A system of physiological botany [microform]

BIOLOGY

LIBRARY

G

SYSTEM

'PHYSIOLOGICAL BOTANY,

BY

THE REV. P. KEITH, F. L. S.
\t

VICAR OF BETHERSDEN, KENT ; AND PERPETUAL SURATE
OF MARK, YORKSHIRE.

IN TWO VOLUMES.

Vere scire est per causas scire.

BACOV,

RSIT

VOL. II.

LONDON:

PRINTED FOR BALDWIN, CRADOCK, AND JOY,

47, PATERNOSTER ROW;
W. BLACKWOOD, EDINBURGH ; AND J. GUMMING, DUBLIN.

1816.

BIOLOGY

UflRARfc

<a

1C

C. Baldwin, Printer,
Knr Bridge-street, Londo*.

CONTENTS OF VOL. II.

BOOK IV.

Of the Phenomena of Vegetable Life 1

Chap. I. Germination of the Seed 2

Sect. I. Conditions of Germination 3

II. Physical Phenomena 14?

III. Chemical Phenomena 27

Chap. II. Food of the Vegetating Plant 4-1

Sect. I. Water 43

Sect. II. Gases 50

III. Vegetable Extract 65

IV. Salts 69

V. Earths 74

VI. Manures 79

Chap. III. Process of Vegetable Nutrition 89

Sect. I. Intro-susception 89

II. Ascent of the Sap 101

III. Cause of the Sap's Ascent 125

IV. Elaboration of the Sap 135

V. Elaboration of Carbonic Acid. . 144

VI. Elaboration of Oxygene 153

VII. Decomposition of Water 176

, VIII. Descent of the Proper Juice . . 182

IX. Causes of Descent 191

Chap. IV. Process of Vegetable Developement 199

Sect. I. Elementary Organs 200

II. Composite Organs 208

III. Circulation of Vegetable Juices 236

IV. Decomposite Organs 245

CONTENTS.

Page
Chap. V. Anomalies of Vegetable Developement. . 268

Sect. I. The Root 269

II. The Trunk 274

III. The Branch 278

IV. The Bud 279

V. The Leaf 282

VI. The Flower 287

VU. The Fruit 293

VIII. Habit 295

IX. Duration 296

X. Virtues 296

Chap. VI. Sexuality of Vegetables 297

Sect. I. Anticipations of the Ancients. . 297
II. Discoveries of the Moderns. . . 302

III. Induction of Particular Proofs.. 309

IV. Objections 328

Chap. VII. Impregnation of the Seed 350

Sect. I. Access of the Pollen 351

II. Agency of the Pollen 358

III. Hybrids 366

Chap. VIII. Changes consequent upon Impregnation. . 371
Sect. I. External Changes 371

II. Internal Changes 373

III. Specific Examples 377

Chap. IX. Propagation of the Species 394?

Sect. I. Equivocal Generation 394

II. Seeds 397

III. Gems 406

IV. Runners 416

V. Slips 417

VI. Layers 418

VII. Suckers 419

VIII. Grafts 420

Chap. X. Causes Limiting Propagation 421

Sect. I. Soils 422

II. Climate 429

III. Altitude . . .433

CONTENTS.

Page

IV. General Remarks 436

Chap. XI. Evidence and Character of Vegetable

Vitality ' '. 438

Sect. I. Excitability -. 439

II. Irritability 458

III. Sensation 462

IV. Instinct 465

V. Definition of the Plant 466

Chap. XII. Casualties affecting the Life of Vegetables 473

Sect. I. Wounds 473

II. Diseases 484

III. Natural decay 505

VOL. II.

UNIVERSITY

r

.

A SYSTEM

or

PHYSIOLOGICAL BOTANY

BOOK IV.

OF THE PHENOMENA OF VEGETABLE
LIFE:

Jb ROM the analysis of the vegetable structure
whether external or internal, and of the primary
and constituent principles of which the vegetable
is composed, or to which it may be reduced, as
exhibited in the several books of the preceding
volume, the transition to the subject of the func-
tions of the vegetable organs is both natural and
easy. It cannot however be said, that the subject
ij> itself of easy investigation, embracing as it does
tl. phenomena, both physical and chemical, of the
whole of the process of vegetation, from the period

VOL. II. B

2 GERMINATION OF THE SEED. CHAP. I.

of the first and incipient symptoms of the agency
of the vital principle as displayed in the evolution
of the seed, till that of its ultimate and complete
extinction as denoted by the death of the plant.
Division The subject therefore necessarily involves the se-
ject. C 3 veral following topics, which shall each constitute
the ground of a separate chapter : — Germination ;
nutriment; digestion; growth and dcvelopement of
parts; anomalies of vegetable developement ; sexu-
ality of vegetables ; impregnation of the vegetable
germe ; changes consequent upon impregnation ;
propagation and dispersion of the species; causes
limiting the dispersion of the species ; evidence and
character of vegetable vitality ; casualties affecting
or destroying the vitality of vegetables.

CHAPTER I.

GERMINATION OF THE SEED.

All plants GERMINATION is that act or operation of the
frPom§seed. vegetative principle by which the embryo is ex-
tricated from its envelopes, and converted into a
plant. This is universally the first part of the
process of vegetation. For it may be regarded as
an indubitable fact, that all plants spring originally
from seed ; the doctrine of equivocal generation
being now most completely exploded, and an ad-
ditional proof adduced of the uniformity of the

SECT. I. CONDITIONS.

operations of nature. But seeds will not germinate
at random, and in all circumstances whatever.
They will germinate only under certain conditions,
and till such conditions take place the vital prin-
ciple lies dormant in the substance of the seed.
But when a seed is placed in the soil., or in cir-
cumstances otherwise favourable to vegetation, the
vital principle is immediately stimulated into action,
producing a variety of combinations, and effecting
a gradual change in the parts of the seed. The
radicle is converted into a root ; the plumelet int6
a trunk or stem with its leaves and branches ; and
a new plant is formed capable of extracting from
the soil or atmosphere the food necessary to its
growth and developement.

What then are the conditions necessary to ger-
mination ? What are the changes produced during
the process ? And by what means are the changes
effected ? These inquiries shall form, respectively the
subject of the three following sections.

SECTION I.
Conditions necessary to Germination.

THE conditions necessary to germination relate
either to the internal state of the seed itself, or to
the circumstances in which it is placed, with re-
gard to surrounding substances.

B 2

GERMINATION OF THE SEED. CHAP. I.

:

SUBSECTION I.

Maturity of the Seed. — The first condition ne-
cessary to germination is, that the seed must have
reached maturity. Unripe seeds seldom germinate,
because their parts are not yet prepared to form
the chemical combinations on which germination
Excep- depends. There are some seeds, however, whose
germination is said to commence in the very seed-
vessel, even before the fruit is ripe, and while it is
yet attached to the parent plant. Such are those
of the Tangekolli of Adanson, and Agave vivipara
of East Florida,* as well as of the Cyamus Nc-
lumbo, of Dr. Smith,-f- or sacred Bean of India ;
to which may be added the seeds of the common
Garden Radish, whose germination I have often
found to be completely effected in the pod, at least
in the case of plants that had been allowed to re-
main after the usual period of gathering. Peas
have been, also, known to germinate even when
gathered and committed to the soil, in a green and
soft state ; £ and I have known a Lemon seed to
send out a radicle an inch and a half long, and a
plumelet visible to the naked eye, before it was yet
extricated from the fruit. But these are examples
of rare occurrence ; though it is sometimes neces-
sary to sow or plant the seed almost as soon as it

* Barton's Elements, p. 58. f Exotic Botany, No. 7.

* Seneb. Pbys. Veg. vol. iii. p. 377.

SECT. I. CONDITIONS.

is fully ripe, as in the case of the Coffee-bean ;
which will not germinate unless it is sown within
five or six weeks after it has been gathered.

But most seeds if guarded from external injury
will retain their germinating faculty for a period of
many years. This has been proved by the experi-
ment of sowing seeds that have been long so kept ;
as well as by the deep ploughing up of fields that
have been long left without cultivation. A field
that was thus ploughed up near Dunkeld, in Scot-
land, after a period of forty years' rest, yielded a
considerable blade of Black Oats without sowing.
It could have been only by the plough's bringing
up to the surface, seeds that had been formerly toa
deeply lodged for germination.

SUBSECTION II.

Exclusion of Light. — The second condition is,
that the seed sown must be defended from the
action of the rays of light. This has no doubt
been long known to be a necessary condition of
germination, if we regard the practice of the har-
rowing or raking in of the grains or seeds sown by
the farmer or gardener as being founded upon it.
But it does not seem to have engaged the notice
of men of science, or to have been proved by direct
and intentional experiment till lately. The first; £Xper
direct experiments that were instituted on this sub
ject, are those of Ingenhoutz,* who found
* Expcr. sur. la Veg. vol. ii.

GERMINATION OF THE SEED. CHAP. I.

seeds germinate faster in the shade than in the sun,
and hence concluded that light is prejudicial to ger-
mination. Senebier,* who afterwards repeated the
experiments of Ingenhoutz with the same result,
drew from them also the same conclusion.

But it remained to be determined whether the
prejudicial effect was to be attributed merely to
the light, or partly to the heat accompanying it.
From the experiments of Ingenhoutz and Senebier,
the injury appeared to be occasioned by the light
only ; because the comparative experiments in the
shade and in the sun, were made at equal tempera-
tures as indicated by the thermometer. With this
conclusion, however, though apparently legitimate,
Of Saus- M. Saussure professes to be dissatisfied, because the
thermometer placed even under the recipient is,
in his opinion, incapable of indicating the actual
degree of the heat of the solar rays impinging on
the surface of the seeds, which he believes to be
carried to a very great height, though still escaping
our instruments of observation. But this mode of
reasoning is, to say the least of it, still more in-
consequential than the former ; because it is setting
up a mere probability from which nothing can be
inferred, in opposition to a direct fact, from which
something surely should be inferred. It may in-
deed be true, that the degree of heat impinging on
the surface of the seed is so great as to impede its
germination ; but as no direct proof can be adduced
in support of the opinion, we must just rest satis.
* Mem. Phys. Chim. vol. iii. p 341,

iure.

SECT. 1. CONDITIONS*

fied with the indications of our instruments, till
such time as other instruments shall he invented
capable of detecting their errors ; and with the pre-
vious conclusion, till such time as some positive fact
shall he opposed to the experiments from which it
is deduced.

SUBSECTION in.

Action of Heat. — A third condition necessary
to germination is the access of heat. No seed has
ever been known to germinate at or below the
freezing point. Hence seeds do not germinate in
winter, even though lodged in their proper soil.
But the vital principle is not necessarily destroyed
in consequence of this exposure ; for the seed will
germinate still, on the return, of spring, when the
ground has been again thawed, and the temperature
raised to the proper degree. But this degree varies Different
considerably in different species of seeds, as is q^e d!f-
obvious from observing the times of their germi'-
nation, whether in the same or in different cli-
mates. For if seeds which naturally sow themselves,
germinate, in different climates, at the same period ;
or in the same climate, at different periods ; the
temperature necessary to their germination must of
consequence be different. Now these cases are
constantly occurring and presenting themselves to
our notice ; and have also been made the subject
of particular observation. Adanson found that
seeds which will germinate in the space of twelve

8 TERMINATION OF THE SEED. CHAP. I.

hours in an ordinary degree of heat, may be made
to germinate in the space of three hours by ex-
posing them to a greater degree of heat ; and that
seeds transported from the climate of Paris to that
of Senegal, have their periods of germination ac-
celerated from one to three days.* Upon the same
principle, seeds transported from a warmer to a
colder climate, have their period of germination
protracted till the temperature of the latter is
raised to that of the former. This is well exem-
plified in the case of our green-house and hot-house
plants, from which it is also obvious that the tem-
perature must not be raised beyond a certain degree,
otherwise the vital principle is totally destroyed.

SUBSECTION IV.

