aérial root, but rapidly grows into a branched spongy body
8-12 em. long similar in appearance to one of the Fungi belonging to the family
Clavariew (ef. fig. 195!, p. 21). The galls produced by Entyloma Aschersonii and
Magnusii on the Composites Helichrysum arenarium and Gnaphalium luteo-album

Fig. 357.—Fungus-galls,

1 Gall on the stem of the Juniper (Juniperus communis) produced by Gymnosporangium clavarieforme. % Gall on the leaves
of Aronia rotundifolia produced by Gymnosporangium conicum.

take the form of outgrowths, varying from the size of a pea to that of a walnut,
developed from special spots on the root. Whether the spherical tubercles growing
on the root-fibres of many Leguminose, especially those of the Bird’s-foot Trefoil
(Lotus corniculatus), the Fenugreek (Trigonella fenum-grecum), Lady’s-Fingers
(Anthyllis Vulneraria), Lupin (Lupinus variabilis), and the Liquorice (Glycyrrhiza
glabra) are to be regarded as true galls caused by the Bacteria-like organisms
invariably to be found in their interior is questionable. According to the most
recent investigations they are the outward expression of a case of symbiosis and
not of pure parasitism.

Gall developments which involve whole roots or rootlets are found on the Alder
(Alnus glutinosa), and on the Cabbage (Brassica oleracea). The gall which is
produced on Alder roots by Frankia Alvi attains the size of a walnut and has a

522 ALTERATION OF FORM BY PARASITIC FUNGI.

curious gnarled appearance; all the fibres of the root-branch thicken in a elub-like
or tuberous manner and become twisted and entangled with one another. The so-
called “ Fingers and Toes”, caused by the Myxomycete (Plasmodiophora Brassica),
is a gall-like hypertrophy on the root of Brassica oleracea, which not uncommonly
grows to the size of a man’s head.

Many woody plants have galls which alter the internal structure as well as the
outward appearance of large tracts of the stem. The parasites settle in the corti-
cal parenchyma, producing hypertrophy there, and afterwards the most varied
distortions and alterations in the wood of that region of the stem. The trunk,
branch, or twig becomes much swollen or knotted and the cortex rent and torn.
Resin or a gummy mucilage sometimes runs out of the rifts in the gall. As such a
parasite exercises its metamorphosing faculty for several years, the canker (as it
may be termed) increases in size continually. Sporangia of varied form and colour
appear annually on the affected places, and again disappear when they have shed
their spores. The part of the stem or branch above the cankerous cushion dwindles
and dies off sooner or later. It rarely happens that the tree or shrub is able to rid
itself of the parasite. Occasionally a growth of wood and cork from the adjoining
healthy part walls in the cankerous spot so that the parasite is destroyed. The
gall produced by Gymnosporangiwm clavarieforme on the trunks and branches
of the common Juniper (Juniperus communis) is an example of this form (see
fig. 3571). From the hypertrophy there project in the early spring golden-
yellow tongues (shown in the figure) consisting of masses of spores embedded in
mucilage. Other similar growths are produced on species of Juniper by Gymno-
sporangium conicum, G. Sabine, and G. tremelloides, but it would take too
long to describe their differences in detail. It is important to mention, however,
that each of these parasites has two stages of development, living on different
hosts, the hypertrophies as well as the associated spore-producing organs of the
parasite being different in the two cases. The “ Acidium stage” produces carti-
laginous swellings (see p. 520) in definite spots on the foliage of various Pome
(Aronia, Crategus, Pyrus, Sorbus), the “ Teleutospore stage” thickenings and
tuberous outgrowths on the trunks of Junipers (Juniperus communis, excelsa,
Sabina), and these parasites can travel from one host to the other in turn. (The
two stages on different hosts are shown in fig. 357; these are not of the same fungus,
but of nearly allied ones, and illustrate the point mentioned.)

The parasite Peziza Willkommii attacks the trunks and branches of the Larch
(Laria Europea), and produces the well-known Larch-disease or “ Larch-canker”.
The parasite having gained access at some point on the stem or branch first pene-
trates the cortical parenchyma, and affects the cambium so as to prevent the
further development of wood in that place. The development of the wood on the
opposite side of the stem, i.e. the formation of annual rings, may proceed for
several years, and in this way the attacked spot on the trunk takes the form of a
depression, which is rendered the more conspicuous should the wood and cortex
surrounding the parasite have undergone a greater thickening than usual. In

ENTIRE LEAVES AFFECTED BY FUNGI. 523

time the patch becomes a sunken, blistered hole from which resin flows; and every
year the fructifications appear above the cortex in the form of numerous little
eup-like structures which are white outside and scarlet-red in the concavity. As
the disease progresses the infected patch gradually spreads, and infected trunks and
branches can be easily distinguished at a distance. Towards the end of summer
the needles on the twigs above the canker turn yellow, while those on the healthy
branches are still a beautiful green. This premature discoloration is a sure sign
of the speedy death of the whole bough. A similar canker is produced on the

Fig. 358.—Various Galls.

1 Gall on the bract-scales of the pistillate flowers of the Gray Alder (Alnus incana) produced by Exoascus Alni-incane.
2 Inflorescence of Valerianella carinata. 3 The same inflorescence with galls produced by a gall-mite. 4 Leaf rosette of
the House-leek (Sempervivum hirtum). 5 Leaf rosette of the same plant which has been attacked by the fungus Endo-
phyllum Sempervivi and has become hypertrophied.

Silver Fir (Abies pectinata) by Beidium elatinum, but instead of being only on
one side of the branch, as in the Larch, it forms a uniform swelling all round it.
Cankers of this kind are produced by a Bacterial organism (Bacillus amylovorus)
on fruit-trees (Apple, Pear, &e.), and on various trees belonging to the Amentifere
(Beeches, Hornbeams, Oaks, &e.) by the Fungus Nectria ditissima.

When whole leaves undergo hypertrophy of the kind we have particularly
remarkable changes of form. For example, the normal leaves forming the rosettes
of the House-leek (Sempervivum hirtum; see fig. 358*) are broadly obovate in
form, being little more than twice as long as they are broad. The leaves of the
same plant after they have been attacked by the parasitie Endophyllum Semper-

524 ALTERATION OF FORM BY PARASITIC FUNGI.

vivi (see fig. 358°) are seven times as long as broad and linear in shape. They
stand ereet, and are of a much paler colour than the healthy leaves. The Wood
Anemone (Anemone nemorosa) affords another example (see fig. 259, p. 229). It
spreads by creeping stems under the surface of the ground, and forms small
colonies in light thickets and in meadows. The plants consist partly of flowering
lateral shoots, and partly of foliage-leaves, which emerge above the ground from
the creeping underground stem. In normal leaves the erect petioles are all the
same length, and the leaflets are extended at about the same level. But when the
Heidium stage of Puccinia fusca has settled on them this becomes altered. The
blades of the infected leaves tower over their healthy neighbours in consequence of
the elongation of their petioles, whilst their leaflets are smaller and less divided.
The length of the petiole in normal leaves is some 12-13 em., in hypertrophied
leaves 15-18 em.; but the size of the altered segments, compared with those of
normal leaves, is as 5:7. Similar changes are observed in leaves of Soldanella
alpina when attacked by Puccinia Soldanelle. The petioles of the infected
leaves are 2-4 times as long as the normal ones, the blade is smaller and
hollowed like a spoon instead of being flat, and the colour is an ochreous yellow
instead of a dark green. The same alterations in the length of the petiole,
and in the size and colouring of the leaf-lamina, are produced in the leaves of
Alchemilla vulgaris by Uromyces Alchemille and in those of Phytewma orbi-
culare by Uromyces Phytewmatum. ‘To this class belongs also the so-called
“curl” disease of Peach and Almond trees, produced by Haxoascus deformans, and
rendered conspicuous by the considerable enlargement, undulation, and bladder-
like expansion of the infected leaf-surface, which acquires generally a very brilliant
coloration.

Floral-leaves are comparatively seldom metamorphosed by Fungal parasites.
In the Alder (Alnus glutinosa and incana) the bracts of the pistillate flowers are
changed by Exoascus Almi-incane (=E. amentorum) into elongated purple-red
spatulate lobes much twisted and bent (see fig. 3581); Peronospora violacea some-
times causes the stamens to change into petal-like structures in the flowers of Knautia
arvensis, so that they then seem to be “double”; Ustilago Maydis causes a growth
of tissue in the pistillate flowers of the Maize, the result being that instead of grains
irregular cushion-like structures 7 cm. in diameter are produced. Taphrina awrea,
which settles on the pistillate flowers of Poplar (Populus alba and tremula) causes
the ovaries to form golden-yellow capsules more than twice the usual size. The
galls produced by Exoascus Pruni on the ovaries of wild Plum, Bullace, Sloe, and
Bird Cherry (Prunus domestica, insititia, spinosa, Padus) belong also to this class.
The tissue of the ovary increases in size, but not in the same way as in fruit forma-
tion. The resulting body is flattened on two sides, brittle and yellow; the seed
inside is abortive, and a hollow space is left in its stead. The gall produced from
the ovary of Prunus domestica has the form of a rather curved pocket, which
looks as if it had been powdered outside with flour at the time the spores ripen.
These hypertrophies, which are popularly termed “pocket-plums”, “ bladder-plums”,

ENTIRE SHOOTS AFFECTED BY FUNGI, 525

&e., fall off the trees at the end of May. They are eaten in many districts, but
have an insipid, sweetish taste.

Galls consisting of whole shoots, both the stem and its leaves being altered by the
parasite, are found principally on trees and shrubs, and only rarely on herbaceous
plants. Examples of the latter, however, are furnished by the metamorphosed
shoots of the Shepherd’s Purse (Capsella Bursa-pastoris) produced by Cystopus
candidus and Peronospora parasitica. Here the leaves, especially the floral-leaves,
as well as the ground-tissue of the stem undergo pronounced hypertrophy. The
petals, which measure only 2 mm. in length in a healthy plant, may become even
15 mm. long; the sepals also elongate, become fleshy and brittle, and are distorted
and crumpled in all manner of ways. Only six stamens are developed in normal
flowers, but in hypertrophied specimens there are often eight. The metamorphosis
produced by Uromyces Pisi in one of the Spurges, Huphorbia Cyparissias, is even
more remarkable. The stem elongates far beyond its usual dimensions, and the
leaves, which are crowded together on normal shoots, are thus separated by con-
siderable intervals. The distance between two adjoining successive leaves in the
healthy Zuphorbia Cyparissias is only 0°5 mm., but in the hypertrophied specimens
it becomes 2-3 mm. Infected shoots on an average are twice as high as healthy
ones. The foliage-leaves, which are thin, flexible, linear, and twelve times as long
as they are broad in the healthy plant, become, in the infected specimens, thick,
brittle, elliptical, and only 2-3 times as long as they are broad. The bluish-green
colour of the normal plant is changed into a yellow-ochre tint, and this contributes
not a little to the odd appearance of the plant. Affected plants are not uncommon
in Switzerland; a locality in which this disease has been very prevalent in recent
years being Saas-Fée in the Saas-thal. The metamorphoses produced on the shoots
of Periwinkles (Vinca herbacea, major, and minor) by the Uredospore-stage of
Puceinia Vince and on shoots of Cirsiwm arvense by the Teleutospore-stage of
Puccinia suaveolens are very like those of the Luphorbia just mentioned, since
the stem becomes much elongated and the leaves shorter, broader, yellow, and brittle.
When flowers are developed on these affected shoots, they are more or less abortive
and sickly, and no fruits or fertile seeds arise therefrom. Frequently the shoots
blossom prematurely. For example, we can at once detect by its elongated rosette-
leaves when Primula Clusiana and minima are infected by Uromyces Primule
integrifolie, and it may be observed when this is the case that the shoots do not
wait until the next spring to develop the flowers laid down in the summer, as usual,
but open them in the autumn of the same year instead.

The Cowberry (Vaccinium Vitis-Idea) is especially worthy of notice among
low woody plants, because two kinds of parasite attack its shoots. Melampsora
Geppertiana, in the Teleutospore-stage, causes a marked, gouty thickening in the
cortical parenchyma, which is converted into a spongy tissue; at first it is flesh-
coloured, but soon assumes a chestnut-brown tint. The stems elongate very much
and grow vertically upwards; and when several of them close together are thus
attacked they present a besom-like appearance. The foliage-leaves are much

526 ALTERATION OF FORM BY PARASITIC FUNGI.

farther apart than in the healthy plant on account of this stretehing of the stem.
The lower leaves of the shoot are transformed into small fringed scales, and the
upper ones are so much shortened that their outline becomes almost circular. The
second parasite to which the Cowberry shoot is subject is Lxobasidiwm Vaceimii (a
near ally of the already mentioned Exobasidiwm Lauri, p. 521). The stem becomes
pale rose-red colour, and rather thickened and spongy, but it does not elongate
much more than usual; the leaves become blistered and curiously convex on the

Fig. 359.—A Witches’ Broom on the Silver Fir, produced by dcidium elatinum.

under surface. The substance of the infected leaves becomes brittle and loses its
chlorophyll. A red tint appears in place of the green, especially on the upper
surface of the leaf, whilst the lower surface, on which the spores develop, looks as if
it had been dusted over with flour. Usually the buds develop prematurely on these
shoots, %.e. the buds which, under ordinary circumstances, would not develop until
the next year push out and form new shoots shortly after they have been laid down.
The axes of these shoots, however, remain short; their leaves are closely crowded,
red in colour, and sessile. From a distance the premature shoots look like large
double red flowers inserted in the dark green of the non-infected Cowberry bush.
The shoots which develop prematurely on the shrubs of the Bog Whortleberry
(Vaccinium uliginosum) by the action of Exobasidium Vaceinii are often met
with in alpine regions, and are even more noticeable on account of their fiery-red

ALTERATION OF FORM BY GALL-PRODUCING INSECTS. 527

colour. The Bearberry (Arctostaphylos Uva-wrsi), Ledwm palustre, and the Marsh
Andromeda (Andromeda polifolia) are subject to similar metamorphoses at the
hands of Exobasidium Vaccinii, so that Vaceiniwm Vitis-Idea may be regarded
as typical of them.

When the shoots of the larger shrubs or trees are metamorphosed by parasitic
Fungi attacking their branches, we have the formation of the structures popularly
termed Witches’ brooms, which were mentioned at the beginning of this chapter.
The stimulus necessary for their formation is afforded in different plants by
different parasites; on Barberry bushes (Berberis vulgaris) by eidium Magel-
henicum (to be distinguished from the common 4. berberidis), on the Gray
Alder (Alnus incana) by Exoaseus epiphyllus, on the Hornbeam (Carpinus
Betulus) by Exoaseus Carpini, on the Bullace (Prunus insititia) by Exoascus
insititie, on other species of the genus Prunus by Exoascus Cerasi, on the
Birch (Betula verrucosa) by Exoascus twrgidus, on the Weymouth Pine (Pinus
Strobus) by Peridermiwm Strobi, and on the Silver Fir (Abies pectinata) by
„Beidium elatinum. Witches’ brooms also occur on the Mastic tree (Pistacia
Lentiscus), and on Beeches, Pines, Larches, Spruce Firs, &e., although hitherto
we have not been able to ascertain definitely what parasitic Fungi are the
cause in these cases. The Witches’ broom of the Silver Fir has been selected
and figured (see fig. 359) as a type of these peculiar structures. It always
grows on one of the horizontally projecting lateral branches of the Fir, and
raises its erect or curved twigs from the upper side, resembling, as it were, an
epiphyte growing on the bark of the horizontal bough. The twigs are grouped
in whorls and not in two rows, as usually happens in the lateral shoots of the
Silver Fir. They are all shortened and thickened, and remarkably soft and
pliable, because the cortical parenchyma has become spongy and the wood is
only slightly developed. The buds, which in healthy tissue are egg-shaped,
are almost spherical here. As in other instances of hypertrophied plant-members,
we have a precocious development, a so-called “prolepsis”, in these Witches’
brooms. The buds swell earlier and unfold earlier than those of healthy twigs.
The leaves remain short, yellow, somewhat crumpled, and fall off when a year
old, while those of normal twigs are long, linear, straight, dark green on the
upper side, and remain in position from 6-8 years. The growth of the twig
is restricted; it dies off in a few years, and then, inserted on the dark green
branches of the Silver Fir, remain the dry, bristling brooms, whose appearance
has stimulated the imagination of the peasantry and given rise to the superstitions
alluded to at the beginning of this chapter.

ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

Certain members of the Arachnoidea, Diptera, and Hymenoptera, which
attack and penetrate the tissues of living plants and incite the formation of
peculiar excrescences, are known as gall-mites, gall-gnats, and gall-wasps. The

528 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

growths, like small rosy-cheeked apples, which occur on the foliage of Oaks,
popularly known as “oak-apples”, are amongst the best known. The terms
“gall” and “gall-apple” were used by writers in the sixteenth century, and (like
the Old English word galle, the French galle, and the Italian galla) are derived
from the Latin word galla, used for these outgrowths by Pliny in his Natural
History. The sixteenth-century writers distinguish between “gall-nuts” and

“ ?

gall-apples”, meaning by the former the small hard outgrowths on the leaves
of Beech-trees. Afterwards the word gall was used for all the outgrowths
produced by animals on green living plants. More than that—the hypertrophies
described in the preceding chapter, produced in green host-plants by the various
families of Fungi, are also included under the term. It has been proposed recently
to substitute the word cecidiwm for gall, and to distinguish the excrescences as
myco-cecidia, nemato-cecidia, phyto-cecidia, diptero-cecidia, &e., according as they
owe their origin to Fungi, Thread-worms (Nematodes), Gall-mites (Phytoptus),
Gnats (Diptera), &e. A systematic classification of this sort, on the lines of
the classification of animals, might be of use to Zoologists, but to the Botanist its
value is only secondary. He must, as in other similar cases, keep to morphology as
the primary ground of classification, and has to arrange the structures according
to their agreement in development. Moreover, in a general review, it is necessary
to consider whether a whole group of plant-organs or one alone undergoes metamor-
phosis; and the starting-point of the outgrowth must also be ascertained; i.e.
whether it is the foliage-leaves, floral-leaves, stems, or root-structures, &e., which
are the head-quarters of the exerescence.

When the gall originating as the nest or temporary habitation of a single
animal or colony of animals is limited to a single plant organ it is said to be
simple; if, on the other hand, several plant organs are concerned in its produetion
it is said to be compound.

Simple galls may, for convenience of description, be divided into (1) Felt-
galls, (2) Mantle-galls, and (3) Solid galls. The Felt-galls are chiefly due to
hypertrophied epidermal cells growing out into hairy coverings of various sorts
and shapes; Mantle and Solid galls, however, are rather more complicated.
In both cases insects are present in swellings of various descriptions, but there
is this essential distinction: — The Mantle-gall is a hollow structure which,
though it may arise in various ways and assume a multiplicity of forms, always
has a portion of the surface of the affected organ for its lining—in other words,
it is a chamber formed by hypertrophied growth around the place occupied
by the insect. In the Solid gall, on the other hand, some spot is pierced by an
insect and the eggs deposited im the tissues (not on the surface), the punctured
spot forms a swelling with the larva inside, but the lining of the chamber is
in no sense a portion or development of the original surface of the organ affected.
Again, whilst in most mantle-galls the cavity of the gall is in open communication
with the outside, and the insect can escape by this aperture (though this is not
invariably the case), in the solid gall there is not such opening, and the insect

FELT-GALLS. 529

has to bore its way out. Needless to say, of both these types there are numerous
modifications, but they fall into the two classes (of mantle and solid galls) according
to their mode of development.

The majority of felt-galls are produced by gall-mites. They form cottony or
felted growths on limited and sharply defined areas of green leaves and stems,
the surface of which is otherwise smooth, or possesses but few hairs. Some-
times they have the form of small tufts, bands, or stripes, sometimes of large spots
with irregular contour. In most instances the felt is situated on the under side
of the foliage-leaf, and the gall-mite usually prefers the projecting veins to the
green surface. In the Lime, Alder, Hornbeam, and Horse-Chestnut, the mites
usually establish themselves in the angles formed by the lateral strands where
they arise from the midrib, the projecting veins forming the framework for the
felted hairs. In the Bramble (Rubus) and the Burnet (Poteriwm) it sometimes
happens that the felt is continued down from the lamina to the leaf-stalk, and
occasionally the green cortex of the succulent twig is covered with felted bands
and spots. In some Brambles and Cinquefoils the sepals become furred by the
action of gall-mites, the usual consequence being that the outline also becomes
distorted. A swelling or slight hollowing of the green leaf-tissue very frequently
accompanies the formation of felted galls, in which case the hairy covering is
only visible on the concave side whilst the other remains smooth. This is most
remarkable in the foliage of the Avens (Gewm), Vine (Vitis), and Walnut-tree
(Juglans), where a dozen white or brown-felted pit-like depressions are sometimes
to be seen on the under side of a single leaf. The colour of the felted hairs is
white in the leaves of Beeches, Limes, Bird Cherry, Brambles, Cinquefoils
and Burnets, green in the common Maple, yellow in the Spindle-tree (Euonymus
verrucosus), sulphur-yellow in Alnus orientalis and Black Poplar (Populus nigra),
carmine red at first and then violet in Alnus viridis and in the Birches (Betula
alba, carpatica, &e.), and brown in the Avens (Gewm macrophyllum), Horse-
Chestnut (@sculus Hippocastanum), and in the Aspen (Populus tremula). The
felted galls which are light in their young stages usually take on a brown tint
afterwards. Microscopie investigation has shown that in the formation of felted
galls, the epidermal cells, originally tabular in shape and closely fitting, swell
out and become transformed into bent and twisted tubes generally shaped like
a club or retort, the stimulus being afforded by a minute gall-mite (Phytoptus).
These cells look like short hairs to the naked eye, and as they stand side by
side in large numbers the covering has a velvety or felted appearance. The mites
which produce the felt, deposit their eggs in the juicy hair-shaped cells, and their
young live on the materials contained in them. It should be mentioned that
formerly these velvety and felted coverings were regarded as Fungi, and were
described as distinct genera under the names Erineum and Phylleriwm (eg. the gall
known as Erineum quereinum on the leaves of Quercus Cerris). To this group
belongs also the gall oceurring on the Wood Meadow Grass (Poa nemoralis) con-

sisting of cells which resemble root-hairs, which is produced by the gnat Hormo-
Vor. IL. 84

530 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

myia Pow. The hair-shaped cells are epidermal, and spring from the stem above
the nodes; they break through the leaf-sheath which proceeds from the adjacent
node, and are arranged in two groups, which grow in opposite directions, so as to
wrap round the stem from the two sides. The whole hairy mass looks as if it had
been parted into two. At first the hairs are white; later they become light brown,
and when the gall is fully developed they have the form of brown felted strands,
wound round the stems and firmly inclosing the larva of the gnat in question.

A large number of simple galls are grouped together under the name of Mantle-
galls. The inseets which give rise to them spend their lives on the surface of the
leaves, where they multiply and attach their eggs to the epidermis. A growth is
excited in certain layers of the cell-tissue by the stimulus which the animals
exercise on their place of settlement. Cavities are thus formed which serve as
dwellings for the animals and their brood, and which surround them like a pro-
tecting mantle. Mantle-galls may be divided according to their structure into
scroll-, pocket-, and covering-galls. Scroll-galls are caused by gall-mites, leaf-lice,
tree-hoppers, and flies, and usually occur on the blades, rarely on the petioles of the
leaves. The surface inhabited by these animals, which, in the ordinary course
of things would have spread out flatly, grows more luxuriantly on one side than
on the other, and the result is the formation of a scroll, 2.e. of a chamber in which
the animals are hidden. It is always the side on which the animals live which
becomes concave, and the leaf is usually curled up lengthwise. In the Alpine
Rose (Rhododendron), Crane’s-bill (Geranium sangwinewm), and Orache (Atriplex
hastata, oblongifolia, &e.), it is the upper side of the leaf which is tenanted by the
insects, and is therefore the one to roll up; it is the lower side, however, in the
Buckthorn (Rhamnus cathartica) and the non-climbing species of Honeysuckle
(Lonicera alpigena, &e.). In many instances the whole leaf-lamina is rolled up,
but more frequently the alteration is restricted to the edge of the leaf when the
margin appears to be bordered with a swollen hollow cushion often corrugated or
undulating. In the Alpine Rose (Rhododendron ferruginewm and hirsutum) both
halves of the leaf-blade are rolled round (see figs. 360° and 360°), but usually the
rolling is so slight that the gall has the form of a boat or hollow trough. Some-
times an alteration in the shape of the leaf accompanies the rolling. For example,
the foliage of the Abele (Populus alba) on which Pachypappa vesicalis establishes
itself when the leaves are very young, exhibits in addition to the rolling a deep
hollowing of the blade. Instead of the short blunt lobes, long pointed segments
are formed, which stand side by side when they are rolled up, and cross over one
another in many ways so that the mantle-gall on the hollow side is shut in by a
veritable lattice-work. The parts of the tissue brought into contact by the rolling
do not fuse together, and therefore the cavity in which the gall-producing insects
live is always in open communication with the exterior. In most cases the tissues
concerned are thickened, brittle, more or less devoid of chlorophyll, and yellow in
colour. Not infrequently a red pigment is formed in them, so that the outside of
the gall has a yellowish-red colour. The seroll-gall produced by the hemipterous

FORMS OF MANTLE-GALLS. 531

Trioza Rhamni on the margin of Buckthorn (Rhammus cathartica) leaves is very
hard and thiekened like cartilage. In many plants the epidermal cells lining the
gall elongate into hairy structures, as in the felt-galls previously deseribed. Their
juicy contents are used as food by the young gall-mites. This is the case, for
example, in the Alpine Rose (Rhododendron ferrugineum, ef. fig. 360°). Pocket-
galls are closely allied to the scroll-like forms. The tissue of the leaf-lamina or

Fig. 360.—Galls.

1 Covering-galls on the petiole of the Black Poplar (Populus nigra) produced by Pemphigus spirotheca. 2 Scroll-galls on the
leaves of an Alpine Rose (Rhododendron ferrugineum) produced by gall-mites. 3 Transverse section of one of these galls.
4and 5 Bud-galls on the branchlets of the Wild Thyme (Thymus Serpyllum) produced by gall-mites. © Blister-like
galls on the leaf of the Red Currant (Ribes rubrum) produced by Myzus ribis. 7 Part of the leaf seen from below.
§ Vertical section of a portion of this gall. Solid gall on the leaf of the Gray Willow (Saliz incana) produced by Nematus
pedunculi. 10 The same gall cut open. 11 Part of the wall of this gall in vertical section. 1, 2, 4, 6, and 9 natural size;
Sand *x 4; Sand? x 8; 8and!! x 50.

petiole and sometimes that of the cortex in young twigs is subjected to a stimulus
where the animals (gall-mites, leaf-lice, diptera) settle, with the result that a hollow
protuberance arises whose excavated cavity serves as a temporary dwelling for the
insects. The protuberances exhibit a great variety of form and shape, and they
differ considerably in their internal structure. The following are the most notice-

able forms. First, the plaited galls. They form deep, plaited, sometimes twisted
channels in the leaf-tissue which open on the upper side by a narrow hole, and

532 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

project like weals on the lower surface of the leaf. The growing tissue which
forms the floor of the channel is yellow and often lined with short hairs. The
channel usually follows the course of the larger veins of the lamina, and some-
times actually traverses one. Plaited galls are produced by gall-mites. The best
known are those on the foliage of Carpinus Betulus, Clematis Flammula and C.
recta, and Ribes alpinum. Wrinkled galls come next to the plaited form. The
protuberance is here limited to the green tissue shut in by strong rib-like
projecting veins, and is only shallow; the upper side of the leaf has bulgings
and protuberances and the lower pits and cavities. The protuberances are
always developed in numbers close together, so that the leaf looks very
much wrinkled in that region. Examples of this form are furnished by the
wrinkled galls on the Elm (Ulmus campestris; see fig. 361 *) produced by the leaf-
louse Schizoneura Ulmi, and on the Red Currant (Ribes rubrum; see figs. 360% 7 ®)
by another leaf-louse, Myzus ribis. In the latter several wrinkles are usually
united into large blister-like protuberances, red on the outside, and covered with
jointed cellular structures bearing glands which look to the naked eye like short
hairs. This form, though resembling certain felted galls, is distinguished from
them by the different form of the hairs arising in consequence of the stimulation.
In the Mouse-ear Hawkweed (Hieracium Pilosella) leaf-fleas (Psyllodes) produce
minute protuberances with narrow mouths, which stand out from the lower side
turned towards the ground like small warts, and when they occur close together
give a corrugated appearance to the leaf. Hollow protuberances of this sort
arising upon restricted areas of the leaf-surface, and growing very actively, give
rise to bag or sack-like structures attached by a very narrow neck. From their
resemblance to a head such galls are sometimes termed capitate galls (Cephalonion).
In others, where the outgrowth is fairly thick-walled and in form horn-like, the
designation horn gall (Ceratonion) has been given. Between these forms numerous
intermediate forms exist which may be compared to pockets, bags, nails, &e.
Many of these galls project from both the upper and lower side of the leaf, as
though a nail had been driven through it—hence the last-mentioned name. The
capitate-gall of the Sloe (Prunus spinosa), caused by a gall-mite, projects almost
as much from the under as from the upper side, whilst the similar gall on the
foliage of the Bird Cherry (Prunus Padus) rises on the upper side as a long
pocket, but below only projects like a small wart. Many capitate and horn-like
galls are developed only on one side, and here again there is a very great variety.
When the protuberances are due to mites the cavity always opens on the lower
side of the leaf. Both the inner wall and mouth of the cavity are covered with
hairs, and sometimes the aperture seems to be actually plugged up by them. In
the bag-shaped protuberances produced by the leaf-louse Tetraneura Ulmi on
Elm leaves, a relatively large slit is formed just at the narrow part of the bag at
the moment when the insects leave the cavity (see fig. 361°). The external surface
of the protuberances caused by mites on the foliage of Alders (Alnus), Maples
(Acer), and Limes (Tilia) is smooth, in those of the Bird Cherry (Prunus Padus),

FORMS OF MANTLE-GALLS. 533

and Wayfaring Tree (Viburnum Lantana) ciliated, whilst in the inflated galls of
the Elm caused by the white woolly leaf-louse (Schizoneura lanuginosa), it is
covered with fine hairs like velvet. The capitate galls on the foliage of Maples,
Alders, and Limes, of the Guelder-rose and Strawberry, are scattered abundantly
over the whole lamina; in the Sloe they stand out chiefly from the margin of the
leaf, and in Elms they occur singly or in groups on its central portions. The size of
these galls depends upon their distribution. Those which rise in hundreds from the

Fig. 361.—Galls.

1-3 Solid galls on a Rose-leaf; 1 of Rhodites Rosa, 2 of Rhodites Eglanteria, 3 of Rhodites spinosissime. 4 Wrinkled galls on
an Elm-leaf (Ulmus campestris) produced by Schizoneura Ulmi. 5 Purse galls on the same leaf, produced by Tetraneura
Ulmi. $% Covering gall on the same leaf, produced by Tetraneura alba. 7 Solid galls on the leafof the Purple Willow
(Salix purpurea), produced by Nematus gallarum. §& Solid galls on the leaves of the same Willow, produced by Nematus
vesicator.

same lamina have a diameter of 1-3 mm., while those which occur singly or in

small groups, often attain a diameter of 2-3 em.

Contrasting with these embossed or pocket-galls are the covering galls, forming

a third type of mantle-gall. In these, as in the embossed forms, the insects pro-

ducing the galls live in their cavities, but the course of development is quite

different in the two cases. The tissue round the place where an animal has settled
or where an egg has been fastened to the epidermis in this type begins to grow,
rising up in the form of a fleshy mound or wall which continues to grow until the
animal is wholly roofed in. The cavity in this case does not arise from an excava-
tion (as in the embossed or “pocket” type), but from an overarching of the tissue. The

534 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

external appearance of these galls is very varied. One of the simplest forms oceurs
on the leaves of the Ash (Fraxinus excelsior, see fig. 362°), where it is produced
by the gall-gnat Diplosis botularia. The insect having laid its eggs in the chan-
nelled depressions above the leaf-veins, fleshy cushions arise on either side of the
groove which meet above and roof them over. The cushions of tissue forming the
roof do not fuse; their succulent edges merely meet, and when the time comes for
the gall-gnats to leave their temporary abode the tissue dries up and shrivels,

Fig. 362.—Galls.

( Pine-apple gall on twigs of the Spruce Fir produced by the Spruce-gall Aphis (Chermes abietis). 2% Covering gall on the
petiole of the pyramidal Poplar (Populus pyramidalis) produced by Pemphigus bursarius. *% Covering galls on an Ash leaf
(Fraxinus excelsior) produced by Diplosis botularia. + Covering gall on Pistacia (Pistacia Lentiscus) produced by Pem-
phigus cornicularius. 5 Solid galls on the cortex of Duvaua longifolia produced by Cecidoses Eremite. ® Longitudinal
section of one these galls. 7 Capsule galls on the leaf of the Turkey Oak (Quercus Cerris) produced by Cecidomyia cerris.
® One of these galls cut through with the operculum still firmly attached, and ® the same with the operculum falling
away; x 3. The remaining figures natural size.

leaving a gaping slit as shown in fig. 362°. The same thing happens on the leaves
or rather leaf-veins of the Stinging-nettle (Urtica dioica) and of the Alder (Alnus
glutinosa), where the galls are produced by gall-gnats (Cecidomyia wrtice, almi),
and on the midrib of Elm leaves (Ulmus campestris; see fig. 361°), where the galls
are produced by a leaf-louse (Tetraneura alba).

The so-called turpentine gall-apples (Carobe di Giude; see fig. 362+), which

SOLID GALLS. 58D

are caused by leaf-lice on various species of Pistacia, also belong to the covering
class. The rudiment of a foliage-leaf, which in the normal course of events would
have developed into a pinnate leaf with dark-green elliptical leaflets, grows out
into a pod-like structure not unlike a locust-bean (fruit of Ceratonia Siliqua).
These galls are longitudinally grooved, and it can be seen more or less distinctly
that the furrows correspond to the edges of the leaflets, only here the leaflets
have become wrapped in, very much thickened and elongated, and fused with one
another. In the cavity inclosed by the fused leaflets lives a colony of leaf-lice
(Pemphigus cornicularius) which have developed under the protection of the gall.
When it is time for them to leave the cavity the top of the pod opens by the
separation and bending back of the tips of the fused leaflets which form the wall
of the cavity (see fig. 362*). The Chinese galls of commerce, produced also by
Aphides (on Rhus semialata), develop much in the same way. They are hollow,
irregularly pear-shaped structures with thin walls covered externally with a gray
down. Two other covering galls which deserve special mention on account of their
form arise on the petioles of the Poplar, particularly on the species Populus nigra,
pyramidalis, and dilatata. The one, caused by a leaf-louse, Pemphigus bwrsarius
(see fig. 362°), consists of a smooth expansion, red in colour externally, on the upper
side of the grooved petiole. If the local swelling be cut through it is seen to be
hollow, the cavity in which the leaf-lice live being shut in by thick fleshy walls.
The fleshy tissue of the walls is formed by a growth of the cells round the place
where the gall-producing insect has settled. A hole is formed at a point remote
from the petiole (where the growing tissue met and formed a dome) as soon as
the time comes for the inhabitants to make their exit. This is bordered by thick
lips as shown in fig. 362°”. The other gall which appears on Poplar petioles, pro-
duced by Pemphigus spvrotheca, is formed by the thickening of the edges of the
grooved petiole, which rise up as fleshy cushions and meet above the depression.
At the same time the petiole undergoes a spiral twisting, and a gall is thus pro-
duced whose cavity is spirally twisted like the interior of a snail’s shell. The
thickened edges of the petiole do not fuse; at first they fit close to one another,
but later on they separate, and a spiral hole out of which the white, downy leaf-
louse can creep is the result (see fig. 3601, p. 531).

We will now leave the mantle-galls and pass on to a consideration of the solid
or tubercular galls. These are of the nature of swellings of limited size on single
plant-organs, and are produced by insects which pierce the plant-tissue and lay
their eggs in the wound. In this way either the epidermis of the chosen spot alone
is injured, or the egg is inserted into the deeper-lying tissues. In both cases an
active cell-division is incited in the neighbourhood of the injury. If, however, the
egg has only been deposited in the epidermis, the larva which arises from it must
penetrate into the interior of the now swollen tissue; when the egg is laid at once
deep down this farther penetration on the part of the larva is of course unnecessary.
The cavity in which the larvae dwell may be called the larval chamber, and this sort
of gall can be classified according to the number of chambers which it contains,

536 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

whether only one or several (cf. figs. 363? and 3637). A great variety is met with
in the structure of the wall of the larval chamber. It always has a layer of juicy,
thin-walled cells immediately surrounding the egg, known as the medulla or pith
of the gall, and an outer layer which surrounds the inner like a skin or bark
(see fig. 3601°). In most instances a third layer is inserted between them which
consists of very hard cells forming a protective layer. It should also be noted that
the layers of the wall of the gall separate in many instances, so that it is possible
to distinguish an “inner” and an “outer gall”. The gall-pith furnishes the larva
with food when it emerges from the egg, and for this purpose the cells are stored
with nourishing substances. The development of the pith takes place with great
rapidity, and begins as soon as the egg has been laid in the tissue. The larva when
hatched finds the inner wall of the chamber which has been fitted for its temporary
abode always provided with the necessary food, and it immediately attacks and
devours the juicy tissue with great avidity. The cells which are demolished,
wonderful to relate, are replaced almost at once. The cells of the gall-pith remain
capable of division as long as the larva in the chamber requires food, and the
surface cells which have been devoured in the gall-chamber are soon replaced by
new cells from below, just as grass which has been mown down or cropped by
cattle in a meadow sends up new stems and leaves. The spheroidal gall arising
on the leaves of Salia incana (ef. fig. 360°) has only one chamber, and here the
larva lives at the expense of the starch and other food-materials contained in the
extremely thin-walled cells which constitute the gall-pith (fig. 360"). The larva
traverses the chamber in a circle, beginning the destruction of the cells at a certain
place and eating on as it continues its peregrination (fig. 3601"). New cells have
already been formed for its nourishment by the time it again reaches the place
from which it started.

The hard and cortical layers are modified in very many ways as protective
measures against the drying up of the gall in summer on the one hand, and
against the attacks of birds and larger animals on the other. For the latter
purpose the cortical layer is often fashioned like the pericarps of fruits which
have to protect the seeds (cf. p. 442). This also explains the bitter substances,
hard skin, furry coat, bristling processes, and numerous other protective structures
which are developed in and on galls just as on pericarps, and which contribute
not a little to the remarkable similarity between galls and fruits. Many peculiar
developments on the surface of these fruit-like galls cannot indeed be explained
in this way, but, as in so many other cases, we conclude that they must afford
some other advantage concerning which our understanding is still at fault.

The external similarity between fruits and solid galls affords us useful points
for classifying the latter into groups, which we may name berry-like, plum-like,
apple-like, nut-like, capsule-like, &c. The currant gall produced by Spathegaster
baccarwm on the male catkins of the Oak has not only the form and size of a Red
Currant berry, but is also succulent and coloured red, and when several of these
galls are formed on the same inflorescence it looks at first sight just as if racemes

SOLID GALLS. 537

of red currants had been borne by some chance or other on Oak twigs. The galls
produced by the Beech-gall gnat (Hormomyia fagi) on the foliage of the Beech
resemble small plums, being surrounded by a hard layer which consists of a stone
kernel and a layer of cells which might be compared to the fleshy part of a plum.
The galls caused by gall-wasps of the genus Aulax on the nutlets of many
Labiatee, especially on Nepeta Pannonica and Salvia officinalis also assume the
form of stone-fruits. The insect lays its eggs in one of the four nutlets developed
at the base of each flower; and within a week this grows into a smooth greenish-
yellow ball which has the external appearance of an unripe cherry. A section
through it shows that it possesses also the same structure as a cherry, plum, or
stone-fruit in general. The succulent outer layer surrounds a hard stony kernel,
but in the cavity of the kernel there lies the white larva of the gall-producer
instead of the seed. These galls fall off just like fruits in July, and lie on the
ground during the winter; and the mature insect does not bite an opening in
the wall of the gall through which it can emerge until the following year. It
has been already remarked at the beginning of this section how strong is the
resemblance between apple-fruits and the spherical oak-galls, known as oak-apples,
which are produced by various Cynipedes (see fig. 364°), together with the small
red-cheeked galls produced by Rhodites Eglanterie and Nematus gallarwm (see
figs. 361° and 361”) on Rose and Willow leaves respectively. Pith-galls which
resemble certain dry fruits are very common. Those produced on the green cortex
of young Oak twigs by Aphilothria Sieboldi (see fig. 3641) remind one of the
fruits of species of Metrosideros, those produced by Neuroterus lanuginosus and
Spathegaster tricolor on the leaves of the Turkey Oak (Quercus Cerris; see figs.
364" and 364") have a decided similarity to the indehiscent fruits of the Wood-
ruff and of the Goose-grass (Asperula odorata and Galiwm Aparine). The
“spangle” galls produced on Oak-leaves by the gall-wasps Newroterus fwmi-
pennis and numismatis resemble the fruits of Omphalodes (see figs. 3647? and
364), and the galls on the leaves of Duvaua longifolia produced by an insect
Cecidoses Eremita have the form of a capsule which opens by an operculum (see
figs. 362° and 362°). Like fruits these galls may appear in all imaginable con-
ditions with smooth, warted, or rugged surfaces, or covered with woolly or velvety
hairs, with bristles -or spines, fringes or claws, or even with moss-like outgrowths.
The galls with moss-like covering occurring on the Wild Rose have been known
from remote times as Bedeguars. They are caused by the Rose-gall wasp (Rhodites
Rose), which deposits its pointed, sometimes hooked eggs early in the spring in
the substance of an undeveloped leaf while it is still folded up in the bud. The
growth of the leaf becomes altered, the first sign being the development of
numerous hairs. The larvee, when they ereep out of the eggs, penetrate deeper
into the tissue of the leaf, and it swells out into a solid gall containing as many
chambers as there are larve. Hairs and fringes continue to form on the exterior
till those curious structures are formed which were said to have the power of
inducing a peaceful sleep when laid under the pillow. Usually the stalks of the

538 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

young bud-leaves are pierced and then the upper portion of the leaf becomes
atrophied. More rarely is the egg laid in the epidermis of one of the leaflets,
in which case the leaves attain their normal size and only this particular leaflet
is decorated with little bedeguars, as shown in fig. 361'. When the petioles of
three young leaf-rudiments are pierced simultaneously, as often happens, three
single galls are produced close together on a shortened axis, and the whole structure
may then attain the size of a pine-cone. é
The portion of meristematic tissue which is pierced by the insect when it
deposits its eggs sometimes remains an open passage; but more often a corky
tissue is formed at the wounded spot which quite closes the chamber wherein the
larva dwells. Under these circumstances the insect when it emerges must itself
make an exit-passage from the gall, and this it does by biting a hole through
it with its mandibles (see fig. 364°). The gall-wasps (Cynipedes) invariably leave
the chamber which has hitherto served them both as a safe habitation and as
an inexhaustible storehouse in this way. This does not occur, however, in some
of those solid galls which owe their origin to gall-gnats of the genera Hormomyia,
Diplosis, and Cecidomyia, for example, in those on the leaf-blade and petiole of
the Aspen (Populus tremula) produced by Diplosis tremulew and on the leaves
of Willows (Salix Caprea, cinerea, grandifolia) by Hormomyia Caprew. Here
the exit-passage is formed during the development of the pith. The gall consists,
as in most other solid galls, of a pith, a hard layer, and an epidermis, but the
enormously developed pith and the hard layer do not quite entirely surround the
small larval chamber, they leave a small aperture on the part of the gall which
is most arched. As long as the epidermis stretches over this place the mouth
of the passage is of course not evident, but when the time comes for the insect
to quit the chamber a gaping slit is spontaneously formed in the tense epidermis.
In many instances the insect or the pupa as it pushes forward may break through
the thin skin. A peculiar closure which might be compared to a lid is formed
in the common solid galls which are produced so abundantly on Beech leaves
by Hormomyia fagi and which have been already alluded to. Just as the pupa
of many Lepidoptera projects out of the hole in the cocoon which the caterpillar
has spun for it far enough to allow the insect to fly away uninjured when it
emerges, so that of Hormomyia fagi presses through the lid-like closure at the base
of the gall, and the winged insect comes out leaving the chrysalis-case behind it.
The opening of some solid galls, which resemble opereulate capsules, and which
may be termed capsule-galls, is especially remarkable and requires a more de-
tailed description. As long as the larva or grub can remain and obtain food in
the larval chamber the gall is completely closed, but when the time approaches
for it to move its quarters and to enter the pupal stage in the ground a circular
line of separation is formed in the tissue, and the part of the wall within the
circle comes away as a lid. The process is seen very prettily in the gall produced
on the leaves of the Turkey Oak (Quercus Cerris) by the gall-gnat Ceeidomyia
cerris (see fig. 3627). In its closed condition the gall is a firm rounded chamber

DEHISCENCE OF CERTAIN GALLS. 539

so embedded in the leaf that it projeets on the upper side as a small pointed
cone, and on the lower side as a dise covered with a thick coating of hairs. In
the autumn a eircular piece like a lid beeomes detached from the lower side of
the chamber. It corresponds exactly with the extent of the hairy disc, and is
so sharply defined that it looks as if it had been eut out with a knife (see figs.
362° and 362°). The operculum falls off, and the larva which had emerged from
the egg and which has lived all the summer in the gall-chamber tumbles out
and makes its way into the ground, where it begins to spin. By the next spring
it has entered the pupal stage, and the gall-gnat creeps out of the chrysalis
about May.