Access of Moisture. — A fourth condition ne-
cessary to germination is the access of moisture.
Seeds will not germinate if they are kept perfectly
dry. Water, therefore, or some liquid equivalent
From rain to it, is essential to germination. Hence rain is
watering.3 always acceptable to the farmer or gardener, imme*
diately after he has sown his seeds ; and if no rain
falls, recourse must be had, if possible, to artificial
watering. But the quantity of water applied is
not a matter of indifference. There may be too
little, or there may be too much. If there is too
little, the seed dies for want of moisture ; if there

* Families des Plantes, vol. i. p. 84.

4

SECT. I. CONDITIONS.

is too much, it then rots. The case is not the
same, however, with all seeds. Some can bear but
little moisture, though others will germinate even
when partially immersed ; as was proved by an
experiment of Du Hamel's, at least in the case of
Peas, which he placed merely upon a piece of wet
sponge, so as to immerse them by nearly the one
half, and which germinated as if placed in the soil.
But this was found to be the most they could bear ;
for when totally immersed in the water they rotted.*
There are some seeds, however, that will germinate S
even when wholly submersed. The seeds of Aqua-
tics must of necessity germinate under water ; and
Peas have been also known to do so under certain
conditions.

SUBSECTION V.

Access of Atmospheric Air. — A fifth condition No gernu-

.... r nation in

necessary to germination, is the access of atmos- vacuo.
pheric air. Seeds will not germinate if placed in
a vacuum. Ray introduced some grains of Lettuce
seed into the receiver of an air-pump, which he
then exhausted. The seeds did not germinate.
But they germinated upon the re-admission of the
air, which is thus proved by consequence to be ne-
cessary to their germination.-)'

The experiments of Homberg do indeed seem
to militate somewhat against this conclusion. They
are recorded in the Memoirs of the French Aca-
* Phys. des Arb. liv. ii. chap. viii. + Phil. Trans. No. xiii.

*O GERMINATION OF THE SEED. CHAP. I,

demy>fbr the year 1669; and the inference deduced
from them is, that seeds in general do not germi-
nate if deprived of atmospheric air; but that Cress-
seed, Lettuce-seed, and a few others will germinate
even in the vacuum of an air pump. But the same
experiments, when afterwards repeated by Boyle,
Muschenbrock, and Boerhaave, with a much better
apparatus, did not confirm the latter part of the
result. On the contrary, they tended all to prove
that no seed germinates in the vacuum of an air-
pump ; and that in the cases of germination men-
tioned by Homberg, the vacuum must have been
very imperfect.

The same experiments were again repeated by
Saussure the younger,* who says that the seeds of
Peas gave indications of germination in vacuo in
the course of four days, but never effected any de*
velopement of their parts beyond the first appear-
ance of the radicle. But is this a sufficient proof
that germination had been really begun ? Perhaps
it might have been nothing more than merely the
effect of the water with which the Peas were moist-
ened, distending their parts ; and perhaps we
should conclude upon the whole, that in a perfect
vacuum no seed will germinate ; but that in the
most perfect vacuum hitherto formed by human art
some seeds may germinate.

filucida- Such were the discoveries of phytologists con-
pneumatic cerning the agency of atmospheric air in the pro-

ehemistiy. *. Saus gur ]a Vo> d]a> j§ sect {<

SECT. I. CONDITIONS. i

cess of germination, at a period when the study of
mechanical pneumatics was but yet in its infancy.
It was not yet foreseen that chemistry, lending its
aid to the developement of the causes of the phe-
nomena of vegetable life,, was to elucidate by means
of pneumatical discovery, the mysteries of germi-
nation. But this has proved to be the fact. The
discovery of the several gases, and of their various
chemical properties, has contributed more than all
other circumstances put together, to explain and
elucidate the phenomena of vegetation. The first By

... . . * . Scheele,

experiments on this obscure but interesting subject

are those of Scheele ; who discovered soon after an(lolhers-
the introduction of pneumatic chemistry, that
Beans did not germinate in any kind of gas1 in-
differently ; but that oxygene gas is necessary to
the process. Achard afterwards proved that no
seed will germinate in nitrogene gas, or carbonic
acid gas, or hydrogene gas, except when mixed
with a certain proportion of oxygene gas ; and
hence concluded that oxygene gas is necessary to
the germination of all seeds_> and the only con-
stituent part of the atmospheric air which is ab-
solutely necessary.

The experiments of M. Achard were afterwards Who find
repeated and confirmed by a number of other
chemists, particularly Cruickshank and Saussure,
who found that seeds will not only not germinate
in nitrogene gas, but will die if put into it even
after germination has been begun, at least if the

12 GERMINATION OF THE SEED. CHAP. I.

radicle only is developed.* Senebier found also
that seeds will not germinate in an artificial atmos-
phere that does not contain at least one eighth part
of its bulk of oxygene ; but that the most favour-
able proportion is when it contains one fourth
part.'f- It has been ascertained, however, that seeds
will germinate even in an atmosphere of pure
oxygene, though not so readily as when presented
in a state of mixture or combination with other
gases. It cannot indeed be necessary that the
oxygene consumed in germination should be pre-
sented to the seed in an uncombined state ; as is
obvious from the natural agency of the atmospheric
air, as well as from direct experiment. Humboldt
found that the process of germination is accelerated
by means of previously steeping the seed in water
impregnated with oxy muriatic acid.^ Cress-seed
treated in this manner germinated in the space of
three hours, though its ordinary period of germi-
nation is not less than thirty-two hours. The ex-
periment was afterwards repeated by Saussure, with
a similar result ; and may be regarded as perfectly
correct. Thus it is known that this acid parts very
readily with its oxygene. The cause, then, of the
rapid germination of the Cress-seed is obvious ; and
the proof that the oxygene does not require to be

* Saussure sur la Vcg.

f Mem. sur 1'Influ. de 1'Air, Nich. Journ. 1801

I Journ, de Phys. xlvii. p. 63,

*ECT. I. CONDITIONS. 1

presented to the germinating seed in an uncom-
bined state, incontrovertible.

In all cases of germination, however, the pre- And ai-

•n f Al waYS !>•-

sence of oxygene is necessary. Jbor even of those ce«sary,
seeds that germinate in water, the germination takes
place only in consequence of the oxygene which the
water contains in an uncombined state. Saussure
introduced into a recipient placed over mercury,
a quantity of boiling water, into which, when it
was cooled down to a proper temperature, he in-
troduced also some grains of Peas, together with
a few seeds of Alisma Plant ago, and Polygonum
amphiblam. They exhibited no symptoms of ger-
mination when the quantity of water introduced
was not more than seven or eight times the weight
of the grains. But when the weight of the water
was an hundred or two hundred times more than
that of the grains, they then germinated ; and the
radicle was developed in proportion to the quantity
of water employed. The solution of the pheno-
menon is as follows : — the boiling had not yet de-
prived the water of the whole of the oxygene it
had originally contained in an uncombined state ;
and it required but to be presented in sufficient
abundance to effect the germination of the seed.*

But the period necessary to complete the pro- Period of
cess of germination is not the same in all seeds, I
even when all the necessary conditions have been
furnished. Some species require a shorter, and
* Sausfure, sur la Veg, chap. i. sect. i.

14 GERMINATION OF THE SEED. CHAP. I.

others a longer period. The Grasses arc among
the number of those plants whose seeds are of the
most rapid germination ; then perhaps cruciform
plants ; then leguminous plants ; then labiate
plants ; then umbelliferous plants ; and in the
last order rosaceous plants, whose seeds germinate
the slowest. The following table indicates the pe-
riods of the germination, of a considerable variety
of seeds as observed by Adanson.*

Da\s.

Wheat, Millet seed 1

Spinage, Beans, Mustard 3
Lettuce, Anise seed. ... 4

Melon, Cucumber, ") Hyssop 30

Cress-seed. 3

Radish, Beet-root .... 6
Barley 7

Days.

Orache 8

Purslain 9

Cabbage . , . . 10

Parsley 40or50

Almond, Chesnut,Peach 1 year
Rose, Hawthorn, Filbert 2 yrs.

SECTION II.
Physical Phenomena.

WHEN a seed is committed to the soil under the
conditions that have been just specified, it begins,
for the most part, soon after to inhale or imbibe
air and moisture, and to expand and augment in
volume. This is uniformly the first symptom of
incipient germination, though not always an in-
fallible symptom ; because the seed may swell with

* Fam. des Plant, torn. i.

SECT. II. PHYSICAL PHENOMENA. 35

moisture merely by being soaked in water, though
the vital principle should be totally extinct. But Evolution
the first infallible symptom of germination is to be aide,6 *
deduced from the prolongation of the radicle be-
yond the extent to which it would attain merely
in consequence of soaking. In the latter case the
augmentation of the radicle is limited by the
extent and capacity of its envelopes, or by the
quantity of moisture necessary to its saturation ;
or by causes inducing incipient putrefaction. But
in the former case its augmentation is circumscribed
by no such limits : for it not only assumes a
swoln and distended appearance in consequence of
the absorption of moisture ; but acquires an addi-
tional and progressive increase in the actual assi-
milation of nutriment, bursting through its proper
integuments, and directing its extremity down-
wards into the soil. (PL IX. Fig. 1 and 2.)

The next step in the process of germination is Of the co-
the evolution of the cotyledon or cotyledons, unless }
the seed is altogether acotyledonous, or the coty-
ledons hypogean. (PL IX. Fig. 2.)

The next step, in the case of seeds furnished Of the
with cotyledons, is that of the extrication of the p
plumelet, or first real leaf, from within or from
between the cotyledon or cotyledons, and its ex-
pansion in the open air. (PL IX. Fig. 3 and 4.)

The last and concluding step is the developement And stem,
of the rudiments of a stem, if the species is fur-

16 iERMlNATlON OF THE SEED. CHAP. J.

nished with a stem, and the plant is complete.
(PL IX. Fig. 3 and 4.)

The above general remarks are founded on the
evidence of the following particular observations.
In a season the most favourable to vegetation,
Malpighi sowed some seeds of the Gourd. At the
end ef the first day the seeds were considerably
swoln, and the envelopes so much moistened that
a fluid oozed out of them when pressed with the
finger. A hole was also discoverable in the enve-
lopes at the summit of the seed, through which the
moisture seemed to be conveyed to the cotyledons,
that had already begun to assume the form of se-
minal leaves. At the end of the second day the
interior membrane seemed to be somewhat torn,
and the plantlet somewhat extended, exhibiting on
a transverse section taken about the middle, longi-
tudinal fibres and tracheae, as well as utricles, bark,
and pitli. The radicle was also distinctly visible.
At the end of the third day the exterior membrane
had become brownish, and its utricles more dis-
tended ; the radicle had burst its integuments ;
and the plumelet had begun to expand. At the
end of the fourth day the plantlet had perceptibly
augmented in size. The radicle was covered with
protuberances from which the lateral branches were
to issue ; and the interior envelope was somewhat
shrivelled, but still covering the seminal and other
leaves, in which the nerves were now perceptible.

SECT. II. PHYSICAL PHENOMENA. I 7

At the end of the sixth day the leaves of
plumelet had escaped from the seed, though still
contained within the cotyledons, being soft but
perceptibly covered with hairs. At the end of the
ninth day the plantlet had wholly escaped from its
integuments, though the plumelet was still enve-
loped in the seminal leaves, yellowish in its ap-
pearance, but gradually assuming a tinge of green,,
At length its extrication was effected, and the ra-
dicle converted into a root, and the rudiments of
a stem developed ; and on the twentieth day the
plant was complete.*

In the course of the summer Ledermuller sowed
some grains of Rye in a good soil. At the end of
an hour the embryo was perceptibly swollen, and a
protuberance distinguishable from which the radicle
was to issue. At the end of the second hour the
radicle was discernible. At the end of twenty-
four hours the embryo had escaped from its inte-
guments. On the second day the fibres of the
root had augmented, but the leaves had not ap-
peared. On the fourth day the first leaf (which
means, as I should think, the cotyledonous sheath
of Gaertner) began to appear above ground; its
colour was red. On the fifth day it had grown to
the length of an inch, and its colour was now green ;
and on the sixth day the second leaf appeared.