Still more peculiar are the galls produced by Cecidoses Eremita on the green

Fig. 363.—Solid Galls.

1 Capsule-like galls on a leaf of the Broad-leaved Lime (Tilia grandifolia) produced by Hormomyia Réaumuriana. 2 Longi-
tudinal section through one of the galls, showing the maggot in the interior; x 2. % Longitudinal section through a
capsule gall from which the inner gall is just being extruded; x 2. 4 Outer gall after the extrusion of the inner gall; x2.
5 Inner gall at the moment when the operculum is thrown off; x 2. © Capsule-galls on the leaf of a Brazilian species of
Celastrus. 7 Longitudinal section through one of these galls; x 2 ® The same after the inner gall has fallen out; x 2.
1 and $ natural size.

cortical tissue of young twigs of Duvaua longifolia, a South American represen-
tative of the Anacardiace (see figs. 362° and 362°). The gall is quite spherical
and very hard, and its large cavity conceals the caterpillar which has been
hatched from the egg. When the time draws near for the formation of the pupa,
a plug with a projecting rim is developed on the side of the gall furthest from
its point of attachment. When the plug is pushed out a circular hole is left
which leads into the gall-chamber through which the caterpillar escapes from its
dwelling. People who have not seen these galls with their own eyes might almost
think this description was the work of imagination. And yet there are still more
wonderful forms in this class of gall-structures. On the foliage of the Lime (Zilia
grandifolia) a growth arises round the eggs of the gall-gnat Hormomyia Réau-
muriana which at first has the form of a flat lens inserted in the green tissue of
the blade, but which gradually enlarges until it projects from the upper side like a

540 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

blunt cone and from the lower as a hemispherical wart. The gall-chamber is
inhabited by the maggot of the gall-gnat. The top of the conical part loses its
colour in July and becomes yellow and brown, and a rim is formed around its
summit. On cutting a vertical section through the gall at this stage it is seen that
the tissue forming the wall of the chamber consists of two parts (see figs. 363 ?).
The inner layer, which contains the maggot, is surrounded by an outer one which
gradually passes into the green substance of the leaf and extends up to the rim just
mentioned. The whole structure has separated into an “outer” and an “inner”
gall, the inner gall resembling an egg lying in an egg-eup (cf. fig. 363°). During
the summer the inner gall separates completely from the outer and is actually
thrown off by it. For the accomplishment of this the tissue of the outer gall swells
up very much, so that it exercises a pressure on the inner gall which is shaped not
unlike a cone, somewhat narrower below than at the top (see fig. 363°). The
extruded inner gall falls on the ground below the Lime-tree and assumes a dark-
brown colour; the outer gall remains as a little crater embedded in the leaf-blade
and ultimately shrivels up (cf. figs. 3631 and 3634). The detached inner gall is
smooth at the blunt and previously upper extremity, and striated at the other; it is
not unlike a detached composite-fruit. The gall-gnat within feeds for a little time
longer on the succulent lining, and then rests through the winter; in the spring it
makes its escape. To do this it bites a ring-shaped groove below the conical top of
the gall and presses against the roof, which, owing to the breaking of the tissues
around the ring, comes away like a lid (see fig. 363°). A similar state of affairs
prevails in a gall formed on the foliage of a Brazilian species of Celastrus (see
figs. 363 ® 7 ®), but here the inner gall (which comes away) has several chambers, and
the outer gall has the form of a cup set in the green blade.

The place of origin of all these solid galls depends of course upon the insects
producing them. These are usually very fastidious about the place where they
will lay their eggs, and it is truly astonishing with what care they search out spots
difficult of access, and at once favourably situated as regards food supply and
likely to afford a safe habitation for their offspring during the larval stages. The
small gall-wasp Blastophaga grossorum lays its eggs in the ovaries of the “gall-
flowers” in the interior of the figs of Ficus Carica (see p. 160 and figs. 240 and
240%, p. 157). The gall-wasps Andricus amenti and Newroterus Schlechtendali
deposit them in the stamens of the Turkey Oak; the gall-wasp Cynips caput-
meduse lays hers in the side of the bract-scales which surround the pistillate
flowers of the Oak (Quercus sessiliflora and pubescens), and so produces a gall with
innumerable stiff-pointed fringes entangled with one another which ward off the
attacks of other animals (see fig. 364°). Countless gall-producing insects deposit
their eggs on the lower side of foliage leaves, some preferring the lamina, others
the veins. Andricus curvator prefers the margin of Oak leaves, Diplosis tremule
the petiole of the Aspen at its junction with the blade. Several gall-wasps, as, for
example, Andricus estivalis and Andricus grossularie, seek out the floral recep-
tacle in the male catkins of the Turkey Oak for the deposition of their eggs, whilst

ALTERATION OF FORM BY GALL-PRODUCING INSECTS. 541

several Cynipedes, e.g. Aphilotria Sieboldi (see fig. 364') lay their eggs in the green
cortex of the young twigs. Solid galls are very rare on roots, but they do occur

Fig. 364.—Various Oak-galls.

1 Solid galls on the cortex produced by Aphilothriz Siebolui. 2 Bud-gall from a foliage-bud produced by Cynips Hartigii.
3 Solid galls on an Oak twig produced by Cynips Kollari. 4 One of these galls cut in half. 5 Bud-galls from foliage-buds
produced by Cynips lucida. © One of these galls cut in half. 7 Leafy bud-galls produced by Aphilothriz gemme.
® Bud-galls from foliage-buds produced by Cynips polycera. % Longitudinal section through one of these galls. 10 Gall
on the pericarp of Quercus pubescens produced by Oynips caput-meduse. 11-14 Spangle galls on a leaf of the Turkey Oak
(Quercus Cerris); 1! produced by Neuroterus lanuginosus; 12 by Neuroterus numismatis; 12 by Neuroterus fumipennis ;
14 by Spathegaster tricolor.

in this situation in the oak, being produced by the gall-wasps Aphilothria radicis
and Biorhiza aptera.

542 ALTERATION OF FORM BY GALL-PRODUCING INSECTS,

When several organs of a plant immediately adjacent to one another are con-
cerned in the production of a gall it is said to be compound. Compound galls are
for the most part produced from buds, and they are all comprehended under the
general name of Bud-galls. They are extraordinarily varied in their characters,
some being merely abbreviated axes clothed with scale-like leaves, in others only
the base of the shoot is involved and above the gall it continues its growth quite
normally, whilst in others again the axial portion of the structure is much swollen,
and the leaves hardly represented at all. It is difficult to give any satisfactory
classification of these bud-galls; still, for the sake of arranging our facts, we may
distinguish these types, viz.:—the ordinary bud-gall, the cuckoo-gall, and eluster-
gall. Ordinary bud-galls involve several, often all, the members of a shoot. The
axis of the shoot is always deformed and abnormally thickened. The swollen portion
contains in its interior one or several larval chambers surrounded by a pith-like
layer. Two varieties of ordinary bud-gall may be distinguished. The first is leafless;
no leaves are present, or, more correctly, they are transformed into tubercles, pegs,
and knobs which merge insensibly into the swollen axis which contains the larval
chamber. The second possesses leaves, the gall being covered with scale-like bracts
or more or less fully developed green foliage-leaves. Amongst the leafless bud-galls
the most interesting are those which are armed with special means of protection
against the attacks of animals on the watch for the larv of the gall-wasps. The
gall shown in figs. 364° and 364°, produced by Cynips polycera on the leaf-buds of
Quercus pubescens and sessiliflora, which to a certain extent affects a whole lateral
shoot, has the form of a young Medlar fruit, and on it may be seen 3-5 metamor-
phosed leaf-structures projecting as stiff-pointed pegs which gradually pass into the
tissue of the shoot axis. This gall is one-chambered, and the tissue of the wall has
separated into an outer layer and an inner spherical pithy gall. The gall shown in fig.
364° is produced by the gall-wasp Cynips Hartigii which lays an egg in the middle
of the leaf-bud of the Oak (Quercus sessiliflora). The bud does not develop into a
leafy shoot, but into a small one-chambered gall with large tooth-like or club-like
processes which represent metamorphosed leaves. The thickened angular ends of
these projections fit closely to one another so as to form a sort of second outer coat
to the gall-chamber through which hostile ichneumon-flies cannot penetrate. The
gall much resembles the cone-fruit of a Cypress in the arrangement and form of its
superficial processes. The galls produced from the buds of various Oaks (Quercus
pendulina, sessiliflora, pubescens) by the gall-wasp Cynips lucida are still more
peculiar (see figs. 364° and 364°). They contain several larval chambers with
abundant pithy tissue, whilst innumerable slender processes resembling limed twigs
in being very sticky on the capitate thickened end project from their exterior.
Ichneumon-flies and other animals hostile to the gall-producers take good care not
to come into contact with these spikes which are to be regarded probably as trans-
formed leaves springing from the swollen axis. Among the galls produced from
leaf-buds belonging to this group there are some in which the leaves are merely
indicated as tubercles. This is the case, for example, in the many-chambered,

BUD-GALLS. 543

spongy gall, red-cheeked on the sunny side but pale elsewhere, which is produced
on the tips of the branches of the Oak by the gall-wasp Dryoterus terminalis, and
looks very like a potato in shape. The leaves are only represented by small ill-
defined knobs and ridges, just as in the potato. To this class of galls belongs
also that to which the term “nut” is popularly applied, and even in commerce, the
name has been transferred from this to the whole of the first group of compound
galls (bud-galls). The “nut” is produced on the Oak by Cynips calicis as an
angular and irregularly-grooved gall which originates at the end of a flower axis,
and the cupule formed of several bract-scales as well as the ovaries are concerned
in the growth. This class of galls also includes the irregular blunt swellings on
Aspen twigs (Populus tremula), which are caused by the larva of a beetle (Saperda
populnea), and in addition the many-chambered woody “canker cushions” as large
as a nut which are produced on the branches of Willows by Nematus medullaris.

The gall shown in fig. 364", which arises on various Oaks (Quercus pedunculata,
sessiliflora, pubescens) by the action of the gall-wasp, Aphilothrix gemma, may be
selected as a type of leafy bud-galls. It resembles the cone of a Hop or Larch,
and is developed from a foliage-bud. It has a much-abbreviated swollen axis, whose
tissue separates into an inner and outer gall, beset with numerous dry, brown lan-
ceolate hairy scales having the form of bract-seales. Bud-galls which are covered
with green foliage-leaves are produced by the gall-wasp Andricus inflator on the
Oak, but they are more commonly met with on herbaceous plants, e.g. by Urophora
cardwi on Cirsium arvense, by Diastrophus Scabiose on several Knapweeds (Cen-
tawrea alpestris, C. Badensis, ©. Scabiosa), by Aulax Hieracii on various Hawkweeds
(Hieracium murorum, sylvaticum, tridentatum, &e.). Usually the foliage-leaves
are stunted, and not infrequently the blades of some of them are quite obliterated,
so that the gall in that region is only furnished with scaly leaf-sheaths. A Sage
growing in the Isle of Crete so often bears leafy bud-galls resembling a small
Quince-apple, produced by a species of Awlax, that Linnzus ealled it Salvia pomi-
fera. The stem of this Sage is swollen out like a ball, and the spherical mass,
covered with a gray felt of hairs on the exterior, is surmounted at the top with a
group of small wrinkled leaves, which look like the persistent calyx of a Quince-
apple. The best known and most widely distributed of these forms, found on the
Hawkweeds named above, consist of knob-like swellings of the stem. The larval
chamber is situated inside the enlarged pith, the ring of vascular bundles, which has
undergone much shifting, forms the protective layer, and the cortex of the affected
region of the stem forms the cortical layer of the gall. The epidermis is densely
covered with hairs.

Leaving the galls which consist of modified foliage-buds, we pass on to such as
consist of metamorphosed flower-buds. They arise from flower-buds in which small
gall-gnats have laid their eggs. The larva hatched from the egg lives in the cavity
of the ovary, or in one of its loculi when there are several, and this space, therefore,
becomes the larval chamber. The corolla, which envelops the ovary in the flower-
bud, remains closed, like a cap on the top of the larval chamber. The calyx becomes

544 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

inflated, enlarged, and sometimes fleshy. The whole gall resembles a bud or small
bulb; it is not unlike one of those bulbils which so often arise instead of flowers
on the flowering axis of certain species of Allium. They occur especially on the
Bird’s-foot Trefoil (Lotus corniculatus), where they are produced by the gall-gnat
Cecidomyia Loti, on the various species of Mullen (Verbasewm Austriacum,
nigrum, Lychnitis, &e.) by Cecidomyia Verbasci, on several species of Germander
(Teucrium montamum, Scordium, &e.), caused by Lactomelopus Teuerii, and on
the Rampion (Phytewma orbieulare), where they are produced by Cecidomyia
phytewmatis.

Closely allied to these bud-galls are those remarkable gall-struetures which are
commonly known in Austria as “cuckoo-buds”. The cuckoo is supposed to be
concerned in their formation, just as it is in that of the frothy saliva-like masses
deposited by the Cicada on the Cuckoo-flower (Cardamine pratensis). The name
“euckoo-galls” may be employed for the whole of this sub-group. They are char-
acterized by their pale whitish colour, soft spongy tissue, and especially by the fact
that they only involve the base of the shoot, while the upper end can continue its
growth unaltered. In this respect they may be compared to a Pine-apple fruit,
where the axis rises above the fleshy collective fruit (cf. p. 436) as a green leafy
tuft, which does not lose its growing power even with the ripening of the fruit.
The history of the development of cuckoo-galls is probably like that of covering
galls; and the main distinction lies in the fact that in the former the gall is pro-
duced not merely from a single organ or some part of it, but from a whole group of
adjoining plant-members. The best known and most widely distributed gall of this
group is produced by the pine-apple aphis Chermes abietis on the twigs of the Spruce
Fir (Abies excelsa, see fig. 3621, p. 534). Early in the spring, before the foliage-leaves
have begun to unfold, the parthenogenetic females, the foundresses of the colony,
attach themselves each to the base of a young leaf and lay a mass of eggs at the
spot to which they have adhered. The larve, hatching, penetrate the surrounding
parts of the shoot with their beaks; the shoot swells, as do the bases of the
needles, and a growth, the Spruce gall or Pine-apple gall results. The gall somewhat
resembles a small Fir-cone about an inch long, with the surface divided into small
convex areas, each bearing a short needle-like projection in the middle; these are
the deformed needles, which, becoming swollen, touch each other on the outside of
the gall. They are separate inside, so that the gall contains a series of cavities or
chambers. In these chambers the larve live in numbers, either entering the
chambers during the growth of the gall or being inclosed by the swelling of the -
surrounding needles—this point is not certainly determined. They remain in the
small cavities so formed and feed, cast their skins, and multiply there. In August
the gall begins to dry up, each of the small cavities opens by a slit in front of the
green needle-point surmounting the cushion (see fig. 362, p. 534), and the winged
insects now leave the place in which they have passed the spring and summer.

Cuckoo-galls are met with almost as frequently on Stellate, viz. on various
species of Bedstraw (Galium Austriacum, boreale, uliginosum, &e.) and Woodruff

BUD-GALLS. 545

(Asperula galioides, tinctoria, &e.) as on Fir-trees. The infected parts of the shoot
remain stunted, and white spongy cuslfion-shaped growths, which are somewhat
grooved, arise at the bases of the leaves. Since the growing tissues of neighbouring
leaves touch one another the grooves or channels form small cavities in which live
the larvee of the gall-producing gnats (Cecidomyia Galii and Asperule). In the
common Bedstraw (Galiwm Mollugo) these spongy growths arise, not from the
bases of the leaves, but from the green cortex of the stem round the insertion of the
leaves and lateral branches. They rise up as cushions and lobes, and several join
together to form a sort of dome, under which the larvee of the gall-gnat dwell. The
foliage-leaves are scarcely altered in form, and when lateral twigs arise from the
place they also are unchanged. It not infrequently happens that short lateral
axes terminated by flowers spring up quite unmodified above the spongy white
euckoo-gall. Cuckoo-galls also oceur on Cruciferse, viz. on Barbarea vulgaris,
Nasturtium palustre, sylvestre, and Sisymbrium Sophia. They are produced by
Cecidomyia Sisymbrii, and originate principally at the bases of the flower-stalks
half-way up the inflorescences. They look like spongy white bodies which surround
the pedicels like the brim of a hat. As the growths from neighbouring pedicels
meet together they roof over chambers which serve as habitations for the larvee of
the gall-gnats. Viewed from outside the galls appear like irregular white bodies
inserted in the inflorescence, which remind one of the fruit of the white Mulberry-
tree.

The term cluster-gall is reserved for that type of bud-gall in which the axis is
much restricted or stunted and covered with densely crowded leaf-structures; it
is in the chinks and recesses between the crowded leaves of these galls that the
insects concerned pass the whole or a portion of their lives. The animals which
cause the galls belong to very different classes. Gnats, leaf-fleas, leaf-lice, and mites
are the commonest varieties. The gnats only live in the galls during the egg and
larval stages, but the others pass their whole life there. They invariably settle
on the end of a shoot while it is still undeveloped in the bud. The axis of the
shoot remains more or less stunted in consequence of the influence the animals
exercise on it and its leaves undergo fundamental alterations. The blade or sheath
of the leaf is deepened and hollowed to afford sufficient space to the animals which
have established themselves between them, and as these parts of the leaves touch
one another recesses are formed not unlike those which are developed in fir-cones
for the growing seeds. The sheathing part of the leaf is often rather thickened,
and its succulent cells serve as food for the animals living in the gall; in other
instances the hollowed leaf-blades are thickly covered with hairs, and this coat
then has the same significance with regard to the insects as the felt of hairs on
isolated leaves already described. Very different forms of galls are produced
according as to whether the free ends of the leaves turn back or remain in contact,
and whether the axis from which the leaves spring is more or less contracted.
Sometimes they remind one of open rosettes, sometimes of closed balls, bunches and

tufts, sometimes of pig-tails and witches’ brooms.
Vou. I. 85

546 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

Clustered galls may be divided into two classes, those which develop in the
region of the flowers and those in the” foliage region respectively. The most
noticeable and best known forms of the galls oceurring in the foliage region on
rudimentary leafy shoots are the following:—First, those peculiar structures on
the tops of Willow twigs (Salix awrita, Caprea, grandifolia, &e.) which are popu-
larly termed “Rose Willows”. They are caused by the gall-gnat Cecidomyia
rosaria. The leaf-bud from which they arise keeps its axis quite short and
develops on it numerous green leaves arranged like the petals of a double rose.
The lowest leaves of the “rose” differ but slightly from the normal foliage of
the particular species of Willow. Usually there seems to be only a shortening
and broadening of the petiole and leaf-sheath, the green blade being almost un-
altered. In the upper inner leaves, however, the sheath-like part of the leaf is
much increased in size, and nearer the centre of the “rose” the leaves become
scale-like. The leaf-blade has entirely disappeared, and the end of the contracted
axis possesses only the remains of leaf-sheaths. It is worth noting that the
number of leaves in a Rose Willow is always greater than would be found on
an unaltered shoot of the same species. For example, if the number of leaves
on the one-year-old shoot of the Sallow (Saliw Caprea) is 25, the number in

,

a “rose” on the same species would be at least twice as large. This can only
be explained by supposing that a “prolepsis” has occurred, i.e. that not only the
shoot laid down for the current year has developed, but also one originating from
a bud of this shoot, which, under normal conditions, would not have developed
until the following year. When autumn comes the rosette-shaped galls on the
Willow bushes show up conspicuously at a distance because the leaves forming
them do not fall off like the rest, but remain behind as brown dried structures
at the ends of the branches. They are also found associated with the catkins.
The rosette-shaped galls produced by the gall-gnat Cecidomyia crategi at the
tips of Hawthorn twigs (Crategus Oxyacantha and monogyna) also claim atten-
tion. They are full of bristles and resemble tiny birds’ nests. The stimulus of
the gnat larve excites a deeper and more frequent segmentation in the leaves
and stipules. Narrower points and fringes which are much bent and which
resemble the antlers of reindeers replace the broad lobes. Also soft spines with
capitate ends rise up from the green cortex of the twigs and from the tissue of
the leaf-blade, especially above the vascular bundles, and 3-5 of them often fuse
together into cock’s-comb-like structures. These bristlmg rosettes on Hawthorn
branches also remain long after the time the ordinary foliage falls off.

In marked contrast to the rosette-like cluster-galls are others whose leaves
all fold together in a ball something like the leaves of a cabbage, the whole
gall having a button-like appearance. The outer leaves are round and hollowed
on their upper side, and they usually fold together like mussel-shells. The inner
leaves have a similar form, but they are much smaller and more concave, and
they have become succulent and paler in colour. The galls produced by Üeei-
domyia genisticola on Genista tinctoria and those which Cecidomyia Veronice

BUD-GALLS. 547

gives rise to on Veronica chameedrys, and which gall-mites produce on the Wild
Thyme (Thymus Serpyllum; see figs. 3604 and 360°, p. 531), form white buttons
on the ends of the shoots which show up conspicuously from the dark green
of the surrounding foliage. The white colour is due to the fact that the outer
leaves, which fold together like mussel-shells, are thickly covered on the outside
with white hairs. Cecidomyia Artemisie produces on the branches of Artemisia
campestris a closed eluster-gall which is cased in white wool like a shroud. On
the other hand, the large, button-shaped, closed eluster-galls which are produced
by Cecidomyia rosaria on Willows (Salix purpurea, &e.) and by a gall-mite on
the spikes of the Brome-grass (Bromus) are green and smooth, or at least they
have not more than the usual number of hairs.

On the shoots of the Yew (Taxus baccata), the Flax (Linum usitatissimum),
Euphorbia Cyparissias, the Moss Campion (Silene acaulis), and several Ericas
(Erica arborea, carnea, &e.) the influence of various gnats (Cecidomyia Taxi,
Euphorbie, Erice, scoparie, &e.) produces galls with linear erect leaves crowded
together into tufts. The base of the crowded leaves and the axis of the gall are
usually rather thickened, so that it looks as if the linear leaves were set on
a rounded button, and this is particularly marked in Euphorbia Cyparissias.
This division includes the gall formations occurring on Juniper twigs (Juniperus
communis), which are caused by the gall-gnat Lasioptera juniperina. The
acicular leaves of the Juniper are arranged in whorls of three on normal shoots.
By reason of the influence of the gall-gnat Hormomyia juniperina the whorls
at the top of the twig become so changed that the last but one represents a cup
bordered with three teeth in consequence of the broadening of the needles, while
the terminal whorl is metamorphosed into a dwelling surrounded by three short
leaflets. This gall closely resembles the cone of the Arbor Vite (Thuja occidentalis,
orientalis, and plicata) in form.

An insect, Livia Juncorum, produces galls on various Rushes (Juncus), espe-
cially Juncus alpinus and lamprocarpus, which look like knots or tassels. The.
axis of the shoot is contracted, the sheathing portions of the leaves which cover
one another are much widened, and the colour is pale except where it is reddened
by exposure to the sun; their appearance is like the outer covering or top of
a tassel. The stunted green blades which spring from the sheathing portions
are thread-like and arranged as the loose strands of the tassel. Not infrequently
short lateral shoots arise in the axils of some of the leaves, and then the whole
structure looks like a bunch of tassels.

Closely allied to these cluster-galls on the stems of Rushes are such as re-
semble tufts and witches’ brooms, produced by mites on the branches of hairy
Willows, especially on the white Willow (Salix alba). Instead of the long leafy
Willow rod which would have emerged under ordinary circumstances from a
foliage-bud, a confused mass of twigs with short leaf-scales is developed which
at first seems a perfect mystery. By careful examination it is seen that the
axis of the shoot laid down in the bud has remained stunted, and that lateral

548 ALTERATION OF FORM BY GALL-PRODUCING INSECTS,

shoots have developed from the axils of its leaves. These lateral shoots again
develop lateral axes in the axils of their leaves, and so on to the third, fourth, and
fifth degree. Thus, in the course of a month, shoots have unfolded, which, except
for the influence of the gall-mites, would not have followed one another for three,
four, five, or even six years, and therefore these galls afford us another instance
of what has been termed “prolepsis” or precocious development of structures
which would not yet arise. Of course all the axes of these shoots are dwarfed
and the leaves which clothe them are diminished in size. The shortening and
diminishing increase gradually, so that the axes and leaves of the fourth and
fifth degree are much smaller than those of the second and third. The last
lateral shoots remain bud-like, and their small sealy leaves fold over one another

like the bracts in the involucre of a Composite. The “ witches’ brooms” which
are caused by gall-mites on Lilae (Syringa vulgaris) and Privet (Ligustrum vul-
gare) bushes are similar in nature to these closed galls on the Willows. Frequently
the metamorphosis of the leaves on the axes of the third, fourth, and fifth degree
includes those of the floral region, and such cases form to some extent a bond of
union between cluster-galls on foliage and on floral regions, respectively.

One of the most remarkable changes exhibited by the gall-structures just men-
tioned, viz. the abbreviation of the axis, is of course not to be noted in eluster-
galls in the floral region. The part of the axis which forms the floral receptacle
does not grow into an elongated shoot, but always remains short, and the floral-
leaves it bears stand close to one another, forming whorls in whose niches and
recesses numerous small animals can hide. But these animals effect other very
marked alterations by their stimulus. In some flowers, instead of the normal
red, blue, white, or yellow petals, green leaflets appear which resemble foliage-
leaves in character, and then we say that the flowers have become “green” or
“leafy”. In other plants the stamens are transformed into petals, and the flowers
are said to be “double”. Finally, it may happen that the carpels which are usually
united together to form a syncarpous ovary stand on the receptacle as distinct
structures, and that-to a certain extent their union has been dissolved. In these
cases we speak of “antholysis” (cf. p. 80). The influence of gall-mites also produces
metamorphosed flowers which may be both green and double, and in which the
pistil may have separated into its individual carpels.

The best flowers for observing these metamorphoses in all imaginable degrees
are the small-flowered species of the Chickweed genus (Cerastiwm macrocarpum,
triviale, &e.), several Caryophyllaceew (Lychnis Viscaria, Saponaria officinalis,
&e.), Crucifere (Cardamine uliginosa, Camelina sativa, Lepidium Draba),
Gentians (Gentiana acaulis, rhetica), Speedwells (Veronica officinalis, saxatilis)
and Milfoils (Achillea Millefolium, nana). In Speedwells the petals come to
resemble leaves. The bunches, rosettes, and balls of small green leaves replacing
the flowers are set close together on the rachis of the inflorescence and form green
racemes and tufts, sometimes even small witches’ brooms. In Veronica saxatilis
the rachis of the raceme, the pedicels, and the bracts are covered with hairs, which

COMPOUND GALLS IN FLOWERS. 549

is not the case when the plants are free from the mites; the foliage-leaves in the
neighbourhood of the raceme are also lobed and deeply indented, which again is
not the case in uninfeeted plants of this species. In the capitula of the above-
named Milfoils the peripheral ray-florets as well as the central tubular ones become
leaf-like, and this gives rise to the most peculiar forms. A capitulum is often sepa-
rated into several stalked sub-capitula, the flowers being metamorphosed into green
funnels with jagged mouths, and into small flat-lobed and toothed foliage-leaves,
whilst short, green, scale-like leaflets rise from the midribs of these leaves repre-
senting the metamorphosed stamens. A very remarkable “doubling” produced by
gall-gnats is to be observed in flowers of the Alpine Rose (Rhododendron ferru-
gineum). The stamens and carpels are changed into red petals by their influence.
Since Rhododendron flowers have ten stamens and five carpels, there should be
only fifteen red leaflets in the centre of each, but as a matter of fact there are
double and treble as many, and there has been not merely a metamorphosis but
also a multiplication of the leaves. The flowers of some plants which belong to
the Valerians, especially of the Corn-salad (Valerianella carinata), of which a
small umbellate eyme is shown in fig. 358°, p. 523, are doubled by the influence of a
gall-mite, but without any multiplication of the petals. The doubling is restricted
to the transformation of the stamens into a whorl of petals. But we also have
another peculiar alteration. The petals become enlarged to more than fifty times
their normal size, and change into fleshy lobes which are fused with one another
into a dise. As all these lobes bend back, and become concave below, cavities
are formed under the flowers in which the gall-mites can dwell (see fig. 358%,
p- 523).

The axis of the inflorescence and the stalks of single flowers are often thickened
and fleshy in these cluster-galls, and they are also stunted and bent in the most
varied manner. If several neighbouring pedicels fuse together, structures like
cocks’-combs, or like a compressed and flattened branch, arise; to these the term
Jaseiation is applied. Sometimes when numerous pedicels arranged in the form of
umbels fuse together we have structures like coral-colonies, or irregular clumps
which are beset with green flowers usually much reduced in size. This is the case
in the fasciations of the Ash (Fraxinus excelsior and Ornus), which are caused by
a gall-mite (Phytoptus), and which oceur so abundantly that it looks as if the tops
of the trees had been sown with them.

The enumeration, here, of various forms of galls commenced with the incon-
spicuous felt-galls on the under side of isolated foliage-leaves, and it ends with the
complex cluster-gall, in which hundreds of flower-stalks and leaves are frequently
concerned. Of course, only types of the individual groups which have been mentioned
in this long series could be instanced, and we cannot make any attempt to describe
all the gall-structures at present known, about 1600 in number. Whether the
extension of gall-researches in tropical regions will yield new forms which stand
outside the pale of the classification given it is difficult to say. Apparently this will
not be the case. Perhaps thousands of hitherto unknown galls might be added

550 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

to the list, but we should expect that they would fall under one or other of the
above-mentioned groups.

Gall-structures have a peculiar significance for the section of the Natwral His-
tory of Plants which deals with the question of the origin of species, since they
show most distinctly how fundamental deviations from the original plan of con-
struction may occur in the adult condition of a portion of a plant.

We must be careful to remember always that the immense variety of structures
which we call galls would not have existed except for the effect produced on the
plants by mites, leaf-lice, gnats, wasps, Ye. The foliage of Rhododendron would not
have been rolled up, but quite flat, if gall-mites had not been present; the branches
of Pistacia Lentiscus would have borne pinnate foliage with shining dark-green
leaflets and not fleshy-red pods if they had not been attacked by leaf-lice; the leaf-
bud of Quercus pubescens would have developed into a long leafy shoot instead of
a body like a medlar if the gall-wasp Cynips polycera had not provoked the
change; the foliage of Veronica saxatilis would not have been lobed like a hand,
but would have had a slightly sinuous margin; and the upper leaves of Thynius
would have been green, spoon-shaped, and smooth on the surface instead of circular
and covered with white hairs, had no gall-mites settled on them. The flowers of
Rhododendron ferrugineum, Lychnis Viscaria, Veronica, Cardamine, &e., would
not have “doubled”, and the stamens would not have changed into petals, if they
had not been under the influence of gall-mites.

Of course, the influence of the animals can only produce these effects on parts
of plants which are in an embryonic condition. Mature stems and leaves may
be eaten and destroyed by insects, but they can no longer be metamorphosed. But
the undifferentiated rudiments upon which the influence is effective are, so to speak,
formless. Leaves, stems, and fruits arise from tissue-masses having the form of
tubercles and cushions, and each tubercle or cushion originates from a few cells
which give no indication of what is to develop from them. Nevertheless, experi-
ence teaches us that the plan of construction for the plant-member proceeding from
these primitive forms is definitely laid down from the beginning for each species,
and the idea that the plan of construction is rooted in the specific constitution of
the protoplasm of the plant—i.e. in the cell or cells which form the primitive stage
or rudiment of the developing leaf, stem, &e., is confirmed. If an alteration in
this plan of construction is produced by these animals, it can only be by some
alteration of the specific constitution of the protoplasm.

How the alteration is effected is just the puzzle which is at present occupying
the attention of naturalists. Once it was thought that the formation of galls was
the result of injuries caused in the growing tissue by the ovipositor or sucking
organ of insects, but recent investigations have not confirmed this view. The cells
actually injured by the insect in laying its eggs perish, and consequently lose the
power of metamorphosis or of producing modified daughter-cells. Cork, closing
over the wound, is always formed from the adjoining living tissue, but for a long

THE ORIGIN OF GALLS. 551

time no gall is produced. The eggs deposited in the tissue, or attached to it, are
also incapable of directly inciting gall-formation. There is no marked alteration
in the neighbourhood until the grub or larva leaves the egg and exeretes a fluid
substance. Then growing cells of the most varied description are formed adjacent
to the larva, and these rapidly assume the peculiar forms which have just been
deseribed. This, of course, applies also to cases where the larva has been hatched
from the egg at some distance from the spot and has had to seek out a tissue
suitable for its dwelling, as also to instances where adult gall-mites and leaf-lice
choose out a suitable place for the deposition of their eggs and then secrete a fluid
round them when they lay them. If the animal dies, the growth and renewal of
the tissue immediately ceases. The cells round the dead body turn brown and die,
so that we may conclude the formation of the gall to be due solely to the substance
excreted by living animals.

Those who investigate galls consider that it is chiefly the acrid “saliva”
excreted by the larvee to liquefy their food which acts on the cell-tissue of the
dwelling they have selected, but there is no doubt that other excretions may also
take part. The chemical composition of this substance is unknown, but we shall
hardly be wrong if we include it in the group of nitrogenous compounds called
enzymes which were discussed at vol. i. p. 464. Enzymes have the power of
altering and decomposing substances, even through the cell-wall, and in this way
we can account very simply for a whole series of otherwise inexplicable phenomena
in the formation of galls. Moreover, urea or closely-allied nitrogenous compounds
may be excreted, so that there is nothing to be said against the view that some
of the substances diffuse into the interior of the plant-cells. It is at least certain
that the fluid substances excreted by the gall-producing animals, in whatever way
they influence the protoplasm in the »plant-cells, do not kill it, but actually
stimulate it to an extraordinary new activity directly demonstrated by the pro-
duction of tissues with a definite external form.

Observation shows that these tissues are formed and fashioned differently
from what they would have been without the influence of this substance. It
follows, therefore, that the substances excreted by the animals have the capacity
of affecting in some way the specific constitution of the protoplasm which deter-
mines the species in the plant-cells influenced by them. It is specially interesting
to note in this connection that it not only is the protoplasm of the cells directly
acted on by the excretion which is stimulated to an altered form of constructive
activity, but that this stimulus is transmitted from cell to cell in ever-widening
circles. The spruce-fir aphis Chermes abietis attaches itself firmly by its beak to
the scale of a Fir bud, and can directly influence only a few cells of the young
shoot hidden in the bud. Nevertheless thousands of cells on this shoot soon begin
to assume an altered form, a proceeding which reminds us strongly of the action
of a ferment (ef. vol. i. p. 505), and also brings to our mind the influence exerted
by the spermatoplasm on the ovary. The spermatoplasm is only directly concerned
with a few cells in the ovule, but these propagate the influence on all sides to

552 ALTERATION OF FORM BY GALL-PRODUCING INSECTS.

the carpels and to the receptacle, and sometimes even to the flower-stalk. All these
parts would not have developed as they have done had it not been that the minute
quantity of spermatoplasm of a pollen-grain had united with a minute cell in the
ovule.

It will be convenient to consider here the already mentioned similarity between
galls and fruits. If the leaf-rudiments in the bud of a Pistacia shrub are not
affected by leaf-lice they develop into shining green pinnate foliage-leaves; but
if the protoplasm in some of the cells has been altered by the excretions of
Pemphigus cornicularius this same rudiment will assume the form of a carpel,
and become fashioned into a hollow body deceptively like a pod. The fact that
the Pistacia shrub bears plum-fruits and not pods makes it still more remarkable,
for the structure arising from the effect of the animal’s excretion, when mature,
is not like the fruit of the Pistacia, as we should naturally have expected, but like
that of a completely different plant species, viz. the Carob (Ceratonia Siliqua).
The same is true of the metamorphosis caused by the excretion of a gall-gnat
(Lasioptera juniperina) on the uppermost leaves of the Juniper (Juniperus
communis) which assume a form very like the fruit of the Arbor Vite (Thuja),
and many other instances might be mentioned in which galls are produced in
certain species of plants by animal excretions, looking outwardly very like the pods,
capsules, nuts, drupes, and berries of other species. This resemblance to certain
fruits is rendered the more pronounced by the development upon the galls of pig-
ments, wax-like excretions, and hairy coverings, but of course they contain no seeds
in their interior—only the larvee of the animals whose excretions produce the
changes of form. The wonderful thing is that the metamorphosis of the growing
tissue into a fruit-like body is always of the greatest advantage to the animal
which has settled in it, since the tissue serves not only for dwelling and food but
also for protection against unfavourable weather and against the attack of foes.

It is also a fact of great importance that different animals produce differently
shaped galls on the same plant. The Bedeguars produced by Rhodites Rose, the
pea-like galls produced by Rhodites eglanteriw, and the clustered protuberances
produced by Rhodites spinosissime may all occur side by side on the same rose-
leaf (see figs. 8361125 p. 533). On the same elm-leaf Schizonewra Ulmi produces a
wrinkled gall, Tetranewra Ulmi a pocket-gall, and Tetraneura alba a covering gall
(see figs. 3614 °® p. 533). The spherical gall of Nematus gallarum and the bladder-
like gall of Nematus vesicator occur close together on the foliage of the Purple
Willow (see figs. 3617 and 361°), and one sees Oak-leaves on which the small
spangle-galls of four different gall-wasps, viz. Newroterus lanuginosus, numis-
matis, fumipennis, and Spathegaster tricolor are all present together (see
figs. 364112131 p, 541). It has been shown that some Oaks, for example, Quercus
pedunculata, may bear as many as 20-30 different forms of gall produced by as
many kinds of gall-wasps. The characteristic shape, colour, and hair-covering of
these forms of-gall is so constant that we can state with certainty what gall-wasps
have given rise to them. These facts force us to the conclusion that the fluids

GENERAL CONSIDERATIONS. 553

excreted by different gall-produeing insects are specifically distinct. It is only in
this way that we can account for the fact that the same vegetable protoplasm is
ineited in one case to produce a fleshy eovering gall, in another a hollow pocket, and
in a third a closed gall-apple as dwellings for the particular insects concerned.

It should also be mentioned that the same species of insect produces very similar
but slightly different galls on different plants. For example, the gall produced
by Nematus pedunculi on the lower side of the white-haired leaves of Salix
incana is covered with a white felt of hairs, that which the same gall-gnat pro-
duces on the smooth leaves of Salix purpurea is smooth; the gall produced by
Rhodites Rose on the light green leaves of Rosa canina is pale yellow and some-
what reddened on that side turned towards the sun; that on the violet leaves of
Rosa rubrifolia produced by the same insect-species is dark violet, &e. These
distinctions, though only insignificant, show how certain external characteristics
founded in the specific constitution of the protoplasm of different plant-species find
expression even in the gall-structures.

These facts confirm the view that the fluids excreted by different species of
insects, as well as the protoplasm of each plant species, have a peculiar composition.
It is then quite obvious that the alteration which the protoplasm of a species of
plant undergoes under the influence of a specific fluid will be subject to definite
laws. The protoplasm of the particular plant-cell receives by reason of the
alteration, as it were, a new definite constitution with tendencies not the same
as before; but since this constitution determines the outer form of the tissue
derived from these cells, the tissue itself will become shaped into a particular specific
form. These conclusions are of importance with respect to the question of the
origin of new species, inasmuch as they throw some light on the processes which
lead to the origin of new forms. We can now say that the alteration in the form
of a plant only occurs if the constitution of the protoplasm which forms the starting-
point of the plant is itself first altered.

The structures known as galls have not the power of maintaining and multi-
plying themselves, but when their task is ended they perish. In other words, the
progeny arising from the seeds of a plant beset with galls exhibits none of the
alterations shown by the members or shoots of the parent plant. If, for example,
an Oak which is covered with galls is propagated by seeds, the offspring show
no trace of the structural alterations exhibited by the branches, foliage, or flowers
of the mother-plant. The only change which is perhaps sometimes retained
in the offspring is the metamorphosis of the stamens into petals, which has long
been known as doubling, and perhaps also the formation of fasciations, &e. in the
floral region, as in Cabbages (where it is known as a Cauliflower). Few attempts
have yet been made to investigate this matter. My own knowledge of the subject
is restricted to some observations made on the Speedwell Veronica officinalis.
Plants of Veronica officinalis which in consequence of the settlement of gall-mites
on them produced double flowers in 1877 in the garden of my country house were
planted close beside others free from gall-mites and with normal flowers. In the

554 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

following year the gall-mites settled on the latter also, and the greater part of their
flowers then became double. The same result was obtained after living gall-mites
were transferred by me to isolated plants of Veronica officinalis with single
flowers. These in the following year also bore some double flowers. Fruits with
ripe seeds were only produced from the flowers which had remained single amongst
the double ones; and the plants which grew up from these seeds always bore single
flowers only. The gall-mites disappeared for some unascertained reason— probably
they died in the winter. Veronica officinalis has only two stamens in each flower,
and in the double flowers both these and the two carpels are changed into petals
so that of course we could not expect fruit and seeds from them. It would not
be impossible, however, that flowers of other plant families which are provided
with a large number of stamens might behave differently. It might happen,
for example, that only some of the stamens would be changed into petals by the
gall-mites, and that the carpels would remain capable of fertilization. If on such
plants fruits and seeds capable of germination should ripen, the latter might
perhaps produce plants with completely and half double flowers. This would be
explained by supposing that the alteration undergone by the protoplasm of the cells
in the outer part of the flower had extended to the inner, especially to the ovules
and seeds, and further to the plants proceeding from these seeds. I would there-
fore not undertake to state that the Stocks (Matthiola annua and imcana), the
Wallflower (Cheiranthus Cheiri), the Pinks (Dianthus Caryophyllus, plumarius,
&e.), the Poppies (Papaver Rhwas and somniferum), various Ranunculacez
(Delphinium, Peonia, Ranunculus), and many other plants which have long been
cultivated in gardens with semi-double flowers, and which produce such flowers
when propagated by seeds, had not gained this characteristic in the first place
by the influence of gall-mites. It is less probable, though not beyond the range
of possibility, that by the grafting of Hawthorn branches whose uppermost leaves
have been deeply segmented by the influence of the gall-gnat Cecidomyia Crategi,
a Hawthorn bush might be produced which would exhibit these deep segmentations
and slits on all its foliage. However, these last remarks are the merest suppositions;
at present we have not the data on which to base any definite conclusions.

THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

The aim of agriculturalists has always been so to cultivate their land as to rear
plants likely to grow luxuriantly, to bear good fruit, and thus to afford an abun-
dant harvest in return for their pains. Gardeners similarly have made it their
endeavour to produce from wild plants races whose flowers are superior to those
of the ancestral stock in form, colour, and scent; and the results of their labours
are the delight and admiration of all lovers of beauty. In both cases the idea has
been to perfect and “ennoble”, and the means adopted have been successful to a
degree calculated to amaze anyone who studies the history of cultivated plants with
attention. The methods which led to these results have not always been deliber-

LARGE PRODUCTION OF NEW GARDEN FORMS. 555

ately adopted, nor have they depended on scientific researches. On the contrary,
chance observations made by growers in the course of their dealings with vegetable
life as it occurs in nature have been the means of suggesting the first unaided
attempts to make crops more productive, fruits and vegetables more palatable, and
flowering-plants more pleasing to the eye.

The most important method adopted has been the artificial crossing of the
species which are brought under cultivation. When we consider that, from time
immemorial, Chinese and Japanese gardeners have produced Asters, Chrysanthe-
mums, Camellias, Pinks, Peonies, and Roses, of which the majority are the results of
crossing, we may assume with certainty that the practice of dusting flowers of one
species with the pollen of another species first came into use in those countries. It
is true that in Europe the contrivance was known to rose-growers at the time of
the Roman Empire, but it was not employed on an extensive scale till the seven-
teenth century, when the fashion for breeding Tulips and Auriculas became the
rage. The gardeners of that day still made a great seeret of their mode of pro-
cedure, and it was not till the latter half of the eighteenth century that the
production of new forms of plants by the aid of artificial crossing was carried on
at all generally. For some decades the rearing of these new forms, which are
‘ealled hybrids, has been one of the most important parts of a gardener’s duties, and
we shall not exaggerate if we put the number of hybrids hitherto produced in
gardens in the course of the nineteenth century at 10,000. Many hybrids which
were great favourites only a short time ago have disappeared from our gardens
and have been replaced by others. As in so many other matters, the fashion
changes; new forms are in constant request, and horticulturists endeavour to meet
the demand by introducing wild plants from the most various regions and crossing
them with those already under cultivation. It is now no longer uncommon for
gardeners, in advertising some plant which has been brought from distant parts, to
recommend it to the trade, not on the ground of its own beauty, but because it
possesses flowers of an exceptional colour or leaves of a peculiar cut, and will there-
fore, in all probability, if crossed with other species, yield handsome new hybrids.
Rose-growers always welcome the discovery of any instance of variation in the Wild
Rose as an important event, because, by crossing this Rose with others, they are
able to produce a large number of new forms, and there is always the chance that
one or other of them may find favour with the public. On an average, 60 newly-
bred Roses come into the market yearly; in the year 1889 the number even
amounted to 115! A Rose cultivator at Meidling, near Vienna, grows in his garden
nearly 4200 different kinds of Rose, and yet he is still far from possessing all the
forms which have been produced in recent times (chiefly by French growers) by
crossing one with another. According to his estimate, the number of Tea and
Indian Roses alone is nearly 1400, and the total number of all the different Roses
which the trade has produced up to the present day amounts to 6400.

The plant-forms which are called into existence by the operation of crossing are,
in the case of Roses, reproduced largely by means of brood-bodies (cuttings and

556 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

layers) as well as by budding and grafting (see vol. i. p. 213); but the first origin
of the new forms is always to be traced to erossing. This statement applies also to
many other plants of which gardeners have taken possession, and especially to cases
where propagation by seed requires more time and trouble than multiplieation of
brood-bodies. The kinds of Tulip, Gladiolus, and Lily produced by crossing are
propagated most easily by means of bulbs, and the tuberous Begonias, Dahlias, and
Gesneracee by tubers, whilst Pinks, Pelargoniums, Cactuses, and many others are
most rapidly reproduced by cuttings. Moreover, these methods ensure the preser-
vation of the peculiarities of the new forms unchanged, and such perpetuation of
characteristics would be much more difficult to achieve if the plants were propa-
gated by means of seeds. On the other hand, a number of new forms which have
originated as the results of crosses effected in gardens, such as those of Petunia, ~
Portulaca, and Viola, are reproduced with less trouble and greater rapidity by
seeds, and that method is in such cases preferred to the cultivation of brood-bodies.

The statement that new forms of plants are bred originally in gardens by any
other method than that of crossing is incorrect; it is sometimes made in ignorance,
but sometimes also with the intention of deceiving. In former times gardeners
believed that, in order to produce new forms, it was sufficient to plant different
species in close proximity to one another. The idea was that if the seeds of such
plants were taken and sown in good soil, there would always be found amongst the
seedlings a few forms differing from the parent; these were to be selected for
especial care in cultivation, and were to be treated as starting-points of new forms.
The gardeners who acted on this assumption had not, it is true, themselves crossed
the flowers; and if this was all they meant, there was no falsehood in the state-
ment. The operation of crossing was, however, performed without their knowledge
by hive- and humble-bees and other insects, and the planting together of the
different species was only of advantage inasmuch as it facilitated the conveyance
of pollen from one species to the stigmas of another. A celebrated grower of the
old school once assured me, in all seriousness, that he did not himself cross the
plants he reared, but that he had repeatedly observed that early in the morning,
soon after a flower opened, it put forth infinitesimally fine threads which radiated
in all directions and reached across to the flowers of other plants, forming in a short
time a web like that of a spider! I would not have mentioned this statement were
it not for the importance of pointing out the unreliable character of so many of the
statements made by gardeners, especially in the past; and I repeat that the person
responsible for the above communication is a well-known and much-esteemed horti-
culturalist. Gross inventions such as the above would, of course, be at once seen
through and rejected by any thoughtful man; nevertheless, in some instances,
reports of growers, likewise untrue or inaccurate, but not bearing the stamp of
improbability so plainly upon the face of them, have been credited and have even
found their way into books, particularly into those whose authors have omitted to
confirm the reports by watching the garden-experiments from beginning to end
themselves. The statements are then not infrequently quoted as “results obtained

THE PRODUCTION OF HYBRIDS. 557

by trustworthy experiments made by gardeners” and relied upon for the foundation
of “laws based upon facts”; theories are then built up upon them, and are copied
from one book to another. It becomes very diflicult afterwards to get rid of such
propositions, especially if they afford support to the hypotheses of distinguished
savants.

An instructive example of the kind of thing referred to is afforded by the
following statement which for a long time obtained currency in works on Botany:
“Hybrids resulting from the crossing of two species exhibit two forms, in each
case, according as the pollen employed in generating them belongs to the one or
to the other species.” There are, of course, two ways in which a pair of species,
which may be represented by the letters A and B, may be crossed. In one case the
pollen from A is transferred to the stigma in B, whilst in the other case the pollen
is taken from B and transferred to the stigma in A. Now, it has been asserted
that it is possible to determine from the form of the hybrid which of the two
parent-species supplied the pollen. The hybrid is said to resemble that parent more
closely from which the pollen was derived so far as its flowers are concerned, hut
to show greater aflinity to the fertilized stock in respect of its foliage. This is,
however, absolutely untrue. All careful experiments made without prejudice have
pointed to the conclusion that it makes no difference to the forms, either of the
leaves or of the flowers, whether the pollen has been taken from the one parent-species
or from the other. Besides this, in most instances the approximation of the hybrid-
form to one or the other stock affects all parts of the hybrid plant in an equal
degree, and not the flowers or the foliage only. In the rare cases where a hybrid
has flowers more like those of one parent and leaves more like those of the other,
it is just as likely for one stock as the other to have yielded the pollen used for the
cross.

But it would be a thankless task to attempt to correct all the hasty, careless,
and erroneous statements, past and present, and it will probably be of greater
utility to give a general survey of what has been ascertained concerning the form
and temperament of hybrids by impartial observers who have taken into account
all the concurrent circumstances, and have allowed for the sources of error inci-
dental to the experiments.

The formation of a hybrid plant presupposes two stock-plants as parents which
have different properties and characters. A cross must take place between the two
—that is to say, the stigma of the one must be dusted with pollen from the other;
the pollen must put forth pollen-tubes and an effectual union between spermato-
plasm and ooplasm must be effected. For the sake of brevity, the plant from which
the pollen, and therefore also the spermatoplasm, is derived is called the paternal
stock or father-plant, and that which has its stigma dusted and its ooplasm ferti-
lized is called the maternal stock or mother-plant. As a plant’s external marks and
characteristics, which are perceptible to our senses, are an expression of its internal
organization and of the specific constitution of its protoplasm, it may be assumed
that the plant-individual which owes its existence to the union of two protoplasts

558 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

of different constitutions possesses marks and attributes, some of which are charac-
teristic of the father and others of the mother. As a matter of fact, the individuals
which growers call by the various names of hybrids, mongrels, and bastards answer
to this supposition. Some of their attributes and external characters are derived
from the paternal, some from the maternal stock. If the relative admixture of the
two stocks were to be determined in the case of a hybrid by summing up the
characteristics transmitted from each source, the share of each parent would in
many cases be found to be a half. In such a case it is usual to say that the hybrid
is a mean between its parents. Examples are afforded by Gewm hybridum, which
originates from crossing Gewm montanum and G. rivale, Hieracvum stoloniflorum,
derived from Hieraciwm awrantiacum and H. piloselleforme, and Nuphar inter-
medium, a eross between Nuphar luteum and N. pumilum. But it also happens
sometimes that the proportion of characters inherited by a hybrid from one of the
parent-stocks amounts to about two-thirds, leaving only one-third as the propor-
tion inherited from the other, and in that case the hybrid is said to exhibit an
approximation to one of the parent-species. The Saxifrage hybrids are very
instructive examples of this class. The stigmas in a flower of Saxifraga aizoides
were dusted with the pollen of S. cesia. Fertilization was successfully effected,
and a capsule containing fertile seeds came to maturity. The plants reared from
these seeds resembled in some cases the intermediate form described by Botanists
under the name of Saxifraga patens; others approximated more closely to the
paternal stock, and a third group to the maternal stock. A similar result was
obtained by crossing a flower of Saxifraga aizoides with the pollen of S. mutata.
From seeds of the same capsule were produced two different kinds of hybrid,
of which one was intermediate between the parents (Saxifraga Hausmann),
whilst the other (Sawifraga inclinata) approximated more closely to S. mutata.
These experiments point to the conclusion that the share which each parent
has in the form of a hybrid depends upon the quantity of its spermatoplasm
or ooplasm, as the case may be, used in the production of the seedling relatively
to the quantity derived from the other parent; and in the case of hybrids issuing
from the same fruit we are forced to suppose that the variability of the degree in
which a particular form is inherited is caused by the existence of quantitative
differences between the several spermatoplasmie and ooplasmie nuclei (or cells)
which coalesce in pairs in the interior of the same ovary.

Important evidence in support of this supposition is derived from experiments
made in connection with the crossing of various composites of the Thistle genus
(Cirsium). In these plants each ovary contains a single ovule only, and therefore
each fruit can only produce a single individual. On the other hand, each capitulum
is composed of a large number of florets, and when a head is in full bloom nearly a
hundred mature stigmas project from it in close proximity to one another. If pollen
from another species is transferred by means of a paint-brush on to these stigmas,
wholesale crossing, so to speak, ensues; and it may be confidently expected that a
proportion of these simultaneous erosses will be effectual. The harvest of fruit

DIVERSITY OF HYBRIDS FROM SAME PARENTS. 559

from the capitula selected for the experiment was not, it is true, very plentiful, but
some fruits invariably came to maturity. If these one-seeded fruits, all of which
have originated at the same time and under similar conditions, are sown, the indi-
viduals produced from them are but seldom like one another. The attributes and
external marks of the paternal and maternal stocks respectively are in some repre-
sented in the proportion of about 2:1, in others in the proportion of 1:2, and ina
third class in practically equal proportions; cases are even known where four, five,
or more distinct forms of hybrid have developed from the fruits of a single
capitulum. I found the most striking differences amongst the hybrids obtained by
crossing a capitulum of Cirsiwm oleracewm with the pollen from a capitulum of
Cirsium heterophyllum. Those produced by crossing a head of Cirsium Pannoni-
cum with pollen from a head of Cirsiwm Erisithales were scarcely less conspicuously
diverse. As it must be presumed that the spermatoplasm and ooplasm—or rather
the spermatoplasmie and ooplasmie nuclei—which have been formed in the adjacent
florets of a capitulum are alike in composition and ultimate structure, the variety
of the hybrids springing from such florets must depend solely on the relation
between the masses of ooplasm and spermatoplasm respectively which coalesce in a
flower, and the ratio between these masses must be in the one case 1:2, in a second
1:1, and ina third 2:1. Of course these ratios give but an approximate measure
of the degree in which each parent has participated in the generation of the inter-
mediate forms. Where five kinds of intermediate forms occur the series would be
approximately represented by the ratios 1:4, 2:3, 1:1, 3:2, and 4:1. The first
time flowers of a head of Cirsiwm Erisithales were crossed with pollen from
Cirsium palustre they produced two different forms of hybrid, one of which
approximated to the paternal, the other to the maternal stock; but no form exactly
midway between the two parent-stocks was obtained. A second trial of the same
experiment resulted in the production of a single form which did occupy this inter-
mediate position. These observations show that there is no definite law governing
the form of hybrids; one might even say that irregularity is here the rule. On one
occasion all the individuals which are the result of a cross between two species are
alike, on another occasion they constitute more or less numerous links in a chain of
intermediate forms.

Hybrids which do not stand midway between the parent-species but approximate
to one or other of them are called goneoclinie (yores=parent, ve=I lean). That
such hybrids may arise from a first cross is established beyond question by the
experiments above recorded; but there is also another process whereby they are
produced, and that is the crossing of a hybrid with one of its parent-stocks. These
crosses are effected in great numbers, and all observers agree that in general the
results are better in such cases than where two species are crossed; that is to say, if
a hybrid’s stigmas are dusted with the pollen of one of the parent-species a larger
number of fertile seeds may be looked for than if the plants crossed were of distinct
species. The individuals resulting from the cross of a hybrid with one of the parent-
stocks also occupy, as might be expected, a position as regards marks and attributes

560 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

intermediate between their progenitors; here again, however, forms are not always
alike, and sometimes several intermediate forms make their appearance. If the
hybrid derived from Cirsiwm Erisithales and ©. Pannonicum, which inherits equally
from both parents, be crossed with pollen from Cirsium Erisithales, the resulting
individuals have a stronger resemblance to the latter species and are instances of
goneoclinie hybrids. But when Cirsiwm Erisithales and C. Pannonicwm are
erossed for a first time hybrids are also produced which are not exactly midway
between the parents but are more like C. Erisithales. These naturally resemble
the goneoelinie hybrid derived from crossing the offspring of ©. Erisithales and C.
Pannonicum with C. Erisithales, and if one were not in a position to follow the
history of the origin of the hybrid in question its characteristics alone would not
furnish sufficient data for a judgment as to the mode of production of the goneo-
clinie hybrid.

Hybrids which are the offspring indirectly of three different species are called
ternary hybrids. The word “indirectly” must be specially emphasized here, lest
the reader should fall into the error of supposing it to be possible that pollen-tubes
from two or more species should simultaneously fertilize a single ovule. Such an
occurrence never happens, not even if a mixture of pollen belonging to two or more
different species be placed upon the stigma of a particular flower. On the other
hand, it has been ascertained by numerous experiments that if the hybrid-offspring
of two species is crossed with the pollen of a third species, or vice versd, another
hybrid is produced. Thus, for instance, if the hybrid of Linaria genistifolia and
L. purpurea is crossed with the pollen of LZ. striata the result is a ternary hybrid.
In one experiment the stigmas in a capitulum of Cirsium Linkianum (the hybrid
offspring of C. Erisithales and ©, Pannonicum) were dusted with pollen taken
from C. palustre. A considerable number of fruits ripened, and the hybrids which
arose from them were ternary hybrids, exhibiting marks and characteristics of
0. Erisithales, C. Pannonicum, and C. palustre respectively. These hybrids, more-
over, were not all alike; some of them bore striking resemblance to Cirsiwm aquilo-
nare, the hybrid produced by crossing C. palustre and ©. Pannonicum, and exhibited
very few of the peculiarities of C. Erisithales, whilst other individuals were ex-
tremely like Cirsiwm ochroleucum, the hybrid obtained by crossing C. Erisithales
and C. palustre, and only showed slight indications of its relation to C. Pannoni-
cum. Growers of garden-flowers have achieved great success in producing orna-
mental ternary hybrids in a number of genera (Achimenes, Begonia, Dianthus,
Gladiolus, &c.). Ternary hybrids of various Willows are also met with in
gardens; one of these is obtained by crossing Salia Cremsensis, a hybrid of Salia
Caprea and S. daphnoides, with 8. viminalis, another by crossing Salia Wichwre
(the hybrid-product of S. incana and S. purpwrea) with S. einerea, and so forth.
Willows have been also used for the prosecution of still further experiments. The
crossing of two hybrids of different parentage on both sides resulted in the genesis of
hybrids combining four species of Willow. Indeed, six different species of Willow
have on one occasion been combined by successive erossing— Wichura having

COMBINATION OF PARENT-CHARACTERS, 561

succeeded in producing in Breslau a compound hybrid in which were united Salia
Caprea, S. daphnoides, 8. Lapponum, 8. purpurea, S. Silesiaca, and S. viminalis.
It need hardly be said that the characteristics of the six ancestral species in such
a case as that of the last-mentioned hybrid are not easily identified. Even where
a hybrid is the offspring of a single cross between two species it is not always easy
to determine its origin from its external appearance, and in the absence of any
knowledge of the history of its production. The characteristics of the parent-stocks
are not combined in all hybrids according to a single definite rule. Sometimes the
combination seems to amount to a complete fusion, so that the form produced might
be compared to an alloy of two metals. Very often a new form is generated which
combines in a definite geometrical ratio the characteristics of the parents in respect
of the position and direction as well as the shape and size of its separate parts. In
that case there is said to be a union of the parental characters. The structural
characters of both stocks are represented unmodified, but are so closely bound
together as to suggest a composite crystal founded upon two different crystalline
forms. Just as in definite combinations of crystals the faces of one component form
. are dominant, and determine the general aspect in one case and those of the other
component form in another case, so in many hybrid plants sometimes the attributes
of the one parent, sometimes those of the other, are most conspicuously reproduced.
Other hybrids again are analogous to combinations in which both erystalline forms
are equally represented. Again, in addition to the above classes of hybrids
wherein the parental characters are either completely merged together or intimately
united there are many cases where those characteristics are present almost un-
changed, and subsist side by side like the particles of a rock. The most common
case of this mixtwre or juxtaposition of properties occurs where the hybrid displays
hairs, glands, or prickles of two forms interspersed together, one of which is identical
with the form of the structure in question exhibited by the maternal stock, whilst
the other has been inherited unchanged from the paternal stock, Or, one part of
the hybrid’s flower may be coloured like one parent and another like the other
parent. Hybrids are also known in which the foliage is almost indistinguishable
from that of one parental stock whilst the flowers are like those of the other, so that.
at first sight a hybrid of the kind looks as if it were a plant of the former species
with flowers of the second species affixed to it for a joke. On closer inspection some
slight differences may be perceived between the leaves and flowers of the hybrid and
those of the parent species respectively, but this does not alter the fact that hybrids
exist whose leaves resemble far more closely those of one parent, whilst their
flowers are more like those of the other. Probably it was the oceurrence of such
a hybrid which suggested the proposition referred to on p. 557 that in the product
of a cross between two species the flowers reveal the paternal and the foliage the
maternal stock. But this statement is incorrect, as was said before, for some
hybrids approximate to the maternal stock in respect of their flowers, and to the
paternal stock in respect of their leaves.

Of the three ways in which the parental characters may be combined in a
Vor. I. 86

562 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

hybrid—z.e. by fusion, by union, or by mixture—one alone sometimes prevails in all
the parts; but usually, on the contrary, there is an incalculable degree of variation
in this connection. There are, for example, Rose hybrids in which the outline of
the leaves exhibits a union, the colour of the flowers a fusion, and the hairs a mix-
ture of the corresponding characters in the parents.

A brief account will now be given of a few examples to illustrate the manner in
which the combination of parental characters in a hybrid is manifested throughout
the structure of the plant and particularly in the forms of the stems, leaves, and
flowers, and in those of thorns, bristles, hairs, and other epidermal appendages. The
species of Willow known as Salia Caprea grows in the form of a little tree, with
thick, straight, erect branches, each of which bears about 25 leaves; Salia repens,
on the other hand, is a low shrub with a procumbent stem and slender, rod-like
branches ascending in curves from it, and each bearing about 40 leaves. The
hybrid of these two is a small tree with a bent stem and ascending branches, which
in length, thickness, curvature, and direction are intermediate between the Salix
Caprea and Salia repens, and which are furnished with some 30 leaves apiece.
Again, the foliage-leaves of Prunella vulgaris have their margins entire, whilst those
of P. laciniata are deeply cut, and their hybrid Prunella intermedia has lobed
leaves. The leaves of Potentilla sterilis (or P. Fragariastrwm) possess three
leaflets, each leaflet being furnished on either side with from four to five serrate
indentations. The leaves of Potentilla micrantha likewise possess three leaflets,
but each leaflet has from seven to ten serrate teeth on each side. In the hybrid
of these two species the leaflets have from six to eight indentations on each side.
The shape of the leaf is, as is well known, intimately connected with the course,
ramification, and disposition of the bundles called nerves. Now, if the net-work of
strands in the leaves of the parent-species is compared with that in the leaves of
the hybrid, it is astonishing to find how the union of the two systems may be
traced in the minutest details. No group of plants lends itself better to this sort
of investigation than the Willows. Even if a single leaf of the hybrid offspring
of two species of Willow is submitted for inspection, it is possible in most cases to
determine, from the number and distribution of the nerves, the identities of both
its parents. Saliz pwrpwrea produces one hybrid when crossed with Salia grandi-
folia, and a second when crossed with Salix Caprea. Salix grandifolia has twice
as many lateral nerves in each leaf as Salia Caprea, and this difference is repro-
duced in the corresponding hybrids, whose leaves in all other respects resemble one
another closely.

The involucral leaves of Composites are well known to be extremely diverse in
shape, and systematic Botanists have always attributed great importance in the
discrimination of species to the size, shape, and margination of these leaves and to
the peculiar appendages at their apices. Now, the hybrids of Composites not
infrequently have involucral leaves which differ widely from the forms character-
istic of the parent-stocks. Thus, for instance, each leaf of the involucre in a
capitulum of Centawrea rupestris terminates in a long yellow prickle, whilst the

COMBINATION OF PARENT-CHARACTERS, 563

corresponding structure in Centawrea Scabiosa is bordered by a broad, membranous,
fringe-like edge of a dark-brown colour. In Centawrea sordida (Grafiana),
the hybrid offspring of these two species, each involucral leaf is edged with a
narrow, light-brown membranous and fringed border, and terminates in a short
yellowish prickle. A very instructive example of the union of parental characters
affecting all the different parts of the floral region is afforded also by the Labiate
Marrubium remotum, which is produced by crossing Marrubiwm peregrinum and
M. vulgare. The small tuft-like inflorescences in the leaf-axils of Marrubium
peregrinum include from 10 to 18 flowers, those of M. vulgare from 4 to 5, and
those of the hybrid M. remotum from 5 to 10. The ealyx of M. peregrinum is
grey and covered with felted hairs, and its margin is provided with five large
subulate teeth which terminate in straight points. The calyx of M. vulgare is
green and sparsely clothed with hairs, and its edge has ten small teeth which
terminate in stiff reflexed points like hooks. Five of these teeth are rather longer
than the rest. The calyx of M. remotum is greyish-green and clothed with a
loose felt; its edge is furnished with five big subulate teeth which terminate in
stiff out-curved points, and have from two to five very small teeth interspersed
between them. The three lobes of the under-lip of the corolla are almost of equal
length in Marrubium peregrinum, whilst in M. vulgare the middle lobe is three
times as long as the two lateral lobes. In the hybrid Marrubiwm remotum the
middle lobe of the lower lip is half as long again as the lateral lobes. An excellent
example is also afforded by Dianthus @nipontanus, a hybrid Pink resulting from
across between Dianthus alpinus and D. swperbus. In D. alpinus the bract-like
scales at the base of the calyx are almost as long as the tube of the calyx itself,
whilst in D. swperbus their relative length is only a quarter or a third; in the
hybrid D. @nipontanus these bracts are half as long as the tube. The petals of
D. alpinus have broad laminz beset at the margin with short triangular teeth,
those of D. swperbus have their laminz slit up into a number of narrow strips, and
those of D. Hnipontanus have deeply-incised lamine, the margins being divided
into linear segments. The dimensions of the various parts of the flower in a hybrid
also exhibit in most cases a combination of the corresponding parental character-
istics. Thus, for instance, the perianth of the Orchid Gymnadenia conopsea has a
long spur—that is to say, the segment of the perianth known as the labellum is
produced backwards into a saceate protuberance supposed to resemble a spur, and
this portion of the petal in Gymnadenia conopsea is 15 mm. in length. In Nigri-
tella nigra, on the other hand, the spur is very short, measuring about 2mm. The
hybrid of these two Orchids, Nigritella suaveolens, has a spur varying from 5 to
7 mm. in length. In Willow hybrids the number of stamens in each flower of the
hybrid is invariably between the corresponding numbers in the two parent-
species. For example, the number of stamens in a flower of Salia alba is 2,in
Salix pentandra 5-12, and in their hybrid Salia Ehrhartiana 3-4.

The cellular structures produced from the epidermis of the stem and leaves
which are differentiated as hairs, bristles, scales, glands, &e., and are classed together

564 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

under the name of investments (indwmentum), are very constant characters in most
species of plants. The occurrence of stellate hairs, in particular, is looked upon by
systematic Botanists as an important point in assisting them to distinguish between
similar species, and so also is the presence of glandular hairs composed of simple
rows of cells, and terminating in globular bladders full of ethereal oils. Hybrids
exhibit the most varied combinations of the indumenta of their parents. In the
majority of cases the characteristics of the two stocks in this respect are mixed, but
less frequently are they united, and in the latter case the shape, size, and number of
hairs, bristles, scales, and glands are intermediate between those of the same appen-
dages in the two parent-species. The Lungwort genus (Pulmonaria), which has a
special tendency to hybridization, includes only a few species, but each one may be
recognized by the nature of its indumentum, Thus, Pulmonaria officinalis is dis-
tinguished by the thousands of short unicellular prickly hairs, scarcely perceptible
to the naked eye, which are interspersed amongst the long scattered bristles on the
upper surfaces of the leaves. In Pulmonaria angustifolia the leaves are destitute
of these minute prickles, but bear on their upper surface a more abundant quantity
of straight appressed bristles of equal length. The leaves of the hybrid derived
from the two preceding species, viz. Pulmonaria hybrida, are richly supplied with
long bristles, and interspersed amongst these may be seen a large number of shorter
bristles which are about two or three times as long as the prickly hairs of Pul-
monaria officinalis, A very instructive example is also afforded by the hybrid
Rhododendron intermedium, which is easily produced by crossing the two Alpine-
Roses (Rhododendron ferrugineum and Rhododendron hirsutum). The upper
faces of the leaves of R. ferrugineum are dark-green, smooth, and shining, whilst
their backs are rusty and dull owing to the presence of a dense crowd of tiny scales.
The margins are not ciliate. The leaves of R. hirsutum are light-green and beset
with scattered whitish glands (see vol. i. p. 232, figs. 54° and 54°), and their margins
are fringed with long hairs. In Rhododendron intermediwm both kinds of epider-
mal appendage are displayed side by side. The under surface of the leaf is furnished
with brown scales, though not so profusely as in Rhododendron ferrugineum, and
its edge is fringed with hairs, but not so thickly as in R. hirsutum. The same sort
of thing occurs in Roses, Cinquefoils, Blackberries, Drabas, Hawkweeds, and many
other plants. Where one parent Rose bears only non-glandular and the other only
glandular hairs the hybrid is sure to be clothed with a mixture of the two kinds
of hairs. Several species of Cinquefoil (Potentilla) have stellate or tufted hairs,
whilst others are entirely free from them and bear none but simple hairs on their
leaves. In hybrids derived from two of these species—one with compound and the
other with simple hairs—stellate or fasciculated hairs are invariably intermixed with
a large number of simple hairs. A few species of the perennial Whitlow-grasses
(Draba), which are indigenous to mountainous districts in Central Europe, have
rectilinear anvil-shaped hairs, whilst others have three- or four-rayed stellate hairs.
In the hybrids which spring from these different species rectilinear and stellate
hairs grow together on the same leaf. If the hairs of two parent-species are of the

MINUTE STRUCTURE OF HYBRIDS. 565

same form but of unequal length, those of their hybrid offspring have a length
which corresponds approximately to the mean between the lengths in the parent-
species. Thus the length of the hairs on the backs of the leaves is 03 mm. in
Salix awrita, 1:2 mm. in Salix repens, and 0°6 mm. in their hybrid Salix plicata.
The hairs in Salix Caprea measure 0°8 mm., in Salix viminalis 03 mm., and in
Salix acuminata, their offspring, 0°5 mm. Whenever one stock is glabrous and the
other hairy, one may be quite sure that the corresponding parts of their hybrid will
be furnished with hairs, but less profusely than the parent-species from which that
particular characteristic is derived. This is the case, for instance, with Primula
Sturt, the hybrid produced by crossing the glabrous Primula minima with Pri-
mula villosa, which has glandular hairs. The leaves of the latter are thickly
covered with these hairs, which vary from 0°. mm. to 1 mm. in length, and Primula
Stwrii has scattered glandular hairs which measure 0'3 mm. The hybrids obtained
by crossing the Purple Willow (Salix purpurea) with the Common Osier (Salix
viminalis) are distinguished by Botanists into two sections, one of which—Salia
rubra—approximates to the Purple Willow and the other—Salia eleagnifolia—to
the Common Osier. The leaves of the Purple Willow when mature are glabrous at
the back, those of the Common Osier have small glistening hairs lying appressed to
their under surfaces, parallel to the lateral nerves, and measuring 03 mm. There
are about 1800 of these hairs on a square millimetre. The hairs of the hybrid
Salix eleagnifolia are of the same length as those of S. viminalis, but there are
only about 800 of them to the square millimetre, whilst the hairs of the hybrid
Salix rubra are somewhat shorter, and there are only 400 to the square millimetre.

Recently the discovery has been made by Wettstein that the form and dis-
position of the cells and tissues in hybrids is also a combination of the corresponding
characteristics in the parent-species. The various species of the Pine genus
(Pinus) may be distinguished with certainty by the anatomical structure of their
needle-shaped leaves, in particular by the thickness of the epidermal cells, the
number of the stone-cells lying beneath the epidermis, and the number of the resin-
ducts. In the hybrids the anatomical characters of the parents in these respects
are united, and the result is indeed often an exact arithmetic mean between the
two. Thus a needle of the Scotch Pine (Pinus sylvestris) contains from 6 to 10
resin-ducts, that of the Mountain Pine, Pinus Mughus (montana), contains from
3 to 5, and that of the hybrid offspring of the two from 5 to 7 such ducts. The
Junipers (Juniperus) afford a similar instance. In their case the leaves are dis-
tinguished by the various thickness and length of the layer of sclerotic-cells which
covers the back of each leaf, by the width of the resin-duct running through the
middle of the leaf, and by the number of the cells encasing that duct. In the
hybrids, such as Juniperus Kanitzii, which is produced by crossing Juniperus
communis and J. subinoides, there is evidently a union of the parental attributes
in the corresponding cellular structures in the leaves. It has also been shown by
Hildebrand that in the Wood-Sorrel (Ovalis) hybrids also the anatomical characters
of the parents are united, but by far the most comprehensive study which has

566 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

been made in recent times into the minute structure of plant-hybrids is by Mac-
farlane. He selected a number of hybrids, and worked through their anatomy
from base to apex in the most painstaking manner. He dealt with roots, stems,
leaves, and the various portions of the flower, always comparing their various
tissues (both as regards size, form, and distribution) with those of their parent-
forms. And his result is to confirm what has been written above, though it is
obvious he had never read these pages. Amongst the more interesting of his
results may be mentioned those on starch-grains. Of course in a great many of
the parent-forms uniting to form a hybrid there is no recognizable difference in the
size or structure of the starch-grains. But in the genus Hedychiwm (belonging
to the family Zingiberacez) exceptions to this rule were found. Thus, those of
Hedychium Sadlerianum are intermediate in form and size between those of its
two parents, H. Gardnerianum and H. coronariwwm; and those of a hybrid between
H. elatwm and H. coronariwm exhibited similar intermediate characters.

It is important to note also that the aromatie substances and colouring matters
produced in the cells of a hybrid are inherited partly from the maternal, and partly
from the paternal stock. As we have several times already had occasion to mention,
the various species of the Rose genus may be recognized at once by their peculiar
scent. The perfume of Rosa Centifolia is the one which in particular is understood
by the rose-scent, but it is very different from that of Rosa alpina, and the latter in
its turn is unlike any of the scents emitted by Rosa arvensis, R. Gallica, R. Indica,
&e. Rosa Nasterana has a scent strongly resembling that of Pinks, whilst Rosa
lutea and R. punica are notorious for their disagreeable smell. Now the hybrid
Roses emit odours in which the scents of the parent-species are merged together in
a great variety of ways. Usually the scent of one stock predominates, and there is
only a suggestion of the other. Sometimes, however, an entirely new scent is
evolved from the fusion of the two, as is the case, for instance (according to Mac-
farlane), in Hedychiwm Sadlerianum, the hybrid between H. Gardnerianum and
H. coronarium; and, again, in other cases, one of the component odours is inten-
sified and the other is extinguished. The same statement applies to the aromatic
substances to which the scent of the foliage is due. The hybrids of Rosa
glutinosa, Rosa rubiginosa, and R. rugosa, with Rosa Gallica and R. Centifolia,
are very interesting in this connection. The aromatic substances which are con-
tained in fruits and excite our nerves of taste are also inherited, partly from the
maternal and partly from the paternal stock. Owing, however, to the difficulty of
naming the various sensations of smell and taste it is of little use to discuss the
subject more fully.

As regards the colouring-matters reproduced in hybrids the first point to notice
is that in cases where the foliage is of different shades of green in the parent-species
the leaves of the hybrid exhibit a shade intermediate between the two. Conspicuous
instances of this are afforded by the hybrid Willows derived from Salia nigricans
and S. purpurea. In both these species the foliage becomes black when it withers,
and this characteristic is transmitted, though not in its full strength, to the hybrids

COLOURS IN HYBRIDS. 567

which S. nigricans and S. purpwrea form with other Willows whose foliage turns
brown when it dries up. The colour of the flowers in hybrids is usually the result
of a fusion of the colours in the parent-species; less frequently it is a mixtwre of the
original colours. The cases of fusion oceur especially amongst the hybrids of
Orchids, Louseworts, Anemones, Pulsatillas, Medicagos, and Mulleins. If the tone
of the red or blue petals in one parent-species is dull and in the other bright, the
same colour reappears in the hybrid, but of a medium tone. Thus the colour of the
petals in Gymnadenia conopsea is rose-red and in Nigritella nigra dark blood-
red, whilst in their hybrid, Nigritella swaveolens, it is bright carmine. The corolla
of Pedicularis incarnata is of a subdued carmine tint, and that of P. recutita of a
dark reddish-brown, whilst their hybrid, P. atrorwbens, has a dark purple corolla.
Where the floral colour of one parent-species is white and that of the other a full
yellow, red, or blue, the hybrid’s flower usually exhibits a pale yellow, red, or blue
coloration. The flowers of Anemone nemorosa are white, those of A. ranunculoides
golden-yellow, and those of their hybrid, A. intermedia, sulphur-yellow. The colour
of the flowers in a hybrid whose parents have yellow and violet, or blue flowers,
respectively, is very remarkable. Medicago media, which is the hybrid offspring
of the yellow-flowered Medicago falcata, and the blue-purple flowered M. sativa
very often has green corollas. The hybrids (Verbasewm commutatum, V. rubigi-
nosum, V. Schmidtii, V. versiflorum, &e.) obtained by crossing the yellow-flowered
Mulleins with Verbasewm phenicewm, whose flowers are a conspicuous purple, all
display a bright brown tint in their corollas. The colour in question is just the
same as that which is produced by mixing gamboge with the purple prepared from
carmine and indigo. Quite a different tint is exhibited by the corolla of Verbascum
pseudopheniceum, the hybrid generated by crossing V. Blattaria and V. pheni-
ceum. One of the parent-species (V. Blattaria) in this case has pale yellow and the
other (V. phenicewm) violet-purple corollas, and in the hybrid (V. pseudopheni-
ceum) the corolla is pale crimson. Nor are cases wanting in which hybrids have
been produced from forms with red and blue flowers respectively. The brilliant
scarlet-Howered Delphiniwm nudicaule has been crossed in the Edinburgh Botanic
Garden with the dark blue-flowered D. cashmirianum, the hybrid product being of
a lurid purple-red hue. Darwin obtained by crossing the red and blue Pimpernels
(Anagallis) a progeny some of which were blue, some red, and some intermediate
in colour. As a final instance of this colour-fusion may be cited the hybrid Pitcher-
plant Nepenthes Mastersiana. This hybrid is produced from N. sanguinea, the
pitchers of which are of large size and vary in colour from greenish-scarlet to
crimson, and of V. Kharsiana, which bears long narrow pitchers, varying from
yellowish-green to dull red-green. The hybrid (says Macfarlane) presents a
corresponding latitude in colour effect, though on the average it is greenish-crimson.

The hybrids which originate from crosses between Primula Awricula, whose
flower is all of one colour, and Primula Carniolica, P. hirsuta, P. Oenensis,
P. villosa, &e., which have bi-coloured flowers, are also of great interest in this con-
nection. P. pubescens, the hybrid produced by crossing P. Awricula and P. hirsuta,

568 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

is the stock from which the garden Auriculas are derived. The colour of the corolla
in P. Auricula is a uniform golden-yellow excepting that at the throat, ze. at the
junction of the tube with the expanded limb, there is a floury efflorescence which,
like that covering the calyx, pedicels, and bracts, is due to a peculiar modification of
the epidermis. The corolla of P. hirsuta is bi-coloured; the segments of the limb
are violet-red, whilst the throat is white. The two tints are sharply marked off
from one another, and in consequence a white five-rayed star is seen in the middle
of the flower. There is in this case no trace of a floury efflorescence. In the
hybrid offspring of these two Primulas both the violet-red of the limb and the
white of the throat are blended with yellow; the former exhibits a touch of brown,
and in the middle of the flower is a pale-yellow star.

It is much less common for those floral colours which are inherited by a hybrid
from the parent-species to be displayed in juxtaposition than in a blended condition.
Since the time of the Roman Empire gardeners have erossed the red-flowered Rosa
Gallica and R. Damascena with the white-flowered Rosa alba and obtained thereby
hybrids in which the petals are striped and spotted longitudinally with red and
white (so-called “ York and Lancaster” roses). Similar cases occur amongst hybrid
Calceolarias, Pinks, Petunias, and Wood-Sorrels, and instances of Tulip and Iris
hybrids are also known where the perianths exhibit the two different colours of the
parent-species side by side in streaks and patches. A hybrid of Iris Florentina and
I. Kochii is especially deserving of notice. The perianth in J. Florentina is milk-
white and that of J. Kochii is dark violet. The hybrid of these two species was
first obtained in May, 1871, in the Botanic Garden at Innsbruck; one of the indivi-
dual plants thus produced had two of the outer and one of the inner members of the
perianth shaped like those of J. Kochii and of a deep violet colour, and one of the
outer and two of the inner members shaped like those of J. Florentina and milky-
white in colour. This arrangement of colours re-appeared year after year until in
1877 a single flower, in which the lower white members had some dark violet
streaks widening out from the middle to the edge of the perianth also made its
appearance. A second plant of the same hybrid developed flowers which only
differed from those of J. Florentina in that a few of the white petals had dark
violet streaks widening out towards the circumference. An equally noteworthy
case is that of a hybrid reared in the Botanic Garden at Florence from 7. Ger-
manica and I. sambucina, of which a specimen was sent to me in 1872. One
inferior and two superior perianth-members displayed on one half of their surfaces
the colour and pattern peculiar to J. sambucina, and on the other half those charac-
teristic of J. Germanica. The rest of the perianth could not be distinguished
except by its smaller size from that of Iris Germanica.

It must not be supposed, however, that the presence of variegated stripes,
patches, or speckles on petals is always an indication of hybridity. Viola poly-
chroma, a very common Alpine species, not infrequently produces simultaneously
two, three, or four open flowers, every one of which presents a different mixture of
tints, and amongst plants of this species covering only a small patch of ground it

GRAFT-HYBRIDS. 569

would be easy to find 100 blossoms with corollas differing from one another in the
distribution of their colours and in the arrangements of the spots and streaks upon
them. Similar phenomena are exhibited by Jris pumila and Polygala amarella.
The flowers in Polygala amarella are equally blue and white or sprinkled with
blue and white, and it is also no rare thing for plants to bear white flowers
interspersed with a few which are sprinkled with blue. In the same way several
species of Anthyllis, Euphrasia, Galeopsis, Linaria, Melittis, Ophrys, Orchis,
Saxifraga, &e., exhibit considerable variation in the colours and markings of their
petals, which yet is not to be attributed either to hybridization or to the influence
of soil or climate. Reference must also be made here to the large number of species
{already mentioned on p. 194) in which the floral coloration is by turns blue and
white, red and white, blue and red, yellow and white, and soon. Heterochromatism,
ae. the change in the coloration and marking of petals, serves, in fact, in some
plants as a specific character. Contrasting with these heterochromatic species are
those with homochromatie flowers, which, as far as experience has shown, invari-
ably present the same colour and pattern, and only exhibit a slight variation in the
depth of the colour when subjected to the influence of light of varying degrees of
intensity. Iris Kochii and I. Florentina, Primula Auricula, and P. hirsuta,
together with other pairs of species referred to above as the progenitors of hybrids
of special interest, belong to the category of plants possessing homochromatic flowers,
and it is obvious that in the hybrid offspring of such plants the floral coloration
would be an important sign of identity.

This will be the most convenient place in which to introduce a few words
concerning the Bizzaria of Italian gardeners, and also concerning so-called graft-
hybrids. The name of Bizzaria has been given by the Italians to an extremely
curious Orange. Gallesio (1839) states that this Orange-tree produces at the same
time foliage, flowers, and fruit identical with the Bitter Orange (Citrus Aurantium)
and with the Citron of Florence (Citrus medica), and likewise compound fruit,
with the two kinds either blended together, both externally and internally, or
segregated in various ways. In the fruits of the Bizzaria which I have seen, five
longitudinal stripes of the colour of a Citron were interpolated in the fruit of the
Orange. Other fruits were, on the whole, like Oranges, excepting as regarded an
eighth of their mass, which in form, colour, and taste resembled a Citron, and was
also peculiar for its extreme convexity. This anomalous segment stretched in the
form of a light-coloured cushion from one pole of the spherical fruit to the other.
Growers maintain that the Bizzaria is the result of a cross between Citrus medica
and Citrus Awrantium, though the gardener who, in 1644, in Florence, raised this
tree, declared it was a seedling which had been grafted, and after the graft had
perished the stock sprouted and produced the Bizzaria (according to which
account it would be a graft-hybrid). In other similar cases of Citrus hybrids, how-
ever, such as the Bergamot Orange, alleged to be a hybrid of the ordinary Lemon
and the Bitter Orange, one finds the characteristics of the parent-species do not

570 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

reappear in juxtaposition (as in the Bizzaria), but are united or fused together.
Whether the case of Bergamot Pears, which are striped green and yellow, and that
of the half dark- and half light-coloured grapes, of which a few occur occasionally
in otherwise ordinary bunches of the fruit, are to be looked upon as parallel
phenomena to that of the Bizzaria must remain uncertain until it has been ascer-
tained to what particular crosses of the various species of Pyrus and Vitis the
innumerable Pear-trees and Vines now cultivated owe their origin.

Over and over again gardeners have asserted that hybrids may also be pro-
duced by budding and grafting, and in order to distinguish plants so arising from
those which are the result of a cross (i.e. from true hybrids), they are called graft-
hybrids. One of these plants, a Laburnum named Cytisus Adami, which exhibits
a curious mixture of the characteristics of Cytisus Laburnum (the ordinary yellow
Laburnum) and Cytisus purpureus in the same individual, has been the subject of
lively discussion in scientific circles. It is indeed difficult to imagine anything
more curious than a plant of Cytisws Adami. Most of the flowers derive their
characters equally from both parent-forms; the calyx is not so thickly clad
with silky hairs as in ©. Laburnwm nor so smooth as in C. pwrpwreus, and the
corollas are of a dirty-red colour, compounded of the purple of C. purpureus
and the yellow of C. Laburnum. But the curious thing is that on many of the
racemes a few blossoms of different appearance are interspersed amongst these red
flowers, some having yellow corollas and silky-haired calices as in C. Laburnum,
and others, still more remarkable, having half their petals like C. purpwreus and
half like ©. Laburnum, or a third of their petals like C. purpwreus and two-thirds
like €. Laburnum, or some one of many other combinations. According to
Schnittspahns, this anomalous form of Cytisus was first produced at Vitry, near
Paris, in the year 1826, by a grower named Adam, who inserted a bud of C. pur-
pureus into a stock of C. Laburnum. The shoot which sprang from the bud was
not a pure branch of C. pwrpwreus, but had characteristies derived both from
C. purpureus and from C. Laburnum. Buds for propagating C. Adami were sent
from Vitry to gardens all over Europe, and were in some cases inserted into stocks
of C. Laburnum, and in other cases into stocks of C. Jacquinianus and C. alpinus.
In many cases gardeners grafted buds of C. purpwreus in addition to those of
C. Adami on to the same stocks, and thus produced shrubs of most extraordinary
appearance. Of the branches some resembled ©. Laburnum, C. Jacquinianus, or
C. alpinus, others Cytisus Adami, and others again (©. purpureus; and amongst
the racemes were many which bore the ordinary flowers of €. Adami, interspersed
with a few blossoms of C. Laburnwm, and others in whose flowers a mixture of
the properties of C. Laburnum and C. pwrpwreus was apparent. The fact of main
interest, however, is that cuttings from Adam’s original plant (the alleged graft-
hybrid of €. Laburnum and C. purpureus) should bear not only flowers of an
intermediate type (as might be looked for in a hybrid), but that on certain branches
the flowers break back (or revert) to the pure form of one or other of the parents,
or that a single flower should exhibit on one half the characters of one parent and

GRAFT-HYBRIDS. 571

on the other those of the other parent. Thus the alleged graft-hybrid bears three
distinct sorts of flowers, and often parti-coloured combinations of the two parent
forms. The anatomical details of the tissues of the Adami-forms have been
examined and compared with those of the two parent-forms by Macfarlane. It
appears that the tissues show a remarkable mingling of the two parent-forms. In
some the one, in others the other parent-form predominates. Though in the
flowers (i.e. the pure Adami-flowers) the mingling is quite consistent with its being
a well-balanced seed-hybrid, in the vegetative regions the strikingly diversified
intermixture of tissues is unlike that met with in any seed-hybrid hitherto
examined. It should be mentioned that where the Adami-plant bears Laburnum
or purpwreus shoots and flowers the anatomical characters of these shoots is
identical with the normal ©. Laburnum and CO. pwrpwreus, respectively. Finally
the Adami-flowers never ripen seeds (the ovules being malformed), though when
the parent-forms occur upon it they ripen fruit and seed.