In both of the above cases the first visible effect
was the swelling of the seed in consequence of the
* Anat. Plant. Pars altera.

VOL. It. C

GERMINATION OF THE SEED. CHAP. I.

absorption of moisture. But it was not yet pre-
cisely ascertained by what particular medium the
moisture had entered ; whether by the whole of the
surface of the envelopes, or only by a particular point.
The latter part of the alternative was soon ren-
dered the most probable.

Mr. Gleichen, having steeped some peas in water
for the space of twenty-four hours, observed that
when they were pressed between the fingers the
water issued from the scar. It seemed therefore
likely that it had also entered by the scar, and in
order to ascertain the fact he covered the scar of a
few seeds with wax, and then put them in water.
But the result was that they did not absorb so
much moisture in several days, as they had ab-
sorbed without the varnish in so many hours. He
observed also that peas with the scar varnished did
not germinate. It followed therefore that water
penetrates the seed chiefly by the scar. A slight
degree of doubt, however, seems to have been at-
tached to this conclusion in consequence of some
experiments of Senebier, who in repeating those
of Gleichen found that seeds did not refuse to
germinate, even when the scar was luted. But as
he acknowledges at the same time that he was
not quite certain whether his lute was water-tight,
it is to be presumed that Gleichen's experiments
were correct.

The moisture then necessary to germination pe-
netrates the seed chiefly by the scar; but partly

4

SECT. II. PHYSICAL PHENOMENA. \Q

also, no doubt, by the foramen, where it exists, and
partly by the surface of the envelopes.

But how is the moisture, which is absorbed at
the scar or otherwise, transmitted to the plantlet,
the radicle of which exhibits the first certain
symptoms of germination ? Does it enter the plant-
let immediately ? or is it conveyed to it through
the medium of some particular channel ? It was
early suspected that the moisture destined to give
developement to the plantlet first passes through
the medium of the cotyledons. This opinion was
founded upon the apparent adaptation of the co-
tyledons for the purpose both of absorbing and
transmitting moisture, in consequence of their soft
and fleshy texture, and of the vessels dispersed
throughout their substance, which, after uniting at
last into one bundle, are incorporated into the very
body of the plantlet, and are by Grew regarded
as the seminal root.* They are sometimes visible
even before germination has taken place ; but par-
ticularly after it has made some progress. On the
surface of the transverse section of the lobes of the
Bean, after it has been well soaked in water, or
after its germination has been begun, they appear
in the form of small spots or specks ; and on the
surface of the longitudinal section, or even on the
natural and inner surface of the lobes, their va-
rious ramifications may.be traced, fewer as they
approach their point of union with the radicle, and

* Anat. of Plants, book i. sect. 24.
C 2

20 GERMINATION OF THE SEED. CHAP. I.

branching out into minuter divisions as they recede
from it.

It passes But it remained to be proved by experiment that
the cotyle- the above are the vessels through which moisture
is conveyed to the plantlet. It was thought that
the fact might be ascertained by means of moisten-
ing the germinating seed with a coloured fluid,
which was accordingly done by Gleichen, Bonnet,
and Senebier, who found as tho result of their re-
spective experiments, that the fluid had tinged the
vessels of the lobes.* This was a presumptive
evidence of their use, but was not quite decisive;
for it was still possible that the fluid might have
entered by the radicle, and then passed into the
lobes. But when Bonnet moistened only part of
the cotyledons with a coloured fluid, he found the
plantkt tinged also. The fact seemed now satis-
factorily ascertained ; but other expedients were
also adopted with a view to prove or confirm it.
The cotyledons were cut off altogether, and the
plantlet thus committed to the soil. This experi-
ment had been made indeed by Malpighi at a much
earlier period, though not with the same view.-|~
But the result was the same in both cases. The
plant perished under the experiment. It perished
even when the cotyledons were cut off after ger-
mination had made some progress ; or if it did not
absolutely perish it remained stunted and dwarfish.

* Scneb. Fhys. Veg. vol. iii. p. 363.
t Anat, Plant. Pars altera, p. 18.

SECT. II. PHYSICAL PHENOMENA. 21

But it had been also observed that seeds which
have lost their cotyledons by means of the depre-
dations of insects do not germinate ; and that ve-
getation also ceases if the plant is too soon deprived
of its cotyledons or seminal leaves, even after the
radicle has become a perfect root.* It follows
therefore that the nutriment necessary to the de-
velopement of the plantlet either originally exists
in, or intermediately passes through, the coty-
ledons.

But if the nutriment destined to the support of First to
the plantlet passes through the cotyledons, to what
part of the plantlet is it first conveyed ? This is
to be ascertained by tracing the fibres dispersed
throughout the lobes, to their point of union and
junction with the plantlet, which according to the
most accurate dissection is the upper extremity of
the radicle.-^ The nutriment therefore destined
to the support of the plantlet first enters the radicle,
and is afterwards conducted to the plumelet. Eller,
indeed, has maintained that there are vessels in the
seed passing immediately from the cotyledons to
the plumelet. But later anatomists have not been
able to discover them. Even the patient and in-
defatigable Hedwig could find no traces of any-
such vessels. It is to be presumed therefore that
they do not exist. But a still stronger ground of
presumption is that, in the phenomena of the ger~

* Seneb. Phys. Veg. p. 373.

t Crew's Anat. of Plants, book. i. sect. 23.

22 GERMINATION OF THE SEED. CHAP. 1.

ruination of the seed, the radicle is always un-
folded the first, and the plumelet only in a sub-
sequent stage of the process.* It follows therefore
that the plumelet derives its nourishment from the
radicle, as the radicle from the cotyledons.
Which But this is by no means the most singular cir-
by descent, cumstance relative to the developement of the parts
in question. The constant and unerring uniformity
with which the radicle and plumelet respectively
exert themselves to gain the position and situation
best suited to the future developement of their
parts, is a phenomenon exhibiting more that is
calculated to excite the admiration of the phy-
tologist.

Invinci- If a seed or nut of any kind is placed in the
proper soil, with the apex of the radicle pointing
downwards, the radicle as it elongates will descend
in a perpendicular direction, and fix itself in the
earth ; and the plumelet issuing from the opposite
extremity of the seed, will assume a vertical di-
rection and ascend into the air. This is the natural
order of the developement of the seminal germe ;
and from the relative situation of its respective
parts, the mode of its developement does not seem
to be at all surprising. But the circumstance ex-
citing our surprise is that the radicle and plumelet
will still continue to effect their developement in
the same manner, however differently the seed may
have been deposited in the soil : for if its posi-
* Grew's Anal, of Plants, book i. sect. 37.

SECT. II. PHYSICAL PHENOMENA. 2$

tion shall accidentally happen to have been in-
verted, so as that the radicle shall be above and
the plumelet beneath, the former will then bend
itself down till it gets a hold of the soil ; and the
latter will, in like manner, bend itself upwards till
it reaches the air. And no human art has ever
been able to make them assume contrary direc-
tions, or to convert the one into the other, as the
root and branch of the vegetating plant may be
afterwards converted. Du Hamel, whom no phy-
tologist has surpassed in the invention of expedients
to unmask or to control the operations of the ve-
getative principle, instituted a variety of experi-
ments with a view to effect this conversion, but
failed in them all. He first placed an acorn be-
tween two wet sponges suspended from the ceiling
of his room, so as that the radicle was uppermost
and the plumelet undermost. The result however
was that the radicle after bursting its integuments
assumed a downward direction, and the plumelet
in its turn an upward direction, till each had
gained its natural position. He then filled a tube
with earth, and planted also an acorn in it, ip ail
inverted position. But the radicle and plumelet
had no sooner escaped from their envelopes than
they began to assume their natural direction as
before. He then filled another tube with earth,
of a diameter so small, that an acorn, when placed
in it, touched the sides of the tube. It was planted
in its natural position, and allowed to remain so

£4 GERMINATION OF THE SEED. CHAP. I.

till the radicle appeared. The tube was then in-
verted and the radicle immediately began to bend
itself downwards. The tube was again inverted,
and the radicle resumed its original direction.*
How ac- < Such is the invincible tendency of the radicle
for by the to fix itself in the soil, and of the plumelet to es-

phytolo- caPe *nto *^e a*r" U°w is this tendency to be
gists. accounted for ? A great many conjectures have
been offered in reply to the inquiry, but without
having done much to elucidate the subject. Some
have attributed the phenomenon to the excess of
the specific gravity of the juices of the radicle be-
yond that of the juices of the plumelet, which in
their progress upwards were supposed to be reduced
by elaboration to a light vapour. But this is not
known to be the fact, or rather it is known not to
be the fact, and consequently forms no ground of
argument. Others have attributed it to the re-
spective action of the sun and earth ; the former
attracting the leaves and stem, and the latter at-
tracting the root. But it happens rather unfortu-
nately for this conjecture, that the phenomenon is
exactly the same, even when seeds are made to ger-
minate in the dark. Du Hamel made the experi-
ment in a dark room ; and obtained the same result
as in the light. The influence of the sun was then
transferred to that of the air, which was thought to
have some peculiar attraction for the plumelet,
which the earth had not. But the attraction of the
* Phys. des Arb, liv, ii. chap, vl

\?m.

SECT. II. PHYSICAL PHENOMENA. 25

air was just as mysterious as that of the sun, and
the subject as much in want of elucidation as
before,

Dr. Darwin has, however, endeavoured to account By Dar*
for the phenomenon chiefly upon the principle now
specified. Supposing the radicle to be naturally
stimulated by moisture, and the cotyledons and
plumelet by air, the difficulty is, as he thinks, easily
solved ; each being thus elongated in the direction
in which it is most excited.* This hypothesis is
no doubt sufficiently ingenious ; but is by no means
to be regarded as a satisfactory solution of the dif-
ficulty. For at this rate all cotyledons ought to rise
above ground, which all cotyledons do not. And
all seeds ought to germinate either in the earth or
water ; though many of them will germinate in
neither; but on trunks or stumps of trees, and
even on the surface of the bare and flinty rock.
The radicle ought also to elongate itself in a ver*
tical direction, if it could be but lodged in the
lower surface of an insulated mass of mould, so as
to have the moisture of the mass and grand ex-
citing cause of its elongation placed above it. Now
this must inevitably have happened in one or other
of Du Hamel's repeated inversions, and yet the
result was always the same ; the radicle having
uniformly bent itself downwards in the direction of
the surface of the earth.

* fhytologia, $ect. ix,

9-6

GERMINATION OF THE SEED. CHAP. I.

By Mr. Knight has also more recently attempted to

account for the descent of the radicle upon the old
but revived principle of gravitation ; strengthened,
as he no doubt thinks, by the result of the follow-
ing experiments. Beans which were made to ger-
minate, after being fastened in all positions to the
circumference of an upright and revolving wheel,
that performed 150 revolutions in a minute, uni-
formly directed the radicle outwards from the
centre, and the plumelet inwards to the centre.
Beans that were so fastened to a horizontal and
revolving wheel, protruded their radicles obliquely
outwards and downwards ; and their plumelets
obliquely inwards and upwards. These effects Mr.
Knight regards as resulting from the centrifugal
influence of the wheel's motion counteracting that
of gravitation, which is consequently in his opinion,
in the natural situation of the seed, the cause of
the radicle's descent.* But if gravitation acts so
very powerfully upon the radicle, why will it not
condescend to exert its influence upon the plumelet
also, which, if not so heavy as the radicle, is at
least specifically heaver than atmospheric air ? And
why does it make an exception in favour even of
some radicles. The radicle of the seeds of the
Missletoe, though adhering merely to the under
surface of a bough and originally protruding itself,
as it must sometimes unquestionably do, in the
direction of the earth's surface, will yet in oppo-
* Nichol, Journ. vol. xiv. p. 4-10.