As a general rule the relations of the graft to the substratum (or stock) are very
different from those manifested in the case of Adam’s experiment. The shoot de-
veloped from the ingrafted bud makes the same use of the substratum in which it
is imbedded as a parasite makes of its host-plant (see vol. i. p. 213). It procures
from the substratum a supply of “crude sap”, and this material is absorbed and
worked up by the protoplasts of the cells of the graft in the same way as the liquid
substances of the soil which are sucked up by roots. It must be premised that those
cells of the graft which take up the crude nutrient sap are adapted to their work in
very much the same way as are the suction-cells of roots, that is to say, they are able
to exercise a selective power, and only admit such substances as are good for the
species to which the scion belongs. Any influence that the substratum might have
on the graft could scarcely be other than such as would be exercised by soils of
various composition. At the most we should expect variations in shape and colour,
which have no permanence, and are not retained by the scion’s posterity. As a
matter of fact, if, for instance, cuttings are taken from an Apricot-tree and grafted
on to various other Amygdalex, or are transferred from a Pear-tree to Quinces,
White-thorns, and other Pomacex, they do not exhibit the slightest alteration in
fruit, flowers, or foliage after entering into organic union with the stock. Again,
when hybrid Roses produced by crossing are propagated by budding and grafting,
the result is the same whatever species of Wild-rose is taken for the substratum or
stock. In all the thousands of cases of propagation by these means none has been
observed in which the stock has had any essential influence upon the form of the
scion.

In 1876 and 1877 certain experiments were made in the Botanic Garden at
Innsbruck on the genus Iris. They were suggested by the fact of the production
of the hybrids of that genus already referred to, and consisted in grafting buds
from the root-stock of one species of Iris on to that of another species of the same
genus. The experiment was attended with perfect success, but the shoots and
flowers developed from the ingrafted buds showed no trace of any influence on the

572 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

part of the substratum. Buds of Iris Kochii grafted on I. Florentina produced
unaltered plants of J. Kochri, and buds of I. Florentina grafted on I. Kochii
developed simply plants of J. Florentina. In the Botanical Garden at Vienna
there is a male Ginkgo-tree (Ginkgo biloba) which, more than a hundred years
ago, was the subject of an important experiment. When the tree was still quite
small the bud of a female tree was grafted upon it by Jacquin, and a lateral branch
was developed from this bud. What we have now is a mighty tree with a number
of branches bearing male flowers, and one large branch bearing female flowers. The
notable thing about the tree is that the grafted branch follows a course of develop-
ment which is obviously different from that of the stock. Every year in the spring
it puts forth foliage about fourteen days later than the male branches, and in the
autumn its leaves are still green long after the rest have turned yellow and, for the
most part, fallen off. From this instance we may infer that the shoots developed
from the grafted bud adhere with the greatest tenacity even to individual charac-
teristics, and do not suffer the substratum to affect them even in respect of their
annual development.

These facts have of recent years led many people to the opinion that the genesis
of graft-hybrids is simply a gardener’s story, and that even the most famous of the
supposed graft-hybrids—Cytisus Adami—does not owe its origin to budding, but
to a cross between Cytisus Laburnum and C. purpureus. Still, in view of the
curious mixing of the parent-characters in Cytisus Adami, as revealed by Mac-
farlane’s investigations, it would perhaps be well to suspend our judgment. It is
true that even in true seed-hybrids (e.g. the Iris hybrids mentioned on p. 568) a
mixing (not a fusion) of the parental characters of the flowers was observed. Fresh
observations in this field are wanted, directed especially with a view to showing
whether or not the sum-total of the characters of Cytisus Adami are absolutely
unique amongst hybrid-plants of whatsoever origin.

A further instance of the same nature may be mentioned, as it has been the
subject of careful scientific investigation and experiment. In 1876 a Jerusalem
Artichoke (Helianthus tuberosus) was grafted upon a Sunflower (Helianthus
annwus) in the neighbourhood of Bristol, and it was alleged that as a consequence
the Sunflower stock had acquired from the Artichoke the property of producing
tubers on its subterranean portions. Quite lately a series of buds of the Artichoke
were grafted on Sunflower stalks by Vöchting, and the results carefully followed.
It was not found that the properties of the one were in any instance transmitted to
the other, although scion and stock grew together in perfect harmony.

The importance of this subject is so great that I cannot refrain from trespassing
for a moment on the domain of Zoology in order to refer to a case which shows that
the animal world also sometimes affords instances of the characteristics of both
parents being manifested in juxtaposition in their hybrid-offspring instead of being
merged together or united in close combination. Tetrao medius is well known to
be a hybrid produced by a crossing between the Black grouse (Tetrao tetrix) and
the Capereailzie (Tetrao Urogallus). This hybrid is so common in Tyrol that the

GRAFT-HYBRIDS. 573

poulterers in Innsbruck receive for sale on an average six specimens every year
from huntsmen in the immediate neighbourhood. The plumage of some individual
examples of Tetrao medius is curiously striped with alternate groups of feathers
inherited from 7. tetrix and 7, Urogallus respectively. In 1879 a huntsman brought
me from the remotest part of the Gschnitzthal in Tyrol a hen of Tetrao medius
whose plumage exhibited a mixture of the feathers of 7. tetria and T. Urogallus,
irregularly distributed in stripes and patches all over the body. The case of this
hybrid affords valuable confirmation of the results of the experiments made on
Tris hybrids, and there can no longer be any doubt of the fact that there are hybrids
generated by crossing in which the parental characters reappear in juxtaposition.

In spite of all this, however, I should not like to deny the possibility of the
existence of graft-hybrids, for there are certain considerations which tend to a con-
trary conclusion. In most cases the relation to the substratum of those cells of the
ingrafted shoot or bud which take the crude nutrient sap from the stem of the
stock-plant is just the same as that of a parasite’s suckers; they are clearly marked
off from the cells of the substratum and are not influenced thereby either in their
shape or in their ultimate structure, whilst, conversely, no essential modification is
undergone by the substratum through the presence of the graft. There is nothing,
however, to exclude the possibility of a fusion between the protoplasmic contents of
adjacent cells taking place at the spot where stock and graft unite, and the con-
sequent development of a tissue which is composed of cells arising from a division
of the cells containing the mixed protoplasms, and which unites the characteristic
features of the tissues belonging to the stock and to the graft respectively. In fact,
something of the kind has been observed in the case of the parasitic Balanophoreie
(see vol. i. p. 194). Now supposing such an intermediate tissue were to be formed
at the junction between a graft and its substratum, one or more shoots might spring
from it and they would doubtless combine the characteristics of the two species
employed as stock and scion.

In relation to the genesis of new forms of plants in nature, the question of the
possibility of the existence of graft-hybrids is of secondary importance ; but it is of
no small moment in connection with the comprehension of the processes involved in
hybridization; for, the researches suggested by this problem have led to the con-
clusion that the marks and attributes of a particular species which are percep-
tible to our senses are an outward sign corresponding to the ultimate structure
and molecular composition of a specific protoplasm, and that wherever the special
characters of two species are united in a single plant-form, that form is built up
from protoplasm which owes its origin to a combination of the protoplasms of two
parent-species.

It is only by adhering to this train of thought that one is able to understand
how it is that, also in the matter of chronological development, the vital manifesta-
tion connected with the shape, anatomical structure, scent, and colour occupy in
hybrids a position intermediate between the corresponding manifestations in the
parental species. In the Botanic Garden at Vienna there has been for many years

574 THE GENESIS OF NEW FORMS AS A RESULT OF CROSSING.

a Buckthorn-shrub, named Rhamnus hybrida, which sprang from a cross between
Rhamnus alpina and Rhammus Alaternus. One of the parent-species, R. alpina,
has deciduous foliage, i.e. leaves which are green in the summer and wither and drop
in the autumn; the other, R. Alaternus, has evergreen leaves, which last through
the winter and remain on the branches for two years. The hybrid, R. hybrida,
possesses leaves which do not fall off in the autumn, nor yet last fresh and green for
two years, but which maintain their verdure through one winter and fall in the
spring when new shoots are sprouting from the buds. The behaviour of hybrids
as regards their season of flowering is also very remarkable. From 1863 to 1874 I
kept notes concerning the flowering of some fifty different kinds of Willow, growing
in the Botanic Garden at Innsbruck, and each year made an entry of the day on
which the first flower opened in each plant, whether a pure species or a hybrid.

EARLIEST DATE OF FLOWERING OF A NUMBER OF WILLOWS GROWING IN THE
BOTANIC GARDEN AT INNSBRUCK.

(The date given is the average for 12 years.)

|
Salix Cremsensis - | March 17 | Salix Caprea - - | March 16 | Salix daphnoides March 18
» Mauternesis > 2301 a). \Gaprea) = Ay eG » purpurea - | April 7
» attenuata - » 25 „ Caprea - - Se il » grandifolia- | March 27
» Wimmeri - 3. 26 „ daphnoides py ls} » imeana - - | April 17
» Austriaca - | April 3| ,, grandifolia - 7, » purpurea - „ i
„ Seringeana - > 3] „ Capre - - sien 9 AUG „ Incana - - ey
» eapnoides - Fy 5 | ,„ cinerea - - | April 10 „ Incana - - nl
„ Intermedia - en 6 „ grandifolia- | March 27 „ Incana - - el
Pe arubra re 5 6 „ Viminalis - | April 3 „ purpurea - es 7
» Kerneri - - LO. » Viminalis - = 3 ae Incanas oS Se) les
» Oenipontana 12 » purpurea - ss 7 SE ıncana Br ay Ly
„ auritoides - 35) Le | 95, spurpurea) = sf 1 „ asia = ~ 3 LD
„ Fenzliana - Peel 5) Tetusar-ı = en! „ glabra - - eh!
„ retusoides - al „ retusa - - De „ Jacquiniana ol
„ alpigena - - 0:23 » retusa - - yo „ hastata- - ee
» excelsior - - ry eS} » fragilis - - Ble} Be MS |
» Ehrhartiana m. ER) ME A PY „ pentandra- | May 6

The name in the first column is that of a hybrid in each case, and the names on the same line in the second and third
columns are those of its parent-stocks.

The above table, which gives the means of the dates recorded in 12 years of the
first opening of the male flowers in 15 species and 17 hybrids produced from them
by a variety of crosses, shows that the hybrids invariably flower on days between
those on which the parent-species enter upon that stage of development. It will be
observed that the two alpine Willows, Salix retusa and Salix Jacquiniana, flowered
on an average in the 12 years on the same day, and that their hybrid Salix
retusoides kept also to that date.

We have hitherto dealt with those of the marks, attributes, and vital phenomena
manifested by hybrids which are derived partly from the one parent-species and
partly from the other, and we must now pass to the consideration of such character-
istics as cannot be attributed to inheritance from those species. There is, in the
first place, the fact that the majority of the hybrids produced from crosses develop

CERTAIN CHARACTERS OF HYBRIDS. 575

with striking rapidity and exuberance; they not uncommonly flower the very first
year after they are sown, whereas the seedlings of the parent-speeies may not attain
to the flowering stage for two or three years; and in respect of the size of the
foliage, and still more that of the flowers, hybrids often exceed both parent-species.
The latter circumstance is indeed one of the chief reasons why growers make such
frequent use of the process of crossing. They are thus enabled to meet the demands
of connoisseurs, who prefer to have plants with conspicuous flowers in their gardens.
The augmentation in the size of the flowers usually ceases after the first, or at any
rate after the second year. Subsequently, the flowers of hybrids become smaller
again. On this account gardeners are in the habit of producing such hybrids as are
especially valued for their large flowers over and over again by the original method.
Of the large number of observations recorded on this subject we will here mention
one as an example. Jsoloma Decaisneanwm of the order Gesneracee is the product
of a cross between /soloma Tydeum and Isoloma sciadocalyx. The seeds obtained
after crossing germinate early, and the seedlings develop rapidly into exceptionally
robust plants. The foliage-leaves are three times as large and the flowers twice as
large as those of the parent-species; in addition, the flowers are much more numerous
than on the parent-plants, and in consequence the hybrid has a much more imposing
and showy appearance than either of its progenitors.

Many plants which grow on soil rich in humus in mountainous regions, such as
the Lungworts (Pulmonaria) and Primulas (Primula), do not thrive particularly
well in gardens, and certain species die after a short time even when cultivated
with the greatest care. Yet the hybrids of such species flourish wonderfully well
under similar circumstances. They blossom luxuriantly, and may be kept in a
state of vigorous growth for many years. Examples of this are afforded by
Primula pubescens and Primula Venzoi. One of the parent-stocks of P.
pubescens, viz. Primula hirsuta, can only be reared if the soil used is expressly
prepared for itself, and if several other special precautions are taken, whereas the
hybrid, P. pubescens, grows exuberantly in ordinary garden-soil. The case of P.
Venzoi, the hybrid-ofispring of Primula tyrolensis and Primula Wulfeniana, is
still more remarkable. Although both the parent species are reared with difficulty,
even when the greatest care is bestowed upon their cultivation, Primula Venzoi
will flourish with extreme luxuriance if planted close to them in the same soil and
under the same external conditions.

Another phenomenon sometimes exhibited by hybrids is a change in the dis-
tribution of the sexes. It often happens, for instance, that hybrids produce
pseudo-hermaphrodite female flowers and pseudo-hermaphrodite male flowers (cf.
p- 294), even where both parent-species have true hermaphrodite flowers. In
Willow hybrids a partial transformation of male into female flowers, and vice
versd, has been not infrequently observed, and we then have moncecious catkins
bearing flowers, half of which are female and half male. This change also occurs
in true species, but only as a rare exception, whilst in the case of hybrids it is by
no means uncommon.

576 THE GENESIS OF NEW SPECIES,

Hybrids also exhibit the phenomenon known as the “doubling” of flowers,
which depends upon the transformation of stamens into petals, independently of
the action of tiny gall-mites, which are the frequent cause of doubling in other
plants (cf. p. 548). Several hybrid Roses, Pinks, and Camellias are only known
with double flowers.

It is difficult to explain the fact, repeatedly confirmed by observation, of the
appearance in hybrids of characters which are not present in either parent-species,
or rather which cannot be traced to inheritance from either of those species. ‘Thus
it sometimes happens that individual plants of a hybrid develop sinuate foliage-
leaves with wavy outline, though in both of the parent-species the leaves are either
entire or only slightly toothed. The hybrid Salvia sylvestris occasionally exhibits
deeply sinuate radical leaves, whilst Salvia nemorosa and Salvia pratensis, the two
species to which it owes its origin, never do so. Another instance of the same kind
is that of a Stock, the hybrid of Matthiola incana and Matthiola Maderensis.
Neither the one nor the other parent-species has sinuate leaves, yet here and there
plants of the hybrid display foliage with the margins so deeply cut as to remind one
at first sight of Matthiola sinuata. Again, in Primula pubescens the leaves are
sometimes more deeply sinuate than in either Primula Auricula or Primula
hirsuta. In hybrids of the Foxglove genus (Digitalis), flowers not infrequently make
their appearance wherein the corolla is produced underneath into a spur as in the
Toad-flax (Linaria). One hybrid produced by crossing two species of Water Lily,
Nymphea Lotus and Nymphea dentata, displayed dark violet lines on its sepals
which are not to be seen in either parent-species. Reference must also be made to
the comparative frequency with which hybrids bearing white flowers spring from
species with blue, violet, red, or yellow blossoms whose non-hybrid offspring only
produce colourless flowers on very rare occasions. Lastly, we may mention the fact
that as from species so also from hybrids varieties may be formed; but they
have no permanence amongst the descendants of a race, passing into other varieties
whenever it undergoes the restrictive influence of a change in external conditions.

3. THE ORIGIN OF SPECIES.

Genesis of New Species.—Derivation of Existing Species.—The Sub-divisions of the Vegetable
Kingdom.

THE GENESIS OF NEW SPECIES.

It is now more than forty years since I discovered, on an island on the Danube
not far from the little town of Dürenstein, a Willow which had till then remained
unknown to Botanists. The plant in question was growing on the island in com-
pany with a number of other Willow-trees and Willow-shrubs belonging to the

THE GENESIS OF NEW SPECIES. 577

species known as Salix incana and Salix daphnoides respectively, and it was
apparently intermediate in form between those two species. The hairs, the system
of ramification, the foliage, and the flowers resembled those of S. incana in some
respects and those of S. daphnoides in others, and a single glance would have
led any unbiassed observer to conjecture that he had to deal with the product of
a cross between these two species.

This discovery,! made in one of the first years of my career as a student of
Botany, chanced upon a time when Botanists were beginning to take a partieularly
keen interest in all cases of intermediate forms observed growing in a state of
nature. Some of the leading men at that time refused to believe in the existence
of any wild hybrids, and were of opinion that the supposed cases were varieties of
species whose presence was to be explained by a tendency in the plant itself to
change its form. They also held the view that all plants between which one or more
intermediate forms had been found to exist were to be included in a single species,
and, in accordance with this, they not infrequently treated three, four, or more kinds
of plant previously classed as distinct species as being really “varieties” of a single
species, because forms obyiously intermediate between them, 7.e. so-called “transitional
forms”, had been discovered. This practice was carried so far that several systematic
Botanists of that day included in one species 5, 10, and even 15 distinct Hawk-
weeds which had been previously described as separate species, the reason for the
change being that they were all linked together by transitional forms. Another
school of Botanists, on the other hand, recognized in most of the so-called transi-
tional forms the results of natural crossing, but they did not deny the existence in
plants of a capacity to form varieties in the Linnean sense in response to changes
of soil or climate.

To my mind even at that time there could be no doubt which of the two oppos-
ing theories concerning the genesis, significance, and position of intermediate forms
was to be preferred. The discovery of the hybrid Willow referred to led to my
paying particular attention to plant-hybrids, and in the course of the last forty
years I have made extensive series of experiments to clear up many obscure points,
and to correct the prejudices which then prevailed.

One misconception as to the nature and significance of hybrids, which had great
weight and found expression in the name of “bastard” assigned to them, consisted
in the idea that they were contrary to nature. The German word “bastart” is defined
by Grimm as a base and useless species. This prejudice was carried so far that
Kant positively denied their independent existence, and believed they must neces-
sarily die out with the first generation. Connected with this notion was another,
according to which hybrids were destitute of the power of producing fertile seeds
and propagating their kind sexually. It probably arose from observation of the
hybrids of the Mullein genus (Verbasewm), which in Central Europe are so common

1The little paper recording the finding of this Willow, with some additional remarks, by Anton Kerner, was
published in 1852 (Vienna, Zool. Bot. Ver. Verhandl. II., 1852). This seems to have been Kerner’s second

definite contribution to science; what would appear to be his first is printed in the same publication a few

months previously.
VoL. II. 87

578 THE GENESIS OF NEW SPECIES.

and conspicuous that they were accepted as the results of crosses between two
species even by those amongst the earlier Botanists who were most disinclined to
recognize the existence of plant-hybrids. Now, these Mullein hybrids do not for
the most part mature any seeds. The pistil itself is usually incompletely developed,
and even if one or other of the fruit-capsules does develop, the ovules in it are
abortive and infertile. Nevertheless it would be erroneous to say that no Mullein
hybrid has ever produced seeds capable of germination. Two: such hybrids were
artificially generated in my garden, viz.:—Verbaseum rubiginosum, by crossing
Verbascum Austriaeum with the pollen of Verbasewm pheniceum, and Verbaseum
pseudophaniceum, by crossing Verbascwm Blattaria with V. pheniceum. The
former of these hybrids, it is true, never produced seeds capable of germination:
but in the case of the second, although most of the capsules were empty and
abortive, a few containing fertile seeds ripened; so that even the hybrids of
Mulleins are not invariably sterile.

Anyone who will look beyond the limited range of that particular genus will be
convinced that in respect of their capacity for sexual reproduction hybrids do not
differ essentially from plants which have been admitted to be “true”, permanent
species by Botanists of all periods. For the case of a few of these true species, as,
for instance, Cochlearia Armoracia, Crambe tataria, Lilium bulbiferum, Lysimachia
Nummularia, Rubus odorus and R. Nutkaensis, it has long been known that if the
stigmas are dusted with pollen from.the stamens in the same flowers very few seeds,
if any, are set, whilst pollen from other flowers is obviously preferred by them. On
the other hand, there are true species whose flowers are pseudo-hermaphrodite, ü.e.
they have the appearance of being bisexual, but are really unisexual (cf. p. 294).
In one individual we find that the ovaries are fully developed, as also the stamens,
but that no pollen capable of fertilizing ovules is produced in the anthers; in
another plant the ovaries are imperfectly developed, whilst the anthers are filled
with effective pollen. For seeds to be set in such circumstances two individuals at
least are requisite, and pollen from a plant bearing pseudo-hermaphrodite male
flowers must be transferred to the stigmas of the pseudo-hermaphrodite female
flowers. Now hybrids with pseudo-hermaphrodite flowers also exist, and in their
case, as in that of true species, two kinds of individual are requisite to produce
seeds capable of germination. Supposing, however, in such a case that the two
kinds of plant necessary for reproduction do not grow close together or do not
flower simultaneously, or that one of them is altogether absent—a contingeney which
must often occur—fertilization cannot be effected, and consequently no seeds can be
formed. It is scarcely necessary to amplify the proposition that dicecious hybrids
behave in this respect in the same manner as true species, and that pollination and
fruit-formation may in them be impeded likewise by dichogamy or by hetero-
stylism. In many hybrids, again, as in true species, the relative positions of
stamens and pistil, the height of the stigma, the length of the filaments, and other
conditions of the kind are not conducive to autogamy, and consequently no trans-
ference of pollen from the anthers to the stigmas in the same flower can take place

THE FERTILITY OF HYBRIDS. 579

either at the beginning or at the end of the period of bloom. Such hybrids are
dependent upon foreign pollen, and if none is brought at the right time by wind or
inseets no pollination or fertilization takes place, and no seeds are developed.

Even these brief references to recently-diseovered phenomena connected with
fertilization are sufficient to indicate that the suppression of the function of fruit-
formation in hybrids is due in most cases to the same causes as operate on true
species. Innumerable experiments have proved that if at the proper time pollen of
the right sort is placed upon the stigmas of hybrids fertile seeds are developed as in
the case of true species.

We must now consider a statement which for long held its place in Botanical
works owing to the positive manner in which it was enunciated by an eminent
authority. The proposition in question, whilst admitting the fertility of hybrids,
asserted that it was conditional on the stigmas being supplied with pollen from one
or other of the parent-stocks, and that no fruit was formed as a result of autogamy.
This assumption rested partly on certain series of experiments performed on garden-
plants by the Botanist Koelreuter in the second half of the eighteenth century."
By crossing two species of Tobaceo-plant (Nicotiana rustica and Nicotiana pani-
culata) Koelreuter produced a hybrid which in its characteristics was an exact
mean between the two parent-species. The stigmas in the flowers of this hybrid
were then dusted with pollen from one of the parents, and the result of this second
cross was another hybrid, the characters of which resembled those of the species
which supplied the pollen more closely than was the case with the first hybrid. The
same treatment was applied to the second hybrid, and thus, after three generations,
a plant was evolved completely resembling the male progenitor. The first hybrid
had, therefore, in a sense, “reverted” to that particular parent-species. The “rever-
sion” of the hybrid to the other parent-species was similarly procured after three
generations. Such a result could naturally not have ensued if the action of the
pollen of the parental stocks on the hybrid had not been entirely effectual. It is
accordingly quite true that hybrids are fertile when the pollen used to fertilize
them is taken from either of the parent-species, but the further assertion that they
are sterile if their own pollen is employed for the purpose is incorrect, at any rate
as a universal proposition. Koelreuter’s own conscientious experiments show con-
elusively that it is possible for hybrids to bring fruits to maturity as a result of
autogamy, and that, as a matter of fact, the majority do develop such fruits. We
may also refer to the large number of plants with ornamental flowers, such as
Begonias, Pansies, and Pinks, which every year in our gardens produce seeds auto-
gamously, and are reproduced in great numbers by means of those seeds (see p. 556).
Some interesting experiments have also been made on Medicago media, the hybrid
of Medicago falcata and M. sativa. This plant, which is, in many places, cultivated
on a large scale for fodder, is propagated continuously by seeds which are in a very

1 Joseph Gottlieb Koelreuter (1733-1806) was the first to investigate the question of hybridization scientifically
and thoroughly. His work, which ranks with the best of modern times, is contained in his Vorläufige Nachricht
von einigen das Geschlecht der Pflanzen betreffenden Versuchen und Beobachtungen (published 1761-1766); a convenient
reprint was issued in 1893.

580 THE GENESIS OF NEW SPECIES,

subordinate degree, if at all, dependent on the parent-species for their production.
Nay more, it would be prejudicial were one of those species to supply the pollen
seeing that the fertility of this hybrid is diminished thereby. We have here a case
of a hybrid manifesting enhanced fertility as compared with one of its parents; for
Medicago falcata is one of those Papilionacez in which autogamy is attended with
very small result. It has been ascertained that in cases where the flowers of that
species are thrown upon their own resources for pollen, out of every 30 flowers
only two or three fruits containing seeds capable of germination are matured. If
flowers of Medicago falcata are crossed with pollen belonging to another species,
such as Medicago sativa, a much larger number of fruits is produced, and it is
stated that the number of seeds is almost doubled. Medicago media usually sets
from six to eight pods in each raceme if the flowers depend upon their own pollen
for fertilization. If, however, pollen is brought to them from Medicago falcata
the degree of fertility is strikingly reduced; the flowers so crossed either remain
quite empty or develop pods whose seeds are not capable of germination. Medicago
media is therefore an instance of a hybrid which is actually injured by being
crossed with one of the parent-species, but is successfully reproduced by autogamy.
The upshot of all these experiments is that the results of autogamy are no different
in hybrids from what they are in species.

We may infer from the same experiments in what way reversions of hybrids to
their parent-species should be regarded. Botanists possessed with the idea that
every hybrid was the product of some process contravening the laws of nature
imagined that this anomaly must be counteracted, and that this was effected by a
tendency existing in the hybrid’s descendants to approximate sometimes to one and
sometimes to the other parent-species, so that in the course of a few generations
they would completely revert to the form of a true species. As the accounts given
by gardeners seemed to confirm the fact of the occurrence of such reversions, no
doubt was raised as to the soundness of this view. The reports of gardeners on the
subject were, however, founded on inaccurate observation, want of knowledge, and
self-deception. In former years the phenomena of pollen-transport in the case of
pseudo-hermaphrodite, dichogamous, and heterostyled flowers, and many other
things connected therewith, were not appreciated at their full value; to most
gardeners they were altogether unknown, and it was only in the rarest instances
that any measures were taken to preserve the species and hybrids reared in gardens
from extraneous pollen. The majority of growers had no suspicion that the fruit
formed on a particular cultivated hybrid might be due to the effect of pollen con-
veyed by the wind or by insects from one of the parent-species flourishing in the
vicinity, and if they noticed that the seedlings arising from that fruit exhibited
characteristics approximating to either of the parent-species they were in the habit
of calling the phenomenon a reversion. But if a gardener takes care that the flowers
of a hybrid under cultivation are only supplied with pollen developed in flowers of
their own kind whilst that of other species is excluded, the plants which arise from
the seeds of the hybrid exhibit the characters of that hybrid unaltered. Thus,

SPECIES AND RACES. 581

hybrids prove true to seed, to use a gardener’s expression, and there is no truth in
the assertion that they have an innate tendency to revert to one of the parent-
forms.

At one time the attempt was mace to distinguish two sorts of hybrids—those
arising between species, which were regarded as sterile, and those arising between
races, Which were regarded as fertile. By “races” are understood forms which, whilst
not differentiated by characters of sufficient importance to rank as species, are yet
reproduced by seed and transmit their characters to their offspring. They seem to
stand midway between what are called varieties and sub-species. Forms arising by
the crossing of species were termed hybrids, those arising by the crossing of races
“blendlings”. But in this matter Botanists argued in a hopeless circle. Firstly, it
was said that if races were crossed the intermediate forms were fertile; whilst those
springing from species were sterile; and, secondly, the distinction between races and
species was defined as consisting in the fact of the fertility of the intermediate
forms produced by crossing races, as compared with the infertility of those derived
from crosses between species. A distinction founded on such reasoning as this is, of
course, destitute of any value or meaning. What, then, is the difference between
races and species? There are certain forms which have a similar physiognomy, an
agreement in certain striking particulars. They are bound together by these common
characteristics into a single group, and it must be supposed that they are nearly
allied in respect of their origin also. But no more than afinity can be predicated
by characters which, though perhaps less striking than the others, are yet trans-
mitted unmodified to descendants and prove themselves to be constant attributes.
It has been sought to apply the term “races” to nearly akin forms of the kind. But
the degree of variation has nothing to do with the conception of a species; the
essential point is that the characters wherein the variation is manifested are trans-
mitted unchanged to the descendants, and this happens as a fact in all the cases to
which the name of race has been affixed. The use of the term would obviously
imply quite a different connotation of the name of species from that which Linnzeus,
with logical exactitude, attached to it. According to him a species was not an
assemblage of individuals of the same form, but an assemblage of individuals of
different forms, constituting a group of units and not itself the unit of the system.
If, like the French system, we were to distinguish the groups of nearly allied
species as “petites especes” from those exhibiting more marked differences and less
nearly akin to one another, which would be known as “grandes especes”, that
would involve quite sufficient recognition of the difference which exists in various
degrees between members of the two categories in question; but the introduction of
the word “race” side by side with the word “species” suggests the idea of some line
of demarcation between the two such as does not in reality exist. Again, if there is
no definite boundary between race and species the separation of blendlings from
hybrids also fails, and with it the proposition that only those hybrids are fertile
which are the offspring of races.

In respect of fertility, then, there is no difference between hybrids and species.

582 THE GENESIS OF NEW SPECIES.

In the one as in the other we find those floral contrivances for bringing about eross-
fertilization in the first place and autogamy in the second, of which an account was
given in the first part of this volume; in the one case as in the other cross-fertiliza-
tion often takes place as a result of those contrivances, and both categories include
forms which are incapable of self-fertilization, and only develop fruits and fertile
seeds in consequence of geitonogamy or xenogamy. Seeing that it has been ascer-
tained also that, provided the pollen from other species is excluded, hybrids transmit
their form unchanged to their posterity, and that the substitution of brood-bodies
for fruits as a means of reproduction and the enhancement of the development of
those bodies in the event of there being no fruit, are phenomena common to species
also, we come to the conclusion that'no line of demarcation between hybrids and
species exists in respect of the function of propagation.

The consideration of all these facts led me years ago to raise the question
whether hybrids could originate species and to answer it in the affirmative.
Looked at from this point of view, the hybrids which have been and are being
produced in nature acquire a special significance, and it becomes important to form
a correct notion as to their existence, behaviour, and distribution in localities where
the life of plants is untrammelled and undisturbed. Only the vegetation of Europe
has been thoroughly studied in this connection, yet this alone affords a fund of
information, and we may take it for granted that what is true for Europe will
apply likewise to the other quarters of the globe.

We shall be rather below than above the mark if we estimate at a thousand the
number of wild hybrids belonging to the Flora of Europe which have been brought
to light during the last forty years. Of these only a small proportion are of the
class of Cryptogams, but this circumstance is due to the fact that it is only lately
that Botanists have paid any attention to hybrid Cryptogams. Future researches
will no doubt establish the hybrid nature of many so-called “transitional forms”.
Amongst Mosses in particular, several hybrids arising from species which grow in
ditches and marshy places (Hypnum aduncum, H. flwitans, H. lycopodioides, &e.)
have been discovered. A few hybrids of the genera Orthotrichum, Grimmia,
Physcomitrium, and Funaria have also been identified. Fern hybrids are known
in the genera Aspidium, Asplenium, Ceterach, Polypodiwm, and Scolopendriwm.
Scolopendrium hybridum, which was observed in Istria, is especially remarkable
as being the result of a cross between two species possessing widely different forms
and included in different genera. The parent-species of this hybrid are, firstly,
Scolopendrium officinarum, which is glabrous and grows in clefts in damp, shady
rocks and walls; and, secondly, Ceterach officinarwm, which has the under surfaces
of its fronds thickly covered with brown scales and flourishes in the crevices of dry
walls exposed to the sun. Amongst the Horse-tails we may mention Equwisetum
inundatum, a rather common hybrid, which owes its existence to the crossing of
Equisetum arvense and E. limoswm.

In the division of the Conifers no less than seven hybrids have been recently

1 Oesterreich. botanische Zeitschrift xxi. p. 34 (1871).

NATURAL HYBRIDS. 583

identified, and this fact is of no little significance when taken in connection with
the circumstance that Europe only possesses 41 species of Conifers. Juniperus
Kanitzii, the hybrid offspring of Juniperus commumis and J. sabinoides, is a very
instructive instance owing to the great diversity in the form of the two parent-
species.

Comparatively few hybrids occur amongst Grasses. The majority belong to the
genus Calamagrostis. Strangely enough, most hybrid grasses have arisen from crosses
between species of different genera, as, for instance, Festuca and Loliwm, Triticum
and Elymus, Triticum and Agilops. The hybrid derived from AZgilops ovata and
Triticum sativum, and known by the name of Egilops triticoides, and the hybrid
Egilops spelteformis, obtained by crossing Egilops triticoides with Tritieum
sativum, have been the subject of lively discussion in their time, and have contri-
buted not a little to clearing up our ideas concerning hybrids. As a set-off to the
Grasses, the groups comprising Reeds, Rushes, and Sedges include a comparatively
large number of hybrids. For example, in the genus Carex instances have been
discovered in the most widely different localities.

Amongst Lilifloree and Iridez only a few wild hybrids have been found, but
on the other hand a large number occur amongst Orchidacew all over Europe. It
is striking how many of these Orchid hybrids spring from species which are placed
by Botanists in different genera. Hybrids are known, for instance, which are derived
respectively from Aceras and Orchis, from Anacamptis and Orchis, from Celo-
glossum and Orchis, from Gymnadenia and Orchis, from Himantoglossum and
Orchis, from Serapias and Orchis, from Gymnadenia and Nigritella, and from
Epipactis and Cephalanthera. The hybrid Epipactis speciosa, lately discovered in
the Erlafthal of Lower Austria, is the result of a cross between Lpipactis rubigi-
nosa and Cephalanthera alba, and is of special interest on account of its manifesting
characters strongly resembling those of species indigenous to regions at a great
distance from the place where the hybrid occurs, for at first sight Zpipactis speciosa
might easily be taken for Epipactis gigantea, which is a native of North America,
or for the Japanese species named Epipactis Thunbergüi.

Hybrids are comparatively numerous amongst the Pond-weed group (Potamo-
geton). These are aquatic plants which discharge their pollen in the form of clouds
of dust, and at the season of pollination raise their flowers above the surface of the
water. Owing to their being completely protogynous (see p. 310), autogamy is out
of the question. The crossing of pairs of species is especially promoted by the
circumstance that the different species flower in definite succession, so that always
just at the time that one species is terminating its period of bloom another is
coming into flower.

Plants which have their flowers in catkins (amentaceous), such as Oaks, Birches,
Alders, Poplars, and Willows, produce an uncommonly large number of hybrids.
In Willows pollination is effected by insects, in the other genera by the wind. This
gives occasion for us to raise, in connection with this group, the question whether
hybrids originate more frequently from entomophilous or from anemophilous plants.

584 THE GENESIS OF NEW SPECIES,

The fact that many more than a hundred Willow hybrids are known looks as if the
agency of insects were the more favourable to hybridization. At the same time we
must bear in mind that the number of species of Willow in Northern and Central
Kurope is very large, whilst the number of different Birches, Alders, and Oaks is
small. Taken in relation to the number of species, the hybrids belonging to the
plants last mentioned are no less numerous than those of Willows, and it appears,
therefore, that hybrids occur as frequently amongst plants whose pollen is dispersed
in the form of dust as amongst plants with adhesive pollen which is transported by
insects. The prevalence of hybrids amongst Pond-weeds points to the same conelu-
sion. A comparison between the Docks and Polygonums even indicates that in
anemophilous plants, such as the Docks, hybrids come into existence more readily
than in the case of entomophilous plants as represented by the Polygonums, for in
scarcely any genus is the number of hybrids so great in proportion to the number
of species as in the Dock genus, and the ratio is certainly higher than it is with the
Polygonums.

As regards the Caryophyllace it is remarkable that Dianthus has many hybrids
and Silene few, although these two genera resemble one another in the distribution
of their sexes and in being chiefly visited by lepidopterous insects. In the genus
Viola hybrids are extremely common. It has been shown that many Violas which
were formerly designated as “transitional forms” are in reality hybrids, and thus
the grounds upon which systematic Botanists treated whole series of species as one
only are removed. As with the Violas in Central Europe so also with their allies the
Cistuses in the South, hybrids are numerous; several kinds of Cistus hybrids occur
so commonly that they were described as species by the Botanists of former times.

It is noticeable in the Cruciferze that no hybrids are formed in nature between
the numerous annual species of this family. There are also only a few hybrids
known which are derived from the perennial species. The genera Roripa and
Draba are, however, exceptional in this respect. The case of Ranunculacese is
similar. In the comprehensive genera Aconitum, Helleborus, and Ranwneulus,
only a few hybrids have been identified with certainty, whilst in Anemone and
Pulsatilla there are almost as many hybrids as species. The case of the hybrid
Water-lily Nuphar intermedium will be discussed later on.

Many hybrids are known in the genera Tilia, Hypericum, Malva, Rhamnus,
Pistacia, Acer, Ewphorbia, and Epilobium, the last alone including fifty different
kinds. This makes it all the more remarkable that so varied a family as the
Umbellifer® yields very few hybrids. Of the numerous hybrids belonging to the
Saxifragacex we may mention as specially noteworthy those derived from species
which differ exceedingly from one another in form and size. One cannot easily
imagine two plants in the limits of a single genus which present a greater contrast
to one another in respect of flowers, leaves, and general mode of growth than is
exhibited in the following cases:—Sawifraga cwsia and S. mutata, S. Aizoon and
S. cuneifolia, S. aizoides and 8. squarrosa, and yet hybrids have sprung from the
crossing of these species.

NATURAL HYBRIDS. 585

About two hundred hybrids, for the most part fertile, have come into existence
in nature within the family of the Rosacew. The genera Geum, Potentilla, Rubus,
Rosa, and Sorbus are inexhaustible in the formation of hybrids. On the other
hand, the Papilionacez, a family allied to the Rosacex, is peculiarly wanting in
hybrids.

This discrepancy between nearly-related families in respect of the number of
their hybrids is again noticeable in the class of plants known as the Monopetale.
The Labiate, e.g. the genera Ajuga, Prunella, Calamintha, Lamiwm, Marrubium,
Mentha, Salvia, and Stachys include numbers of hybrids, whilst the Boraginacez
have very few. Of the latter only one or two hybrids are known, and these belong
to the genera Pulmonaria and Symphytum. The Scrophulariacex and Rhinanthaceze
have long been noted for the great variety of their hybrids; the genera Pedicularis
and Verbascwm in particular exhibit a great wealth of forms, Pedicularis in alpine
regions and Verbascwm on the shores of the Mediterranean. Verbascum alone
includes more than fifty. In the case of Gentianacew, also, the products of a great
number of different crosses are found in the Alps, the chief parent-species being the
long-stalked Gentiana lutea, G. Pannonica, G. punctata, and G. purpurea. Pri-
mulacex, whether growing on the upper or the lower levels of mountains, are
famous for the abundance of their hybrids. In the genera Androsace, Primula,
and Soldanella the number of hybrids identified by Botanists surpasses the number
of the species from which they have sprung. The Ericacez, although comparatively
poorly represented in Europe, exhibit several hybrids derived from the genera Hrica,
Rhododendron, and Vaccinium.

Hybrids are also specially numerous in the family of the Rubiacex, the genus
Galiwm being the most prolific in this respect. But the greatest number of all is
to be found amongst the Composite. More than two hundred hybrids have been
identified in the genera Achillea, Cardwus, Centaurea, Cirsium, Hieracium, Inula,
and Lappa alone. Of hybrid Composite the following are particularly worthy of
notice: — Erigeron Hiilsenii, which is the result of a cross between Zrigeron
Canadense, an annual species brought into Europe from America, and Erigeron
acer, a perennial species indigenous to Europe, and, secondly, the Cudweed hybrids,
Filago mixta, F. neglecta, F. subspicata, &e., which spring from crosses between
annual species, and are, therefore, exceptional, for annual species in general rarely
produce hybrids.

In many cases only a few individual instances of these natural hybrids have
been observed; in some, indeed, one single specimen alone has as yet been discovered.
The majority, however, grow by the hundred or by the thousand in the localities
proper to them, and many are represented by immense numbers of plants, and
possess a wide area of distribution. Salvia betonicifolia, a hybrid derived from
Salvia nemorosa and S. nutans, occurs as commonly as its progenitors in places on
the grassland in the central parts of Siebenbiirgen (Hungary); Marrubiwm remotum,
a hybrid of Marrubium peregrinum and M. vulgare, is to be found everywhere on
the plains of South-Eastern Europe, especially in the flat country by the Theiss and

586 THE GENESIS OF NEW SPECIES,

the lower Danube; Roripa anceps, the hybrid of Zoripa amphibia and R. sylvestris,
is met with all over the distriet forming the basin of the Baltie; Primula digenea,
a hybrid derived from Primula vulgaris and P. elatior, grows in its thousands in
the upland meadows of the Eastern Alps; Betula alpestris, produced by the erossing
of Betula alba and B. nana, is met with in great abundance in the Jura, in Scandi-
navia, and in the North of Russia, and here and there entire copses are composed
of it; Nigritella suaveolens, a hybrid produced from Gymnadenia conopsea and
Nigritella nigra, is so common in the Central Alps, for instance, in the Pusterthal
of Tyrol, that hundreds of specimens are sometimes encountered in a single meadow;
Primula Salisburgensis, the hybrid of Primula glutinosa and P. minima, is repre-
sented by a host of plants on the Tyrolese Alps, as, for instance, on the Muttenjoch
and the neighbouring mountains which separate the Gschnitzthal from the Obern-
bergthal.

Several hundreds of other cases of the kind might be mentioned, but the limits
of this book will not allow me to do more than give the following names selected
from the long list that lies before me:

HYBRID. PARENTS.
Asplenium Germanicum....cccccccceee Asplenium Ruta-muraria x A. septentrionale.
Calamogrostis acutiflord.........c0000 C. arundinacea x C. epigeios.
Carex Beenninghausiand....00..0.++++ C. paniculata x C. remota.
Seiwpus Duval ......0...0scceerenosones S. lacustris x S. Pollichü.
TUNCUS MiffUSUS.1.0.200eeeceeceeeeeeeeeees J. effusus x J. glaucus.
Onchis: Dietrichvand,...<c-----~--0 +000 O. tridentata x O. ustulata.
Potamogeton spathulatus...........00 P. polygonifolius x P. rufescens.
IROpUlUsiCONESCENS:.e-- ce eesaassscoresese P. alba x P. tremula.
Sal Austmacda.seoee.seeonneneonnernene S. grandifolia x S. purpurea.
Rumes MATUMUS ..00.seerveceveceeceees R. aquaticus x R. Hydrolapathum
Polygonum mülbı.......euasssonsensennee P. Hydropiper x P. Persicaria.
Cistus Florentinus...esserserseneenseene C. monspeliensis x C. salvifolius.
Draba Hoppeantir....ccscccvecreceevees D. Fladnizensis x D. Carinthiaca.
Loripa stenocarpa seeunesneeneeereeeenen R. palustris x R. sylvestris.
Pulsatilla Hakelii.........02.c.0000ce0es P. patens x P. pratensis.
Drosera Ob0VAtH.......-.0..vseevseveeve D. longifolia x D. rotundifolia.
Epilobium salieifoliumsmeseneessereeeen E. alsinifolium x E. montanum.
Sorbus latifolia..-...crnesanonsnaneneneee: S. Aria x S. torminalis.
Potentilla procumbens........+0..022+0+ P. erecta x P. reptans.
Mentha nemoros@a .....eccceeccvecveceeeee M. aquatica x M. sylvestris.
Pedicularis atrorwbens.........00ece0ee P. incarnata x P. recutita.
Verbascum rubiginosum eeceeeeeeeeee V. Austriacum x V. pheniceum.
Acanthus spinulosus aussunsuneneeneenen A. mollis x A. spinosissimus.
Gentiana Charpentiert.........cc0ce0es @. lutea x G. punctata.
Primula pubescens ........00+.00.000000e P. Auricula x P. hirsuta.
Vaccinium intermedium .......0000000+ V. Myrtillus x V. Vitis-idaea.
BTCC MUCkOnfünsenneseenzaneenengeen sense E. ciliaris x E. Tetraliz.
Cirsium tatarteumM.....cccccecevecereceee C. canum x C. oleraceum.
LDuppa MUBENS)... 12. -oecasseenecannnavere L. minor x L. tomentosa.
Hieracium stoloniflorum.....+.-+0.+++- H. aurantiacum x H. piloselleforme.