S£CT. III. CHEMICAL PHENOMENA. *27

sition to the power of gravitation, bend itself up-
wards till it reaches the bough, and insinuate itself
into the very substance of the bark above it ? Till
these questions can be satisfactorily answered they
must be regarded as presenting an insurmountable
obstacle to the adoption of Mr. Knight's hypothesis.

If I were to offer a conjecture in addition to the Ascribed
many that have been already offered, I should say tive prm-
that the invincible tendency of the radicle to fix Clp e
itself in the earth or other proper soil ; and of the
plumelet to ascend into the air, arises from a power
inherent in the vegetable subject, analogous to what
we call instinct in the animal subject, infallibly
directing it to the situation best suited to the ac-
quisition of nutriment and consequent develope-
ment of its parts. And upon this hypothesis we
include all varieties of plants whatever, parasitical
as well as others ; for let them attach themselves to
whatever substance they will, to them it still affords
a fit and proper soil.

SECTION III.
Chemical Phenomena.

THE chemical phenomena of germination con- As effect
sist chiefly in the changes that are effected in the
nutriment destined for the support and develope-
ment of the embryo till it is converted into a plant.
It was already shown that this nutriment either

28 GERMINATION OF THE SEED. CHAP. I.

passes through the cotyledons, or is contained in
them ; because the embryo dies when they are pre-
maturely cut off. But the farinaceous substance of
the cotyledons, at least in exalbuminous seeds, is a
proof that they themselves contain the nutriment.
They are to be regarded therefore as repositories of
the food destined for the support of the embryo in
its germinating state. And if the seed is furnished
with a distinct and separate albumen, then is the
albumen to be regarded as the repository of food,
and the cotyledon or cotyledons as its channel of
conveyance. But the food thus contained in the
albumen or cotyledons is not yet fitted for the
immediate nourishment of the embryo. Some pre-
vious preparation is necessary ; some change must
be effected in its properties. And this change is
effected by the intervention of chemical agency.
"Action of It has been shown in the foregoing section that a
inoisture. see(^ is no sooner placed in the earth than it begins
to imbibe moisture. But the moisture thus im-
bibed isjmnrellTately absorbed by the cotyledons or
albumen, which it readily penetrates, and on which
it immediately begins to operate a chemical change,
dissolving part of their farina, or mixing with their
oily particles and forming a sort of emulsive juice;
the consequence of which change is a slight degree
of fermentation, induced, perhaps, by the mixture of
the starch and gluten of the cotyledons in the water
which they have absorbed, and indicated by the
extraction of a quantity of carbonic acid gas as well
i

SECT. III. CHEMICAL PHENOMENA. 2

as by the smell and taste of the seed.* This is the
commencement of the process of germination,
which takes place even though no oxygene gas is
present.-^ But if no oxygene gas is present, then
the process stops ; which shows that the agency of
oxygene gas is indispensable to germination.

Accordingly, when oxygene gas is present it is Of inhal-
gradually inhaled by the seed ; and the farina of the
cotyledons is found to have changed its savour.
Sometimes it becomes acid^J but generally sweet,
resembling the taste of sugar ; and is consequently
converted into sugar or some substance analogous to
it. This is a further proof that a degree of fermen-
tation has been induced ; because the result is pre-
cisely the same in the process of the fermentation of
Barley when converted into malt, as known by the
name of the saccharine fermentation ; in which
oxygene gas is absorbed, heat and carbonic acid
evolved, and a tendency to germination indicated
by the shooting of the radicle. The effect of
oxygene therefore in the process is that of convert-
ing the farina of the albumen or cotyledons into a
mild and saccharine food, fit for the nourishment of
the infant plant.

But in what manner does the oxygene operate,
and on what principles of the seed does it act ?
Does it act merely as a stimulant to principles which

* Seneb. Phys. Veg. vol. iii. p. 408.
f Thomson's Chemistry, vol. iv. p. 374.
£ Saussure sur la Veget.

$0 TERMINATION OF THE SEED. CHAP. I.

the seed already contains ; or, does it form a com-
bination with the substance of the seed, and
identify itself with the germinating embryo? Or,
does it abstract from the seed any particular princi-
ple of its composition, and so effect the change that
follows ? The suppositions contained in these ques-
tions have each had their defenders and opponents ;
though there is now, as I believe, but one opinion
on the subject.

According Humholdt thought that the oxygene acts merely
"11 as a stimulant ; and his opinion was founded upon
the fact that seeds germinate faster, as it appeared, in
pure oxygene gas than in common air ; but particu-
larly when steeped in water impregnated with oxy-
muriatic acid, according to his own discovery. But
this conclusion, though sufficiently plausible at first
sight, is by no means sufficiently warranted by the
premises. In pursuit of facts, however, to esta-
blish and confirm it, Humboldt was fortunate
enough to stumble upon discoveries of some im-
portance. He found that seeds brought both from
the East and West Indies, which had constantly re-
fused to germinate at Vienna, germinated very
readily when treated with oxy muriatic acid, even
after having been kept for a period of from twenty
to thirty years. This fact seemed extremely
favourable to his opinion, and contributed no doubt
to give it a considerable currency at the time, which
on some part of the Continent perhaps it still re-
tains, as we find his conclusion to have been adopts

SECT. til. CHEMICAL PHENOMENA. 3 1

ed, and his language re-echoed, by Professor Will-
denow of Berlin, without seeming to know any
thing of the facts and experiments by which it has
been disproved.*

M. Hollo was of opinion that the oxygene con- Rollo,
sumed in the process of germination is in part
absorbed by the grain, and assimilated to its sub-
stance ; and in part employed along with the carbon
of the seed to form carbonic acid. His opinion
was founded on the following fact which he had
observed in watching the process of the germination
of some grains of Barley confined in an artificial
atmosphere. When the seeds were made to germi-
nate in pure oxygene gas, the oxygene gradually
disappeared, and its place was found to be occupied by
carbonic acid gas.-}~ The above conclusion seemed
to follow almost necessarily from the premises;
but as the phenomena had not yet been subjected
to any particular analysis, it could only be regarded
in the light of a conjecture.

In this stage of inquiry Saussure the younger, Saussure
having directed his attention to the subject, per- younger.
ceived that the only means of ascertaining the fact
was that of comparing the quantity of oxygene gas
consumed with the quantity entering into the com-
position of carbonic acid gas evolved during the
process. If the quantity of the former proved to
be greater than that of the latter, it was to be

* Princ. of Bot. Engl. Trans, p. 257.
f Anna!, du Chira. vol. xxv. p. 37-

32 GERMINATION OF THE SEED. CHAP. f.

inferred that a portion of oxygene gas had been
actually assimilated to the substance of the seed.
But if the two quantities proved to be constantly
equal, then it was to be inferred that the oxygene
gas had not been assimilated to the substance of
the seed, but only employed for the purpose of
abstracting from it part of its carbon in the forma-
tion of carbonic acid gas.*

It was obvious that the ascertaining of the respec-
tive quantities must have given much elucidation to
the subject ; and the difficulty of ascertaining them
seemed not to be great. Lavoisier had discovered
that oxygene in combining with carbon by conbus-
tion undergoes no perceptible alteration of volume,
and that 100 cubic inches of carbonic acid gas con-
tain 98 cubic inches of oxygene gas. But the result
of combination from germinating seeds must be
precisely the same as from combustion ; it was
easy therefore to ascertain the quantity of oxygene
extricated along with the carbonic acid. Accord-
ingly M. Saussure instituted a set of experiments
to ascertain the proportion between the quantity
of oxygene inhaled and the quantity evolved in
the carbonic acid. The grains or seeds employed
were those of Peas, Beans, Barley, Lettuce, and
Cress, and the issue was as follows : In an at-
mosphere of 100 cubic inches of common air,
known to contain about 21 cubic inches of oxygene,
and 79 of nitrogen, when a number of these seeds
* Sur. la Yegct. chap. i. sect, ii.

SLCT. HI. CHEMICAL PHENOMENA. 3$

were made to germinate, it was found that if 14
cubic inches of carbonic acid gas were formed
during the process, seven cubic inches of oxygene
gas remained uncombined in the atmosphere ; and
if sever* cubic inches of carbon acid gas were formed
during the process, then 14 cubic inches of oxygene
gas remained uncombined in the receiver. From
which it followed, undeniably, that the quantity of
carbonic acid gas that was evolved during the process
of germination was precisely equal to the quantity that
had been absorbed during the same process. There Whose
was consequently no actual fixation of oxygene in confirmel
the seed ; and the oxygene it had inhaled was em-
ployed solely for the purpose of diminishing the
quantity of its carbon. The change then effected
in the farina of the albumen or cotyledons, by which
it is converted into a nutriment fit for the infant
plant, consists in diminishing the proportion of its
carbon, and in augmenting, by consequence, that of
its oxygene and hydrogene principles which the
seed is also known to possess.*

It had been ascertained that seeds may be made Germina-

r tion in

to germinate in an atmosphere or pure oxygene gas ; pure Oxy*
and from the experiments of M. Humboldt it ap- Sene-
peared that their germination is thus sooner effected
than in an atmosphere of common air. But Saussure>
in repeating some comparative experiments on this
subject, did not find any difference in the respective
periods of germination. The only perceptible dif-

* Saussure sur la Vegetation, chjp. i. sect. iii.
VOL. II. D

S4 GERMINATION OF THE SEED. CHAP. I*,

ference was in the comparative lengths of the radi-
cles ; the radicles of such as had been made to
germinate in pure oxygene gas having made less
progress in the same period of time than the
radicles of such as had been made to germinate in
atmospheric air.

Applica- This may be accounted for in two ways ; the
boniSl" oxygene in its pure state might have abstracted too
detrimen- great a quantity of carbon from the seed ; or the
carbonic gas evolved in too great abundance might
have been prejudicial to the developement of the
infant plant. For it has been found that carbonic
acid gas is not useful to vegetables in general, ex-
cept in proportion as they can decompose it ; and
seeds before the developement of the plumelet do
not seem capable of effecting that decomposition ;
and in short it seems that the application of car-
bonic acid, in almost any proportion, retards rather
than accelerates the commencement of germina-
tion.*

Dose of It was further remarked, by Saussure, that dif-
ferent species of seeds require different doses of
oxygene to excite germination. The quantity con-
sumed by the seeds of Beans and Lettuce, before
tKe commencement of germination, seemed to be
equal, and was estimated at the lOOdth part of their
weight. But the quantity consumed before that period
by grains of Wheat, Barley, and Purslain, which
seemed also to be equal, was only about the lOOOdth
* Saussure sur la Vegetation, chap. i. sect. iii.

SECT. III. CHEMICAL PHENOMENA. 35

part of their weight. The carbon lost at the same
time is only about the one third part of these quanti-
ties ; and the oxygene gas consumed is in proportion
to the weight of the seeds, not in proportion to their
size or number.