The fact that hybrids exhibit every conceivable degree of frequency of oceur-
rence might lead one to suppose that the rare hybrids were those that had been most
recently produced, and that they exist only as isolated plants because they have not

PERMANENCE OF HYBRIDS, 587

yet had time to disperse and multiply. This conception would not, however, accord
with the actual condition of affairs. In point of fact, the floral contrivances which
exist for promoting crosses between different species occasion a constant origination
of hybrids, but it is certainly not the case that they all have the prospect of becom-
ing new species. Many are called, but few are chosen. In only a fraction of the
total number of fresh plant-forms produced yearly by inter-specifie crosses do we
find the power to survive and multiply. The first condition that must be fulfilled if
a hybrid is to become a species is that it be fertile, 7.e. that its flowers yield seeds
capable of germination as a consequence of fertilization with their own pollen. By
“their own pollen” is here meant not only that which is developed in the same
flower as the stigma which receives it, or in some flower on the same plant, but also
pollen belonging to other plants provided they belong to the same hybrid-formation.
To this condition another is added in the case of dicecious, pseudo-hermaphrodite,
and completely dichogamous flowers, viz.: that several individuals of the hybrid
must make their appearance at the same time, and that of these at least one must
bear male flowers and one female flowers. If we suppose the case of a Willow
hybrid, of which all the individual-plants bear catkins of male flowers only,
obviously no propagation by means of fruits is possible. If none but female flowers
are borne, these may be crossed with the parent-species and give rise to goneoclinic
hybrids (ef. p. 559), and perhaps, in addition, ternary hybrids may be produced, but
no unmodified descendants can be expected from the fruits of a Willow of the kind.
The same thing applies in the case of Cirsiwm, the separate individuals of this genus
being differentiated into those bearing pseudo-hermaphrodite male flowers and those
bearing pseudo-hermaphrodite female flowers (see p. 294). This affords sufficient
explanation of the fact that although Willows and Cirsiums are continually develop-
ing numberless hybrids, few instances are known which one can affirm to be the
beginnings of new species. It usually happens, in fact, in the case of these hybrids,
that all the plants which arise together at a particular spot are furnished exclusively
either with true or pseudo-hermaphrodite male flowers, or else with true or pseudo-
hermaphrodite female flowers. The goneoelinie hybrids produced from the latter
are for the most part represented by greater numbers of individuals. Moreover,
amongst those individuals both sexes much more frequently make their appearance;
hence, they have a far better prospect of being preserved,

The development of a hybrid into a species is also dependent on the conditions
determined by the habitat. When a species thrives well at a particular place, is
represented by a large number of individual plants, and renews itself in descendants
which are in the main unchanged, it may be assumed that the organization of that
species is suited to the soil and climate of the habitat in question. If there were no
such harmonious relation there could be no question of the species flourishing, but
on the contrary is would sooner or later die out. This suitability of the climate and
soil to the organization manifested in the plant’s external form must also exist in
the case of the newly developed hybrid if the few individuals which spring up at
any particular place are to survive in their original settlements, and to give rise to

588 THE GENESIS OF NEW SPECIES,

a numerous progeny. Sometimes such suitability does exist, but sometimes also it
does not. In the latter case the hybrid is suppressed as soon as it sees the light.
But even if its organization is adapted to the soil and elimate of the place of origin,
it has to enter upon a struggle with the species already established there, and
especially with its own parent-species. If the latter grow luxuriantly and in large
numbers at the spot, it is not easy for the new form to take possession of the
ground. In two cases only is there any prospect of the place of origin becoming a
permanent home for the hybrid’s descendants: firstly, where the hybrid, in virtue
of its particular attributes, is equally well, or perhaps even better adapted to the
habitat of the parent-species than are the plants already established there, and
secondly, when the hybrid originates at a spot more or less removed from the place
where the parent-species grow and encounters conditions of soil and climate which
agree with it better than with the parent-species.

That these conditions of the origin of species from hybrids are sometimes
fulfilled will now be shown by a few examples. In the Tyrolese Alps, to the
south of Innsbruck, at the head of the valleys known as the Stubaithal and the
Gschnitzthal, there are certain mountains which rise steeply to a height of from
2500 to 3000 metres. The base of these mountains is composed of crystalline
schist; midway up their ascent mixed strata of schist and limestone are encoun-
tered; and above these strata there is limestone and also dolomite, rising abruptly
and forming the peaks and ridges. Half-way up the sides, where the soil exhibits
great variety, an extraordinarily rich flora is developed. Plants which are, except
in this instance, peculiar to schist formations, and others usually only found on
limestone, here grow close together. Amongst other species the Alpine Roses,
Rhododendron ferrugineum and R. hirsutum, grow side by side on the same soil
and on the same slopes. Associated with them is a third species of Alpine Rose,
Rhododendron intermedium, which has sprung from the crossing of R. ferru-
gineum and R. hirsutum. At several places, e.g. on the eastern and northern
slopes of the Hohe Burgstall, in the Stubaithal, and on the Padaster Alp in the
Gschnitzthal, Rhododendron intermedium oceurs more commonly than either of
the parent-species. Like the latter, it grows on soil rich in humus, flowers
abundantly, develops fruits with fertile seeds, and transmits its characteristics
unaltered to its descendants. Here and there isolated plants are found which must
be ranked as goneoclinie hybrids, but plants of Rhododendron intermediwm form
the larger proportion of the Alpine Roses which clothe the mountain-sides. This
form accords in every particular with the requirements demanded of a species, and
is quite as much a systematic entity as either R. ferrugineum or R. hirsutum.
The following is the explanation of how.this has come to pass: The colour of the
flowers is a little lighter than in R. ferrugineum and richer than in R. hirsutum;
it is a brilliant carmine tint, and enables one even at a distance to identify every
plant of the hybrid. Hive- and bumble-bees hovering about in search of honey
are more attracted by flowers of R. intermedium than by the others, owing to
the superior brillianey of their coloration, and the result is that these flowers are

INSTANCES OF SUCCESSFUL HYBRIDS. 559

erossed with pollen of their own kind. If no inseets appear upon the scene, auto-
gamy takes place. In either case fertile seeds are developed, and give rise to plants
which do not differ from the parent-form. In places where detritus from the
adjacent limestone and dolomitie cliffs is mixed with the humus of the soil the
seedlings thrive distinctly better than those of R. ferruginewm and no less well
than those of R. hirsutum. Thus, so far as the soil is concerned, R. intermediwm
has an advantage over R. ferruginewm, and in respect of insect-visits it is better
off than either of the parent-species. These advantages, though apparently insig-
nificant, are not merely sutlicient to prevent R. intermediwm from yielding to the
parent-species in the struggle for existence at the places in question, but even give
it rather a better chance of prevailing.

As a second instance, we will take Salvia sylvestris, the hybrid offspring of
Salvia nemorosa and Salvia pratensis. This plant grows in dry meadows all over
the low country to the south of Vienna, as, for instance, on the banks of the river
Leitha, which separates Austria proper from Hungary. The landscape there is
slightly undulating, the elevations are composed of boulders and clay, and wherever
the latter is present in great quantities, especially on the gentle slopes of the rising
ground, Salvia nemorosa constitutes an important item in the vegetation. The
hollows are full of a dark moist earth, with a rich admixture of humus, and there
we find meadows in which Salvia pratensis grows luxuriantly. These two kinds
of habitat usually pass quite gradually into one another, and the parts common to
both consist of dry meadow-lands. Salvia nemorosa does not thrive in the intri-
cate grass-carpet of these meadows, and is rarely to be seen there, whilst for Salvia
pratensis the soil is too dry, so that that species also is but poorly represented on
the areas in question. On the other hand, these dry meadows are the most suitable
ground for the hybrid Salvia sylvestris, and it thrives exceedingly upon them.
Its flowers are much visited by insects; its fruits ripen in as large numbers as
in the case of S. nemorosa or S. pratensis, and have been found by experiment to
be fertile in a proportion of more than 60 per cent. Salvia sylvestris has
therefore scattered itself all over this dry meadow-land, and manifests all the
characteristics essential to our conception of a species.

A third example is Nuphar intermediwm, a hybrid derived from Nuphar
lutewm and Nuphar pumilum. This plant grows in lakes in the Black Forest
and in the Vosges. It is also scattered over North Germany, and occurs with
increasing frequency in Central and Northern Russia and in Sweden. It has been
found as far north as Lapland. At the northern extremity of this large area of
distribution Nuphar intermediwm is more abundant than the species from which
it is derived; indeed in many places it oecurs in their absence, and in fact passes
beyond the northern limits of their area of distribution. In these situations there
is, of course, no possibility of the hybrid’s crossing with either of the parent-
species or of the formation of goneoclinie hybrids. Nuphar intermediwm subsists
independently there, multiplies without change of form, and has in fact established
itself as a species. This phenomenon is explained as follows: The northern limit of

590 THE GENESIS OF NEW SPECIES,

the distribution of each of the three Water-lilies in question is determined by their
not being able to ripen fruits beyond that limit. Of the three, Nuphar lutewm flowers
the latest, and therefore its fruits are also the latest to ripen, whence it follows
that it is the first to fall behind; that is to say, it reaches the northern limit of
distribution sooner than the others, and ceases to ripen fruit in regions where the
others are still able to do so. But Nuphar pumilum and N. intermedium are also
different from one another in this respect. In Norbotten and Lapland Nuphar
intermedium ripens its fruits a little earlier than N. pumilwm, and it is conse-
quently able to extend rather further north than N. pumilum. The further north
plants go, the shorter becomes the time allotted for the performance of their annual
work; and those which ripen their fruits early have a great advantage over those
which ripen later. Concerning Nwphar intermedium, it has also been ascertained
that the individual plants produced in nature are more fruitful than those
reared in gardens from artificial crosses. In the case of plants obtained in this
manner in the Botanic Gardens at Königsberg each capsule contained from 15 to
18 fertile seeds, whilst capsules ripened in the small lakes of the Black Forest
contained from 38 to 63, and others taken from plants growing in Lapland con-
tained from 41 to 72 such seeds. From these data we may infer, in the first place,
that N. intermediwm is most prolific in situations beyond the range of the parent-
species; and, secondly, that it would be wrong to suppose that because a hybrid
may be comparatively infertile or actually sterile in a particular locality, such
infertility is a characteristic of the plant wherever it may occur.

As may be gathered from the above account of these three examples, the advan-
tage which a hybrid may possess over the parent-species, whereby it is enabled
to subsist and multiply side by side with those species, is not always of the same
kind. In one ease it is the more vivid coloration of the flowers, in another the fact
of the hybrid being better adapted to a particular state of the ground, whilst in
the third the earlier ripening of the fruits, which enables the hybrid to stand a
more rigorous climate, gives the requisite advantage. These do not, of course,
exhaust, by a long way, the possible sources of superiority, and there are many
instances of hybrids which thrive better than the parent-species when the climate
becomes milder, moister, or drier, as the case may be. It is obvious that of all the
different advantages which may come into play those connected with climatic con-
ditions are the most important, and the genesis of hybrids is probably most fre-
quently due to the operation of this kind of advantage.

Far too little significance has been attached to the fact that the greater number
of hybrids are not found in districts where the parent-species grow together with
equal luxuriance, but occur where one or other of those species is meagrely repre-
sented, owing to the climate not being favourable to its distribution. Again, large
numbers of hybrids are found in parts where the boundaries of several species
coincide. In Europe such regions exist in the strips of land where the advance-
posts of the Floras of the Baltic and Black Sea, and the Floras of the Baltic and
the Mediterranean, respectively, encounter one another, and particularly in the

THE DISTRIBUTION OF HYBRIDS. 591

lower limits of the Alpine Flora. Another characteristie of these borderlands is
the fact that the separate hybrids growing on them are almost always represented
by a large number of individuals, and the consequence is that there is no great
chance of their crossing with the parent-species and gradually reverting, in succes-
sive generations, to those species. If isolated individuals belonging to a particular
hybrid grow in the midst of thousands of plants of the parent-stocks, their stigmas
will, in all probability, be dusted with pollen from the latter species. This proba-
bility diminishes, however, as the number of individuals of the parent-species
flowering in the same locality as the hybrid diminishes; if that number is small
the hybrid is thrown mainly upon its own resources for fertilization, and, provided
it is self-fertile, there is nothing to prevent its multiplying and becoming dispersed.

Connected with the above is the further fact that in the neighbourhood of a
hybrid which has become a species there is sometimes no trace of one of the parent-
species, it having completely died out. The slightest change in climatic conditions
may cause the plants of a particular stock to suceumb at the confines of the stock’s
area of distribution, where they are only present in small numbers, and are anything
but strong; and when this happens we find the other parent-species alone growing
side by side with the hybrid, and even that species is possibly not so well adapted
as the hybrid to the altered conditions. Of cases in point we will select two from
the East of Europe and two from the West.

When Epilobium alsinefolium and Epilobium palustre are crossed a hybrid is
obtained which, when fertilized with its own pollen, yields a large quantity of fertile
seeds. The plants reared from these seeds exhibit the same characteristics as
the plant from which the seeds were taken. This hybrid grows together with
the parent-species in the Riesengebirge, and has received the name of Lpilobiwm
scatwriginum. It is likewise a native of the Bihar Gebirge, on the confines of
Hungary and Transylvania, and is of very common occurrence in the springs and
rivulets in the vicinity of the Hochkamm (a mountain of this chain). Yet, of the
two parent-species, only one, viz. Epilobium palustre, grows amongst these moun-
tains. Again, Prunella hybrida is a hybrid springing from Prunella laciniata
and Prunella vulgaris. It is widely distributed in the Wienerwald district, and in
some places is commoner than the parent-species, whilst in Moravia and Bohemia it
‘occurs in places where one of the latter, viz. Prunella laciniata, is entirely absent.
A third instance is afforded by Primula brevistyla, called also Primula variabilis,
a hybrid derived from Primula vulgaris and P. officinalis. This plant is true to
seed, and is met with everywhere throughout almost the whole of Europe in
company with both parent-species. In some districts of France it is found also in
places where one or other of the latter species does not grow at all, and even where
both are absent. Our fourth example, Linaria stricta, is the hybrid of Linaria
striata and Linaria vulgaris. It occurs in many places in the West of Europe,
together with its progenitors, but in the South of France, in the neighbourhood of
Montpellier, it is found growing with Linaria striata alone, whilst the other parent-
stock, LZ. vulgaris, is never found in the district.

592 THE GENESIS OF NEW SPECIES.

We shall have another opportunity of deseribing the way in which the lines of
demarcation of the ranges of entire floras become displaced in consequence of the
changes which the climate of a region is liable to undergo in course of time. These
displacements of floral regions are, as a rule, the result of very slow and inconspicu-
ous migrations on the part of the plants constituting the floras in question. The
direction of migration is invariably towards the places whose climatic conditions
agree best with the organization of the plants, and is, in the case of any one species,
either an advance or a retreat, according to the nature of the circumstances which
impel the species to migrate. The different plants of a flora do not all migrate in
a host together. Some species abandon their former home entirely and establish
themselves in a new locality more or less remote from it; others leave a few of
their kind behind in the old settlement at isolated spots which happen to be in
peculiarly favourable situations, and many succumb to the effects of the new con-
ditions or to the hardships incidental to the migration, and so die out. These
changes in the range of floras are naturally accompanied by all sorts of alterations
in the social relationships of the plants concerned especially with regard to the
co-existence of hybrids and their progenitors. It may happen that one or both
parent-species are left behind, whilst the hybrid advances, or the hybrid may
remain behind, whilst one of the parent-species advances; or, again, one of the
parent-stocks or both may die out. The facts concerning these local displacements
explain the phenomenon that species which, from their characteristics, may be
looked upon as hybrids of two other species, occupy in each case a district which
is separated, and often at a considerable distance, from the areas inhabited by the
species supposed to be their progenitors. The characteristics of the kind of Sorrel
named Rwmex Patientia lead one to the conclusion that it is a hybrid derived from
Rumex aquaticus and Rumex erispus. It is found, however, growing wild in
Hungary and in Bosnia in parts where neither Rwmex aquaticus nor R. erispus
oceurs at all. In Herzegovina there grows fairly commonly a Mieromeria which
has been named by one of my friends Micromeria Kerneri. So far as its charac-
teristics are concerned it must be considered to be a hybrid of Micromeria graca
and Micromeria Juliana; yet neither of these two species grows in Herzegovina at
the present time, and they are not met with at any nearer spot than the part of
Dalmatia which stretches westward from Herzegovina, and belongs to the area of
distribution of the Mediterranean flora. In the little upland valleys of Planail and
Plawen, which run down from the mountains of the Oetzthal into the valley of the
Adige, there grows a Pulsatilla named Putsatilla nutans. If it occurred in company
with Pulsatilla vulgaris and Pulsatilla montana, all Botanists would be unanimous
in looking upon it as the product of a cross between those two species. Yet Pulsa-
tilla vulgaris and P. montana do not grow in the high valleys in question, but are
first met with at a distance of many miles from them, the former in the Unterinnthal -
and the latter in the Vintschgau (a portion of the Adige valley).

Inasmuch as the last-mentioned cases have to do with processes which have
taken place long ago they partly belong to the next chapter, where the genesis of

THE GENESIS OF NEW SPECIES. 593

species in the past will be discussed. They here bring to a natural conclusion a
series of examples adduced to show in what manner a genesis of new species may
ensue in the present, and may have taken place in the past. No sharp line of
demarcation is to be found between different epochs in this connection any more
than in the case of any of the other phenomena which, in the aggregate, constitute
the history of species.

Now that it has been shown how new species arise from hybrids, or, in other
words, from the crossing of species in pairs, the question presents itself whether, in
addition to this one method, there are not also others leading to the same result.
In answering this question we must bear in mind that every permanent change in
external form which is inherited by a plant's descendants must be preceded by a
change in the constitution of the protoplasm, and that so far as investigation has
elicited the facts, the centre of the change is located exclusively in a particular
protoplast which lies hidden in the ovary and there receives the spermatoplasm.
The stimulus which causes the change in this protoplast can only proceed from the
spermatoplasm, and every speculation concerning the formation of new species must
therefore be associated with the question whether in the intercrossing of plants of
one species and in autogamy the protoplasm in the course of its journey to the
ooplasm may, as a result of its exposure to new external conditions, undergo modi-
fications of so fundamental a kind that its influence on the ooplasm is subject to
corresponding variations. In the first place, it might be imagined that the pollinated
stigmas do not always act in the same way upon the spermatoplasm of the pollen-
cell. Reference has already been made to the fact that a stigma may sometimes be
almost simultaneously dusted with the pollen of very different plants (see p. 404),
but that it has the power of exercising a selection, and that in every case only one
kind of pollen is induced to put forth tubes by which a real fertilization is accom-
plished. The other kinds of pollen upon the stigma are not known to have a direct
effect upon the ovule. But that there is some interaction between them and the
protoplasm in the cells of the stigma is evidenced by the fact that they swell up
wherever they are in contact, and (as has been shown, p. 414) are frequently found
developing pollen-tubes. Now it is possible that the reciprocal action of the contents
of these pollen-cells and the contents of the stigmatic cells may produce some change
in the latter, which is transmitted to the contents of those other pollen-tubes which
are to enter into combination with the ooplasm. Such modification might conceiv-
ably affect the nature of the stimulus imparted to the ooplasm, and this alteration
in the stimulus might be manifested in a change in the form of the individual
arising from the fertilized ooplasm. The likelihood of all these possibilities and
assumptions being satisfied is extremely small, but as no researches have yet been
instituted into the matter, it cannot be dismissed with an unconditional negative.

In artificial crosses between different species of Cirsiwm it has often been noticed
that pollen-cells taken from a single capitulum vary in their effects upon the stigmas
of a second capitulum, inasmuch as the seeds produced by the different florets,

though all fertilized with the same kind of pollen, yield dissimilar plants when
Vou. II. 88

594 THE GENESIS OF NEW SPECIES.

they germinate. The variation is limited, it is true, to the different degrees in
which the seedlings resemble one or other of the parent-plants. If the cross is
between two plants of the same species no such variation can occur, seeing that the
plants crossed are alike in form. But there is still the question whether differences
in the age, size, and luxuriance of growth of the individuals which cross may not
have some influence on the result. So far as my experiments show, these differences
have no effect on the genesis of new forms, and have no prospect of becoming per-
manent characters in the offspring. A poor stunted plant growing on dry soil may
produce seeds which, on being planted in a good moist soil give rise, under favour-
able conditions, to well-developed plants capable of flowering luxuriantly. As is
well known, the first flowers of an inflorescence are always much larger than those
which subsequently open at the apices of the spike or raceme, or on the ultimate
ramifications of the cyme as the case may be. Now, if the large earliest flowers
are crossed one with another, and likewise the small latest flowers, and the seeds so
obtained in each case are kept separate but reared under similar conditions, the
plants produced from them do not differ in the slightest degree from one another,
but in their turn bear flowers, of which the first are the largest and the last the
smallest. Notwithstanding these results, however, I should not like, without
further investigation, to deny the possibility of the specific constitution of the
spermatoplasm undergoing some change as a result of external influences in the
course of its development, whether during its imprisonment in anthers or antheridia
or on its way to the ooplasm, or to say such change might not cause the descendants
of the plants concerned to differ in form from the individual from which they
sprang.

It has been established beyond all doubt that modifications of form directly
induced by conditions of soil or climate are not hereditary, and that every change
of form which persists in the descendants is only brought about as the result of a
process of fertilization, or, in other words, that new species can only arise through
fertilization. Herein lies also the solution of the marvellous phenomenon known as
the alternation of generations, and of the question why plants in general flower and
undergo fertilization. To these processes is due the genesis of new species. The
propagation of plants, their multiplication and dispersal, may also be effected by
means of brood-bodies, and as a matter of fact these processes are continuously
operating on a vast seale. But the plants reproduced by brood-bodies retain the
form of their ancestors unaltered, and no new forms arise in this way. Suppose
that a locality is occupied exclusively by plants which multiply by brood-bodies
only and do not change their form, and that in consequence of a change in the
climate such species as are not adapted to the new conditions abandon their homes,
or else languish and die out, the probability is that many of the vacated spots will
remain unoccupied owing to there being no recruits in the neighbourhood, or from
out its confines, that are better adapted to the new conditions. If, on the other
hand, the area in question is inhabited by plants which reproduce sexually and
which, by crossing one with another, produce descendants of diverse forms, there is

DERIVATION OF EXISTING SPECIES. 595

every probability that amongst the assemblage of new forms some will be better
adapted to the new conditions when a change of climate occurs than those of the old
species which are driven out thereby, and that these new forms will therefore be
able to take the place of the latter.

It is only from this standpoint that we can properly understand the phenomena
of the alternation of generations, the separation of the sexes, dichogamy, and all
the rest of the wonderful floral contrivances, the object of which is to facilitate the
crossing of two species during the first stage of flowering and only to allow of
crossing between plants of one species, or of geitonogamy, autogamy, or cleisto-
gamy in the event of no inter-specifie crossing taking place. Asa result of these
contrivances, numberless new forms are continually being generated which are
respectively adapted to all the most various conditions of soil and climate. So
long as no change in climatic conditions takes place, the majority of these forms
have very little chance of surviving and of naturalizing themselves as species
amongst the plants already established in the same locality. But when, in conse-
quence of a change of climate, the ranks of the species in possession of the ground
are thinned through the abdication of many of those best adapted to the condi-
tions of life previously existing, the real significance of the new forms which have
arisen as a result of the sexual process is manifested in the fact of those which are
best adapted to the new conditions taking possession of the spots vacated and
settling down there as new species.

DERIVATION OF EXISTING SPECIES.

The plants preserved as fossils in former ages are not only the forerunners
but the ancestors of the existing vegetation of to-day. There was no general
rejuvenescence and extinction of organisms coincident with the beginning and end
of the several “periods” of the history of the earth. The changes in the organic
world, like those in the inorganic crust of the earth, were accomplished gradually by
slow degrees, and the organisms of the present day are a continuation of, and have
been slowly evolved from, those of former ages.

So far, there is little difference of opinion amongst naturalists; but as to the
causes of the differences in form between the vegetation of the present and the past,
the most various theories are held. Nor is this surprising, seeing how largely our
conclusions are based on conjectures. And when the flood-gates of speculation are
rolled back it is not always that the proven is clearly distinguished from the
unproven. An import is attached to isolated facts which they do not merit, and—
most mischievous of all—the existence of wide lacun® in our knowledge is con-
cealed, or these lacune are dexterously bridged over with unmeaning, high-sounding
words and hollow phrases which, while astonishing us for the moment, leave us
chastened and confounded. The confirmed mistrust aroused by these extravagances
which obtains concerning all that bears on the derivation of species demands that
we should devote a brief consideration to the prevailing theories, and especially to

596 DERIVATION OF EXISTING SPECIES,

such as bear upon the conversion of species of former times into those of the exist-
ing vegetation.

A change in the conditions of life has, according to a widely-spread view, been
the immediate cause of a change in the vegetation. The altered conditions of life
provoke new wants in the plant, and these new requirements have led to a trans-
formation of their organs. Stimulated by use, the organs in question become
enlarged and further developed; others, no longer of service, become smaller,
atrophy, and disappear. It is the cumulative result of these small and almost
imperceptible changes that in course of time becomes apparent. These structural
changes are transmitted to the progeny, and with an increasing tenacity, the
greater the number of generations which have been exposed to the altered condi-
tions. This, the theory of adaptations, has provoked wide discussion and criticism.
It is urged against it that, whether wild or cultivated plants be considered, it is
only isolated or a few individuals, never the whole of the members of a species,
which exhibit these variations and transmit them to their offspring. If these new
characters are immediately due to the soil or climate, then all the individuals of a
species, exposed to like conditions of growth (environment), should exhibit them
and hand them on to their offspring. The permanence of the influence—and to
this many naturalists and others attach great importanee—is without significance
in this matter. When a change is called forth—be it by an altered source of
nourishment, by the influence of heat or cold, light or darkness, moisture or dry-
ness—it must become apparent upon the growing plant, since a change in the plant
stands to a change in the environment as effect to cause. If the cause ceases, so
also does the effect, equally after the lapse of a year or a hundred years. But a
much more potent criticism of the theory of adaptation is the result of a series
of experiments which were carried out for the solution of these questions. From
them we see that an altered environment calls forth certain changes in the plants
submitted to it, but that these are not transmitted to the offspring, are not heredi-
tary, and that the influences of soil and climate do not provoke a fundamental
change in the constitution of the protoplasm. Influences of this sort can induce a
diseased condition in a plant and can even kill it, but they cannot bring about a
change which can be transmitted to the next generation. Though soil and climate
play a most important part in the struggle of species and varieties for existence,
and though the environment has a great influence on the origin of varieties and on
the distribution and migration of plants—as the immediate stimulus to the origin
of new and transmissible characters, and thus to the modification of species, change
of environment is without significance.

Another theory dealing with the origin and modification of species is that
known as the theory of progressive transformation by inherent forces. According
to it, the impulse to change resides in the inherent tendency of all species to
perfect themselves. This theory transcends all experience and depends on premises
and draws conclusions essentially metaphysical in nature; it deals only in part
with the results of scientific observation. It presupposes a creation of living

VARIOUS THEORIES, 597

protoplasts endowed with the capacity to alter their constitution on their own
initiative; and, further, that these alterations take place along predetermined lines
in a direction leading from a lower to a higher platform; consequently the
imperfect organism necessarily, in course of time, passes over into a highly
developed, perfect one. Against this theory the following may be urged: The
first assumption involves creation. The question is: Is it possible for a living
protoplast to be formed from inorganie matter without the co-operation of already
existing living beings? The question obviously concerns the present and future
as well as the past, for what has happened once may again take place, for the
forces of nature, according to the laws of the conservation of matter and energy,
remain the same for all time. The discussion of this question resolves itself into
this: whether a little bit of protoplasm can arise from inorganic matter, and after
its origin can acquire the capacity of growing by the absorption of food from its
environment, &c.; in a word, whether it can exhibit those changes and movements
which we term life. When first organic compounds (formic acid, urea, sugar, &c.)
were synthesized in chemical laboratories from inorganic substances like ammonia,
carbonic acid, and water—compounds which formerly had only been produced as a
result of the activity of living protoplasm—naturalists began to think that these
things might take place in nature independent of already existing plants. It
seemed possible that these substances might, under the uncontrolled forces of
nature, unite and arrange themselves in the same manner as occurs within a
vegetable cell. The tendency of matter to combine, which plays so important
a part in nature, was pointed out, and especially the similarity between the
structure of crystals and that of certain cells; the properties of finely-divided
soil also were called to mind, how it absorbed gases, took up water in varying
quantities, altered salt-solutions, separating certain of their constituents, and what
was especially noteworthy, increased the capacity of many simple substances to
combine. This was at a time when chief importance was attached to the chemical
properties of protoplasm; it was thought that, once given the substance, it would
form itself into cells like erystals. Of the ultimate structure of protoplasm and
of the nucleus knowledge was as yet very incomplete. The tendency of that time
was to explain all those phenomena which constitute life as the resultant of the
various forces which form inorganic bodies, and to deny the existence of any wide
gulf between the living and non-living world.

The experiments to produce living matter had all of them negative results.
But this of course is no proof of its impossibility; for it can always be urged that
wrong methods were followed, and improper conditions imposed. Nor, on the
other hand, does it follow from the fact that hitherto living matter has never
been known to originate independently of existing organisms, that its production
is impossible. Since we cannot arrive at definite results by experiment, the in-
vestigator must depend on other considerations.

The second assumption of the theory of transformation from internal causes.
that plants have the inherent capacity to modify their internal constitution and,

598 DERIVATION OF EXISTING SPECIES,

similarly, their external form spontaneously, has been so fully met by the obser-
vations recorded in the last chapter that it is hardly necessary to deal with it
now at great length. I shall content myself with pointing out that it is impossible
to give a natural explanation of such a phenomenon. Every variation presupposes
a corresponding disturbance; for the acquirement of any new structural character
the plan of construction must undergo some fundamental alteration. The naturalist
is unable to grapple with the phrases “internal causes”, “internal force”, “force
of transformation”, “tendency to differentiate”, “principle of progressive trans-
formation”, when attempting to explain variation in a natural manner upon
mechanical principles. Nor is the likening of this transformation to the meta-
morphosis which every individual passes through at various periods of its existence
at all to the point, since metamorphosis repeats itself with great constancy in
every species according to the plan of construction which is laid down in the
specific constitution of the protoplasm. That the protoplasm of any species should,
in the absence of any impulse or stimulus from outside, be able spontaneously to
alter its plan of construction contradicts all our experience of the normal action
of natural forces. Even should we conceive vital force, the dormant energy of
the protoplasm, to be converted into an active form, it could only give rise to
movements which have their origin in the specific constitution of the protoplasm.
And now we come to the assumption that this inherent force of transformation
is a progressive one, that it leads to a higher or more perfect development. But
what is to be regarded as a higher development amongst plants? A tree with
its brightly coloured flowers and luscious fruits seems more highly developed to
the non-botanist than a low herb with inconspicuous flowers, or than the green
filaments of a Spirogyra destitute of flowers. The supporters of the theory under
discussion assert that the highest development is that which exhibits the greatest
complexity of form, and in which division of labour is carried furthest. And in
this assertion they do not essentially differ from the popular view. Complexity
of form and division of labour are undoubtedly carried further in an Apple-tree
than in the Spirogyra of the ponds and ditches. But it must not be forgotten
that the differentiation of a plant-body into various tissues, the production of
wood, bast, and cork in its stem, of cuticle, stomates, and hairs on its leaves, of
various colouring-matters and aromatic substances in its petals, and of sweet juices
in its fruits, stands in harmonious relation to the environment of the plant in
question. Change the conditions, and imagine the Apple-tree submerged in a pond;
it is no longer in harmony with its surroundings, its complexity of tissues, its
wood, stomates, &e., are not so well adapted for these conditions as are the Spiro-
gyras and Water-weeds equipped with organs of another type. The size of a
plant is often—in the popular estimate—the indication of its high organization.
A big plant gives the impression of possessing a more perfect development than
a small one. But this criterion leads to no satisfactory result; it is sufficient to
instance the case of certain huge sea-weeds (Macrocystis) of the southern seas, which
exceed our greatest forest trees in height. Many Thallophytes, only visible under

VARIOUS THEORIES. 599

the mieroscope, show a greater complexity of structure of their eonstituent cells
than do many Flowering Plants; and, should especial importance be attached to this
character, Diatoms and Desmids must be regarded as more highly organized than
many small annual Composites. The idea of progressive development implies a
recognition of that species of plant which is most highly developed and which
stands upon the apex of the pyramid, or, at any rate, of the group of plants which
has already reached the furthest point—is it the Aristolochiacewe, Cannacex, Mag-
noliacew, the Orchids, the Composites, the Ranuneulacez, the Papilionacez, or the
Pomegranates? Any one who has studied carefully the structure of these plants
knows well that it is impossible to make an estimate of this kind. In a book
of Botany one group must be treated first and another last, but this does not
necessarily imply that the last is the most highly developed; indeed the various
writers of systematic works begin and end with the most various groups. Like the
theory of adaptability, that of progressive transformations from inherent forces fails
to give us a reasonable explanation of the variations which plants have undergone
in process of time.

A third theory, based on the observations of modern times, is as follows: That
variations of form in the offspring arise through crossing, from the union of two
dissimilar protoplasts. This theory, based on the union of unlike forms, has been
fully sketched out in the last chapter. It assumes the existence in former times of
a vegetation rich in forms—an assumption amply justified by the fossil remains
which have been preserved. New forms arose, not by a progressive development
such as has been alluded to, but by a transformation or metamorphosis of those
already in existence. It was from the union of existent types that incipient new
species were produced. By the periodic recurrence of changes in climatie con-
ditions the areas of plant-distribution have received continual displacements, and it
was then that these incipient species or varieties were put to the test. Those well-
suited to the fresh conditions settled down into new species. They replaced their
less well-adapted ancestors in the plant-community, and they played the same part
as these had formerly done. A change indeed is brought about; but not (on the
lines of the theory of adaptability) as a direct result of climatic influences, nor from
an inherent tendency to progressive development. It arises rather from a change
in the specific constitution of the protoplasm in consequence of the crossing of
unlike forms. In basing the transformation of species on a crossing of this nature
we are relieved the necessity of picturing lacune in a vegetation as a result of
elimatie changes, or of any serious disturbance of the inter-relations of its various
component forms. Bacteria and Moulds, Mosses and Lichens, Ferns, Grasses, Palms,
and Coniferous Trees, have all of them a special function to fulfil in the great
community of plants, and they are to a certain degree dependent on one another.
Were one removed the whole would be affected, and it might well happen, did a
given group come to speedy extinction, that the whole community of plants might
suffer. But in every group at all times and in all places a reserve of new forms
continually arises by crossing, so that this danger is averted. With elimatie

600 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

changes, of the older, less fit forms some are extinguished, whilst young, new
forms step into their places. Thus we see also that the conversion of Mosses
into Ferns, of Ferns into Conifers, and of Grasses into Pinks, &e., as assumed
by the theory of progressive transformation, would be a positive disadvantage
to plants as a community, and that its tendency would be in the direction of
anything but real progress.

It is important to recognize the fact that in the production of new forms by
crossing, it is not especially such forms as are constituted to resist an anticipated
change of climate that are produced. Of the forms which arise, some are fitted
for a more inhospitable, others for a milder climate; but it cannot be said of any
that they possess an assured future. Such only are able to maintain, propagate,
and establish themselves, as are from their internal organization and external form
in harmony with the prevailing climatie conditions of the moment. Those so
constituted that they are unable to thrive under the given external conditions
linger and become extinct; they are outstripped and overgrown by such as find
the environment to their liking. Hence we speak of the struggle for existence.
Plants in harmony with their surroundings are the victors, and they establish
themselves upon the arena of this encounter. This, briefly, is Darwin’s theory of
Natural Selection, a theory which marks an advance upon all other theories of the
origin of new species. Though many views may be held as to the precise manner
of origin and transformation of forms, there can be no difference of opinion as to
the significance of the struggle for existence and of the survival in this struggle
of those forms best fitted by their organization to the circumstances of the environ-
ment.

THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

The fact that the savants of ancient times made no attempt to classify plants
according to their structural characters is explained by their limited botanical
knowledge. Their interest was restricted to such plants as were in use as drugs,
poisons, and charms, to vegetables, fruits, and cereals, finally, to such as were
of value for decorative purposes and as symbols of religious observances. Nor
was the number of these plants considerable. Some five hundred forms were
known to Theophrastus (300 B.c.), whilst Pliny (23-79 A.D.) records about twice that
number. The characters of these few plants could be retained in the memory
for the purposes of comparative investigations, and their recognition depended in
large part upon the general impression gained in the ordinary intercourse with
nature. Enumerations of plants were based far more on their medicinal or
economic uses, on their hurtfulness and beneficence for mankind, than on any
structural characters they might possess in common. Even in the herbals of the
sixteenth century, containing, as they did, new descriptions and incomparable
woodeuts, were the medicinal and economic properties of the various plants still
especially emphasized; Botany was still almost exclusively the handmaiden of
medicine and agriculture.

OLDER SYSTEMS OF CLASSIFICATION. 601

The first botanical writer to break with these old traditions was Clusius
(1526-1609); he described plants as he observed them, quite apart from their
value to man. Clusius, though a Belgian, spent many years of his life at Vienna,
and thoroughly explored the Flora of Austro-Hungary; previously he had investi-
gated the plants of Spain and Portugal. To England he paid more than one
visit, and received many exotic plants from Sir Francis Drake, the voyager. In
his Rariorum Plantarum Historia, published originally in 1576, we find the
first attempt to classify plants according to their similar characters. In separate
books he deals with trees, shrubs, and under-shrubs, bulbous plants, sweet-smelling
flowers, scentless flowers, poisonous, narcotic, and acrid plants, with plants having a
milky juice, and with Umbellifers, Ferns, Grasses, Leguminose, and certain Crypto-
gamic plants. In those days some 4000 plants were distinguished by Botanists,
and the want of some system of classification was gradually felt. The groups
of Clusius and his contemporaries were inadequate, and the system of Cesalpino
(1519-1603), published in the first book of his De Plantis Libri XVI (1583),
failed to obtain the recognition it undoubtedly deserved—perhaps because it
was only sketched out in outline and lacked a full and detailed rendering.
Cesalpino was the first to convert observation into real scientifie research; he
drew attention to the more hidden organs of plants, to the position of the seeds,
the number and mode of insertion of the cotyledons, &e., to the presence or absence
of flowers.

It is to Tournefort (1656-1708), a Frenchman, that we owe the first complete
review of known plants in synoptical form. In his Institutiones Rei Herbarie
(published 1700) 10,146 species of plants are distinguished and arranged in 698
genera, which again are assembled under 22 classes. Classes 1-15 include herbs
and under-shrubs, 16 and 17 flowerless plants (Cryptogams), and 18-22 shrubs
and trees. The herbs, shrubs, and trees are distinguished by the form of their
flowers, especial importance being attached to the presence of calyx and corolla,
to the regularity or irregularity of the flower, and to the petals—whether they
are free or united with one another. Not long afterwards Linneus produced
a classification of plants based on the distribution of the sexes, and especially upon
the number of the stamens in the flowers. The terms species and variety, genus
and class, were more clearly and intelligibly defined than heretofore, and his 1050
genera were included under the 24 classes already enumerated (p. 288). The
Linnean classification, known as the Sexual System, enjoyed an unprecedented
recognition. It constituted a well-arranged summary of a great mass of scattered
observations, and made it possible for species to be identified by means of concise
descriptions. It was not the fault of this accomplished and renowned naturalist
if a greater importance were attached to his system than he himself ever intended.
Linneus never regarded these 24 classes as real and natural branches of the
vegetable kingdom, and expressly says so; it was constructed for convenience of
reference and identification of species. A real natural system, founded on the
true affinities of plants as indicated by their structural characters, he regarded

602 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

as the highest aim of botanical endeavour. He never completed a natural system,
leaving only a fragment (published 1738).

The eredit of actually founding a natural system of plants is usually attributed
to Bernard de Jussieu (1699-1777) and his nephew Antoine Laurent de Jussieu
(1748-1836). For many years this system only found expression in the laying
out of the beds in the Botanie Garden of Trianon (at Versailles); it first became
generally known some thirty years after its inception, when the younger de
Jussieu published his Genera Plantarum (1789). A hundred families of plants
are distinguished and grouped under fifteen classes, which, in their turn, fall
under three main co-ordinated divisions (Acotyledones, Monocotyledones, Dicoty-
ledones). The three main divisions' are founded upon the structure of the
embryo at germination. In the Acotyledones the embryo consists of but a
single cell and is destitute of cotyledons, in the Monocotyledones it is multicellular
and provided with one cotyledon, whilst in Dicotyledones there are two cotyledons.
The Acotyledones are equivalent to the Cryptogamia of Linnzeus (his 24th class,
cf. p. 290) and constitute the 1st class of the new system. The Monocotyledones
fall into three classes according to the relative position of the stamens to the
ovary (Monohypogyn®, Monoperigyne, Monoepisyn®). The Dicotyledones are
first subdivided into three groups according to the structure of the perianth,
viz., into those destitute of petals (Apetalz); those with distinct calyx and corolla,
the petals being united (Monopetale); and those also having calyx and corolla,
with all the petals free from one another (Polypetale). Each of these groups is
subdivided into three classes, based on the relative position of stamens to ovary
(in the case of the Monopetalz of corolla to ovary). Since in the Dicotyledones
with unisexual flowers it was impossible to indicate the relative position of
stamens and ovaries, a special class (Diclines irregulares) was set aside for them.
The institution of this last class does not mark an advance towards a natural
system; whilst the limitations of the other classes in respect of the relative positions
of stamens to ovary is cumbrous and unnatural, still they are less artificial than
those of the Linnean Sexual System. The distinctive features of the system of
de Jussieu are the broad characters upon which the families are based—the whole
structure of the plant being taken into consideration—and especially the recogni-
tion of Monocotyledons and Dicotyledons as equivalent groups of Flowering

1A. L. DE JUSSIEU’S SYSTEM OF 1789.
Class.
PA COLY GU ONS ne: RANDE I.
Staminahypogyna...n.enneenansscnenseneesnrnneorennnresnnennsenene I.
Monocotyledones...........:.cssseeeereeeeeeee | perigyna
epigyna
fi Stamina epigyna...................
Apataleas- anne perigyna....
hypogyna..
(ae hypogyna .

perigyna. .
Antheris connatis................:0-:.0+ X.
| epigyna { distiniotisy. ..c2 eoenieieckcet XI.
(SEE GEA TESS soecoco: Haecneae te ca Saseene ‚X
Polypetalz.............. ett

perigyna.. ‘
Dichneriirrepularee 24%... ace cce cactus eaatcvavecuactosvanes svectncedweracet ln hun ee

Dicotyledones

OLDER SYSTEMS OF CLASSIFICATION. 603

Plants. A. P. De Candolle! (1778-1841) in his Théorie Elémentaire de la Botanique,
ou Exposition des Principes de la Classification natwrelle (published 1813), dis-
tinguished between cellular and vascular plants (Cellulares and Vaseulares). The
former are constructed of cells alone, whilst in the latter vessels also are
met with. The cellular plants were divided into those without leaves (Cellu-
lares aphylle) and those provided with leaves (Cellulares foliacew). The
vascular plants were divided according to anatomical views current at the
time into those in which the vascular bundles were scattered through the stem
and were supposed to originate from within (Endogen»), and into those in which
the vascular bundles were arranged in a ring and were added to from without
(Exogene). The group Endogen included the Vascular Cryptogams (Endogenze
eryptogame), forms destitute of flowers, and the Monocotyledons of de Jussieu
(Endogen® phanerogame). The Exogen, the equivalent of de Jussieu’s Dicoty-
ledones, were divided into those with a simple perianth (Monochlamydez), and
those with a distinct calyx and corolla (Diplochlamydez). The latter are further
subdivided into three groups: the Corolliflore, in which the petals are united
into a continuous corolla; the Calyeiflor®, in which the petals are inserted upon
the calyx; and the Thalamiflore, in which the petals are free and inserted upon
the floral receptacle. Although De Candolle based his system upon characters
essentially different from those used by de Jussieu, and although in both systems
there are many deviations in the limitations of the classes and families, there is
on the whole an agreement in many essential particulars. Especially may we
note the recognition of Monocotyledons and Dicotyledons (though under different
names) as the two contrasting main divisions of Flowering Plants. And further,
that the Cellular and Vascular Cryptogams are sharply distinguished from
one another. The main groups, the Cellular and Vascular Cryptogams, the Mono-
cotyledons and Dicotyledons, are met with (under various names) from this time
onwards in all later schemes of classification; and, so far as we can tell, appear
to constitute so many natural groups—groups, that is, of which the members
are all more nearly allied by descent to one another than to the members of the
other groups.

Following De Candolle many Botanists elaborated schemes of classification
during the first half of the nineteenth century; these included Reichenbach, Oken,
Agardh, Martius, Brongniart, Bartling, Endlicher, Lindley, and many others. To
the non-botanist, recognizing the fact that there can be but one real natural system

14. P. DE CANDOLLE'’S SYSTEM.

I. VASCULAR OR COTYLEDONOUS PLANTS. VASCULAR OR COTYLEDONOUS PLANTS
1. EXOGEN& OR DICOTYLEDONB. (continued).
A. Perianth double (calyx and corolla). 2. ENDOGENE OR MONOCOTYLEDONS.
Thalamiflore (petals distinct, inserted on A, Phanerogams (=true Monocotyledons).
the receptacle). B. Cryptogams (= Vascular Cryptogams and
Calyciflore (petals free and inserted on Naiadacew).
the calyx). II. CELLULAR OR ACOTYLEDONOUS PLANTS.
Corolliflor (petals united together). A. Foliaces (leafy =Mosses and Liverworts).

B. Monochlamydew (perianth simple). B. Aphyll (not having leaves=Thallophytes.)

604 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

of plants, this great variety of specialist opinion is somewhat surprising, and tends
to shake his confidence in all botanical systems. But it must be remembered that
in the development of a natural system the imagination plays a much more im-
portant part than in the elaboration of an artificial one, nor can prevailing currents
of thought, or the particular habit of mind of the observer, be without their in-
fluence. Very prominently does this appear in the case of the Botanists who came
under the influence of what has been termed nature-philosophy during the early
portion of this century. Thus Reichenbach and Oken proposed systems which can
only appear to us absurd; but it would be wearisome and useless to follow their
absurdities in detail.

The system of classification proposed by Endlicher! (1805-1849), and published
in his Genera Plantarum secundum ordines Natwrales disposita (published 1836-
1840) is based on the systems of de Jussieu and De Candolle. In it 6838 genera,
arranged in 277 families or orders, are included. Here for the first time are the
Coniferze and Gnetacez distinguished as a special group, and designated as Gymno-
sperms. Here also is that group of cellular plants known as the Thallophyta care-
fully distinguished into three series, the Alge, Lichens, and Fungi. But we still
find these groups treated as equivalent to the Horse-tails, Ferns, Lycopods, &e.; so
also with the Gymnosperms, they are not treated as a distinct subdivision, but only
as a class of Dicotyledons (Acramphibrya), the other classes of which are the
Apetala, Gamopetala (= Monopetale), and Dialypetala (= Polypetale).

In fairly recent times Bentham and Hooker, in their well-known Genera Plant-
arum (published 1862-1883), follow essentially the systems of De Candolle and
Endlicher. They assemble all flowering plants (100,220 species) into 8417 genera,
and these under 210 families or orders. Of these orders 3 belong to the Gymno-
sperms, 35 to the Monocotyledons, 36 to the Monochlamydez, 46 to the Gamopetale,
and 90 to the Polypetale.

1 ENDLICHER’S SYSTEM.

I. THALLOPHYTA (no opposition of stem and root). II. CORMOPHYTA—Continued.
PROTOPHYTA. AMPHIBRYA (stem growing at the circum-
Alge. ference).
Lichenes. Includes Monoeotyledons.
en ACRAMPHIBRYA (stem growing at both point
ungi. z
and circumference).
II. CORMOPHYTA (opposition of stem and root). Gymnosperma (ovules naked, fertilized
ACROBRYA (stem growing at the point only). directly from the micropyle).
Anophyta (Liverworts and Mosses). Apetala (Perianth 0, rudim. or simple).
Protophyta (Vascular Cryptogams and Gamopetala (Perianth double, petals
Cycads). united).
Hysterophyta (certain parasites, Bala- Dialypetala (Perianth double, petals
nophorez, Rafflesiaces, &c.). free).

2THE MAIN DIVISIONS OF BENTHAM AND HOOKER’S SYSTEM
(FoR FLOWERING PLANTS ONLY).

DICOTYLEDONES. DicoTyLEDONES— Continued.
Polypetale. Monochlamydez.
Gamopetalz. Gymnospermx.

MONOCOTYLEDONES.

CLASSIFICATION OF THALLOPHYTES. 605

Though the grouping of Dicotyledons (according to the characters of the
perianth) into Monochlamydex (= Apetalee), Gamopetalee (= Monopetalze), and Poly-
petal (= Dialypetale), is very generally recognized to be an unnatural one, it is
no easy task to replace it by a better one. The families. belonging to the great
group Dicotyledons show the most multifarious relations to one another. An
arrangement, based on the assumption that these families have been developed one
from another, is not discoverable; whilst an arrangement in linear series is as
unnatural as one resembling a tree with its branches. Very appropriate was
Linnzeus’s comparison of the limitations of these families with the dovetailing of
the frontiers of countries on a map. One family stands in touch with two, another
with three, others again with four or more allied families. This contact or rela-
tionship occurs on the most various sides. Some families are extremely large and
comprehensive, others relatively small, and, as it were, jammed in between them;
whilst others resemble scattered islands off the coast of a continent.

Well worthy of consideration is the system of Alexander Braun,! published in
1864 in Ascherson’s Flora der Provinz Brandenburg. Though the division of
Dieotyledons into Apetale, Sympetale, and Eleutheropetale suggests at first sight
the classifications of de Jussieu and Endlicher, there is a difference, and an important
one. A large number of the families included by the older Botanists in the Apetalze
are here placed in the Eleutheropetale. With the Eleutheropetale are ranked
those plants “in which calyx and corolla are typically present, the latter consisting
of separate petals”. They are ranged in 24 Alliances or Cohorts—Hydropeltidine,
Polycarpice, Rhceadine, Parietales, Passiflorine, Guttiferee, Lamprophylle, Hes-
perides, Franguline, Aisculine, Terebinthine, Gruinales, Columnifer®, Urticine,
Tricoceze, Caryophylline, Saxifragin®, Juliflore, Umbelliflore, Myrtiflore, Thy-
melzinz, Santaline, Rosiflore, Leguminose. In recent times we have the systems
of Eichler and Engler. They follow the lines laid down by Alexander Braun, but,
carrying his method further, the group Apetale (or Monochlamydez) is entirely
abolished, its members being referred in part to the Sympetale, and in part to the
Eleutheropetale (= Archichlamydez of Engler).

During the last fifty years our knowledge of the Cryptogams constituting the
group Thallophyta (founded by Endlicher, ef. foot-note, p. 604) has increased by
leaps and bounds. Several attempts have been made to bring together the results
of the various researches upon this group, and to utilize them for classificatory

1 ALEXANDER BRAUN’S SYSTEM.

I. BRYOPHYTA. Ill. ANTHOPHYTA (Flowering Plants).
1. Thallodea (Algs, Lichens, and Fungi). A. GYMNOSPERME (seeds exposed).
2. Thallophyllodea (Characex, Mosses, and 1. Frondoss (Cycads).
Liverworts). 2. Aceross (Conifers).

B. ANGIOSPERME (seeds in an ovary).
1. Monocotyledones.
2. Dicotyledones.
a. Apetale.
b. Sympetale.
c. Eleutheropetal®,

II. CORMOPHYTA.
1. Phyllopterides (Ferns and Equisetums).
2. Maschalopterides (Lycopods),
3. Hydropterides (Rhizocarps).

606 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

purposes. The old division into Algee, Fungi, and Lichens, based on the presence or
absence of chlorophyll and on the mode of life of the forms in question, has been
by many authors abandoned. Cohn in 1872 divided the Thallophytes, according to
their methods of reproduction, into seven groups: Schizosporex, Zygosporee, Basidio-
spores, Ascosporex, Tetraspores, Zoosporex, and Oospores. Sachs, in 1874, follow-
ing somewhat similar lines, made four classes: Protophyta, Zygosporez, Oospore:e,
and Carpospores, in each of which groups both chlorophyll-containing (Algz) and
colourless forms (Fungi) occur, as may be seen by a perusal of the classification
quoted below.’ Goebel (1882) returns in part to the older method and distinguishes
between Algze and Fungi; but with these as groups of equal systematic importance
he ranks the Myxomycetes, Diatomacex, and Schizophyta. The Alg® he divides
into Chlorophycee (Green Alg»), Pheophycee (Brown Alg»), and Rhodophyce»
(Red Sea-weeds); and the Fungi into Chytridiacex, Ustilaginee, Phycomycetes,
Ascomycetes, Aicidiomycetes, Basidiomycetes. Warming (1884) returns completely
to the older method, dividing the Thallophytes into Algw and Fungi, ranking the
Myxomycetes with the Fungi, and the Diatoms and Schizophycee with the Algze.
The balance of opinion at the present time, largely swayed by the views and
researches of Brefeld upon the Fungi, favours a grouping of the bulk of Thallo-
phytes into Alge and Fungi. Brefeld regards the various families of Fungi as
more intimately related amongst themselves than are these families to corresponding
families of Alge. That Fungi have arisen from Algz at some remote period, and
have then amongst themselves undergone development along various lines, is very
generally held; but the view that the different families of Fungi stand in near
relationship to the several algal groups—as indicated, for instance, in the system of
Sachs, (cf. foot-note below)—is not at present the prevalent one. And amongst the
Algee, also, the attempt to classify the various forms into families according to the
relative simplicity or complexity of their organs of reproduction (as Sachs suggested)
no longer tinds general favour. Amongst the Algz we find a number of extensive

1SACHS’S CLASSIFICATION OF THALLOPHYTES.
I. PROTOPHYTA.

Containing Chlorophyll. Not containing Chlorophyll.
Cyanophycee. Schizomycetes.
Palmellaces (in part). Saccharomycetes,
II. ZYGOSPORER.
Conjugating Cells Motile.
Pandorines Myxomycetes,
(Hydrodictye:e).

Conjugating Cells Stationary.
Conjugate. | Zygomycetes.

III. OosPOREE.

Sph:roplea.

5 Saprolegnies.
Vaucheria ... ".. (Cosloblastee), 2. unl cas vanes Kaan Peronosporex.
Volvocines.

(Edogone.
Fucoideze.

IV. CARPOSPOREE.
Coleochsztex. Ascomycetes (including Lichens).
Floridex. AHcidiomycetes (Uredinez).
Characes, Basidiomycetes.

THE EVOLUTION OF PLANTS, 607

groups, within the limits of each of which all stages of complexity in reproduetion
occur. The attempt to string together forms agreeing in reproductive methods
makes it necessary to break up groups which on general grounds seem to be natural
families. And as it is a natural system that we are striving after, systems like that
of Sachs (which may be compared to the artificial sexual system of Linnzeus) must
be abandoned. That the publication of the Sachsian system in his widely-read
“ Text-book ” has done great service to Botany there can be no doubt; it has stimu-
lated thought and observation, and has led more speedily than would otherwise
have been the case to the establishment of broad and probably sound views as to
the relations of the Thallophytes. However, the Myxomycetes, approaching as they
do certain groups of the animal kingdom, are kept apart from the rest of the
Thallophytes in the most recent system.

The classification of plants according to their similarity of structure—species
into genera, genera into families or orders, families into alliances or cohorts, these
into classes, and classes into two chief branches or phyla, the Cryptogams and
Phanerogams—leads to the presumption that these two chief branches have arisen
from a common stock, have diverged from a common stem. A consideration of all
animal and plant forms similarly leads us to the belief that the main stems of
the Animal and Vegetable Kingdoms, respectively, meet at their points of origin.
By studying systems of classification drawn up on paper and restricted to two
dimensions of space, we involuntarily conceive the classes and orders of the vegetable
kingdom, as a tree which continually branches, finally ending in thousands of twigs
which represent the various species. Such is, rightly or wrongly, the conception of
all Botanists who have concerned themselves with the construction of a natural
system. They only differ in so far that some regard the Thallophytes as standing
at the base, and derive from these the Liverworts and Mosses, from these the
Ferns, &e., and so on to the Gymnosperms and Angiosperms; whilst others make a
subdivision of the main trunk at once into Cryptogams and Phanerogams, each of
these continually branching according to the various classes and families. Others
again, whilst conceiving the whole vegetable kingdom as having a common origin,
regard this as the centre of a sphere, and that the several phyla and classes radiate
out from this, producing numerous branches and twigs at the surface of the sphere.
Each of these hypotheses presupposes, in the first instance, the existence (or spon-
taneous generation) of a few Thallophytes of extremely simple structure which have
become differentiated, ü.e. given rise to more complex offspring which form the
beginnings of the branches of the tree. To this kind of development of a tree-
structure, the terms Phylogenesis or Phylogeny (from gun, a tribe; and yewdo,
to produce) is given. Obviously, not only the original forms possess the capacity
of differentiating, but their offspring also, and so on through the entire tree. But
views are divided as to whether this continued differentiation follows a predeter-
mined plan, is due to definite inherent forces, or whether it may not be restricted in
this sense and due to other and external causes.

608 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

That a natural system has been evolved along lines resembling the ramifications
of a tree, which commenced with simply organized structures and terminated with
the most complex ones, finds a certain confirmation when the history of develop-
ment of the individual (ontogeny, from 4», dvros, being; and yexdw, to produce) is
compared with its position upon the phylogenetic tree. As we know, the greatest
of all flowering trees begins its existence as a single protoplasmic mass. This
surrounds itself with a cell-wall and increases in size and complexity at the expense
of nutriment derived from its environment. Gradually cells and tissues arise and
the young organism becomes segmented into an axis and appendages. These, again,
assume the most varied forms corresponding to a subdivision of labour. Ultimately
the uppermost and last-produced members of the plant are transformed into flowers
and fruits. It is thought that, just asa plant is gradually differentiated in this way
so have all plants undergone a similar transformation, step by step. The egg-cell,
the starting-point of the individual, may be compared to a Myxomycete, the cell-
complex which arises from the egg-cell after fertilization to a Thallophyte, the
segmented axis and appendages of the seedling to a Vascular Cryptogam, and the
complete plant-body, finally, to a Flowering Plant.

This comparison, like so many others which captivated the imaginative faculties
in the days of the speculations of nature-philosophy, has found many adherents;
indeed, it has served as dogma and guiding light in many investigations. But it
is difficult to harmonize it with other theories well-proved by experience. The
main burden of this comparison (known as the “ Recapitulation-theory ”) is that
the vegetable kingdom as a whole has undergone a developmental history and
transformation resembling that of a single member of the group of Flowering
Plants. But first it must be asked, what is the meaning of metamorphosis in the
individual, and what object has been attained by it? Though the actual processes
taking place in the living protoplasm in metamorphosis are unknown, this much
seems certain: That these changes occur along lines sufficiently well indicated;
that the fashioning of the successive stages of any given species is accomplished
according to a definite plan; that external influences, such as soil and climate, do
not permanently affect this plan; and that consequently the plan of construction
of these successively appearing stages is laid down in the protoplasm itself. The
ultimate objeet of metamorphosis in plants is the production of fruit; and with
the formation of an ovary the metamorphosis ends, the fertilized egg-cell beginning
the metamorphosis all over again, @.e. it is the starting-point of a series of trans-
formations along identical lines. And this applies equally to the Apple-tree and
to the Palm, to the Pine, the Horse-tail, the Moss, the Bladder-wrack, Stonewort, to
the Mould, and to the simplest of green Algze. Only in the last-named forms are
the intermediate stages fewer than in the first-named. But it will hardly be sug-
gested that the latter have not on this account attained the end in view. Simple
plants whose fertilization and fruit-formation is accomplished under water, whether
it be on inundated land, in the mud of a river, or at the bottom of a lake, attain
this end without a complex metamorphosis of petals and stamens; whilst many

THE EVOLUTION OF PLANTS. 609

of the denizens of the ocean have no need of segmentation into stem and leaf.
Indeed, such a metamorphosis for this purpose would be a disadvantage, anything
but a progressive development. Similarly is it inconceivable, from all we know
of the relations between external conditions and the form of an organism, that
a Fern (for instance), unable to aceomplish its fertilization in dew or rain-water,
should in consequence depart from its usual habit and strike out a new line of
metamorphosis. Thus we may conclude! that the development of the individual
(Ontogeny) eannot be regarded as an epitome of the ancestral history or line of
descent of that individual, and, further, that ontogeny gives no support to the
assumption of a ramifying phylogenetie tree starting with simple forms and ending
with complex much-differentiated ones.

The results of developmental investigations showing a marked similarity in the
form of organs serving similar purposes in the most different groups of plants have
been brought forward in support of the assumption that Flowering Plants have
arisen from simple Cellular Plants by a series of progressive transformations.
Though these organs are in some groups of more simple, in others of more complex
structure, their similarity is unmistakable; it is upon this that the view is widely
based that organisms exhibiting similar organs have been derived from one another.
But this inference is inadmissible. The similarity in question finds a simpler ex-
planation as the expression of the attainment of a common object. Thus fertiliza-
tion consists in the coming together and uniting of two portions of protoplasm
which have originated at a distance from one another; the similarity of ways and
means in attaining this object are obvious. In one case water is employed as a
means, in another the air. There is, truly, a difference in detail, but the general
similarity remains. From this general similarity all we are justified in inferring is
that the organisms in question all reproduce themselves by fertilization, not that
they have a common origin.

This conclusion leads to the question whether, in view of the diversity of the
organs of fertilization, several distinct stems of plants may not have co-existed
all along. We know from observation and experiment that new forms do not
as a rule arise from offshoots, but from fruits. New groups of plants might thus
(so it was said) arise from existing ones solely by the sexual method. Complex
Thallophytes might arise from the fruits of simpler ones, Ferns from the fruits
of Mosses, and soon. Assumptions of this kind belong to a period at which the
phenomena of fertilization and fruit-production, especially in the Cellular Plants,
were only very imperfectly understood. No Botanist nowadays would suggest the
possibility of a Spirogyra or a Ulothria, or an Edogoniwm, or a Stonewort, arising
from the fruit of a Vaucheria. It might well happen that a new species could
arise by the crossing of two dichogamous species of Vaucheria, but this new form
would be essentially a Vaucheria, and its methods of fertilization would be essen-
tially similar to that of its parent-forms. It is likewise as impossible for the male
protoplasm of a Vaucheria to enter the chamber in which the conjugation of the

1See editorial note prefacing this volume.
Vou. II. 89

610 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

sexual cells of Spirogyra takes place (cf. vol. i. Plate I. fig. 1), or for this spermato-
plasm to fuse with the gametes of Ulothria (cf. p. 49), as for the gametes of
Ulothrix to enter and fuse with the egg-cell of a Vaucheria; no new group of
plants could have arisen in this way. We may conclude then that plants belonging
to groups with a marked diversity in their sexual characters have not arisen from
one another, but belong to stems which have co-existed as distinct types from
the first.

Nor must we omit to notice the observations which have been made in regard to
symbiosis and the inter-relations of green and non-green plants. It has already
been pointed out (vol. i. pp. 263, 264) how that the continuation of plant-life, and
indeed all life, is dependent on the activity which saprophytic plants exhibit in the
decomposition of dead organisms. Green plants could not exist independent of
colourless saprophytes, nor these latter without green plants. This must ever have
been the case, and
it must so remain.
R We may then draw
another conclusion,
viz. that those colour-
less plants which by
their activity bring
about the decomposi-

tion of green plants
Fig. 365.—Spirophyton from the Upper Devonian. cannot have arisen
from green plants,

but that from the beginning they have belonged to a distinct stem.

It is to Paleontology that we must look for the most trustworthy solution
of the question as to whether numerous plant-stems have existed side by side from
the first, or whether the groups which at present co-exist have in process of time
branched forth from a single stem. Were it a fact that those forms which show
a far-reaching division of labour, and a complex structure of organs, which we term
“higher plants”, have arisen from others of very simple mode of life and possessing
a simple structure and which are known as “lower plants”, then should we expect
the earth to have been covered formerly by lower plants alone. And then, fol-
lowing this epoch, would have come a time when plants would have existed which
might have served as the starting-points of the later-appearing distinct groups. We
should expect to find in those strata of the earth’s crust regarded by geologists
as the oldest of all nothing but the remains of very simple Thallophytes, then,
following these, Wracks, Red Sea-weeds, and Lichens, and after these Stoneworts
(Chara), Mosses, or some other type of plant which, having given rise respectively
to Stoneworts and Mosses, has, after this differentiation, become extinct.

From the graphite, which is looked upon as the oldest trace of vegetable life
on the earth, unfortunately we obtain no conclusive evidence on this matter. From
its presence on slate mountains together with crystalline limestone and pyrites

THE VEGETATION OF FORMER TIMES. 611

we might conclude that it originated from plants adhering to the limestone reefs
formed by animals or from sea-plants which lived on the borders of these limestone
cliffs. Where graphite is found in greatest quantity one is tempted to think it
might have been derived from peat moors. As we have said, all these are merely
suppositions, for since the carbon, lime, and silicates have become erystalline all
the points for the determination of the families to which the graphite-forming
plants belonged are lacking. It might be noted here, by the way, that although
graphite does indeed furnish the oldest traces of plant-life on the earth this does
not prove that the plants which gave rise to it were necessarily the first which

Fig. 366.—Riella helicophylla growing under water. Enlarged.

existed there. It is doubtful whether the rock which is associated with graphite
formed the first hard crust of the earth. Much more probably this rock was com-
posed of other broken rocks just as it has itself been again demolished, furnishing
the material for new strata.

The shapes of vegetable remains from palsozoie formations are fairly easily
recognizable. Those which were formerly regarded as fossil Sea-wracks have
indeed been more recently interpreted as the trails of worms and medusx, but
some of them are without doubt the remains of Sea-wracks. The only other
known lowly plant which at that time had an aquatic habit is the curious
Spirophyton, the so-called Cock’s-tail Alga (see accompanying fig. 365). This,
though some regard it as of purely inorganic origin, may perhaps be regarded
as a submerged Liverwort; at any rate it is not without resemblance to Riella
Reuteri, which at the present time lives in the Lake of Geneva, and to the
Algerian Riella helicophylla (see fig. 366). No trace is to be found of Thallo-

612 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

phytes which may have existed on land, but we have huge tree-like Vascular
Cryptogams with trunks, fronds, and leaves which are to be placed side by side
with our present-day Equisetums, Ferns, and Lycopods. Cycads and Conifers
also are not absent from the Coal Measures. No Angiospermous flowering plants
have hitherto been demonstrated in these strata, but it would be foolish to
regard this fact as a proof that neither Thallophytes nor Angiosperms flourished
at this period. That which has been preserved to us from this time certainly
forms but a small fraction of the old vegetation, and is restricted apparently to
the flora of peat-moors which were just as poor in species and just as monotonous
as they are to-day. The plants which at the present time predominate on the
moors are still the Equisetums, Ferns, Lycopods, and Conifers, and, in tropical
regions, the Cycads; only a few species from each group, but standing in thousands
side by side and aggregated into dense communities. Anyone who has worked
out the history of these moors knows that the soil must have been prepared
for these plants by other growths. Lquisetum limosum, Aspidium Thelypteris,
Lycopodium inundatwm, &e., do not flourish in soil poor in humus; in order
to obtain their requisite food and to develop they require soil which is saturated
with the dead remains of earlier settlers. Experience tells us that the plants
which appear as the first inhabitants belong to widely different groups (see vol. i.
p: 268). Now if we hold to the view that the formation of peat-moors in long-
past ages occurred just as in the present day, we must assume that the colonies
of Equisetums, Ferns, Lycopods, and Cycads were preceded by other plants which,
as the first settlers, prepared the soil. We cannot indeed determine from the
surviving remains to which groups these first settlers belonged; but, looking back
on the history of our present peat-moors, it seems not improbable that among
them were both Thallophytes and Angiospermous flowering plants.

The fact that the fossil remains of Equisetums, Lycopods, and Cycads, which
spread so widely over the peat-moors of palozoic times, have reached us in such
good condition is explained by the presence of humus-acids, which are formed
universally in the peat (see vol. i. p. 263). There are four conditions which render
it possible for a plant to be preserved as a fossil: humus-acids form the first; the
second is the resin which exudes from the pine-wood and forms amber; the third is
mud and sand brought by floods; and the fourth the silicification and calcification
of the cell-wall or the formation of a lime incrustation which is precipitated from
calcareous water on to the various parts of the plant.. It is certain that these four
conditions have always been effective, but it is doubtful whether all the fossils
formed in the fourth manner at all periods have remained. For many older strata
have long been destroyed and used in the building up of younger layers, and many
risings and sinkings of these strata have taken place. It would indeed be difficult
to find a single place on the earth’s surface which has not been repeatedly above
and under the sea. Much that might lead us to definite conclusions at present lies
inaccessible to us, covered with immense masses of water at the bottom of the sea,
and the view has actually been suggested from studies made on the few accessible

THE VEGETATION OF FORMER TIMES. 613

and closely investigated spots on the earth’s surface that the fossil remains found
there are not more than a minute fragment of the vegetation of periods long
elapsed.

With these remarks we might mention that it is not beyond the range of possi-
bility that, in addition to the Vascular Cryptogams, Cycads, and Conifers growing on
peat-moors, plants of other habitats, especially those of fresh and salt water, or
perhaps of sand-dunes and river-banks, might be found in the strata of paleozoic
times. But no one would doubt that among these would be Angiospermous Phane-
rogams, and this throws some light on plant remains which have come to us from
the mesozoie period. For example, in the upper layers of the chalk we find, in
addition to the plants of peat-moors, the inhabitants of a luxuriant forest-flora of
Angiospermous flowering plants. There are Planes, Birches, Beeches, Oaks, Poplars,
Willows, Fig and Laurel trees, Maples, Ivy and other Araliaceze, Bread-fruit trees,
Tulip-trees and Magnolias, Cherry-trees, and Leguminose of the division Cxsal-
pines, Palms, Rushes, and Grasses. If we do not believe in the theory that these
Angiosperms were first created in the mesozoic period, and still less in the greater
marvel that they have sprung from the Vascular Cryptogams, Cycads, and Conifers,
we are forced to the conclusion that they too must have existed as far back as the
paleozoic time. It is to be specially noted that not the slightest trace of inter-
mediate or transitional forms which might connect the aforesaid Angiospermic
Phanerogams with the Gymnosperms or with the Vascular Cryptogams has been
found. One leaf is immediately recognized as belonging to a Tulip-tree, a second to
Maple, a third toa Fig-tree, a fourth toa Palm, &e., but no plant has been discovered
anywhere which would perhaps form a connecting link between the Palms or Figs
and the Conifers or Vascular Cryptogams.

Even a cursory glance at the plant-forms named shows that they were members
of mixed forests. It may be assumed, however, that other plant communities peopled
the earth at the same time as these forests. The rocky terraces and boulders, as
well as the flat dry land, were certainly not destitute of vegetation. Nor is it
surprising that no fossil remains of the inhabitants of these places have remained.
The under-shrubs and herbs of a dry soil decompose immediately after their death,
and leave behind only formless humus, which mixes with the soil. Just as little
fossil remains will reach posterity of the Lichens and Mosses, Pinks and Composites,
Saxifrages and succulent plants which inhabit the rocks on the dry mountain-
slopes at the present day, as of the Tulips and Irises, Umbellifere and Saltworts of
the steppe-flora; and a great mistake would be made if, millions of years afterwards,
it were reasoned from the lack of fossil remains of these plants that they could not
have existed in our time. It would be just as wrong for us to argue from the
absence of such plants in the strata of earlier periods that they had never existed
in those times. The same thing applies to most fresh-water and marine Algz, and
to the numberless saprophytes which effect the destruction of dead animal and
vegetable bodies above and under water, and thus maintain the eternal cycle of life
as a whole. Of the first-mentioned the only fossil remains which can be recognized

614 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

are those of Diatoms, whose cell-wall is transformed into an imperishable siliceous
frustule, together with those Florides which provide themselves like corals with a
calcareous skeleton, and some tough Sea-wracks. It is, however, a very significant
fact that the innumerable fossil Diatoms which come to us in so-called tripoli-powder
and Diatom-earth, and the many caleareous Floridex which come down to us as
Nullipore banks are deceptively like those living at the present day, that these
groups have remained unaltered for eons, and that no form has been discovered in
any of the older strata which could be regarded as a link with another group. No
fossil remains are known beyond doubt to exist of the numerous aquatie plants
with delicate cell-walls which perish as rapidly as they develop, of the Spherella
species which give a red colour to rain-water and to the snow-field, of the micro-
scopic Desmids, of the green filaments of Spirogyra, of the remarkable green tubes
of Vaucheria pictured in plate L, &e. Some woody Polyporus species of Fungi have
reached us, but in forms which look very like those at present growing on old
tree-trunks. Some species of Moulds have been preserved in amber. I have before
me a piece of amber in which insects are imbedded; from one of them spreads a
web of mycelial threads which doubtless belonged to some mould-like Fungus such
as to-day attacks various insects. The myceliums of various F ungi, also, are found
penetrating the tissues of many of the fossil cryptogamic stems of the Coal Measures.
This fact is very instructive, since it shows that in the tertiary period, and in much
earlier periods also, the relation of saprophytic plants to the dead bodies of
animals and plants were the same as they are to-day. All these results taken
together prove that delicate Thallophytes whose cells do not become siliceous or cal-
careous, or which are not inclosed in resin, cannot be preserved in a fossil condition.
But no one would conclude from this that the groups to which such delicate
growths belong were not represented in earlier periods.

On comparing the past and present of the Vegetable Kingdom from these points
of view, more especially with regard to the question whether existing groups
stood side by side in earlier periods also, or whether, in the course of time, they
have sprung from a single individual or from a few spontaneously-generated indi-
viduals, we are obliged to decide in favour of the former. The so-called “higher”
plants are not derived from the so-called “lower”; the groups of higher and lower
plants co-existed from the beginning side by side. But variations within the limits
of each group have always taken place. New species, ?.e. new groups of species,
arose in consequence of the crossing of the species already in existence. Of these
the species which were best suited to the climatic conditions of the time being
survived. But the variation in the formation of new species never went so far as
to do away with the characteristics of the group. We immediately recognize in
the fossil Laurel-trees, Magnolias, Oaks, Palms, Grasses, Pines, Equisetums, Ferns,
Lycopods, Floridex, Diatoms, and Moulds the ancestors of the now existing species.
This would be impossible if the group-characteristics had disappeared in the modifi-
cations which the species have undergone.

When I now attempt the task of stating in detail what has been furnished by

THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 615

theoretical considerations, and of bringing forward the various groups which have
from the beginning existed side by side, distinguishing them by the enumeration
of their peculiar characteristics, [am not blind to the enormous difficulties of the
undertaking. Although Paleontology, Morphology, and Physiology afford valuable
results, they are not enough, and neither of the three sciences gives sufficient data
for the complete solution of the problem. One of the greatest obstacles is the afore-
said incompleteness of the geological record. From the existing remains we may
indeed conclude on the whole that numerous groups stood side by side in the
mesozoic and pal®ozoie periods, but the evidence of many groups which exist at
the present day without transitional forms is wanting, and when we assume their
existence we make use indeed of a justifiable hypothesis, but have no proof what-
ever. The danger, on the other hand, of establishing homologies from the similarity
of an organ which is observed in groups of species now living has already been
mentioned (see p. 609). Up to a certain point all organs which have similar work
to perform agree with one another. This agreement is the more pronounced the
greater the similarity of the conditions under which the organs have to do the
work. Species of very different groups which live under water exhibit many
characteristics in common; plants whose pollen-grains are transported by the wind
show a great agreement in the structure and position of the parts of the flower.
In the same way the form of flower-visiting insects necessitates a number of similar
characteristics in the flowers visited. For example, we might instance the sweep-
ing hairs on the style of the Proteacex and of the Composites, as well as certain
developments which are met with in the flowers of Aroids, which are visited by
small flies, and also in the Aristolochiacee. In spite of this consideration, however,
the similarity in the structure and form of organs, both of those serving for pro-
pagation and for nourishment and growth, must obviously be kept to the forefront;
similarity must always be an important factor in the limitation of groups.

As we have in the preceding chapter established the fact that each species is
built up by protoplasm with a specific constitution, the question might be pro-
pounded whether each plant-group has not something in common in this respect.
Many observations argue differently for this view. It has been repeatedly stated
that the Moulds, Oscillatoriez, Sea-wracks, Stoneworts, &c. give off a scent which,
although it differs according to the species, is yet very similar upon the whole, and
that one is justified in assuming a specific constitution of the protoplasm in each of
these groups on this account. Moreover, the scent which the Mosses exhale is
found in no other group of plants. The same is true of Ferns. The delicate fronds
of the tropical Filmy Ferns exhale the same peculiar scent as the larger Ferns of
our forests. The Coniferze, Umbellifere, Labiatee, Leguminosee, and Cruciferse
exhibit similar conditions. Is it not also a striking phenomenon that the parasitic
Fungus Cronartiwm asclepiadewm should settle on Cynanchum Vincetoxicum, as
well as on Gentiana asclepiadea, i.e. upon two plants which the Botanist certainly
places in different families, but which he regards as belonging to the same alliance?
To these facts many others might be added, especially with regard to the choice of

616 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

vegetable food by animals. But our knowledge in this respeet is so fragmentary
and uncertain that for the present we cannot make use of these conditions in the
limitations of the groups.

The capacity for sexual union is of the utmost importance in defining plant
groups. Species which can unite sexually belong undoubtedly to the same group.
Nothing can be urged against this prineiple, and if it could be universally applied,
the division of the groups would be settled. But in this matter there are very
many pros and cons. The converse of the proposition requires consideration. It
will not do to say that all plants which cannot unite sexually belong to different
groups. It has been shown that crossings can be successfully effected in Orchids
which all Botanists regard as members of different genera, but, on the other hand,
it is demonstrated that crossings between very similar species of the Umbellifer
family lead to no fruit formation. No one, however, would conclude from this
that these Umbellifers belonged to different groups. On reflecting in what a small
number of flowering plants the fertilizing process has hitherto been observed, and
remembering that the fertilization of many Thallophytes is still totally unknown,
the hope of being able to utilize these conditions in limiting the groups becomes
very much lessened.

In the review of the various groups of the vegetable kingdom which follows’
no attempt is made to present the groups in the form of an ideal natural system.
So far as the Thallophytes, Bryophytes, Pteridophytes, and Gymnosperms are con-
cerned, there is a very general consensus of opinion amongst Botanists, and the
serial arrangement here followed is in harmony with it. But as regards the Angio-
spermous flowering plants, and in particular the Dicotyledons, it is as yet too early
in a book of this nature to embody all the most recent suggestions as to the affinities
of the various families. Attention was drawn on p. 605 to the system of Alexander
Braun, and it was pointed out that he was the first to try and break up the large
and unsatisfactory class Monochlamyde or Apetalz, and to relegate its families in
part to their true position. This attempt has been very fully carried out by Eichler
(1883), and by Engler (1892); these two Botanists admitting only two classes of
Dicotyledons (Choripetalz or Archichlamydez and Sympetalz). But as yet many of
their placings of individual families are but tentative, and we may well wait a few
years for a system on these lines to settle down into more or less permanent form. An
instance of too hasty rearrangement of a natural system to meet recently discovered
facts may be quoted here. In 1891 Treub discovered that Caswarina possessed chala-
zogamic fertilization, and in 1892 Engler (following Treub) separated Casuarina from
all other Angiosperms as the sole genus in a new class Chalazogame. Since then
it has been found (see p. 413) that chalazogamie fertilization is much more general
than was at first supposed, and that in the group Amentacee it is widely spread,
though by no means of universal occurrence. To break up the Amentacex in the
drastic manner involved, if the class Chalazogamz» be maintained, seems a most

1Cf. editorial note at commencement of this volume.

THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 617

undesirable and unnatural thing to do; it will on the whole be best to abolish a
special class of Chalazogams, and, if thought necessary, to rearrange the families
which constitute the Amentaces®, but not to sever them from one another. For the
Angiosperms we shall in the main follow the arrangement of the well-known
Genera Plantarum of Bentham and Hooker, though we reserve our freedom to
deal with certain families as seems well to us.

The vegetable kingdom we divide first into four main divisions or phyla: (1) The
Myxothallophyta, including the Myxomycetes only, a group standing apart from
(2) the Thallophyta, which include the various classes of Alg® and Fungi. Then
follows (3) the Archegoniatze, forms possessing archegonia and fertilized by motile
spermatozoids, and including the Liverworts and Mosses, and the series of the Ferns
(Phyla (1) (2) and (3) constitute what are usually referred to as “Cryptogams”), and
(4) the Phanerogamia or flowering plants, fertilized by means of pollen-tubes. They
fall into two sub-phyla, Gymnosperms and Angiosperms, and the latter into two
classes, Monocotyledons and Dicotyledons. Finally we have the 3 sub-classes of
Dieotyledons—Monochlamydex, Monopetale, and Polypetale. Here, in outline, is
the system :—

(1) MYXOTHALLOPHYTA, containing 1 class only.

(2) THALLOPHYTA, containing 5 classes.
I. Schizophyta.
Il. Dinoflagellata.
III. Bacillariales.
IV. Gamophycee.
V. Fungi.
(3) ARCHIGONIATEE, containing 2 classes.
I. Bryophyta.
II. Pteridophyta.

(4) PHANEROGAMZS, containing 2 sub-phyla,
A. GYMNOSPERME.
B. ANGIOSPERM#, containing 2 classes.

I. Monocotyledones.

II. Dicotyledones, containing 3 sub-classes.
a. Monochlamydez.
db. Monopetale.
c. Polypetale.

Each class (or sub-class) is further divided into a number of cohorts or alliances,
and each of these alliances into orders or families. The alliances will be taken one
by one in the following pages, their main characters generally indicated, and the
families which they comprise enumerated. It will not be possible within the limits
of this book to deal with the several families in at all a comprehensive manner,
though the endeavour will be made to point out structural and other characters of
interest, and where certain genera or groups of genera have a special interest these
will be alluded to. No attempt is made to observe any due sense of proportion in
treating of the different alliances. Thus a small alliance containing but few mem-
bers of especial interest will receive more detailed consideration than one vastly

618 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

larger, the numerous representatives of which are unrelieved in their monotony.
This method, truly, is an unconventional one, but in view of the restrictions of
space, perhaps better suited to our purpose than any other.

PHytum 1.—MYXOTHALLOPHYTA.

Organisms destitute of chlorophyll, whose vegetative state consists of a mass of naked proto-
plasm (plasmodium). Reproduction by spores, from which arise swarm-spores or myx-
amcebee, which unite again into plasmodia.

Alliance I—Myxomycetes, Slime-Fungi.

For the most part saprophytie upon dead organie and especially vegetable sub-
stances; they occur chiefly on accumulations of the dead parts of plants—leaves,

Fig. 367.—Myxomycetes.

1 A group of sporangia of Stemonitis fusca. 2 A single sporangium; x 6. 3 Dendritic mass of sporangia of Spumaria alba on
a Grass leaf. 4Sporangium of Dictydium cernuum; x 25. 5A group of sporangia of the same. 6 and? Sporangia of
Craterium minutum; 6x 25. 8 Sporangia of Arcyria punicea. %Asingle sporangium; x10. 1° Part of the net-like
capillitium of the same; x160. ™ Fructification of Lycogala epidendrum on a piece of wood. 12 Leocarpus fragilis; a
plasmodium on the right; several sporangia on the left.

tan, rotting wood, and the like; they are rarely parasitic. Their life-history is as
follows:—On the germination of the spores the membrane bursts, and a slimy,
nucleated mass of protoplasm escapes, which either swims in water by means of a

THALLOPHYTA. 619

single flagellum, or creeps about on a damp substratum; these motile bodies are the
myxanebe. These amcebs increase at the expense of absorbed nutriment, and
undergo repeated division. Ultimately they fuse together into masses of naked
protoplasm—the plasmodium-stage—which creep about until spore-formation sets
in. The plasmodium is transformed into the reproductive stage, numerous sporangia
arising all over its surface. This stage in different cases shows the most varied
structure, as may be seen by reference to fig. 367. Either the whole plasmodium is
transformed into a single sporangium, as in Lycogala epidendrum (fig. 367), or a
number of sporangia arise. A portion of the protoplasm becomes hardened to form
the wall of the sporangium, whilst the contents is resolved into a mass of dust-like
spores. In addition there arises in the majority of forms a sort of internal skeleton,
the capillitiwm, which may consist either of a number of elongated tubes with
characteristic thickenings on their walls, or these tubes may be united together into
a continuous network (fig. 367°). On the bursting of the sporangium the spores
are scattered and carried away by currents of air. They germinate when they
reach a moist substratum, and the life-cycle is passed through anew. Under un-
favourable conditions a plasmodium may become encysted, forming a transitory
resting-stage. If placed in water, the plasmodium escapes from the cyst, and
continues its life-history even after a lapse of several months. The substance of
the membrane, whether of the sporangial wall, spores, or capillitium, does not seem
to consist of cellulose, but rather of a congealed protoplasm. We see, then, that the
life-history of a Myxomycete is divided into a nutritive stage consisting of naked,
membraneless, protoplasmic masses, and a sporangial, spore-producing stage. In
respect of their nutritive stage the Myxomycetes very nearly resemble certain
groups of the Protozoa, and on the strength of this resemblance they are regarded
by many Botanists and Zoologists as belonging rather to the animal than to the
vegetable kingdom. In their manner of reproduction they certainly show analogies
to many of the Fungi however.

Plasmodiophora Brassice is a parasitic Myxomycete which attacks the roots of
the Cabbage, causing the disease known as “ Fingers and toes” (cf. p. 522).

Fossil Myxomycetes are not known. About 450 species have been distinguished.

PHYLUM 2.—THALLOPHYTA.

A large and very heterogeneous collection of plant-forms is included under this
term. The word (Greek @adnés, and ¢urév) literally means plants with undifferentiated
shoots, and includes practically all plants standing below the Mosses and Liverworts
in complexity of organization. It is impossible to characterize positively a group,
or rather a collection of groups, which shows so wide a range of organization as we
find among the Thallophytes. They are often characterized negatively as plants
whose bodies show no distinction between axis and appendages (stem and leaves).
To such a plant-body the name thallus is given. But though this definition holds
good for the great majority of the Thallophytes, yet there are forms (e.g. Bryopsis,

620 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

the verticillate Siphone®, Draparnaldia, many of the Brown Sea-weeds) which
do show a distinetion between axis and appendages, though the distinetion is not
usually so marked as that between the stem and leaves of a higher plant. Simi-
larly, though for the most part possessing a relatively low organization, some
Thallophytes (especially the higher Fungi and certain of the Brown Sea-weeds)
show considerable differentiation of structure. The Thallophyta consist of many
divergent and more or less sharply characterized groups. These include the Green
Algee (Chlorophycee, which includes the alliances Protocoecoidexr, Siphonex, Con-
fervoideze, Conjugate, and Charales), the Brown Sea-weeds (Phawophycew), the Red
Sea-weeds (Rhodophycew or Floridee), the Blue-green Als» (Cyanophycee or
Schizophycec), the Bacteria (Schizomycetes, here included with the last-named
group in one class, the Schizophyta), the Diatoms (Bacillariales), and the Fungi.
Some Botanists consider that the Myxomycetes (or Mycetozow), and the Dino-
flagellata (Peridinee) are also plants. These last groups are almost certainly
branches of the Protozoa; and though possessing certain plant-like characters (as
indicated above), they show no near affinity with other plant groups. Whether
they should be considered as plants or animals must therefore remain a matter of
opinion.

The same may be said of certain other organisms regarded by zoologists as
Flagellate Protozoa, but showing undoubted affinities with the lower forms of
Green Alg®. There exists, in fact, an unbroken series of forms, connecting un-
doubted Protozoa, having mouths by which they eat solid food, with undoubted
green plants depending entirely on soluble inorganic food. The dividing line
between animals and plants is here obviously an artificial one, and is naturally
drawn by different authorities at different points in the series.

The name Thallophyta, then, is given to all plant-forms below a certain grade
of organization, and includes many separate and widely divergent lines of descent.
The Thallophytes may be pictured as the shrubby growth around the base of the
phylogenetic tree representing the plant kingdom. The lower part of the main
trunk of the tree, that is to say, the line of descent by which the higher plants
have originated, is probably represented by certain of the Green Algze.

Class I—SCHIZOPHYTA.

For the most part exceedingly small organisms, which propagate entirely by
asexual methods. They consist of isolated cells, cell-filaments, surfaces, or masses.
Though till recently regarded as without nuclei, these bodies have been found in a
number of forms, and this view is being abandoned. They include both coloured
and colourless forms; but the coloured forms never exhibit pure chlorophyll.

THALLOPHYTA. 621

Alliance II.—Cyanophyce®, the Blue-green Alga.
Families: Chroococcace®, Nostocacee.

Includes pigmented forms in which in addition to chlorophyll phycocyanin is
present, giving the cells a bluish, violet, or reddish tint. They occur in water or
in moist places, and their cells may be united together into aggregates of various
kinds. The cell-walls are usually mucilaginous, so that the cells or filaments cling
together in colonies, or they are inclosed in special sheaths. The simpler forms
included under the Chroococcacez are unicellular; the products of their division
may either remain united into colonies or become quite free from one another.
The rest are filamentous, and are included under the Nostocaces, whose filaments
can become segmented into small portions which move away by a peculiar motion
not yet fully understood (ef. vol. i. p. 40). At times also certain cells become
resting-spores and can endure climatic vicissitudes. They are widely dispersed
over the globe, and are met with in cold glacier-streams and have been found
living in hot springs at a temperature of even 85° C. Some 800 living species are
distinguished.

Chroococcacee.—Includes the unicellular forms. Gleocapsa (vol.i., Plate I. n, 0)
forms little mucilaginous colonies, often found on the moist window-panes of hot-
houses. Merismopedia forms films on stagnant water, and Clathrocystis like
certain of the Nostocacez (alluded to below) arises in quantity in water. A
form probably referable to this group (Dermoglaa Limi) developed in 1874 in
such quantities off the Adriatic coasts as to seriously interfere with the fishing
industry. A commission was appointed to investigate the matter, but in six weeks
the Dermoglea vanished as suddenly as it had appeared.