But it has been said that seeds will germinate Experi-
even in mediums deprived of oxygene ; and the mediums
germination of seeds placed in water, or in the va- J ^y!
cuum of an air pump, has been adduced as a proof. Sene-
It is plain, however, from the experiments already
related, that the germination of the seeds so situated
was effected merely in consequence of the uncom-
bined oxygene yet remaining in the water, or of
the oxygene remaining in the receiver that was not
yet completely exhausted. These alleged proofs
therefore are of no value. But Huber and Senebier
give an account of experiments in which grains are
said to have germinated in atmospheres even of
pure nitrogene and hydrogene gas.^ Carbonic acid
gas was also evolved during the process as in other
cases of germination ; and it was asked, whence is
the oxygene derived necessary to the formation of
the carbonic acid ? Senebier accounts for it upon the
principles of the decomposition of the water con-
tained in the seed ; which he seems to be extremely
anxious to establish. But Saussure, who being Unsuc-
somewhat sceptical on the subject was induced to
repeat the experiments that had given the above
result, or to institute others of a similar nature, has
* Senebier, Phys. Veget. vol. ill. p. 338.
D '2

36 GERMINATION OF THE SEED. CHAP. I.

proved in the most satisfactory manner that no
seeds will germinate in an atmosphere of pure nitro-
gene or hydrogene gas ; and that the seeming ex-
ceptions to the rule may be all accounted for from
the action of the uncombined oxygene contained in
the water in which the seed had been placed or
previously steeped. For so far are seeds from ger-
minating in an atmosphere of nitrogene gas that,
even after germination has been begun and the
radicle developed, they will die if put into it, at
least unless the leaves of the plantlet have been
developed also. The seeds of Peas, Watercress,
and of Polygonum amphibium, when put into an
atmosphere of nitrogene gas in this state, all died
without any further developement of parts.* Seeds
immersed in water do indeed evolve a portion of
carbonic acid, of carburetted hydrogene, and of nitro-
gene. But these are elements which separate from
the substance of the seed during fermentation, and
are observed only when it is found to be in a state
of putrefaction. If seeds are placed in a small
quantity of water and confined in hydrogene gas,
the volume of their atmosphere is considerably
diminished, and the remainder is carbonic oxide.
But this also is the effect of putrefaction. The car-
bonic acid which they form of their own substance
is decomposed by the hydrogene with the assistance
of the caloric disengaged in fermentation. Water
is thus formed, and the carbonic acid, deprived of
* Saussure sur Ja Vegetation, chap. vi. sect. i.

SECT. III. CHEMICAL PHENOMENA. $7

part of its oxygene, is converted into carbonic
oxide. * The phenomena therefore observed by
Huber and Senebier were not the result of germina-
tion, but of putrefaction ; and there is no proof of
the decomposition of the water contained in the
seed during the progress of germination, because
there is no hydrogene or oxygene evolved during
that process.

There were other grounds, however, on which Decompo-
the decomposition of water was supposed to be ef- water. °
fected during the germination of the seed. M. Rollo
had observed that many seeds during the process
of germination are converted from a mucilage into
a sort of sugar ; but finding that this effect never took
place in mediums deprived of oxygene, and knowing
that sugar contains more oxygene than mucilage,
he concluded that oxygene was in this case either
abstracted from the atmosphere, or obtained from
the decomposition of the water with which the seed
was surrounded. It could not be abstracted from
the atmosphere of the seed, because the quantity of
oxygene in the atmosphere of the germinating seed
remains the same ; it was therefore of necessity
obtained from the decomposition of water with
which the seed was surrounded.^

But the same effect will follow if we suppose, Doubtful,
with Saussure, that the carbon of the seed is dimi-

* Saussure sur la Vegetation, chap. vi. sect. iv.
t Annal. do Chim. vol. xxv. p. 44.

38 GERMINATION OF THE SEED. CHAP. I.

nished ; which will also agree better with the actual
phenomena of germination. It must be confessed,
however, that this explanation is still liable to some
objection ; because it has been found that any given
weight of seeds dried after germination contain
more carbon than the same weight of seeds dried
before germination. But by the indefatigable in-
dustry and profound investigations of M. Saussure,
this objection has been obviated also.

If a seed of any kind whatever, dried as much
as possible, is weighed and made to germinate by
the aid of water in a close vessel, and if after ger-
mination it is taken and dried again, it will be found
to have lost in weight even beyond the allowance
for carbon which it must have lost, and mucilage
which it may have lost, during the process. This is
the fact according to the repeated experiments of
Saussure.* To what cause is it to be attributed ?
Saussure attributes it to a diminishing of the water
formerly existing in the seed in a fixed state.
Disproved. A quantity of Peas which had been gathered for
some years, and placed for some weeks in a stove
heated to 2O° of Reaumur, were found to weigh
200 grains. They were then made to germinate in
a large vessel placed over mercury, containing about
five times their weight of water with an atmosphere
of common air. When the process of germination was
completed, 4«5 cubic inches of carbonic acid gas were
found to have been formed in the receiver, which, ac-
* Sur. Ja Veg. chap. i. sect. iii.

SECT. III. CHEMICAL PHENOMENA.

cording to the calculation of Lavoisier, contain 0'85
parts of a grain of carbon. The water which was
now evaporated, left as a residue 075 parts of a
grain of mucilage and extract ; and the seeds, which
were again dried, evolved during the process a
quantity of carbon in the form of carbonic acid
very nearly equal to the quantity lost in germina-
tion. The seeds therefore ought to have weighed
200 — 0-85 + 2 — 075 = 197-5 grains ; but their
actual weight was only 18Q grains. Now besides
the principles already mentioned they could have
lost only water, and their loss in that respect
amounted to 8'5 grains. It remained, however, to
be determined whether the loss was occasioned by
means of the process of fermentation, or by that of
the drying of the seeds ; and the result of the in-
quiry was that it was occasioned by the latter : be-
cause when the process of vegetation was allowed
to proceed to double, or even triple the time, the
loss of weight remained the same ; but when the
period of drying was prolonged the loss of weight
was more considerable.

Seeds, then, during the process of drying after
germination, lose under the modification of water
part of their oxygene and hydrogene, which in ef-
fect augments the proportion of their carbon. It
follows therefore of necessity, that any given weight
of seeds dried after germination contains more car-
bon than the same weight of seeds dried before
germination. But the direct agency of oxygene is

GERMINATION OF THE SEED. CHAP. I.

still the same both in germination and putrefaction
— namely, the abstraction of carbon. The results
are indeed different. But their difference is easily
accounted for ; because in the latter case the seed
loses a considerable quantity of water, or of hydro-
gene and oxygene, which in the former case it
retains ; and hence the proportion of its carbon is
of necessity augmented.

Such are the phenomena, physical or chemical,
observable in the germination of the seed ; air and
moisture are absorbed from the soil or atmosphere
by the scar, foramen, or envelopes. Their agency is
immediately exerted on the farina of the albumen
or cotyledons ; and a food is thus prepared for the
nourishment of the tender embryo, to which it
passes through the medium of the vessels of the
cotyledons, or, as they have been also denominated,
the seminal root. The radicle gives the first indi-
cations of life, expanding and bursting its integu-
ments, and at length fixing itself in the soil : the
plumelet next unfolds its parts, developing the ru-
diments of leaf, branch, Land trunk : and finally
the seminal leaves decay and drop off; and the
embryo has been converted into a plant capable of
abstracting immediately from the soil or atmosphere
the nourishment necessary to its future growth.

41

CHAPTER II.

OF THE FOOD OF THE VEGETATING PLANT.

IF the embryo when converted into a plant and Derived
fixed in the soil is now capable of abstracting from earth and
the earth or atmosphere the nutriment necessary t
its growth and developement, the next object of
the phytologist's inquiry will be that of ascertaining
the substances which it actually abstracts, or the
food of the vegetating plant,

What then are the component principles of the
soil and atmosphere ? The investigations and dis-
coveries of modern chemists have done much to
elucidate this dark and intricate subject. Soil, in
general, may be regarded as consisting of earths,
water, vegetable mould, decayed animal substances,
salts, ores, alkalies, gases, perhaps in a proportion
corresponding to the order in which they are now
enumerated ; which is at any rate the fact with re-
gard to the three first, though their relative propor-
tions are by no means uniform. The atmosphere has
been also found to consist of at least four species of
elastic matter — nitrogene, oxygene, carbonic acid
gas, and vapour ; together with a multitude of mi-
nute particles detached from the solid bodies occu-
pying the surface of the earth, and wafted upon
the winds. The two former ingredients exist in

2

42 FOOD OF THE VEGETATING PLANT. CHAP. K

the proportion of about four to one ; carbonic acid
gas in the proportion of about one part in J 00 ;
and vapour in a proportion still less.* Such then
are the component principles of the soil and at-
mosphere, and sources of vegetable nourishment.
Byseleo But the whole of the ingredients of the soil and
atmosphere are not taken up indiscriminately by
the plant and converted into vegetable food, be-
cause plants do not thrive indiscriminately in all
varieties of soil. Part only of the ingredients are
selected, and in certain proportions ; as is evident
from the analysis of the vegetable substance given
in the foregoing book, in which it was found that
carbon, hydrogene, oxygene, and nitrogene, are the
principal ingredients of plants ; while the other in-
gredients contained in them occur but in very small
proportions. It does not, however, follow that these
ingredients enter the plant in an uncombined and
insulated state, because they do not always so exist
in the soil and atmosphere ; it follows only that
they are inhaled or absorbed by the vegetating
plant under one modification or another. The plant
then does not select such principles as are the most
abundant in the soil and atmosphere ; nor in the
proportions in which they exist ; nor in an uncom-
bined and insulated state. But what are the sub-
stances actually selected ; in what state are they
taken up ; and in what proportions ? In order to
give arrangement and elucidation to the subject, I
* De Luc on Evaporation.

SECT. I. WATER.

shall consider it under the six following heads :
Water, Gases, Vegetable Extracts, Salts, Earths,
Manures.

SECTION I.
Water.

As water is necessary to the commencement of Absorbed
vegetation so also is it necessary to its progress. ro0t. G
Plants will not continue to vegetate unless their
roots are supplied with water ; and if they are kept
long without it the leaves will droop and become
flaccid, and assume a withered appearance. Now
this is evidently owing to the loss of water. For if
the roots are again well supplied with water the
weight of the plant is increased, and its freshness
restored. But many plants will grow, and thrive,
and effect the developement of all their parts, if the
root is merely immersed in water, though not fixed
in the soil. Lilies, Hyacinths, and a variety of
plants with bulbous roots, may be so reared, and are
often to be met with so vegetating ; and many
plants will also vegetate though wholly immersed.
Most of the marine plants are of this description.
It can scarcely be doubted therefore that water
serves for the purpose of a vegetable aliment.

But if plants cannot be made to vegetate without
water ; and if they will vegetate, some, when partly
immersed without the assistance of soil ; and some

4

44 FOOD OF THE VEGETATING PLANT. CHAP. I.

even when totally immersed so as that no other

food seems to have access to them ; does it not

Thought follow that water is the sole food of plants, the soil

solelfood being merely the basis on which they rest ; and

of plants. the rcceptacie Of their food ? This opinion has had

many advocates ; and the arguments and experi-

ments adduced in support of it were at one time

thought to have completely established its truth.

It was indeed the prevailing opinion of the seven-

teenth century, and was embraced by several phi-

losophers even of the eighteenth century ; but its

ablest and most zealous advocates were Van Hel-

mont, Boyle, Du Hamel, and Bonnet, who con-

tended that water, by virtue of the vital energy of

the plant, was sufficient to form all the different

substances contained in vegetables.

Theopi- Van Helmont planted a Willow weighing 50lb.

nioncoun- . ...

tenanced in an earthen vessel containing a known quantity
^ eart^ which had been previously dried in an

of Van oven. He moistened it with distilled water, or

Helmont,

with rain water, and took care to prevent any ac-
cession of other earth. At the end of five years
the plant was taken up and weighed. Its weight,
together with that of all its leaves, was l6Q4-lb.
and the weight of the earth, only two ounces less
than at first, giving an accession of JJQ-flb., which
is to be accounted for only from the water with
which the earth was moistened. Hence it was con-
eluded that water is the sole food of plants ; the
two ounces of earth lost being regarded as bearing

SECT. I. WATER. 45

too small a proportion to the increased weight of
the willow to deserve any notice in the calcu-
lation.*

Boyle dried a quantity of earth in an oven, which Boyle,
after having weighed he put into an earthen pot.
He then sowed some Gourd seed in the earth and
watered it with spring or rain water. A plant was
ultimately produced that weighed three pounds ;
and in a subsequent experiment, a plant that
weighed four pounds ; and yet the weight of the
earth, when dried and weighed again, was not per-
ceptibly diminished. This seemed to give weight
to the foregoing conclusion.