Nostocacee are, for the most part, filamentous, though in some forms the cells
may become isolated. Nostoc itself is common, and takes the form of irregular
gelatinous colonies, which contain numerous interwoven necklace-like filaments.
In some districts, owing to its sudden appearance after rain, it has received the
name of “ Falling Stars’, This explains the allusion in the following lines from

Dryden's Edipus:—
“The tapers of the gods,
The sun and moon, run down like waxen globes;
The shooting stars end all in purple jellies,
And chaos is at hand”,

A species common in China, N. edule, is used as a thickening for soup, and an
allied form, Hormosiphon arcticus, abounds in the Arctie regions upon floating ice.
Anabena Flos-aque, Aphanizomenon Flos-aque, &e., appear in fresh and brackish
water—sometimes in enormous quantities, and to considerable depths. The T’richo-
desmium Erythrewm—another of these “flowers of the sea”—referred to at vol. i.
p. 389, belongs also to this group. Very little is really known about the life-
histories of these interesting plants, which so frequently appear in great quantities
at or near the surface of the water and then as mysteriously disappear. But now

622 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

that systematie observations are being made of the organisms which occur at the
surface (e.g. at the Biological station on the Plöner See, Schleswig-Holstein) we may
hope that these lacunz in our knowledge may be filled up. Recent investigations
(by Klebahn) upon several of these “flowers of the sea” (Gloiotrichia echinulata,
Anabena Flos-aque, Aphanizomenon Flos-aque, Trichodesmium, &e.) seem to
indicate that they possess special organs of flotation designated “ gas-vacuoles”.
It would appear that these natant forms have in consequence a smaller specific
gravity than the surrounding water, and if the surface be quite unruffled tend
to float, whilst any disturbance, such as waves, &e., is sufficient to cause their
distribution through the upper layers of the water. Whether these “flowers” pass
another stage deep down in the water is not fully ascertained. Their spores, so
far as they have been observed, do not seem to possess “ gas-vacuoles”, and sink to
the bottom. The phenomenon here indicated is not unlike that occurring in the
Protozoon Arcella, the protoplasm of which is able by secreting a bubble of gas to
rise to the surface, and, by absorbing it, to cause the organism to sink. The
Oscillarias consist of filaments of dise-like cells; they exhibit curious gliding
movements, which have been already alluded to (ef. vol. i. p. 40). Rivularia is
distinguished by the fact that its filaments are whip-like, ending in a fine point,
whilst in Seytonema this distinction of base and apex is not found. They generally
occur in more or less mucilaginous masses.

A number of the Schizophycex are associated with certain Fungi to form
Lichens (cf. later, and vol. i. p. 244); and certain of them occur embedded in the
tissues of other plants. Thus species of Nostoc are met with in certain Liverworts
(Anthoceros) and in the roots of Cycas; and Anabena in special cavities in the
leaves of the Rhizocarp Azolla. It is not known what may be the exact physio-
logical relations between these Blue-green Algz and the plants they inhabit—
whether they are parasitic or symbiotic.

Alliance I1J.—Schizomycetes, the Bacteria.

On the whole, in the matter of their structure and aggregation, present many
characters in common with the Blue-green Algee. They are, however, destitute of
the characteristic pigment of that group, and pass their lives as parasites and
saprophytes, obtaining their food from ready-formed organic matter. Nuclei have
been distinguished in some few forms, and the cells are inclosed in a membrane
which, though often mucilaginous, does not consist of cellulose. In size the cells
reach very small dimensions, and may be regarded as the smallest of all plant-
forms. A number of different forms are distinguished; the Cocci, consisting of
minute round cells; short rod-like forms, the Bacteria; longer rod-like forms, the
Bacilli; various spiral forms known as Spirillum, Vibrio, and Spirochste; filamen-
tous forms, Leptothrix and Crenothrix. A very common mode of occurrence of the
various forms is in gelatinous masses, to which the name Zooglcea has been applied
(ef. fig. 368%). Propagation takes place vegetatively by cell-division so long as the

THALLOPHYTA. 623

eonditions remain favourable for further growth. When the substratum is
exhausted, &e., spores are formed which can remain for long periods—until, indeed,
circumstances are again favourable for renewed development. These spores may
arise either inside the bacterial cells (=endospores), the protoplasm contracting
somewhat and forming a new wall around itself, or the cells may become trans-
formed entirely into spores (=arthospores), the wall becoming specially thickened.
In no case is there any sexual process. Whilst many Bacteria are. only known
under certain forms and are regarded as species of the genera Micrococcus, Bac-
terium, Bacillus, Spirillum, &e., others are known which, in the course of their
development, pass through several such forms, and are termed pleomorphic. That
all Bacteria are thus pleomorphic seems improbable, though the discovery that
pleomorphism existed at one time led to the wildest generalizations. Large
numbers of Bacteria display an active movement which, though formerly attri-
buted to various contractions of their bodies, are now known to be due to cilia.
These cilia may be borne in tufts of 5 or 6 at the two ends of the organism, as in
Spirillum Undula, or they may be solitary at one extremity, as in the Cholera
Bacterium (Spirochete cholere asiatice), or they may be scattered over the surface
of the organism, as in the Hay-bacillus, Bacillus subtilis. It is due to the extreme
fineness of these cilia that they were not recognized long ago.

Though the forms under which Bacteria occur are relatively few, their mode of
life and special activity is exceedingly varied. The interest attaching to Bacteria
rests largely on their effects on the substratum from which they draw their food.
Taking, first, the saprophytes. These split up their substratum into simple sub-
stances. In some cases there is a complete oxidation, with production of carbon
dioxide and water; in others this is only partial, as in some of the cases of
fermentation, e.g. when alcohol is oxidized into acetie acid by the activity of the
vinegar organisms Bacillus and Micrococcus aceti (ef. figs. 368° and 3684), Or
there may be a decomposition unaccompanied by simple oxidation, as in many
cases of fermentation, e.g. as when sugar is split into alcohol and carbon dioxide.
Often these operations are accompanied by the development of a foul-smelling gas,
when we speak of putrefaction. The number of saprophytic Bacteria which excite
characteristic splittings in their substrata is considerable. In addition to those
already quoted, we may mention Bacillus Amylobacter, the organism of butyric
acid fermentation; Bacillus lactieus, which causes milk to become sour; Leuconostoc
mesenteroides, which has the power of converting large quantities of sugar into a
gelatinous mass in a very short space of time. Again, in a number of forms the
production of a special colouring matter is associated with the activity of the
organisms, as is the case with Micrococcus prodigiosus (cf. fig. 83681), the “blood-
portent” which makes its appearance on various starchy food-stuffs, and Beggiatoa
roseo-persicina, found on decaying vegetable matter in water, and known as
“peach-mud”. Many Bacteria are parasitic in the bodies of animals, and some
among them are harmless. This is the case with Sarcina ventriculi (fig. 368"),
known only in the human alimentary canal in the form of packets of cells. Harm-

624 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

less also are a number of Bacteria found on the mucous membrane of the mouth.
On the other hand, many are associated with definite diseases. Spirochete Ober-
meieri (fig. 368°) is found in the blood in great quantities during relapsing fever;
Bacillus anthracis (figs. 3687 and 368°) causes anthrax in cattle, &e.; and a great
many other diseases—diphtheria, cholera (figs. 368° and 368°), tuberculosis, leprosy,
&e.—are associated with the activity of specific bacterial organisms. Nor must we
omit to mention the numerous forms which occur in the soil, some of which are
concerned in the process of nitrification, 7.e. which oxidize ammonia into nitric acid,
thus rendering this source of nitrogen available to higher plants, whilst others

Fig. 368.—Bacteria,

1 The *‘blood-portent,” Micrococcus prodigiosus. 2 Zooglea-form of same. 3 Bacterium aceti. 4The same more highly
magnified. 5 Spirochete cholere asiatice. ® The same more highly magnified. 7 Bacillus anthracis and red blood-
corpuscles. 3 The same more highly magnified. 9% Spirochcete Obermeieri and red blood-corpuscles. 10 Sarcina ventricult.
1, 2, 8, 5, 7,9 x 300; 10 x 800; 4 6, 8 x 2000.

actually fix free nitrogen, as is the case with the organism occurring in the root-
tubercles of many leguminous plants (cf. p. 521). There is no doubt this organism
(Rhizobium, as it has been called) can store up free nitrogen, and that leguminous
plants, when associated with it, obtain nitrogen not to be accounted for as combined
nitrogen obtained from the soil. Curious also is the activity of the sulphur and
iron Bacteria. The former (e.g. Beggiatoa alba) have the power of reducing the
sulphates contained in the waters which they inhabit and of storing up sulphur-
grains in their protoplasm; whilst the latter (eg. Crenothriz Kihniana), not
uncommon in water-pipes, where they often develop in enormous quantities, store
up iron in the gelatinous sheaths of their filaments.

That Bacteria existed in former times, and were then, as now, the agents of
decomposition, seems probable in view of the condition revealed by residues of dead

THALLOPHYTA, 625

plants in the coal measures. It is thought that Bacillus Amylobacter has been
identitied in a silicified state.
Of living Bacteria a very large number have been distinguished.

Class IL.—DINOFLAGELLATA, Peridinez.
Alliance IV,

This compact group of unicellular organisms is, as has been said above, a
branch of the Flagellate Protozoa. They have therefore no very near affinities with
other plant groups, though the nutrition of many is thoroughly plant-like. They
would come nearest to the motile (Flagellate) forms of Protococcoidew (see p. 628).

The great characteristic of the group is the possession of two flagella, one directed
longitudinally and attached to the anterior end of the body, the other transversely
directed and often situated in a circular transverse groove. There is sometimes also
a longitudinal furrow. It is this transverse flagellum which is specially concerned
in movement.

There is often a cell membrane of cellulose, and the cell possesses green or
brownish chromatophores containing chlorophyll and a single large nucleus.

Reproduction is effected by binary fission, usually during a resting stage of the
cell.

Most of the forms are marine, and some are the cause of sea-phosphorescence.

The group is divided into two sections—the Adinida without, and the Dinifera
with a transverse furrow.

Ceratium and Peridiniwm are two well-known genera.

Class IIL.—BACILLARIALES.
Alliance V.
Family: Diatomacee, Diatoms.

These are a large group of unicellular plants which grow both in fresh and salt
water and upon moist soil. As a rule they occur together in large numbers. The
protoplasm is coloured brown by a brown pigment, diatomin, which masks the
chlorophyll which is also present. The colouring matter is restricted to special
chromatophores, which may be few or numerous. The cell-wall is inerusted with
silica, and is a very characteristic feature of the Diatom. The wall consists of two
halves or valves (frustules) which fit into one another like the lid on to a pill-box.
These valves are smooth or variously sculptured, dotted, ribbed, &e., and enjoy a
wide popularity as microscopic objects on account of the beauty and delicacy of
their tracery. Some idea of the variety and form of Diatom-cells may be obtained
from the accompanying figure 369. In the colonial forms the cells are attached
to the substratum directly (fig. 3691) or by means of branching filaments (fig. 369 ™).
Others are attached to one another in zigzag chains or continuous ribbons (figs.

369% and 3691), Others, again, are embedded in mucilage. Many of the forms
Vou. II. 90

626 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

exhibit a curious ereeping movement, which is explained as being due to an
external sheath or to filaments of protoplasm; the median line (or “raphe ”) shown
by certain forms (e.g. Navicula, fig. 369*) is interpreted as a narrow slit at which
this external protoplasm is extruded. Diatoms propagate by continuous longitudi-
nal division; the valves are slightly separated, and division takes place parallel to
the faces of the valves. Each daughter-cell thus possesses one of the valves of the
mother-cell, and they complete their integument by secreting another on the side
away from it. The new valve is always slightly smaller than the other one and

Fig. 369.— Diatoms,

1 Several individuals of Synedra Ulna attached to a cell of an aquatic plant. 2 A single individual of Synedra Ulna more
highly magnified. ®and # Navicula Liber, seen from the side and from in front. 5 and 6 Similar views of Navicula
tumida. 7 Triceratium Favus. 8 Campylodiscus spiralis, ® Pleurosigma angulatum. 1 and 1! Grammatophora ser-
pentina. 12 and 13 Two views of Gomphonema capitatum. 14 Gomphonema capitatum on branched stalks which are
attached to some algal filament. 15 Diatom vulgare; the cells hang together into a zigzag band. and 7 Fragillaria
virescens, showing an individual from two aspects and a row of six joined together into a ribbon. 13 Cocconema Cistula.
19 Two individuals of Cocconema Cistula inclosed in a mucilaginous envelope preliminary to auxospore-formation. 20 The
two auxospores have elongated, and the old cases are seen to right and left; there is no conjugation in this instance. All
highly magnified.

fits under its rim, so that the Diatoms arising in this way become smaller and
smaller till a certain minimum is reached. When this diminution has gone on for
a certain period an enlargement is attained by the formation of what are termed
aumospores. The contents of the cell gather themselves together, they become free
from the valves, enlarge, and then put on new valves. In other cases an actual
conjugation takes place, two individuals uniting into an auxospore; or each may
divide into two daughter-cells, which fuse in pairs, forming two auxospores. Fig.
369! shows two cells of Cocconema Cistula embedded in mucilage previous to
auxospore-formation; in fig. 369° each cell has escaped from its valves, and has
doubled its original length. In this instance, however, there is no accompanying
conjugation,

Diatoms are very widely distributed over the globe, and occur in quantities in

THALLOPHYTA, 627

the surface layers of the sea; some 30 species have been found amongst the inor-
ganie dust of the snow-field. There are some 2000 species of living forms.

Considerable deposits of Diatoms oceur in various parts of the world; of these
the most remarkable is that of Richmond, Virginia, U.S.A. It is said to extend for
many miles and to be 40 ft. deep. They are found in secondary, tertiary, and more
recent rocks. Siliceous marl eonsists entirely of the tests of Diatoms. A block
of such a Diatom-deposit some two eubie feet in bulk from a fresh-water lake in
Australia is exhibited in the Botanical Department of the British Museum; the
number of Diatoms contained in it (there are 21 different species) is estimated as
exceeding 12 billions (12 x 10°),

Class IV.—GAMOPHYCEE.
Sub-class I—CHLOROPHYCEE, the Green Alge.

There can hardly be a more fascinating group of plants than this, whether to
the strictly seientifie botanist or to the more catholic lover of nature. In the first
place, the Green Algw are among the most widely diffused of plant-forms. They
grow practically in every place where enough moisture, together with light and air,
are to be had. Between tide-marks on almost every coast, floating on the surface of
the deep sea, covering damp earth, walls, palings, and tree trunks, sticking to the
surface of leaves in the moist atmosphere of tropical forests and jungles, and
inhabiting almost every river, brook, pond, ditch, or casual pool of rain-water in all
quarters of the globe, are members of this ubiquitous group to be found. Nor are
they wanting from more extraordinary situations. In Switzerland, Norway, and
other countries where snow is more or less permanent, the bright red patches on its
surface, known as “red snow”, are formed by the microscopic Alga (Spherella niva-
lis) shown in Plate I. of the first volume. Other forms, not so far removed from
Spherella, live in the intercellular spaces of higher plants, such as the Ivy-leaved
Duckweed (Lemna trisulca), the Moneywort (Lysimachia nummularia), and
others. Yet other Algze are found inhabiting the jelly of certain fresh-water
sponges in the East Indies, where they seem to live in a regular symbiosis with
their hosts. But perhaps the most curious dwelling-places of all are the hollow
hairs of the Three-toed Sloth (Bradypus tridactylus), which are inhabited by an
Alga called Trichophilus.

In the second place, many of the Green Algz (and among these some of the
very commonest) are the most beautiful forms of life imaginable, and the main
features of their structure can be made out with quite low powers of the microscope.

But perhaps the greatest claim on our interest is made by the fact that we must
look among the Green Algz not only for indications of the origin of all plant life,
and of the forms from which the whole of the higher plant world arose, but also for
hints towards the solution of some of the most difficult and fundamental problems
with which Biologists are occupied, questions as to the real nature and origin of
sexual reproduction, as to the distinction between gametes and asexual reproduc-

628 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

tive cells, as to the physiological conditions which determine their formation, and
finally, questions as to the division of labour in the protoplast itself, the funetion
of the nucleus and its relation to the protoplasm, and how far the latter can be
resolved into separate, but mutually co-operative parts.

The framework of our knowledge on the former group of questions has been, and
is being, built up largely from a study of the Green Algw; of the latter—and even
more fundamental—we know, as yet, very little, but the same group of plants is
already beginning to yield important results, and we have every reason to expect
an even richer harvest in the immediate future.

We shall now proceed to a brief review of the groups into which the Chloro-
phycez may be divided, mention being made of the more interesting forms in each
group.

The sub-class Chlorophycex may be defined as follows:—Thallus of very various
form, one- or many-celled, coloured green by chlorophyll which is contained in
chromatophores of very various shape: the green colour rarely masked by other
pigments. Reproduction by motile zoospores, and by gametes, which either resemble
small zoospores, and are equal in size (isoplanogametes), or are differentiated into
two categories; first, relatively small, active male gametes—called spermatozoids
when they are very highly differentiated—and secondly, relatively large, passive
female gametes—known as eggs or oospheres when they are quite passive. The cell
produced by the fusion of the bodies of two gametes is called the zygote, and gives
rise to a new plant either mediately or immediately. When the gametes are
sexually differentiated, the zygote (now called a fertilized egg or oospore) is pro-
duced only by the fusion of a male with a female gamete.

Other reproductive cells are known as aplanospores and akinetes. Aplanospores
are formed by the protoplasm of a cell of the thallus rounding itself off and putting
on a new cell-wall, or dividing into several parts, each of which acquires a separate
cell-wall. Akinetes are simply single cells of the thallus, whose original walls
thicken directly, the cells becoming separated from the rest of the thallus. These
two categories of reproductive cells germinate at once to form new plants. The
Chlorophycee comprehend the following alliances:—Protococcoidee, Siphonez,
Confervoideze, Conjugatze, and Charales.

Alliance VI.—Protococcoidee.

Families: Chlamydomonadece, Volvocew, Plewrococcacew, Endospheracee,
Hydrodictyacee.

Unicellular forms, actively swimming, floating, or fixed in habit, living either
singly or united into colonies.

Family Chlamydomonadee. This family consists of minute green (sometimes
red) organisms which spend the greater part of their life actively swimming about
in water. Several species of the genus Chlamydomonas are very common in
stagnant water. Each Chlamydomonas-cell consists of a roundish mass of proto-

THALLOPHYTA. 629

plasm covered by a delicate cell-wall of cellulose. At first sight the whole body
appears green, but on careful examination it will be seen that the green colouring-
matter is really confined to a layer on the surface of the body. This chlorophyll-
layer or chromatophore is specially thickened at one end (the posterior end) of the
body, and a small, clear, spherical body (the pyrenoid) is often to be seen inclosed
in this thickened portion. Round the sides of the body the chromatophore is
thinner, and towards the anterior end it stops, leaving a small area of colourless
protoplasm to occupy the front extremity of the organism. This is in connection
with another small mass of colourless protoplasm which occupies the hollow of the
cup-shaped chromatophore.

A minute red speck is visible at one side of the body, situated sometimes on the
surface, sometimes at the limit between the chromatophore and the central colour-
less protoplasm. The rotation of the Chlamydomonas about its antero-posterior
axis, which accompanies the jerky, forward movement (ef. vol. i. p. 29) can be well
traced by the aid of this eye-spot, which can be seen to be carried round and
round as the organism turns on its axis. The means by which the Chlamydomonas
moves are not at first sight apparent. But when the cell has come to rest, and
especially if it has been killed and its protoplasm fixed with a dilute solution of
iodine, a pair of very delicate protoplasmic filaments, called flagella, can often be
seen projecting from the colourless anterior spot of protoplasm. It is by the con-
tinual lashing of these flagella that the Chlamydomonas is pulled through the
water. The iodine will also bring into view a small spherical nucleus, stained dark
brown, situated in the colourless central protoplasm, and will stain the neighbour-
hood of the pyrenoid a dark blue. This last phenomenon is due to the formation
of starch by the protoplasm round the pyrenoid. The exact part played by the
pyrenoid is very obscure, but there can be no doubt that it influences in some way
the formation or deposition of starch by the protoplasm.

The movements of Chlamydomonas are often in direct relation to light, the
organisms moving towards a source of light of moderate intensity. Thus if a glass
vessel filled with water containing Chlamydomonas be placed in a sunny window,
there will be a general movement of the swarming cells to the sunny side of the
vessel, causing the water to become much greener on that side. There is some evi-
dence that it is the eye-spot which enables the organism to perceive the direction
from which light is proceeding. Nearly all the motile Protococcoidex, as well as
zoospores and gametes which are sensitive to light, possess an eye-spot, and it has
been thought that the eye-spot-pigment (a substance called hematochrome) may act
in the same way as the visual purple in the retina of the eye.

If specimens of Chlamydomonas be kept for a day or two in water, some of them
will often be found to have divided to form daughter individuals, which still remain
inclosed- within the cellulose membrane of the mother. This division is preceded by
the drawing in of the flagella. The protoplasm of the body then withdraws itself
from the wall, and divides transversely to form two roundish masses. Each of the
latter may either at once put on a cell-wall and develop flagella, or it may divide

630 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

again, so that four daughter individuals instead of two are formed. Eventually the
daughters escape from the membrane of the mother, leaving it quite empty.

The process of reproduction by simple division of all the protoplasm of an indi-
vidual’s body into parts, each of which forms the body of a daughter individual, is
an example of almost the simplest type of reproduction known. It is true that in
the lower Protozoa, which have no rigid cellulose membrane, we find an even simpler
type. Since the entire organism consists of protoplasm, there is nothing left of the
parent individual after division has taken place. The body of the parent simply
becomes the body of the offspring. In the type of Chlamydomonas we have the
dead cellulose membrane representing all that is left of the body of the parent. In
many of the higher Algze, and in all plants above the level of Thallophytes, only a
part of the protoplasm of the plant-body is used in the formation of the reproductive
cells. The rest must then eventually die. But in these lower forms, where all the
protoplasm of the body is used in the production of new individuals, death, as a
necessary event, can hardly be said to occur.

Gametes are formed in Chlamydomonas in exactly the same way as daughter
individuals. They are, however, smaller and have no cell-wall. In one species at
least the gametes are of two sizes. Of the smaller (microgametes) eight are produced
from a parent individual, while only two of the larger size (megagametes) are formed
from the parent cell. In the process of conjugation a microgamete and megagamete
come into contact at their anterior colourless ends, the flagella are drawn in, and a
thick cellulose membrane is secreted round the bodies of both. The protoplasm of
the microgamete then passes over into the space inclosed by the part of the mem-
brane belonging to the megagamete, and completely fuses with the protoplasm of
the latter. A wall is then formed, cutting off the empty shell of the microgamete.
The contents of the zygote eventually divides to form two or four new individuals
which escape from its membrane. In the conjugation of most species where there
is no distinction in size between the gametes, a cell-wall is only acquired after the
foundation of the zygote. This is the regular course of events in the conjugation of
the motile gametes of Green Ale.

The genus Spherella resembles Chlamydomonas in the fundamental points of its
structure. The main distinction is the existence of a considerable space separating
the membrane from the main body of the protoplasm of Spherella. This space is
bridged by fine strands of protoplasm, which radiate from the central mass and end
in fine branches under the membrane. The anterior colourless protoplasm is drawn
out into a beak, and to the extremity of this the two flagella are attached. The
lagella often pass through two very delicate cellulose tubes, which in the common
species, S. plwvialis, diverge from the extremity of the beak, and end on either side
at the membrane. In another species (S. Biitschliz) the beak runs right up to the
membrane, and the flagella-tubes, which are short and slightly curved, lie on the
outer surface of the membrane.

Spherella pluvialis is a very well-known microscopic object, being extremely
common in pools of rain-water. Its protoplasm often contains a good deal of the red

THALLOPHYTA. 631

pigment hematochrome, which may almost completely mask its green colour. It
was from this circumstance that it received its name of Haematococeus pluvialis.
Hematochrome is even more constantly present in Spherella nivalis, the “red snow”,
whose appearance and life-history have already been described (vol. i. p. 39). 8.
Bütschlii has its hematochrome concentrated in an eye-spot like that of Chlamy-
domonas.

The Volvocee differ from the Chlamydomonadee in consisting of motile colonies
of cells, the members of each colony being united in a common investment. The
bodies of the individuals composing the colony are also joined in some genera by
protoplasmic processes. The body of each individual is identical, in the fundamen-
tal points of its structure, with that of a Chlamydomonas or of a Spherella. The
Volvocece present us with an interesting series of forms, showing a gradually increas-
ing sexual differentiation of gametes, and, in the higher forms, an interesting sub-
ordination of the individual to the colony as a whole.

Goniwm is a form in which the colony consists of (usually) sixteen Chlamydo-
monas-like cells arranged in a flat plate, which swims in a line at right angles to
its surface, the flagella of the central cells of the dise projecting forwards, those of
the peripheral cells obliquely outwards and forwards. All the cells are inclosed in
a general mucilaginous envelope, and are joined to one another by protoplasmic
processes.

Reproduction is effected by the division of the constituent cells of the colony in
two planes at right angles to one another and to the plane of the colony, so that each
mother colony produces sixteen daughter colonies, whose discs of cells all lie in the
same plane. Meanwhile, the mother cells are separated from one another by the
gradual liquefaction of the general mucilaginous envelope, and thus the daughter
colonies become independent.

Formation of isogametes also takes place, but is not thoroughly understood.

Stephanosphera is a very beautiful form, occurring especially in pools of rain-
water collected in rock hollows in hilly districts. It is often found in company with
Spherella pluvialis. The colony consists of a ring of (usually) eight Spherella-lilke
cells arranged in the equatorial plane of a spherical or ovoid cellulose membrane.

When reproduction is about to occur, the constituent cells draw in the protoplas-
mic processes by which they are attached to the general membrane; each secretes a
membrane of its own, and then its protoplasm divides in two planes to form eight
(sometimes seven) daughter-cells. When these have acquired flagella they begin to
swarm, and eventually escape by bursting the membrane of the mother colony.

Gametes are formed in the same way, but usually by more divisions, as many as
thirty-two being sometimes produced from a single cell. In most cases all the cells
of a colony divide at once to form gametes, but this is not invariably the case.
Each bundle of gametes produced from a single cell breaks up, and all the gametes
begin to swarm within the colony. The gametes are spindle-shaped, each with two
flagella and an eye-spot. They conjugate in pairs, usually inside the general mem-
brane, but conjugation never takes place between two gemetes derived from the

632 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

same mother cell. The actual process of pairing has been fully deseribed, and it
may be taken as a type of the course of events, as it has been observed in all Alg®
with isoplanogametes whose pairing has been fully investigated. Out of the erowd
of gametes swarming in all directions, two approach and stroke each other with
their flagella; in some cases the two separate and both become again lost in the
crowd, but, when pairing is going to take place, they become firmly fixed together
by their colourless anterior ends. The long axes of their bodies may then lie in one
straight line, or may diverge at a wide angle. A rotation of each of the pairing
gametes about its fixed anterior end now always occurs, the bodies becoming gradu-
ally approximated, so that their long axes come to lie nearly parallel. Fusion of the
protoplasm follows, beginning at the already joined anterior ends, and progressing
rapidly backwards till a single mass of protoplasm is formed. The four flagella still
move actively, and the Zygozoospore, as this active type of zygote is often called,
escapes from the general membrane of the mother colony, becomes spherical by
shortening of its long axis, loses its flagella, and puts on a cell-wall. The protoplasm
soon loses its green colour, becoming reddish, and the zygote enters on a resting
period. Eventually its protoplasm divides, producing zoospores, each of which gives
rise to a new colony.

The division of the cells of a colony to form zoospores or gametes begins in the
evening, and is finished soon after sunrise. In dull weather, however, its comple-
tion is delayed far into the day. This dependence of the formation of zoospores
and gametes upon the influence of light, if not invariable, is found very widely
among the Green Alge.

Pandorina is a fairly common form in ponds, &e. The colony consists of
sixteen wedge-shaped cells arranged in a sphere, and covered by a general invest-
ment, which is of considerable density at its external surface. The apex of each
wedge is directed towards the centre of the sphere, and there is little space left
between the adjacent cells. The formation of daughter-colonies is similar to that
obtaining in Gonium and Stephanosphera. The young colonies escape by liquefac-
tion of the investing membrane. Colonies of gametes are formed in the same
way, but often consist of eight instead of sixteen cells, and the acquirement of
flagella and liquefaction of the mother membrane takes place more slowly. Event-
ually the membrane of each gamete-colony also becomes liquefied, and most of the
gametes swarm out into the water. A great number of mother colonies of different
sizes simultaneously take part in this production of gametes, so that the water
becomes filled with masses of swarming gametes of very variable dimensions. No
distinct size-categories are, however, to be distinguished. Conjugation now takes
place between pairs of gametes either of the same or of different sizes; with this
exception, that the largest gametes do not fuse with one another. They are rela-
tively inactive, sometimes, indeed, remaining fixed in their colonies, and are sought
out and paired with by the smaller and more active individuals. Here, then, we
have a most interesting stage in the evolution of sex. The largest, relatively
passive, gametes may fairly be called female, while the different sizes of smaller

THALLOPHYTA. 633

gametes, though not sexually ditferentiated inter se, since conjugation is apparently
possible between any two, whatever their relative size, may perhaps be considered
as male in relation to the largest.

It is probable that fully-differentiated male and female gametes arose from
forms such as we find in Pandorina, by the suppression of the intermediate sizes,
the smaller and more active gametes taking on the function of actively seeking out
the larger passive individuals, which on their side contribute practically the whole
of the stock of food required by the zygote in germination. In correspondence with
this we find the chromatophore (chlorophyll-corpuscle), which may be considered as
the specially food-producing organ of the algal cell, much reduced and eventually
functionless or absent altogether in the more highly differentiated male gametes
(spermatozoids).

Eudorina has a colony of sixteen or thirty-two almost spherical cells consider-
ably separated from one another, and inclosed in a general investment like that of
Pandorina. In the production of daughter-colonies Eudorina resembles the lower
forms of the volvocine series, but in the sexual differentiation of the gametes there
is a decided advance upon that obtaining in Pandorina. The perfectly passive
female gametes (oospheres) hardly differ from the ordinary cells of a vegetative
colony, while the active male gametes (spermatozoids) are formed in bundles of
sixty-four by successive divisions of similar cells. Here, then, we find the marked
difference in size between the two categories of gametes brought about, as it very
often is among the Algze (and, indeed, among many other plants and animals), by a
marked difference in the number of divisions occurring in their respective mother-
cells. The present case in which strictly comparable cells on the one hand directly
give rise to eggs, and on the other divide to form sixty-four spermatozoids each, is
rather extreme, but we have already met with a similar case in a species of
Chlamydomonas.

Each spermatozoid of Eudorina is elub-shaped, with a colourless pointed
anterior end bearing two flagella and possessing an eye-spot, and a yellowish thick
posterior extremity representing the (reduced) chlorophyllous portion of the typical
volvocine cell. The spermatozoid bundle (male colony) escapes from its mother-cell-
membrane, and swarms as a whole towards a female colony. On reaching the latter
the spermatozoids get their flagella, become entangled in the thick mucilage, and
rapidly separating from one another, worm their way into the female colony. Some
succeed in fusing with the individual female gametes, and each zygote thus formed
will eventually give rise to a new Eudorina colony.

A form recently discovered almost at the same time in three different States of
North America, and known as Pleodorina, shows an important difference from the
types we have hitherto been considering. Each spherical colony consists of about
128 cells, but not all of these are capable of producing daughter-colonies, This
power is confined to those cells which occupy the posterior half or two-thirds of the
sphere (it should be explained that the colony moves forward in relation to a
definite axis). The smaller anteriorly-placed cells are thus purely vegetative in

634 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

funetion, and necessarily die after the reproductive cells have given rise to daughter-
colonies. This is the first time we have met with such natural death among the
Algs, and it is very clearly seen to be connected with the separation of the assimila-
tive and reproductive functions. The formation of gametes in Pleodorina has
unfortunately not yet been observed.

The remarkable and beautiful organism called Volwox has been known for more
than two centuries, and has long been among the most favourite of microscopic
objects. The purely scientific interest which it has aroused has been as great as
the esthetic admiration which it has excited. Long and animated controversies
have raged on the question as to whether it was to be regarded as an animal or a
plant, as an individual or as a colony of individuals. And although these ques-
tions have now lost much of their actuality through the gradual recognition by
naturalists that we have absolutely no eriteria by which they can be settled, there
have arisen problems which promise quite as much interest and excitement for the
future.

Volvoxw is much larger than the forms hitherto described. The colony is
spherical, and possesses a single layer of cells on its surface. In V. Globator the
sphere may be over a millimetre in diameter, but more usually its diameter is only
some three-quarters of a millimetre. A particularly large specimen may possess as
many as 22,000 cells (10,000 is a more usual number). Many of the cells, however,
as in Pleodorina, are simply vegetative, and take no part in the reproduction of
the colony. Usually, in fact, only a very small minority of the cells are repro-
ductive.

The two species of Volvox differ from each other in a great number of points,
but we have only space for a very brief description of some of the most interesting.

The cells of Volvow Globator are all united together by very stout processes.
Each cell, which is inclosed in a separate cell-wall, possesses all the ordinary features
of the Chlamydomonas type.

Daughter-colonies are developed from special cells, usually eight in number,
called parthenogonidia. They are always formed in the posterior part of the
mother-colony, early becoming larger than the ordinary vegetative cells. Each
divides repeatedly, and forms a hollow sphere of closely-packed cells, which, after
the last division, mostly acquire the characters of the adult vegetative cells, the
remainder gradually increasing in size to form the reproductive cells. The young
colonies then escape from the mother, apparently by pushing themselves against
and making rents in its posterior wall. Subsequently the cell-membranes swell a
good deal, separating the cell-bodies from one another, and the colony attains its
adult size.

In other cases gametes may be formed in a young colony. About five celis
(androgonidia), strongly resembling the parthenogonidia, divide to form dises or
hollow spheres of a hundred or more spermatozoids. The spermatozoids resemble
in a general way those of Hudorina, but are peculiar in having the pair of flagella
inserted laterally at the base of the colourless beak and near the eye-spot. In the

THALLOPHYTA. 635

same colonies, but a little later than the androgonidia, about thirty much larger
spherical cells, the oospheres, are developed, and these are duly fertilized, but by
spermatozoids derived from another colony. The zygote has a sculptured exine.
Parthenogonidia are not found in those colonies which produce gametes.

Volvox aureus (= V. minor), the commoner form, is usually much smaller than
Y. Globator, and has rounded cells more widely separated and connected by very
delicate processes. But perhaps its most striking characteristic is the very great
variability in the number and distribution of the reproductive cells. The partheno-
gonidia, which vary in number from one to sixteen, may either occur alone or in
one colony with androgonidia or oospheres, or both. Most of the sexual colonies
are dicecious, though this is not always the case. The colonies containing androgo-
nidia unaccompanied by other reproductive cells often develop very numerous (up
to 1100) spermatozoid bund:es, the androgonidia forming one-third of all the cells of
the colony. The spermatozoids differ from those of V. Globator by their larger size,
by their terminal flagella at the end of a shorter beak, and by the possession of a
well-developed leaf-green chromatophore. We must, therefore, consider V. awreus
as not so highly developed, in some respects at least, as V. Globator.

A Volvox-colony always swims in the direction of a given axis passing through
its body, and at the same time rotates to the right or left about an axis which is
inclined obliquely to the antero-posterior axis. The eye-spots of the vegetative cells
are much better developed in the anterior half of the colony, and are always
situated on the side of the cell nearest the anterior pole. These facts tend to
support the view of the function of eye-spots in general suggested above.

Volvox stands at the head of the series of colonial (ecenobe-forming) organisms
which we have been tracing, a series diverging from a Chlamydomonas- or Sphe-
rella-like type, and whose successive forms gradually increase in size, complexity,
and sexual differentiation. Volvow itself has been well spoken of as “the culmina-
tion of Nature’s attempt to evolve a higher organism out of a ccenobe”. It was an
attempt which failed, or rather which could not be carried any further than Volvox
itself. A delicate, easily-ruptured Volvow-sphere could certainly not continue to
exist if it were much more than a millimetre in diameter. As it is, the wall is often
split, and all sorts of smaller organisms get inside, resulting in the more or less
speedy collapse of the Volvox-colony.

But there are other series diverging from the Chlamydomonade», and some at
least of them have followed lines on which it was possible for higher and more
varied plant-forms to be developed.

At the first stage along one of these lines of descent we find ourselves among
forms in which the dominant phase of the life-history falls in a resting stage, either
fixed or freely floating in the water. From this resting stage motile forms (zoo-
spores), corresponding with the free-swimming Chlamydomonas individuals, are
directly developed. These zoospores, after a short period of swarming, come to rest,
often fixing themselves by their anterior end to some solid object. With little or
no change in the constitution and appearance of the cell the main portion of the

636 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

life eyele is passed in this fixed condition, and cell divisions take place, the products
eventually again developing flagella and being set free as zoospores. The genera
Chlorangium and Physocytiwm are examples of the simplest form of this type of
life-history. Forms with a rather more complicated structure in the fixed stage are
found in the genera Mischococcus (a common form on the surface of threads of the
higher Alge), Huglenopsis (a newly-discovered American plant), and their allies:
In these the protoplasm of the zoospore, after fixing itself and putting on a delicate
cell-wall, pushes out the surface of its membrane away from the substratum, thus
forming a tube of gradually increasing length, the apex of which is always occupied
by the protoplasm. Division of the protoplasm and subsequent pushing out of the
wall of the tube in different directions by the daughter-cells results in a branching
of the hollow stalk, and in this way quite a considerable branching plant-body
may be produced. Eventually some or all of the cells occupying the apices of the
various branches of the tube acquire flagella and escape into the water as zoospores,
which again settle on solid objects and give rise to new plants.

Other forms in which the cell derived from a zoospore multiplies by division, the
products eventually again giving rise to zoospores, are Schizochlamys, Botryococcus,
Dictyospherium and Tetraspora. In these, however, the immotile phase is not fixed,
but forms floating colonies of various conformation. Into this topic we cannot
enter further, except to remark that Tetraspora forms flat colonies of cells arranged
in one plane and held together by the swollen mucilaginous cell-walls. Cell division
takes place in planes at right angles to that of the colony. This type of colony is
specially interesting, as it suggests the form of thallus found in Ulvwacee, which in
turn appears to lead on to the higher forms Confervoidew.

Plewrococcacee.—More or less closely allied to the above-mentioned genera are
others which do not form zoospores at all. These types with no motile phase in
their life-cycle may be conveniently classed together as Plewrocoecacee. The type-
genus Plewrococcus contains some of the most widely-distributed algal forms known.
P. vulgaris forms the bulk of the green coating of damp earth, tree trunks, palings,
&e., in all regions of the globe. It consists of roundish cells, dividing in three diree-
tions in space and thus forming solid masses of cells hanging together in multiples of
two, and often flattened by lateral contact. Each cell contains several parietal chro-
matophores which may, however, fuse together to form a single one. Resting aki-
netes are formed by the cells ceasing to divide, becoming spherical, and thickening
their walls. At the same time oil appears in the protoplasm. It is probably mainly
in this phase that Plewrococcus gets distributed by the wind from one place of growth
to another. Owing to the resemblance of the akinetes of some of the confervoid
Algze to those of Plewrococcus, it has often been stated, and indeed is still held by
some algologists that Plewrococcus itself is merely a growth-phase of these higher
Alg®. But recent eulture-experiments leave little room for doubt that Plewrococcus
is a perfectly autonomous form, although it may often be associated with pleurococcoid
stages of other Alge. Eremosphera is a pretty form, common in fresh water, with
single floating spherical cells. Each cell contains numerous separate chlorophyll-

THALLOPHYTA, 637

bodies, embedded in a parietal layer of protoplasm, and a nucleus suspended by
protoplasmic strands in the centre of the cell. Multiplication is effected by division
of the protoplasm into two daughter-cells which escape by rupture of the mother-
cell membrane. Scenedesmus is another motionless floating fresh-water form. It
consists of oblong cells united into groups of two, four, or eight, which lie side by
side, palisade fashion. Some or all of the cells often possess straight or horn-like
projections of their walls, which give the cell groups a very characteristic appear-
ance. The single solid chromatophore oceupies nearly the whole cell cavity. Chlo-
rella is a genus whose cells are symbiotic with Radiolaria (yellow cells). Other
forms live in a similar relation with certain Coelenterates and Platyhelminths.
Several help to form lichens. Since the various genera of Plewrococcacee differ
thus very widely in the form and structure of their cells, and indeed are only united
by the negative character of the absence of zoospores, it is almost certain that they
cannot be considered as forming a natural group. The various genera are very
probably allied to different neighbouring groups from which they have been derived
by the suppression of the habit of forming zoospores.

The Endospheracew are a small and very natural group of unicellular Alge,
characterized by their habit of living in the intercellular spaces of various higher
plants. They possess motile zoospores, or gametes, or both, but the motionless cells
produced from these do not undergo vegetative divisions. Very possibly they
represent a separate line of descent from the Chlamydomonades, a line of descent
in which the motionless cell has become the dominant phase in the life-cycle, and
has been specially adapted to the new conditions of life, but differs from the motion-
less cells of the “ Tetrasporace” in directly forming zoospores without undergoing
purely vegetative divisions.

Two forms of Endosphzeraceze may be taken as illustrations of this type of life-
history.

Chlorochytriwm Lemne inhabits the intercellular spaces immediately under the
epidermis of the leaves of Lemna trisulca (the Ivy-leaved Duckweed). Each plant
consists of a single, thick-walled, oval cell with a parietal chromatophore containing
numerous pyrenoids and a large central vacuole. Very numerous pear-shaped
isogametes are formed by successive divisions of the protoplasm of the cell. Then
a layer of substance outside the mass of gametes (probably the ectoplasm of the
cell) begins to swell strongly, and bursts not only the cell-wall but also the super-
incumbent tissue of the Duckweed leaf, forming a sphere of mucilage in which the
gametes begin to swarm and to conjugate in pairs. Spherical zygozoospores are
thus produced; these escape from the mucilage, and after some free swarming in
the surrounding water, settle on the boundary between two epidermal cells of a
Duckweed leaf, draw in their flagella, put on a cell-membrane, and form a definite
parietal chlorophyll-body with a single pyrenoid. After two or three days a delicate,
colourless tube is put out, which forces its way between the two epidermal cells of
the leaf, and reaches an intercellular space. The contents of the zygote slowly pass
over into the apex of this tube, which gradually increases in size and assumes the

638 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

characters of a young vegetative cell, the original zygote-wall remaining on the
surface of the leaf as a mere cellulose knob.

The generations rapidly succeed one another during the summer months, the
last-formed cells of the season becoming packed with starch grains and passing the
winter in this state. These resting cells can withstand desiccation, in case the pond
in which the duckweed lives becomes dried up.

Phyllobium dimorphum forms large immotile cells between the tracheids of
the vascular bundles in the leaves of the creeping Moneywort (Lysimachia
nummularia). This plant lives in damp woods and other shady places. The Rhine
plain in the neighbourhood of Strasburg, where Phyllobiwm was first found in the
leaves of the Moneywort, is usually flooded during the month of June, partly by
the rising of the river, and partly by the thunderstorms which usually occur about
that time of the year. The Phyllobiwm-cells take this opportunity to form their
gametes, which are of two distinct sizes, each cell producing gametes of one size
only. After the escape of the gametes into the surrounding water conjugation
occurs. The zygozoospores produced have only two flagella, the body and flagella
of each microgamete being completely lost in the megagamete, just as the body of
a spermatozoid is completely lost in the substance of the egg. After coming to rest
on the surface of a Lysimachia leaf, and acquiring cell-membranes, the zygotes put
out delicate tubes which enter the stomata of the leaf. If a leaf is infected by a
few zygotes only, the tubes formed reach the vascular bundles, and forcing their
way between the elements of the wood, grow forward in the bundles, branching
when they branch, and attaining to a considerable length. Eventually, towards the
end of the summer, the protoplasmic contents of each tube becoming concentrated
in one spot, this part of the tube swells and is cut off from the remainder by the
formation of transverse partitions. The swollen part of the tube thus forms a large
cell which rests during the winter, and in the next summer will produce gametes.
If, on the other hand, the leaf is infected by a large number of zygotes, most of the
tubes never get any further than the intercellular spaces immediately under the
stomata. In this position they form small resting cells in large numbers. These
eventually form zoospores, which apparently behave, on germination, just like the
zygozoospores. ‘The dimorphism of the resting cells of Phyllobiwm thus depends
directly on the amount of space at the disposal of the germ tubes, This conclusion
can be confirmed by cultivating the germ tubes apart from the leaves of the host.

The purpose of the germ tubes of Chlorochytrium, Phyllobiwm, and their allies
in penetrating the leaves of their hosts, seems to be simply that they may gain the
advantage of a quiet protected place for their development. Just in the same way
Diatoms and other unicellular forms often live comfortably in the empty cells of
Algs, the intercellular spaces of the Bog-moss (Sphagnum), and similar situations.
Only in the case of these Endospherez the association of the Alga with its habitat
is invariable and adaptive, not merely casual and unrelated. But the Endosphzerex
are not parasites in any sense. They take no food from their “hosts” nor do they
exercise any appreciable influence on the latter. This is sufliciently proved by the

THALLOPHYTA. 639

fact that Lemna trisulea lives quite happily and can flower when infested with
Chlorochytriwm, and that the germ tubes of Phyllobiwm dimorphum usually enter
dead leaves of the Moneywort. Another form which always enters the living leaves
of a river-weed, continues its course of development whether the leaves die or re-
main alive. It is not, however, difficult to imagine how a form like Phyllobiwm,
living as it does in the vascular bundles of its host, might acquire a parasitic habit
by tapping the food supplies. As a matter of fact certain confervoid Alge are
known whose presence results in the death of the leaves they inhabit, though pro-
bably not by direct appropriation of the food of the host.