Du Hamel placed some bulbous roots merely in DuHamer,.
moss or wet sponges, and they vegetated ; and n^
Beans and Peas when so treated even flourished
and produced fruit.*}- Bonnet in repeating the ex-
periments of Du Hamel had the same result; and
in trying its operation upon vines, found that they
produced excellent grapes. Nothing further seemed
necessary to determine the point at issue ; and it
was accordingly believed that water is the sole food
of plants, and that the other substances which they
may contain are formed merely from the water, by
virtue of the vital energy of the plant.

But though these experiments have the appear-
ance of being somewhat decisive, yet there are
others by the same experimenters which are not
quite so favourable to the opinion they were in-

* Phys. des Arb. liv. v. chap. i. + Ibid.

40 FOOD OF THE VEGETATING PLANT. CHAP. I.

tended to support. Du Hamel reared in the above
manner plants of the Horse-chesnut and Almond
to some considerable size, and an Oak till it was
eight years old.* And though he informs us that
they died at last only from neglect of watering ;
yet it seems extremely doubtful whether they
would have continued to vegetate much longer
even if they had been watered ever so regularly:
for he admits in the first place that they made less
and less progress every year ; and in the second
place, that their roots were found to be in a very
bad state.

Which are But if they had even continued to vegetate, still
dent to the experiments were insufficient to decide the

def^dtethe point in question. Their insufficiency was first
pointed out by Bergman in 1773, who showed from
the experiments of Margraif, that in one pound of
rain water there is contained one grain of earth.-f-
Earth, therefore, must have been absorbed along
with the. water; so that even the boasted experi-
ment of Van Helmont, on which so much stress had
been laid, amounted to nothing. For the rain-
water employed in the experiment must have con-
tained in it as much earth as could have been well
expected to exist in the willow at the end of five
years. And if not, then it is easy to point out
an additional source of supply : for it has been
shown by Hales and others, that unglazed earthen
vessels when placed in the earth, will readily ab-
* Phys cles Arb. liv. v. chap. i. I Opusc. vol. v. p. 92.

SECT. I. WATER. 47

sorb moisture;* so that, according to Mr. Kirwan's
remark, the earthen vessel in which the willow
was planted must have absorbed moisture from the
surrounding soil, impregnated with whatever sub-
stances the earth contained. The access of earth
therefore is accounted for without the joint efforts
of the water and vital energy of the plant, and no
satisfactory proof alleged of the similar formation of
other substances.

The subject was afterwards investigated by Has- Inference
senfratz, who saw the insufficiency of the foregoing fratz that
proofs, and objected to them because no account
was given of the proportions of carbon at the com- ^
mencement and termination of the respective ex-
periments. Did not the carbon of the plant in-
crease also as well as its other ingredients ? And
yet the carbon could not be supposed to be formed
from the water. To clear up this point he analyzed
the bulbs of the Hyacinth and of several other
plants, together with a number of Kidney-beans,
and Cress-seeds, with a view to discover the quan-
tity of carbon they contained, and consequently
by calculation the quantity contained in any given
weight of similar bulbs or seeds. He then made
a number of each to vegetate in pure water, some
within doors, and others in the open air, having
first ascertained their weight. They germinated,
grew up, and flowered ; but produced no seed.
They were afterwards gathered, leaves and all, and
* Veg. Stat.vol. i. p. 5.

48 FOOD OF THE VEGETATING PLANT. CHAP. L

subjected to a chemical analysis, the result of which
was, that the carbo« contained in each was some-
what less than the quantity which existed in the
bulb or seed from which the plant had sprung.*
From this singular and unexpected result Hassen-
fratz concluded, as he was no doubt well entitled,
that water is not the sole food of plants ; because
plants vegetating in pure water receive no accession
of carbon, without which they cannot produce
perfect seeds.

pedi-.ced But although this conclusion is certainly right,
nedus^re- ye^ ^le premises from which it is deduced are as
mnes, certainly wrong ; and yet they seem to have been
admitted by some phytological inquirers who were
no doubt well qualified to judge of their value.
But at this rate we must believe that Du Hamel's
Oak of eight years old, and Van Helmont's Willow
that was increased in weight by upwards of lOOlb.,
contained no more carbon, even including all the
leaves that fell annually, than the original acorn
or original plant; and we must believe that the
seeds of aquatics contain as much carbon as the
plants they produce, together with all their seeds,
which is an absurdity. Senebier saw the impossi-
bility of admitting the premises, and rejected them ;
Which but Saussure put them again to the test of ex-
rejects^ periment. Having gathered some plants of the
Mentha piperita, he found that 100 parts in weight
of the green vegetable substance were reduced by
* Annal. de Chim. vol. xiii. p. 178.

SECT. I. WATER. 49

drying to 40.2Q, which were found by experiment
to contain 10.96 of charcoal. He then took a
number of plants of the same species, and placed
them by the roots in bottles filled with distilled
water ; exposing them to the sun on the outside of
a window, but sheltering them from the rain.
After ten weeks of vegetation the ICO parts of
mint weighed in their green state to 21 6 parts,
which were reduced by drying to 62. They had
augmented therefore in dried vegetable matter
21.71 parts; but they had augmented also in their
quantity of carbon : for the 62 parts of dried
vegetable substance furnished 15.78 of charcoal.*
A similar result was obtained from a similar expe- Though
riment upon Beans, from which we may infer the bfishes'the
accuracy of Saussure, and the consequent inaccuracy
of Hassenfratz, who was no doubt misled by some
circumstance not taken into the account. Perhaps
the plants on which he made his experiments were
not sufficiently exposed to the light of the sun ;
so that if he corrected one error he committed also
another. While we maintain, therefore, that water
is not the sole food of plants, and is not convertible
into the whole of the ingredients of the vegetable
substance, even with the aid of the vital energy ;
We must at the same time admit that plants, though
vegetating merely in water, do yet augment the
quantity of their carbon.

* Sur la Veg. chap. ii. sect« v.
VOL. II. X

5Q FOOD OF THE VEGETATING PLANT. CHAP. I.

SECTION II.

Gases.

WHEN it was found that water is insufficient to
constitute the sole food of plants, recourse was next
had to the assistance of the atmospheric air ; and
it was believed that the vital energy of the plant
is at least capable of furnishing all the different in-
gredients of the vegetable substance, by means of
decomposing and combining, in different ways, at-
mospheric air and water. But as this extravagant
conjecture is founded on no proof, it is conse-
quently of no value. It must be confessed, however,
Atmos- that atmospheric air is indispensably necessary to
nidTs1Cenir *^e health an^ vigour of the plant, as may be seen
sable to ve- by looking at the different aspects of plants exposed
to a free circulation of air, and plants deprived of
it : the former are vigorous and luxuriant ; the
latter weak and stunted. It may be seen also by
means of experiment even upon a small scale. If
a plant is placed under a glass to which no new
supply of air has access, it soon begins to languish,
and at length withers and dies ; but particularly if
it is placed under the exhausted receiver of an air-
pump ; as might indeed be expected from the
failure of the germination of the seed in similar
circumstances. According to the experiments of
Saussure, plants of Peas, though completely deve-
loped and furnished with their leaves, died in the

SECT. II. GASES. 51

space of three days, when put into the exhausted
receiver of an air-pump whether in the shade or the
sun. But plants with thick and succulent leaves
seem capable of supporting vegetation in vacuo, at
least if exposed to the sun. A plant of the Cactus
Opuntia lived more than a month in this state
without showing any symptoms of decay, except
that the epidermis seemed dry, which again reco-
vered its freshness, however, in the atmospheric
air.* And though plants with thin leaves gene-
rally died under the experiment, yet there were
exceptions even among them. A plant of the Po~
tygonum Persicaria lived for six months in the
vacuum of an air-pump, and was at the end of the
experiment as fresh and vigorous as at the be-
ginning, with the exception of two or three leaves
near the root, which were withered. The same was
the case also with plants of the Epilobium molle,
Epilobium hirsutum, Ly thrum Salicaria, and Inula
dy sent erica. They were placed in the light, but not
so as to receive the direct rays of the sun ; to which
when they were exposed they withered, even though
the rays were but feeble.

It has been said indeed that roses will remain
longer fresh in vacuo than in common air. But
this is a mistake. In the latter case the petals, no
doubt, fall sooner; but this is merely the natural
effect of vegetation, and not a symptom of decom-
position or decay, as is proved from the inspection
* Sur la Veg. chap. vi. sect. v.
E 2

FOOD OF THE VEGETATING PLANT. CHAP. I.

of the petals even after they have fallen, in their
still exhaling an agreeable though faint odour. But
in the former case, though the petals remain longer
attached to the plant, and retain their form and
colour, and appear to be fresh and fragrant; yet
when you put them to the test, they are found to
exhale a strong and fetid odour, the sure symptom
of inward putrefaction.5*

But although we admit the great utility of at*
mospheric air, and even its absolute necessity to
the support of vegetable life, we must not attribute
to it more than is due, and conclude without proof
that air, together with water, forms the whole of
vegetable aliment. And yet in support of this
doctrine it has been said that many plants do
evidently effect the developement of their parts,
without the aid of any other nourishment beyond
that of air, rains, and dews ; and the Mosses and
Lichens, and some other tribes of plants have been
quoted as affording examples.

It must be admitted no doubt that plants of slow
growth and tenacious of life, such as many of the
Mosses, and some of the succulent plants, do in-
deed effect the developement of their parts, without
the aid of any other nourishment beyond what they
derive from the atmosphere. But plants of rapid
growth, such as annuals, can never effect that de-
velopement without the aid of nourishment derived
from the soil. Saussure tried the experiment upon
* Saus. sur la Veg. chap. vi. sect. v.

SECT. II. GASES. 53

Beans, Peas, and Cresses, by placing them in horse-
hair, or in pure sand, and moistening them with
distilled water. They grew indeed, and some of
them even flowered, but never produced perfect
seeds.* And Giobert and Hassenfratz, who had
made similar experiments, had also similar results.
It is plain therefore that some essential principle
of nourishment was wanting, which is furnished
by the soil ; and that atmospheric air and water
are not the only principles constituting the food of
plants.

But as in germination so also in the progress of Or at least
vegetation, it is part only of the component prin- compo- U'
ciple of the atmospheric air that are adapted to the nent ParU-
purposes of vegetable nutrition, and selected by
the plant as a food. Let us take them in the order
of their reversed proportions.

SUBSECTION I.

Carbonic acid gas. — In the process of the ger-
mination of the seed, the effect of the application
of carbonic acid gas was found to be altogether
prejudicial. But in the process of subsequent ve- Beneficial
getation its application has been found, on the con- t[
trary, to be extremely beneficial. Plants will notlun
indeed vegetate in an atmosphere of pure carbonic
acid, as was first ascertained by Dr. Priestley, who
found that sprigs of mint growing in water, and
* Sur la Veg, chap, viii. sect, i.

54 FOOD OF THE VEGETATING PLANT. CHAP. I.

placed over wort in a state of fermentation, gene-
rally became quite dead in the space of a day, and
did not even recover when put into an atmosphere
of common air.*

But Dr. Percival, of Manchester, observed that
a plant of Mint, immersed in water by the root and
exposed to a current of atmospheric air mixed with
carbonic acid gas, was more vigorous and luxuriant
than a plant of the same species similarly situated
and exposed to a current of pure atmospheric air.-j"
Improving upon this hint, Saussure made some
experiments with a view to determine the dose of
carbonic acid gas which, being mixed with atmos-
pheric air, is the most favourable to vegetation.
Having made some Peas to germinate in water till
they acquired the height of four inches and weighed
about twenty grains, he then placed a number of
them in glasses filled with water by threes, so as
that the roots only were immersed, and introduced
them into receivers filled with different mixtures
of common air and carbonic acid gas. They were
situated so as to receive the direct rays of the sun,
moderated when too intense. The mean augmen-
tation in weight of such as were placed in pure
atmospheric air, and exposed during ten days to
the sun, was eight grains to each plant. Such as
*vere exposed to the sun, in an atmosphere of pure
carbonic acid gas, faded and withered away without
any further developement. In an atmosphere con-
* Priestley on Air, vol. i. p. 36. i Manch. Trans, vol. ii,

SECT. II. GASES. 55

taining three-fourths or two-thirds of its volume of
carbonic acid gas, they withered also ; but in an
atmosphere containing only one half of its volume
of carbonic acid they lived seven days. And in an
atmosphere containing but one fourth of its volume
of the same gas, they lived ten days and augmented
their weight by five grains. Lastly, the mean aug-
mentation in weight of such as were placed in an
atmosphere of common air, containing one-twelfth
part of carbonic acid gas, was eleven grains. This
experiment was repeated frequently, and was found
to yield a uniform result; the plants always suc-
ceeding better than in pure atmospheric air. Car-
bonic acid gas, therefore, is of great utility to the
growth of plants vegetating in the sun, as applied
to the leaves and branches ; and whatever increases
the proportion of this gas in their atmosphere, at
least within a given degpee, forwards vegetation.*

But the result was not the same when the plant But j>re-
was placed in the shade; the smallest dose of car-i^lhe °
bonic acid gas, in addition to that of the atmospheric shade>
air, being then prejudicial to vegetation. This
appears from the following experiments : Plants
kept in the shade, and placed in an atmosphere con-
taining one-fourth of its volume of carbonic acid
gas, died on the sixth day ; and when the atmos-
phere contained only one-twelfth of its volume of
this gas, they lived indeed ten days, but weighed
only three grains ; while those in pure atmospheric
* Sur la Veg. chap, ii, sect. v.

56 FOOD OF THE VEGETATING PLANT. CHAP. I.

air weighed five grains. Carbonic acid gas, there-
fore, as applied to the leaves and branches of plants,
is prejudicial to their vegetation in the shade, if
administered in a proportion beyond that in which
it exists in atmospheric air.

Its influ- But it is also beneficial to the growth of the
pHedtot£eplant when applied to the root. This Saussure as-
certained by experiment also. Two boards pierced
with a number of holes were made to float in two
vessels filled, one with distilled water, and the
other with water impregnated with carbonic acid
gas. On each of these boards was placed a number
of Peas that had been lately made to germinate in
distilled water. Their radicles at the commence-
ment of the experiment were two lines and a half
long. At the end of ten days the roots in contact
with the distilled water were longer by five inches,
than those in contact with the acidulated water;
and the stalks and leaves were developed in the
same proportion. But at the end of a mpnth the
plants vegetating in the acidulated water had ac-
quired the same dimensions as the others, and at
the end of six weeks had considerably surpassed
them. It follows, therefore, that carbonic acid gas
as applied to the roots of plants is also beneficial
to their growth, at least in the more advanced
stages of vegetation.

SEC?. II. GASES.

SUBSECTION II.

Oxygene. — As oxygene is essential to the com-
mencement and progress of germination ; so also
it is essential to the progress of vegetation. This
is clearly proved by the following experiments of
Saussure : Having pulled up some young plants of
the Horse-chesnut, furnished with their leaves and
weighing about 4 60 grains, he introduced their roots,
which were nearly a foot in length, into receivers
of about sixty cubic inches in capacity, and luted
the base of the stem to the neck of the receiver.
Into one of the receivers, each of which contained
a quantity of distilled water, he introduced twenty-
eight cubic inches of nitrogene which was in con-
tact with the upper part of the root, while the
under part was immersed in the water. Into
another he introduced an equal quantity of hy-
drogene ; and into a third an equal quantity of
carbonic acid. The plant whose root was in con-itsbene-
tact with the carbonic acid died in the course of flu^'at
eight days : the others lived a fortnight, but had *£plied to
not diminished the volume of their atmosphere.
But plants which were placed at the same time in
a similar apparatus, furnished with atmospheric air,
gave a very different result ; for at the end of three
weeks when the experiment was stopped, they were
still fresh and vigorous^ and the volume of their at-

58 FOOD OF THE VEGETATING PLANT. CHAP. I.

mosphere was diminished.* It is obvious, then,
that the presence of oxygene is beneficial to the
growth of the vegetable,, at least as applied to the
root ; because that is the only principle which had
access to the root in the last experiment, which
had not access to it in the former.

Branch But oxygene is beneficial to vegetation as applied
also to the other parts of the plant as well as to the
root. Branches of woody plants taken in the
spring, immediately before the expansion of the
bud, and enclosed in receivers filled with common
air, together with a small quantity of water to
supply them with moisture, developed their leaves
as if attached to the parent plant. And this de-
velopement was effected solely by means of the
oxygene contained in the receiver ; for in mediums
deprived of oxygene no developement took place.-}-
The presence of oxygene therefore is necessary to
the developement of the leaves.

Flower But it is necessary also to the developement of
the flower and fruit. The flower-bud will not ex-
pand if confined in an atmosphere deprived of
oxygene ; nor will the fruit ripen. Flower-buds
confined in an atmosphere of pure nitrogene faded
without expanding. A bunch of unripe Grapes
introduced into a globe of glass which was luted
by its orifice to the bough, and exposed to the sun,
ripened without effecting any material alteration
* Sur la Vcg. chap. iii. sect. vi. f Ibid. sect. viii.

SECT. II. GASES. 59

in its atmosphere. But when a bunch was placed
in the same circumstance, with the addition of a
quantity of lime, the atmosphere was contaminated,
and the Grapes did not ripen.* Oxygene therefore
is essential to the developement of the vegetating
plant.

But how is this beneficial effect operated? IsHowef-
the oxygene actually inhaled into the body of
the plant and converted into a vegetable food ; or
is its operation merely external ? Oxygene is ac-
tually inhaled, at least under certain circumstances.
Saussure having suspended a plant of the Cactus
0 punt ia, after sun-set, in a receiver containing
forty-eight cubic inches of atmospheric air deprived
of its carbonic acid, but of which six cubic inches
were displaced by the leaves, found early next
morning, after making the necessary corrections
relative to change of temperature and pressure,
that the atmosphere of the plant had diminished in
volume four cubic inches. The remaining air when
examined contained but T^V of oxygene, though
before the introduction of the Cactus it had con-
tained -iW °f the same gas. It follows, therefore,
that the diminution of quantity had affected the
oxygene only. But the oxygene did not exist in
the atmosphere of the plant under any combination
whatever ; for the application of lime water gave
no indications of the presence of carbonic acid.
The oxygene of the atmosphere, therefore, must
* Sur la Veg. chap. iii. sect. ix.

60 FOOD OF THE VEGETATING PLANT. CHAP. I.

have been abstracted by the leaves of the Cactus.
From which it also follows that the leaves of vege-
tating plants do actually inhale oxygene, at least in
course of the night.

Similar experiments on vegetating plants gave
similar results, but the quantity of oxygene ab-
stracted was not always in the same proportion. In
the present case it was very considerable, amounting
to three-fourths of the volume of the leaves, while
in other cases it was often not more than one-half
of their volume.

SUBSECTION III.

Nitrogene. — Though nitrogene gas constitutes
by far the greater part of the mass of atmospheric
air, it does not seem capable of affording nutriment
Notave- to plants; for as seeds will not germinate in it,
food, 6 so neither will plants vegetate. It was regarded,
however, as constituting a vegetable food by some
of the earlier pneumatic chemists, particularly by
Priestley, who found, as it seems, that some sprigs
of Mint on which he had made the experiment
vegetated better in phlogisticated air than in either
dephlogisticated or common air;* and hence he
inferred that phlogisticated air, the nitrogene of
modern chemists, serves as a vegetable food.-f- In
this opinion he was followed by Ingenhoutz,^

* Priestley on Air, vol. iv. p. 327. f Ibid. vol. v. p. 13.
I Exper. sur les Yeg. vol. ii. p. 146.

6

SECT. II. GASES. 6l

whose experiments appear to have given a similar
result ; contradicted, however, by the result of the
experiments of Senebier, Woodhouse, and Saussure,
on the same subject.

Branches of Populus nigra and Satix alba,
whose leaf-buds were just ready to open, were in-
troduced by Saussure into an atmosphere of ni-
trogene both in the shade and sun. They effected
no farther developement of parts, but were found
to be in a state of putrefaction after a period of five
days ; but in an atmosphere of common air they
readily effected their developement, and continued
to vegetate for many weeks. Roses and Lilies ga-
thered two or three hours before their expansion,
and treated in the same manner, gave similar
results.

It must be admitted, however, that many plants Though
will continue to vegetate for a time in an atmosphere p°^s will
of nitrogene gas, when their leaves have been pre- fo
viously developed ; but they are such plants only
as present a great extent of surface, and consume
but little oxygene in the shade. A plant of the
Cactus Opuntia, nourished with water and placed
in an atmosphere of nitrogene gas exposed to the
influence of the sun, was found capable of sup-
porting vegetation for the space of three weeks ;
but it was greatly injured by the experiment, and
in the shade it lived only five days. A plant of
the Scdum telephium when treated in the above
* Sur la Veg. chap, vi. sect. ii.

62 FOOD OF THE VEGETATING PLANT. CHAP. f.

manner gave a similar result ; and yet these plants
vegetated to an indefinite time in an atmosphere of
common air.

From the above experiments it seems to follow
that nitrogene gas, at least in its pure state, is un-
favourable to vegetation ; but particularly in the
shade. And yet there are some plants, such as the
Vinca minor, Ly thrum Salicaria, Inula dysenterica,
Epilobium hirsutum, and Polygonum Persicaria,
that seem to succeed equally well in an atmosphere
of nitrogene gas as in an atmosphere of common
air. A plant of the Lythrum Salicaria, selected
for the purpose of experiment, was put into a re-
ceiver containing sixty-five cubic inches of nitrogene
gas, of which it displaced about one-eighth of a
cubic inch. It had its roots immersed in about an
ounce of water, and was exposed to the rays of the
sun, when it grew and became so luxuriant that it
was more than once necessary to remove it into a
larger receiver. But this luxuriance of growth
seems incompatible with the previous conclusion.
At the end of two months however, when the ex-
periment was stopped, the receiver was found to
contain the same quantity of nitrogene gas as at
the beginning. The plant could have derived no
nutriment, therefore, from its atmosphere. But
this was the case also in all of the preceding ex-
amples. There was no diminution in the original
quantity of nitrogene introduced into the receiver.
It follows therefore that nitrogene gas, at least in

SECT. II. GASES. 63

its pure state, is not only incapable of affording a
vegetable aliment, but is not even inhaled into the
plant. But nitrogene is found in almost all vege-
tables, particularly in the wood, in extract, and in
their green parts. Whence then is their nitrogene
derived ? From the extractive principle of vegetable
mould.

SUBSECTION IV.

Hydrogene Gas. — A plant of the Epilobium
hirsutum^ which was confined by Priestley in a
receiver filled with inflammable air or hydrogene,
consumed one-third of its atmosphere and was still
green.* Hence Priestley inferred that it serves as Thought
a vegetable food, and constitutes even the true and iey toTe'a
proper pabulum of the plant. But the experiments
of later phytologists do not at all countenance this
opinion. Saussure introduced a plant of the Ly-
thrum Salicaria into a receiver containing sixty
cubic inches of hydrogene gas, and exposed it to
the sun. Its vegetation was perhaps somewhat
more vigorous than that of plants confined in an
atmosphere of nitrogene ; but it had abstracted
no nourishment from its atmosphere, nor effected
any material change upon it. For at the end of
five weeks of experiment, when its asmosphere was
fired by the electric spark along with the proper
quantity of oxygene, the result was the formation

* Priestley on Air, vol. iv. p, 323.
5

64 *OOD OF THE VEGETATING PLANT. CHAP. I.

of water. The volume of its atmosphere was in-
deed diminished during the period of its vegetation;
but this is to be accounted for by another cause, as
will appear in the course of tracing the progress of
vegetation.*
But foond Our conclusion therefore must be that hydrogene

to be un- ,, • i i

favourable is unfavourable to vegetation, and does not serve aa
tatiot?" the food of plants. But hydrogene is contained
in plants as is evident from their analysis ; and if
they refuse it when presented to them in a gaseous
state, in what state do they then acquire it? To this
question it is sufficient for the present to reply, that
if plants do not acquire their hydrogene in the state
of gas, they may at least acquire it in the state of
water, which is indisputably a vegetable food, and
of which hydrogene constitutes one of the com-
ponent parts.