Resembling the Zndosphere® in possessing motionless cells which form zoospores
but do not undergo vegetative divisions, are certain common fresh-water forms of
which Characium and Sciadiwm may be mentioned. A plant of Sciadiwm ori-
ginally consists of a single cylindrical cell whose contents breaks up into zoospores.
These zoospores have acquired the peculiar habit of settling on the rim of the
mother-cell, instead of seeking out fresh spots for their development. Each zoospore
produces a single cell like the mother, so that a whorl of cells of the new genera-
tion is formed on the top of the original cell. This process may be repeated for
two or three generations, after which the zoospores will settle on some other object
and start fresh “ plants”.

The Hydrodictyacew are a group of Algz which form immotile colonies. The
cells of these colonies resemble the single cells of the forms we have just been con-
sidering in producing zoospores or gametes, but undergoing no vegetative divisions.
The colony is formed by the joining together in a definite way of the group of
zoospores formed in a single cell of the mother-colony. Each of these zoospores
then develops into an adult vegetative cell.

The recently discovered genus Huastropsis (so called from its likeness to the
Desmid Euastrum) is the simplest type of the family. It consists of two mitre-
shaped cells joined to one another by their bases. Each cell contains a parietal
chromatophore with a single pyrenoid, and a single nucleus. The contents breaks
up by successive divisions into 2-32 zoospores, which escape from the cell surrounded
by a general membrane. After oscillating for about a quarter of an hour, the zoo-
spores become attached in pairs by their anterior ends. Each pair then takes on
the characters of the two-celled colony.

Pediastrum (fig. 370°) consists of a dise of cells, of which the marginal ones are
often drawn out into lobes or processes, The chromatophore is parietal with a
single pyrenoid; there are numerous nuclei. The formation of zoospores is like that
of Euastropsis, but their movement is more lively, and eventually all the zoospores
formed in a single cell join together to form a new Pediastrum-colony (figs. 3707
and 370°). Gametes are formed in the same way as the zoospores, but are smaller
and more numerous. They escape from the investing membrane, swim freely in
the water, and fuse in pairs to form zygotes. From these zygotes new Pediastrum-
colonies are produced indirectly, probably by a method like that obtaining in
Hydrodictyon.

640 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

Hydrodictyon, the Water-net (figs. 370! and 370°) is a beautiful organism
forming net-like eolonies of cylindrical cells, which are joined end to end, forming
the sides of the polygonal meshes. Each cell may be as much as 1 centimetre in
length. A thin layer of protoplasm containing numerous small nuclei lines the
wall and incloses a large central vacuole. The chromatophore, or chlorophyll-layer
of the protoplasm, contains many pyrenoids, each surrounded by a sheath of starch
grains. Fine-grained starch is also scattered through the substance of the chro-

ers IN

ies 1

NAD)
SER

Fig. 370.—Hydrodictyaces.

1 The Water-net (Hydrodictyon utrieulatum), nat. size. 2A portion of the same magnified 50 diameters. 3, 4, and 5 Formation
of zoospores in a cell of Hydrodictyon, showing their union together, and escape as a young net; x 300, ® Pediastrum
granulatum; development and escape of zoospores, the lightly-dotted chambers already vacated. 7 and ® Zoospores after
their escape arranged as a new Pediastrum plant; x 240.

matophore. This stroma-starch appears in great quantity when growth is checked
and assimilation remains active, disappearing again if assimilation is stopped. The
pyrenoid-starch, on the other hand, seems to be withdrawn from the ordinary meta-
bolism of the cell, since it is formed round each pyrenoid early in the life of the
cell, and remains there under all circumstances, unless the cell is on the point of
actual starvation in the dark, till the onset of reproduction. When zoospores are
about to be formed the pyrenoids together with their starch disappear, and abund-
ant stroma-starch appears. At the same time the nuclei multiply a good deal by
division, and eventually the whole of the protoplasm divides to form a great num-

THALLOPHYTA. 641

ber of zoospores. These zoospores, however, never become free like those of Pedt-
astrum, but remain joined together by strands of protoplasm, and after a certain
amount of shifting backwards and forwards, come to rest with their ends in contact.
Bach then gradually assumes the characters of a Hydrodictyon-cell, the young
colony eventually escaping from the mother-cell (figs. 370 % #5). Gametes are formed
in the same way as zoospores, but are smaller and more numerous. ‘The spherical
zygote gradually increases in size, and its contents breaks up into 2-5 large zoo-
spores, which develop into large cells with pointed processes, the so-called poly-
hedre. In the interior of each polyhedron an embryonic Hydrodictyon-net is
developed from swarm-spores, and in the cells of this ordinary Hydrodictyon
colonies are found.

It has been shown experimentally that any Hydrodictyon-net above a certain
size and age is capable of producing either zoospores or gametes, and that the
stimulus to the formation of one or the other is given by external conditions.
Thus bright light, fresh water rich in inorganic nutritive salts, and fairly high
temperatures, are favourable to the production of zoospores, while the reverse of
these conditions, and especially the presence of organic substances, such as sugar,
tend to make the cells of a net produce gametes. The conditions favourable to
zoospore-formation are also of course, favourable to active vegetative growth,
and no doubt the abundant formation of new protoplasm is a necessary preliminary
to the production of zoospores. A slight check to the processes of assimilation and
growth is apparently necessary in order to give play to the zoospore-forming forces.
Thus, experimentally, a change from a strong solution of nutritive salts to fresh
water will induce the formation of zoospores in nets which would simply have gone
on growing if left in the nutritive solution. A similar check is probably given by
the waning light in many Algee in which zoospores are produced at night. For the
production of gametes, on the other hand, an actual reversal of the conditions
favourable to growth is necessary. In nature this probably happens when by very
active growth the whole of the water of a pool is filled with nets, the inorganic
food and oxygen are exhausted, and the normal chemical processes of the cell
receive a check. The formation of gametes and zygotes under these conditions is
obviously adaptive, since the zygote can, although it need not, rest during several
months till the conditions are quite altered. We may therefore conclude that,
whereas zoospores are especially designed to multiply and distribute the species,
zygotes are intended to preserve it under unfavourable conditions. It is probable
that the production of large zoospores and polyhedra is a necessary part of the
life-cycle following the germination of the zygote, and cannot be altered by the
incidence of different conditions.

Alliance VII.—Siphonee.

Thallus consisting of a tube, often much branched, and containing many nuclei.
This tube is the production of a single cell, but in the more complicated forms is

often shut off into compartments by transverse septa. Reproduction by zoospores
Vou. I. 91

642 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

and planogametes, or spermatozoids and eggs: in very many forms no reproductive
cells are known. The higher forms of Siphonez often produce plant-bodies of very
definite and characteristic external form, and of considerable size. In some cases
these simulate the external form of various higher plants.

Families: Botrydiacee, Phyllosiphonacee, Vaucheriacee, Bryopsidacee,
Caulerpacee, Codiacew, Valoniacew, Verticellate.

Botrydiacew.—Botrydium granulatum is a little plant found growing espe-
cially on loam at the damp edges of ponds and ditches. It consists of a club-shaped
or balloon-shaped green shoot-portion, about 1-4 millimetres in diameter, continuous
with a simple or branched tubular colourless root-portion which is embedded in the
substratum. The entire plant consists of a single cell, that is to say, its cavity is
continuous throughout. The wall is lined with a thin layer of protoplasm, which
contains many nuclei, and, in the shoot, a net-like chlorophyll-layer.

Botrydium can reproduce itself in very various ways, according to the incidence
of external conditions. The simplest form of propagation is by budding, which
takes place under conditions favourable to the ordinary vegetation of the plant.
The shoot-portion of a small vegetative plant sends out a process which swells to
the size of the mother shoot, puts out a colourless root, and is then constricted off
to form a separate plant. But if the plants are covered with water they cannot
go on growing comfortably, and accordingly the protoplasm breaks up to form a
number of zoospores, each with a single flagellum and two lateral chromatophores.
The mass of zoospores is subjected to considerable pressure by the swelling up of a
ring-like area of the wall, and the tension becomes so great as to rupture the wall
in the centre of the ring and expel the mass of zoospores into the water. On damp
soil the zoospores come to rest, and germinate to form new plants. If a zoospore
cannot escape from the water it enters on a resting stage, which gives rise to a new
plant directly it finds itself on damp soil. Further, if a young plant is exposed to
bright sunlight, its protoplasm breaks up into a number of spherical cells, each of
which puts on a cell-wall. If now these spherical cells (gametangia) are placed in
water, the contents of each breaks up into spindle-shaped, biflagellate gametes,
which conjugate in pairs to form zygotes. These zygotes can rest for a longer or
shorter time, but if placed on damp earth they at once germinate to form new
plants. If, on the other hand, the gametangia are placed in water after being kept
for two years they give rise to biflagellate cells which rather resemble the gametes,
but which on damp soil germinate directly to form vegetative plants. Finally, if
the gametangia are at once placed on damp soil, their contents does not break up,
but the whole gametangium germinates and produces a plant. Supposing a large
Botrydium-plant, with a balloon-shaped shoot, be exposed to insolation (bright
light) its contents, instead of forming gametangia, travels down into the root, and
the protoplasm there divides to form rows of root-cells, each with an independent
cell-wall. If a root containing root-cells be placed in water, the protoplasm of each
cell breaks up into a number of zoospores: if the root be placed on damp earth each

THALLOPHYTA. 643

root-cell sends out a tube which grows into a young vegetative plant: if left in the
soil, the latter remaining damp, each root-cell germinates to form a peculiar thick-
walled plant called a hypnosporangium which can withstand desiccation, and which
in water gives rise to a number of zoospores.

The above facts may be briefly expressed by saying that any stage in the life-
history of Botrydium tends (1) on damp soil to form vegetative plants, (2) in water
to form zoospores or gametes, (3) in dry conditions to form resting cells. There
can, then, be no doubt that here, as in the case of Hydrodictyon, we are justified in
saying that the form which any given set of conditions tends to produce is adapted
to meet those conditions.

Phyllosiphonacee.—Phyllosiphon Arisari is an Alga living in the intercellular
spaces of the leaves of Arisarum vulgare in Southern France and Italy. Its
thallus consists of a much-branched tube, the parietal protoplasm containing many
nuclei and small dise-shaped chromatophores. Unlike the Endospheree, the pre-
sence of Phyllosiphon has a considerable effect on its host, causing blotches of dead
tissue to appear in the leaves. As the Alga can presumably assimilate quite well
for itself, this destruction of tissue is probably caused by withdrawal of water from
the cells of the host. The only kind of reproductive cells which Phyllosiphon is
known to produce are aplanospores (non-motile spores). These are formed by the
division of the whole of the protoplasm of the thallus. They are extruded by the
swelling of the inner membrane of the tube which bursts the outer membrane just
under a stoma, shooting out a jet of mucilage in which the aplanospores are em-
bedded. The latter germinate directly, the germ-tubes entering the leaf between
two epidermal cells.

Vaucheriacee.—This family includes only the well-known and widely distri-
buted genus Vaucheria. Different species of Vaucheria grow in brackish and fresh
water, both running and stagnant, or in the air in damp situations. The thallus
consists of relatively coarse branched tubes, quite visible to the naked eye. The
interior of the tube is lined by a layer of protoplasm containing numerous disc-
shaped chlorophyll-grains and many nuclei. The Vaucheria-plant is fixed to
its substratum by short-branched, colourless processes, but, except in connection
with the formation of reproductive cells, transverse septa are not formed in the
tubes.

The gametes of Vaucheria are formed in special organs, known as antheridia
and oogonia. The distinction of sex is very strongly marked, the male gametes or
spermatozoids being very small oval cells, each with two laterally inserted flagella,
while the female gametes or eggs are very large and quite motionless. The
antheridia are often spirally curved branches of the main tube, a transverse wall
separating the upper part of the spiral, the antheridium proper, from the lower part,
which is continuous with the cavity of the vegetative tube. Sometimes, however, the
antheridium is straight and club-shaped, and in other cases it may be separated
from the main tube by an intermediate cell. The thirty-five species of Vaucheria
are classified according to the characters of their antheridia. The oogonia are

644 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

ovoid or spherical, and usually possess a lateral beak. While the antheridium pro-
duces a large number of the small spermatozoids, the oogonium gives rise to a
single large egg. An account has already been given of the process of fertilization
(see p. 58, and figs. 204° and 204° on p. 53).

Vaucheria also produces peculiar zoospores, whose development and subsequent
behaviour have been described on pp. 23 and 24 of vol. i. (see Plate I a-d). The
cilia with which the surface of the zoospore is clothed are arranged in pairs, and in
the colourless external layer of protoplasm just below each pair of cilia is situated a
single nucleus. This suggests that the zoospore of Vaucheria is to be regarded as
really equivalent to a great many zoospores which have not separated during
development, each nucleus, with its pair of cilia and a certain amount of chloro-
phyll and protoplasm, representing an ordinary zoospore. It has been found that
if, as often happens, the zoospore breaks into two during its struggles to escape
from the end of its tube, the front part rounds itself off and swims away, behaving
just like an entire zoospore. In some species of Vaucheria the zoospores are
only partially clothed with cilia and come to rest soon after their escape. In yet
others they have no cilia at all, and either escape by dissolution of the end of the
tube, or germinate in situ. Here then we have a transition from the formation
of active zoospores to the production of passive aplanospores.

The occurrence and form of reproduction is here even more entirely under the
control of conditions than is the case in Hydrodictyon. The age and size of the
plant are no longer factors, since sexual organs and zoospores can be formed on
quite short germ-tubes. Cultivation of the plant in a solution rich in inorganic
food-salts always gives it a tendency to produce zoospores, but the immediate
stimulus to their formation is given by a distinct change in the conditions, just as
is the case in the Water-net. In Vaucheria this change is especially necessary,
since each zoospore is formed in the apex of a tube, and apical growth must be
stopped in order to allow free play to the zoospore-forming forces.

The nature of the change, so far as regards the medium, is apparently im-
material—it may be a change from running water to still water, or from a damp
atmosphere to water, or in the temperature or concentration of the culture-solution,
but it is a change from light to darkness which is especially effective. This is quite
contrary to the case of Hydrodictyon. The presence of water and a temperature
between 3° and 26° C. are absolutely necessary conditions of zoospore-formation.

The former condition is obviously adaptive. The formation of sexual organs
is specially induced by the replacement of organic salts by organic substances (e.g.
sugar), just as in the case of the gametes of Hydrodictyon, but antheridia and
oogonia, which are formed much more frequently and easily than are the Water-net
gametes, often appear in the presence of salts, and when growing in a damp atmos-
phere. Light and a temperature above 3° C. are absolutely necessary conditions.

The most striking point in the physiology of the reproduction of Vaucheria is
the prominent part played by the sexual organs. These are undoubtedly the princi-
pal means of propagation the plant possesses, the zoospores, which usually fulfil this

THALLOPHYTA. 645

röle, having fallen to a subordinate position. Only in forms like Vaucheria clavata,
adapted to life in rapidly-flowing water, have the zoospores a primary importance.
Sexual reproduction is here difficult, and zoospores are always produced in abun-
dance on the slightest change of conditions.

Bryopsidacee.—This family consists of marine, mostly tropical, forms. The
plant-body of Bryopsis has quite a definite form, and consists of a tube forming the
main axis, fixed below by short root branches, and bearing above in acropetal suc-
cession a series of branches, some of unlimited, some of limited growth. In these
latter are formed swarming cells which are of two sizes, the smaller being yellowish,
while the larger have each a green chromatophore. It seems very probable that
these are anisogametes, but their conjugation has not been observed.

Derbesia is a genus like Bryopsis in many respects, but with special zoosporangia
which produce curious zoospores, each with an anterior crown of cilia.

Caulerpacee—The genus Caulerpa contains nearly one hundred species, which
present the most varied external forms, simulating those of many of the higher
plants, such as Mosses, Ferns, Mare’s-tails, Cactuses, Conifers, &e. Each plant, how-
ever, consists simply of a single much-branched but uninterrupted tube, the branches
taking the forms of roots, leafy shoots, &e. The tube is supported internally by a
complicated system of “beams” of cellulose which run out from the walls.

The Caulerpas live mainly in tropical and subtropical seas. They often grow
together in large masses, forming great beds of sea-weed, their creeping stems or
“rhizomes” extending many yards. No reproductive cells have as yet been found
in any of them, multiplication taking place apparently solely by the breaking off of
parts of the thallus, which drift and fix themselves elsewhere.

Codiacee.—Under this name we may conveniently place together a group of
forms specially characterized by a thallus consisting of richly-branched tubes, which
are interwoven to form a mass of more or less solid character, which possesses in
each genus a definite and characteristic external conformation. Thus, Penicillus has
a long cylindrical “stalk” fixed below by “rhizoids” and bearing above a head of
free dichotomously branching radiating filaments. The older parts of the stalk are
strongly incrusted with calcium carbonate.

Udotea has a stalk often creeping and branching, bearing flat fan-shaped
fronds. Spherical bodies, the nature of which is unknown, are borne on short side
branches of the tubes of which the frond is built up. Halimeda possesses a thallus
mainly composed of series of heart- or kidney-shaped segments, which give many of
the species the appearance of an Opuntia. There is usually a considerable deposit
of calcium carbonate covering the thallus. Roundish structures, produced in grape-
like bunches on the edges of the segments, liberate swarming cells whose behaviour
has not been followed.

Codiwm has no well differentiated stalk or segments; the thallus is very various
in form, and is differentiated into a well-marked pith and cortex, the tubes being
mainly longitudinal and loosely packed in the former, while the latter consists of
club-shaped closely-packed branches arranged at right angles to the surface. In

646 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

certain branches of the latter swarmers of two sizes are produced. Analogy would
lead us to suppose that at least the smaller of these are gametes, but their behaviour
has not been observed. Some species of Codiwm (e.g. C. tomentosum, with a dichoto-
mously branched furry thallus) occur on our own coasts. The remaining Codiacee
are largely tropical, but very widely distributed.

Valoniacee.—We may include in this family an assemblage of genera whose
thallus consists of a branching tube, usually forming transverse walls, but with no
interweaving of the branches such as we get in Codiacex.

The simplest type is found in Valonia, a form which at first consists of a single
club-shaped cell, which produces a whorl of branches at its upper end. Each of
these may again produce a whorl of branches of the second order.

A group of very beautiful genera form leaf-like structures, the branching of the
thallus taking place in one plane. Strwvea consists originally of a single cell, which
grows apically and becomes divided by transverse walls into a series of segments.
Each of these segments bears a pair of branches coming off right and left, and each
branch behaves like the main axis. The secondary and tertiary branches thus pro-
duced come into contact, fixing themselves one to another by means of curious little
rosette-like organs called tenacula, and the whole thus forms a net-like structure
with larger or smaller meshes between the branches. The definite usually oval form
of the “leaf”, of which the main axis forms the midrib, and the primary branches
the principal veins, is due to the latter, after they have attained a certain length,
ceasing to produce branches on the side towards the base of the thallus, and at the
same time bending forwards and inwards to join the primary branch next in front.

Struvea delicatula sometimes lives in the tissue of a Sponge belonging to the
genus Halichondria. There is a reciprocal effect on the form of the two organisms,
the Alga only taking on the characteristic Struvea-form when part of its thallus
grows out clear of the body of the Sponge. In consequence of this it was for some
time not suspected that this sponge-inhabiting Alga had any connection with
Struvea. Neither organism seems to suffer from the association, and there is some
evidence for regarding it as a case of true symbiosis.

Anadyomene is another very beautiful form resembling Struwvea in the construc-
tion of its thallus, but with no meshes between the cells. It consists of two kinds
of cells, the more elongated form the “ ribs” of the thallus, the smaller and more
rounded make up the intermediate tissue.

The genus Boodlea, in which the branching takes place in more than one plane,
forms a transitional form connecting these genera with Cladophora, which is usually
regarded as belonging to the Confervoidez.

Verticillate.—In this group of the Siphone® the thallus consists of a long
cylindrical undivided stalk, fixed below by rhizoids, and bearing above acropetal
whorls of simple or branched appendages of limited growth. In some of these
appendages gametes may be produced; zoospores are apparently absent. It includes
two sub-families, the Acetabulariee and Dasycladez.

Acetabulariee.—Fertile and sterile appendages distinct. Acetabularia mediter-

THALLOPHYTA. 647

ranea: the lower part of the long cylindrical stalk is incrusted with ealeium car-
bonate, and fixed to its substratum by short irregularly branched rhizoids, The
rhizoid-bearing portion is called the foot, and below it there is a thin-walled branched
continuation of the stalk, called the basal division. Near the apex of the stalk are
borne 1-4 whorls of polychotomously branched sterile appendages, which soon
fall off.

Above these is an umbrella-shaped whorl of simple appendages in lateral contact,
whose cavities are not shut off from that of the stalk. The whole of the upper part
of the plant dies off each autumn, only the foot and basal division remaining alive
through the winter. In the spring a new shoot is produced. Apparently after
several years the contents of each simple appendage of the umbrella (which may
now be a centimetre or more in diameter) divides up into a number of oval bodies,
each surrounded by a fairly thick wall and containing chlorophyll and starch.
These are the gametangia. After their escape by the dissolution of the umbrella,
the contents of each divides up to form a number of gametes. Considerable pressure,
caused by swelling of the ectoplasm and osmotic tension in the vacuole of the game-
tangium, bursts off a lid at one end, and the gametes escape. Conjugation only
occurs between gametes derived from distinct gametangia.

Dasyeladee.—No distinction between fertile and sterile appendages. Dasycladus
has a single stalk-cell fixed below like Acetabularia, but bearing very numerous
whorls of appendages, which stand so close together as to give the entire plant
a resemblance to a minute fox’s brush. Each appendage bears a terminal whorl
of branches, and in the middle of these is a shortly-stalked, nearly spherical
gametangium. The gametes conjugate, but apparently only with those from
certain other plants. This fact at first led to the supposition that we had here
a physiological distinction of sex in gametes, which im external appearance are all
alike. This is, however, quite an unjustifiable and unnecessary assumption. We
have no right to predicate sexual differences between gametes which do not show
any of the well-recognized characters of male and female reproductive cells. The
tendency to avoid pairing with closely related gametes, which we may call exogamy,
is quite a distinct phenomenon, not only among isogamous Algs, but also among
many of the higher plants, where it coexists with strongly-marked sex. The pheno-
mena of self-sterility is an extreme case of this.

Neomeris and Cymopolia are two tropical and subtropical genera, whose thallus
is very strongly inerusted with calcium carbonate. The arrangement of the
branches resembles that found in Dasycladus, but on the ends of the younger ones
hairs are borne, which serve to protect the growing apex of the plant. In Cymo-
polia, of which the main stalk branches, and the thallus attains a considerable size,
these hairs are borne by simple branches produced on special constricted and uncal-
cified zones of the stalk. The apices of the secondary branches are in both genera
swollen up, and in close lateral contact, thus forming a continuous surface on the
exterior of the plant. The calcium carbonate is deposited as a thick layer under-
neath these swollen ends.

648 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

A whole series of fossil forms from the chalk and tertiary deposits serve to con-
nect the various existing types of these and allied genera,

Alliance VIII. —Confervoidex.

The Algs® ineluded under this alliance possess a type of thallus composed of dis-
tinct and separate cells. These cells are united usually into linear series, which form
branched or unbranched threads. In a few families, however, cell-division takes
place in two, or even three, dimensions, resembling some Protococceoide in the forma-
tion of cell-surfaces or cell-masses. Zoospores are produced by nearly all confervoid
forms. Aplanospores and akinetes are common. The gametes may be isogamous,
or they may show marked sexual differentiation.

Families: Ulvacece, Ulotrichacee, Cylindrocapsacee, CEdogoniacee, Clado-
phoracee, Gomontiacee, Spheropleacee, Chatophoracee, Trentepohliacee, Mycoi-
deacee, Coleocheetacec.

Ulvacee.—This family is usually regarded as the lowest of the confervoid series.
It is characterized especially by forming cell-surfaces instead of filaments. Zoo-
spores with four flagella and isogametes with two, as well as akinetes, are
formed in the group. Monostroma very much resembles Tetraspora among the
Protococcoidez, from which we may suppose the confervoid forms to have arisen
in evolution. The thallus consists of a single layer of roundish or angular cells. In
germination, the zygote divides to form a small hollow sphere, which splits, and
extends itself to form a flat plate. At first fixed by rhizoids, the thallus later floats
freely in the water. The chromatophore is a parietal plate, covering more or less of
the cell-wall, and contains a single pyrenoid. Gametes (which may develop without
conjugation), or zoospores may be formed in almost any cell of the thallus.

Ulva differs from Monostroma in possessing a thallus of two layers of cells,
those of each layer dividing independently of the other. The zygote germinates to
form a fixed cell thread, which later on produces the two-layered thallus. Ulva
latissima (the Green Laver or Sea-lettuce) is very common on the rocks of our
coasts near high-tide mark. It forms large green wavy fronds firmly fixed to the
substratum. It is sometimes used as an article of food.

Enteromorpha is a large genus, several species of which are common on our
coasts, and some in fresh water. The thallus forms a branched hollow tube, the
wall of which is one cell thick. Any cell of the thallus may act as the apical cell
of a branch. The apex of the branch is solid, but the cells soon round themselves
off to form the wall of the tube. The gametes and zoospores resemble those of
Monostroma and Ulva.

Letterstedtia is a Cape and Australian form much like Ulva, but with a deeply-
lobed thallus. Zoospores are produced only in the cells of the lobes.

Ulotrichacew.—This family contains several genera common in fresh water, and
some marine forms. The thallus consists of an unbranched filament of cells seldom
much longer than they are broad. The chromatophore is single, parietal, and of

THALLOPHYTA. 649

very various form. Zoospores are formed in most genera. Gametes, where known,
are motile and isogamous. Aplanospores and akinetes are very commonly formed,
under unfavourable conditions.

Ulothrix (fig. 371), the best-known genus, possesses cells of very variable length.
The chromatophore, which contains several pyrenoids, is an interrupted cylinder,
and may or may not occupy the whole length of the cell. When the conditions are
suddenly changed, zoospores or gametes are very readily formed, the former 1-4
the latter 4-32 in a cell. According to the size of the mother-cell and the number
of divisions taking place, the size of the zoospores and gametes varies greatly, the

Ps

SIREN
YY ) i%

i

Fig. 371.—Ulothriz zonata.

1 Two filaments of this plant. 2 Escape of gametes in packets. *Spherical packet of gametes free from the filament. 4Separa-
tion of the gametes. 5 Gametes swimming about and pairing. ® Products of pairing of gametes (zygotes) attached to
substratum. 7-9 Zygote giving rise to zoospores. 19 Two zoospores. 1x 250; 2-10 x 400. (Partly after Dodel-Port.)

only constant distinction between them being the number of flagella, which in the
zoospores are four, in the gametes two (cf. figs. 371!’ and 371°). The zoospores or
gametes escape from the mother-cell through a hole in the wall. They are surrounded
by a bladder derived, probably, from ectoplasm. The swelling of this in the water
helps to drag them out of the cell-cavity. The tension of the vacuole of the mother-
cell, which is visible among the zoospores or gametes as a smaller bladder, also assists
in pressing out the mass (figs. 371%%*). The zoospore settles on some solid object,
and, after putting out a short root-process from its colourless anterior end, produces
a new cell-thread. Some of the gametes develop parthenogenetically, in which case
they germinate just like zoospores, but produce usually smaller and weaker plants.
The gametes which conjugate (see figs. 371° and 371°) produce zygotes which sink
to the bottom of the water, and after a period of rest grow into unicellular plants,
each of which forms 2-14 zoospores (figs. 371%75°), These probably give rise te
ordinary plants.

650 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

The asexual generations of Ulothrix are produced during the autumn and
winter, gametes being formed in spring, and the zygote resting through the summer.
This course of events differs from that obtaining in most Algz with a similar life-
history. Ulothria seems especially adapted to life in cold water.

Hormidium is a genus whose members grow largely on damp earth, tree trunks,
&e. The chromatophore is solid, with radiating processes and a central pyrenoid.
The cells of some species divide longitudinally, so as to form threads two cells
broad.

Various other genera are common in fresh water.

Cylindrocapsacee.—Cylindrocapsa forms unbranched threads of short cells with
very thick walls, each thread being fixed in the young state by a cellulose foot.
The gametes show a considerable sexual differentiation. The males are pear-shaped,
elongated, yellow, with two flagella at the anterior end. They are produced two in
an antheridium, which is formed by the division of an ordinary cell into two or
four. The protoplasm of an ordinary cell rounds itself off directly to become an
egg, the wall swelling and bursting at one side to allow of the entrance of the
spermatozoids. Parthenogenesis also occurs.

Edogoniacee.—(Edogonium has a thallus consisting of an unbranched thread,
of rather long cells, of which the basal one is fixed to some solid object. The
chromatophore often forms a continuous parietal layer containing several pyrenoids.
All the cells, except the basal one, are capable of division. When division is going
to occur a rim of cellulose is formed inside the cell close to the upper transverse
wall. After the nucleus has divided, and the new transverse wall is formed, the rim
is opened, as it were, by a circular cut from without, and the tension of the cell
causes a pulling-out of the substance of the rim. The result is the intercalation
of a new cylindrical piece of cell-wall in the upper daughter-cell. The young
transverse wall now moves up to the lower edge of the intercalated piece of mem-
brane. The latter soon acquires the ordinary thickness of a side wall, but the
segment of the old cell-wall above the spot at which the rim was formed remains
projecting beyond the new piece like the eaves of a house beyond its side walls.
After the cell has divided again, another projecting piece will be left in the same
way, and the series of eave-like projections so formed are a very characteristic
feature of the cells of an @dogoniwm-thread. The zoospores of @dogoniwm are
formed singly in the cells of a thread. The entire cell-body, with the exception of
the ectoplasm, rounds itself off and escapes from the cell by a split in the wall.
An anterior circlet of cilia surrounds the colourless “mouth place,” of the zoospore.
In germination, the zoospore fixes itself by the mouth place, sending out short fixing
processes, puts on a cell-membrane, and then grows out to form a new thread.

The gametes of Edogonium are sexually differentiated.

The oogonium is formed by the swelling-up of the uppermost daughter-cell after
a division. The contents round off to form a single large oosphere. Either a round
hole appears in the wall, or a circular split is formed at the upper end of the
oogonium, the part of the filament above rotating through a few degrees so as to

THALLOPHYTA. 651

leave an opening. A certain amount of the protoplasm of the oosphere is extruded
at this spot, and forms a sort of canal of mucilage, through which a spermatozoid
passes in fertilization. The spermatozoids are produced one or two in an anther-
idium, which are short cells poor in chlorophyll, formed by the repeated division of
certain cells of a thread. The spermatozoids resemble small zoospores. In some
cases they are not produced directly from the cells of a thread, but the latter give
rise to special zoospores called androspores, which escape and settle either on or in
the immediate neighbourhood of an oogonium. The androspore then germinates,
producing a small structure called a dwarf male. This consists of a very few cells,
one or more of which become antheridia, and opening by a lid, gives rise to sper-
matozoids, one of which pierces the canal of the oogonium, and fuses with the
oosphere. The oospore, which is of a red or brown colour, produces four zoospores
in germination.

Bulbochete is a genus resembling Edogonium in its life-history, but consists
of a branched thread, only the basal cell being capable of dividing. The cells
bear characteristic hairs, swollen at the base, whence the name of the genus.

Species of (Edogonium and Bulbochete, which are both genera of considerable
size, are found in our ponds and ditches.

The next three families are distinguished from all other Confervoidew by pos-
sessing more than one nucleus in each cell.

Cladophoracee.—Cladophora is a very widely distributed genus, inhabiting both
fresh and salt water. A great number of species have been described, but it is
doubtful whether many of the forms are entitled to specific rank.

The thallus has a very characteristic habit. It is fixed below by an elongated
basal cell, and is profusely branched, sometimes forming a spherical mass. The
elongated cells possess parietal chromatophores, which cover the whole cell-wall,
and possess many pyrenoids. Sometimes the chlorophyll-layer is separable into
distinct angular plates. There are many nuclei in the layer of protoplasm imme-
diately within the chlorophyll.

Many zoospores are produced in each cell. The nuclei divide a good deal, the
pyrenoids disappear, and the protoplasm then divides into a number of separate
masses, each of which forms a single zoospore with either four or two flagella.
Gametes with two flagella are formed in many species quite like the zoospores.
The zygote germinates directly to form a new Cladophora-plant.

The Cladophoraceze show on the one hand a transition to the Siphonez, and on
the other, through certain genera with unbranched thallus and few nuclei in each
cell, to the Ulotrichacex.

Gomontiacee.—Gomontia polyrhiza is an isolated form which perforates the
shells of various marine molluses, such as the whelk, the oyster, the mussel, Xe.
The thallus radiates on the surface of the shell, and sends branches into the sub-
stance, gradually disintegrating it. Certain branches become zoosporangia or
aplanosporangia; these lose their attachment to the thallus and form fresh rhizoids.
The zoospores are pear-shaped, and germinate directly to form a new thallus.

652 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM,

Spheropleacee.—Spheroplea annulina is a curious Alga which appears occa-
sionally on flooded fields or in other situations. Its thallus consists of simple
threads of cells which are of very various length, sometimes enormously long. The
side walls are thin, but the transverse walls are often thick, and both are liable to
have curious thick and quite irregular projections of cellulose. The chromatophores
form irregular rings at intervals, and contain many pyrenoids. There are many
nuclei, and several variable vacuoles in each cell. All the cells may produce sexual
organs, the threads being either moncecious or dicecious. The contents of the cells
which become antheridia become yellow-red, and break up to form a great number
of elongated, pointed spermatozoids. These escape through small holes in the wall.
In the oogonia the protoplasm divides to form one or two series of spherical
oospheres, each with a colourless spot. The oospore has three membranes, of which
the outermost is folded so as to give the oospore a star-like appearance.

In germination the oospore produces 1-8 zoospores, which have a green posterior
and a pale-red anterior end. Each eventually stretches itself to form a spindle-
shaped cell, and a multiplication of nuclei and pyrenoids takes place before trans-
verse divisions occur and a new Spheroplea-filament is produced. Parthenogenesis
occurs, but apparently no zoospores are formed other than those produced in the
germination of the oospore.

Chetophoracee.—This family contains forms with a branching thallus, the
branches often ending in fine hairs. The chromatophore is parietal, with one or
more pyrenoids. Zoospores with two or four, and gametes with two flagella are
produced.

Stigeoclonium, Draparnaldia, and Chetophora are three genera common in fresh-
water in this country, and all very slimy to the touch. In the first-named genus the
thallus is fixed by means of a basal dise of cells, the sole; the branching is simple
and irregular, the branches often ending in long multicellular hairs. Draparnaldia
shows a marked distinction between axis and appendages. The axial cells are
much larger, and at the same time poorer in chlorophyll than those of the branches.
The branches come off in bunches, and often end in many-celled hairs. The chro-
matophore possesses many pyrenoids varying in number according to the size of
the cell. Chatophora possesses a thallus whose threads radiate and branch in all
directions. The whole is surrounded by a mucilaginous investment of considerable
firmness, sometimes almost leathery in consistence, so that a Chatophora-plant has
the appearance of a slimy green ball.

There are several other genera belonging to this family, many of them being
epiphytic or endophytic. Entoderma lives in the cell-membranes of the Brown
Sea-weed Hetocarpus.

Trentepohliacee.—This family differs from the last in possessing no hairs, and in
forming its zoospores in special zoosporangia.

Trentepohlia is a fairly large genus containing forms mostly living in the air
on damp stones and similar situations. The thallus consists of rounded thick-walled
cells, and is dichotomously or irregularly branched, partly creeping, partly upright.

THALLOPHYTA. 653

The chromatophores are many, disc-like, and angular, with no pyrenoids. The cell-
contents is usually much marked with hematochrome. The zoosporangia and gamet-
angia are usually terminal, often swollen cells. The gametes and zoospores are
much alike. Trentepohlia Iolithus, growing on damp stones, is known as the
“ Violet-stone ” from possessing a scent which recalls that of violets. 7. wmbrina is
often attacked by lichen-forming Fungi. 7. spongophila inhabits the jelly of
Ephydatia (Spongilla) fluviatilis in a certain volcanie lake in Sumatra. The
situation is very advantageous to the Alga, but the Sponge seems to suffer from
the piercing of its tissue by the guest. Trichophilus is a nearly allied form which
lives in the hollow hairs of the Three-Toed Sloth.

Mycoideacece.—These are epiphytic or parasitic forms nearly allied to the two
preceding families, and probably derived from one of them. They form regular
dises of cells often attached to the host by much-branched unicellular rhizoids. The
dise grows by regular divisions of its marginal cells. Zoospores and sometimes
gametes are formed in all or some of the cells.

Cheetopeltis forms very regular discs of cells on fresh-water plants in Europe.

Mycoidea (Mycoidea parasitica) forms dises of cells between the cuticle and
epidermal cells of Camellias, Rhododendrons, &e. in the East Indies and South
America. In this position it withdraws a good deal of water from the tissue of the
leaf, and this leads to the dying of the leaf-cells in a gradually increasing area
round the parasite. Eventually a hole is formed right through the leaf, and the
Mycoidea-thallus occupying a position all round the area of dead tissue continues
to increase. Zoospores are only formed in the wet season, at which time alone have
they any chance of swarming and germinating on the surface of the leaf. In this
position primary (embryonic) dises are formed, many of which die, and others are
attacked by Fungi to form Lichens, but some succeed in sending processes through
the cuticle and establishing themselves below.

Coleochetacee.—This family contains a single small genus, Coleochete, which
forms radiating, dichotomously branching rows of cells, usually on the surface of
other plants in fresh-water. If the cell-rows are in lateral contact, a close disc is
formed (C. scutata), if separate a looser one (C. soluta), or the branching may be
rather irregular (C. divergens). The chromatophore is parietal and disc-shaped,
and contains a single pyrenoid.

Zoospores can be produced in all or only the end cells of the rows. A single one
is formed from each cell. In germination a new plant is directly formed.

Coleochete is oogamous, the plants being either moncecious or dicecious. The
oogonium is always formed from the end cell of a row. The cell swells and puts
out a narrow tube which opens at the end, and extrudes a drop of mucilage. The
protoplasm of the swollen basal part then rounds itself off. In the forms with a
dise-shaped thallus, the antheridia are produced by the division into four of the
members of certain cell-groups. Each daughter-cell (antheridium) then liberates a
single spermatozoid. In the branching forms certain end cells form flask-shaped
swellings (antheridia), which are eut off from the mother-cell by transverse walls.

654 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

Each antheridium then liberates a spermatozoid. Fertilization has not been observed,
but there can be no doubt that a spermatozoid passes down the neck of the oogonium
and fuses with the oosphere. Subsequently the neck of the oogonium breaks off,
the oospore puts on a cell-wall, and the neighbouring cells branch so as to form a
closely investing cortex of cells round the oospore. The contents of these cortical
cells turn red-brown; and after a resting stage the cortex comes off, the oospore
having in the meanwhile divided to form a dise of cells, each of which gives rise to
a zoospore, which escapes and germinates to form a new plant.

The structure of the oogonium, and the formation of a cortex round the oospore,
as well as the formation of “carpospores” by the latter, recall the simpler Red
Sea-weeds, a group which some authorities consider to be derived from some form
like Coleochete.

The indirect formation of new plants by the products of division of the zygote,
a phenomenon we have already met with in Pandorina, Hydrodictyon, Ulothria,
(Edogonium, and other forms, is probably the means by which the sporophyte
generation of Mosses and Liverworts arose. At first the zygote gave rise at once
to spores, but later on a certain amount of sterile tissue was produced in addition,
and this formed the body of the sporophyte.

Alliance [X.—Conjugate.

Families: Desmidioider, Spirogyracee, Zygnemacee, Mougeotiacee.

This is a very sharply characterized alliance of Green Alge. It is indeed
difficult to determine its affinities. The forms belonging to it are especially charac-
terized by never forming zoospores, and by possessing aplanogametes, 1.e. gametes
which, instead of escaping from the mother-cell and swarming freely, never leave
the cavities of the cells in which they are produced. When conjugation is about to
occur the two cells (gametangia), the contents of which will form gametes, approach
one another, and their walls come into contact, either directly, or by the putting out
from one or both cells of a short cellulose tube. The area of wall at the place of
contact breaks down, and the whole or part of the contents of each cell then fuses
with the corresponding protoplasm of the other to form a zygote.

The chromatophores of the Conjugate, though very various in the different
families, are all very different from the types met with among the other Green
Alge.

I. Desmidioidee. Cell-contents and outline symmetrically arranged on each
side of a given median plane which is often coincident with a more or less deep
constriction. Often unicellular.

Il. Zygnemoidee. Cells cylindrical, without median constriction, always form-
ing threads.

1. Spirogyracee. Chromatophores one or more, parietal, spiral.
2. Zygnemacee. Chromatophores two, axile, roundish.
3. Mougeotiacee. Chromatophore single, axile, plate-like.

THALLOPHYTA. 655

Desmidioidee.—The Desmids are a large family of fresh-water forms numbering
over a thousand species. Perhaps their most favourite habitat in this country is
the water which collects and stands between mosses and similar plants on imper-
vious soils. Many of the Desmids are among the most beautiful of algal forms.

The great characteristic of the Desmid-cell is its almost invariable division into
two symmetrical halves, often separated by a circular constriction (cf. fig. 372).
The cell-membrane usually consists in fact of two distinct valves whose edges meet
in this median plane. In cell-division these two valves are forced apart, a new
cylindrical piece of membrane being intercalated between them. A transverse wall

Fig. 372. Desmids.

1 Micrasterias papillifera. 2 Micrasterias morsa. > Cosmarium polygonum. + Xanthidiwm aculeatum. 5 Staurastrum
Jurcatum. ® Euastrum oblongum. 7 Penium Brebissonii. 8 Closterium Lunula. ° Xanthidium octocorne. 10 Staur-
astrum alternans (two views). 11 Cosmarium tetraophthalmum, 12 Aptogonum Desmidium. All the figures magnified
about 200 times.

is then formed at the equator, and each half of the new piece of wall gradually
assumes the characters of the old half-cell to which it belongs.

The actual form of the cell is very various; it is often lobed, and its wall
seulptured in various ways. A good idea of the shapes of some of the commoner
types can be obtained by an inspection of fig. 372; see also Plate I, i, k.

The chromatophores are also extremely various in form. A common type is an
axile rod bearing longitudinal plates which radiate in all directions. Each chroma-
tophore contains one or more pyrenoids.

The cell-membrane is usually perforated by series of regularly arranged, very
minute pores which give exit to extremely delicate filaments of protoplasm. The
projecting end of each filament is surrounded by a mass of mucilage, and these
masses together form a complete sheath covering the entire cell, and sometimes even

656 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM.

groups of cells (ef. similar phenomenon in Diatoms, p. 626). Many Desmids possess
the power of locomotion. Their movement is slow and creeping, and although the
means by which it is brought about are by no means fully understood, it has been
shown to have a connection with the excretion of mucilage, and to stand in relation
with light and gravitation. Some forms (e.g. Closteriwm and Penium, figs. 372°
and 372") have a curious rotating movement, one end being temporarily fixed while
the other moves up towards the source of light.

Conjugation takes place as already described, the conjugating cells -either
coming into direct contact, or putting out short tubes. The conjoined tubes are
known as the conjugation-canal. The zygote may be formed either in this or in
one of the conjugating cells. The membrane of the zygote consists of three layers,
the outer one being sculptured in various ways. In germination, the outer, sculp-
tured membrane is burst open, and the protoplasm divides to form 2-8 cells which
gradually take on the characters of the adult individual.

The cells of the thread-forming Desmids (ef. fig. 372?) possess all the characters
of the unicellular types, the daughter cells simply remaining together after division
(which always occurs in one plane) has taken place.

Spirogyracee.—This family contains the single genus Spirogyra, many species
of which are amongst the commonest Algs in our ponds and ditches. They form
green or yellowish-green slimy masses on the mud at the bottom or floating at the
surface of the water. Such a Spirogyra-mass usually contains several species,
although the bull of it is often formed by one.

The cells of the different species vary much in diameter, from the delicate S.
tenwissima which is only about one hundredth of a millimetre across, to S. crassa,
which forms coarse threads as much as one seventh of a millimetre thick. Roughly
speaking, the broader the cell, the greater number of chromatophores it possesses
The smaller species possess only one spiral band in each cell (Plate I., 1), the largest
as many as eight or nine.

Each Spirogyra-cell is a cylinder, in most cases considerably longer than it is
broad (though the relation of length to breadth is variable even in one and the same
species), with a very delicate layer of protoplasm lining the wall, and a large central
vacuole. Each chromatophore forms a band embedded in the protoplasm, and
twisting spirally round and round the cell at an approximately constant angle.
When there are more bands than one they cross each other at regular intervals,
forming a beautiful lattice-work. In some species each band makes several com-
plete turns in its course down the cell (fig. 373); in others, it may be inclined at
such a small angle with the long axis that it makes less than a complete turn in the
length of the cell. In S. orthospira the bands are practically parallel with the long
axis, so that they do not follow a spiral course at all, but form straight bands.
Each chromatophore may be isodiametric, or, on the other hand, it may form a
flattened band. In the latter case its edges are usually irregularly scalloped. A
single row of pyrenoids at larger or smaller intervals is found in each chromato-
phore.

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