SUBSECTION V.

Carbonic Oxide. — When plants were confined

by Saussure in atmospheres of carbonic oxide, they

Unfavour- required nearly the same condition to support ve-

able to ve- . , . .. .

getation. getation, and exhibited nearly the same pheno-
mena as in nitrogene. Such as were deprived of
their green parts died in the course of a few days.
The vegetation of Peas whose leaves were com-
pletely developed was languid in the sun, and did
not succeed at all in the shade. The Epilobium

* Sur la Veg. chap. vi. sect. 4.

SECT. III. EXTRACT. 65

hirsutum, Lythrum Salicaria, and Polygonum
Per sic aria, vegetated indeed as in common air:
but at the end of six weeks of experiment, they
had neither decomposed the oxide constituting
their atmosphere, nor diminished its quantity.* It
cannot, therefore, be regarded as favourable ta ve-
getation.

SECTION III.

^ Vegetable Extract.

WHEN it was found that atmospheric air and
water are not even conjointly capable of furnishing
the whole of the aliment necessary to the develope-
ment of the plant, it was then alleged that, with
the exception of water, all substances constituting
a vegetable food must at least be administered to
the plant in a gaseous state. But this also is a con-
jecture unsupported by proof; for even with re-
gard to such plants as grow upon the barren rock,
or in pure sand, it cannot be said that they receive
no nourishment whatever besides water, except in a
gaseous state. Many of the particles of decayed
animal and vegetable substances which float in the
atmosphere and attach themselves to the leaves,
must be supposed to enter the plant in solution
with the moisture which the leaves imbibe ; and
so also similar substances contained in the soil must

* Sur la Veg. chap. vi. sect. iii.
VOL. II. F

66 FOOD OF THE VEGETATING PLANT. CHAP. I.

be supposed to enter it by the root : but these sub-
stances may certainly contain vegetable nourish-
ment ; and they will perhaps be found to be taken
up by the plant in proportion to their degree of
solubility in water and to the quantity in which
they exist in the soil. Now one of the most im-
portant of these substances is vegetable extract.
As a com- When plants have attained to the maturity of
part of their species, the principles of decay begin gradually
mouldble to operate upon them, till they at length die and are
converted into the dust from which they sprang, thu&
resembling the animal to whom they afford support.
The substance to which they are finally converted
has been denominated vegetable mould. And this,
as might be expected, constitutes a considerable
proportion of the soil. The chance then is, that it
, is again converted into vegetable nourishment, and
Is soluble again enters the plant. But it cannot wholly enter
andhence the plant because it is not wholly soluble in water.
byStheable ^art °^ lt> however, is soluble and consequently
root. capable of being absorbed by the root, and that is the
substance which has been denominated extract.

Saussure filled a large vessel with pure mould of
turf, and moistened it with distilled or rain water
till k was saturated. At the end of .five days, when
it was subjected to the action of the press, 10,000
parts in weight of the expressed and filtered fluid
yielded by evaporation to dryness 20 parts of extract.
In a similar experiment upon the mould of a kitchea-
garden which had been manured with dung, 10,000

SECT. III. EXTRACT. 6

parts of fluid yielded 10 of extract. And in a simi-
lar experiment upon mould taken from a well cul-
tivated corn-field, 10,OOO parts of fluid yielded four
parts of extract.* Such was the result in these
particular cases*

But the quantity of extract that may be separated
from pure mould formed by nature upon the sur-
face of the globe is not in general very consider-
able. After 13 decoctions, all that could be separated
from mould of this sort was about TV of its weight ;
and yet this seems to be more than sufficient for the
purposes of vegetation : for a mould containing this
quantity was found by experiment to be less fertile,
at least for Peas and Beans, than a mould that con-
tained only one half or two thirds the quantity.^

But if the quantity of extract must not be too
much, neither must it be too little. Plants that
were put to vegetate in mould deprived of its ex-
tract, as far as repeated decoctions could deprive it,
were found to be much less vigorous and luxuriant
than plants vegetating in mould not deprived of its
extract : and yet the only perceptible difference
between them is, that the former can imbibe and
retain a much greater quantity of water than the
latter.;}:

From this last experiment, as well as from theConsti
great proportion in which it exists in the living viable
plant, it evidently follows that extract constitutes a [^n°n"

nitrogen e.

* Sur la Veg. chap. v. sect. ii. f Ibid. J Ibid.
F 2

gg FOOD OF THE VEGETATING PLANT. CHAP. II.

vegetable food. But extract contains nitrogene;
for it yields by distillation a fluid impregnated with
ammonia. The difficulty, therefore, of accounting
for the introduction of nitrogene into the vegetating
plant, as well as for its existence in the mature
vegetable substance, is done away ; for although
the plant refuses it when presented in a gaseous
state, it is plain that it must admit it along with thtf
extract.

But it seems also probable that a small quantity
of carbonic acid gas enters the plant along with the
extractive principle, as it is known to contain this
gas also. The mould analysed by Saussure was
quite dry before the commencement of the experi-
ment, and the water employed to moisten it con-
tained no carbonic acid. But the solution contained
some; for when it was mixed with lime-water,
carbonate of line was precipitated, though not in
a quantity much exceeding that of its precipitation
by spring-water in general. 100 cubic inches of
the solution yielded by experiment an air con-
taining two cubic inches of carbonic acid gas. This
is no doubt a small proportion : but it appears
from a variety of considerations, that the quantity
of this gas taken up by the roots of plants is not
great ; consequently they do not require a great sup-
from the soil.

SE€T. IV. SALTS. 6

SECTION IV.

Salts.

MOST plants are found by analysis to contain a
certain proportion of salts — such as nitrate, muriate,
and sulphate of potass or soda — as has been already
shown. How do plants acquire them ? In the
earlier periods of phytological investigation., when
every effect was attributed to the agency of the
vital principle as exerted upon the air and water
which the plant inhales or absorbs, it was thought
that the salts contained in vegetables are formed in
the process of vegetation : but this is also one of
those extravagant conjectures of which further re-
search has exposed the absurdity. The salts which Absorbed
have been detected in vegetables are known to exist tion.
in the soil. It is most likely therefore that the root
absorbs them in solution with the water by which
the plant is nourished. It is at least certain that
plants may be made to take up by the roots a con-
siderable proportion of salts in a state of artificial
solution. M. Saussure prepared ] 0 different solutions,
consisting each of 40 cubic inches of distilled water,
together with 12 grains of the peculiar salt or other
substance on which the experiment of absorption was
to be made. The first solution contained muriate of
potass ; the second, muriate of soda ; the third,
muriate of lime ; the fourth, sulphate of soda ; the

70 FOOD OF THE VEGETATING PLANT. CHAP. U

fifth, muriate of ammonia ; the sixth, acetate of lime ;
the seventh, sulphate of copper ; the eighth, crystal-
lized sugar; the tenth, vegetable extract. Plants
of Polygonum Persicaria and Bidens cannabina
were then immersed in each of these solutions with
the fpllowing result : — In the solutions of muriate of
potass, muriate of soda, sulphate of soda, nitrate of
lime, and extract, the former species vegetated in
the shade for five weeks, developing their parts ;
but in the other solutions they died in the course
of a few days. The latter species succeeded or failed
in nearly the same way. It was afterwards found
that a portion of the salts had been taken up along
with the water by wfyich they were held in solution ;
and if we suppose the quantity contained in each of
the solutions to be divided into 100 parts, the ratio
of their absorption may be shown as follows : — In
consuming one half of the water assigned to the ex-
periment, plants of the Polygonum had absorbed 14
parts of muriate of potass, 1 3 of muriate of soda, four of
nitrate of lime, J4 of sulphate of soda, 12 of muriate
of ammonia, eight of acetate of lime, 47 of sulphate of
copper, nine of gum, 2/ of sugar, and five of extract.
Plants of the Bidensh&d absorbed the several salts in
portions not very different.* But without minutely
regarding proportions, the fact is thus clearly ascer-
tained that plants are capable of taking up salts by
the root, at least when presented to them in a state
of artificial solution ; and if so, there is then reason to

* Sur la Veg. chap. viii. sect. ii.

SECT. IV. SALTS. 71

presume that salts are also taken up by the roots of
plants vegetating even in their natural habitats.

But if salts are thus taken up by the root of the Whether

1*1

vegetating plant, does it appear that they are taken f0'0edget
up as a food ? Some plants, it must be confessed, are
injured by the application of salts, as is evident from
the experiments of Saussure; but others are as
evidently benefited by it. Trefoil and Lucern have
their growth much accelerated by the application of
sulphate of lime, though many other plants are not
at all influenced by its action. The Parietaria
Nettle, and Borge, will not thrive except in such
soils as contain nitrate of lime or nitrate of potass :
and plants inhabiting the sea coast, as was observed
by Du Hamel, will not thrive in a soil that does
not contain muriate of soda.

It has been thought, however, that the salts are
not actually taken up by the root, though converted
to purposes of utility by acting as astringents or
corrosives in stopping up the orifices of the vessels
of the plant, and preventing the admission of too
much water : but it is to be recollected that the
salts in question are found 'by analysis in the very
substance of the plant, and must consequently have
entered in solution. It has been also thought that
salts are favourable to vegetation only in proportion
as they hasten the putrefaction of vegetable sub-
stances contained in the soil, or attract the humidity
of the atmosphere. But sulphate of lime is not
deliquescent ; and if its action consist merely in

72 FOOD OF THE VEGETATING PLANT. CHAP. II.

accelerating putrefaction, why is its beneficial effect
confined but to a small number of plants ?

Lastly, some writers have contended that the
salts which are found in vegetables are merely ac-
cidental in their occurrence, and not necessary to the
health or perfection of the individual ; because they
are found to exist in but a very small proportion,
both in the soil and plant : but as there are many
species in which some salts are to be met with con-
stantly and uniformly, at least if they have vegetated
in a soil in which they are found to thrive,, we can
scarcely regard their occurrence as being merely ac-
cidental, or as producing no beneficial eifect upon
the plant. But the proportion of salts lodged in
the soil is not so small as is generally believed.
Re-agents do not indeed detect a great quantity in
general ; but that is because the alkaline salts of
mould, like the alkaline salts of vegetables, are to
be discovered chiefly in the remains of combustion ;
and because the ashes of the greater part of vege-
table moulds do not readily part with their salts in
boiling water. This difficulty of solution is thought
by Saussure to be owing to a semivitrifaction that
takes place in the mould when the ashes are
abundant. An hundred parts of mould furnished by
combustion 50 parts of ashes which did not give
out their salts to boiling water. But 10O parts only
of dried extract from the same mould yielded only
14 parts of ashes ; and 10O parts of the ashes
formed with boiling water a ley which contained

SECT. IV. SALTS. 73

25 parts composed of potass in an uncombined
state, and of alkaline sulphates and muriates ;
and yet, upon further analysis, it was found that the
water had not extracted more than one half of the
salts which the ashes contained. The soil, therefore,
contains an abundant supply of salts for all the
purposes of vegetation. It may even in some cases
contain too much ; for it is to be recollected
that saline substances are beneficial to vegetation
only when applied in very small quantities. If they
are administered in great abundance they destroy
the plant.

And the argument against their utility that has
been drawn from the small proportion in which
they are found to exist in the plant itself, is al-
together inadmissible; because it is very well
known that some particular ingredient may be
essential to the composition of a body, and yet con-
stitute but a very small proportion of its mass.
Atmospheric air contains only about one part in the
lOOth of carbonic acid ; and yet no one will venture
to affirm that carbonic acid gas is merely an adven-
titious and accidental element existing by chance in
the air of the atmosphere, and not an essential
ingredient in its composition. Phosphate of lime'
constitutes but a very small proportion of animal
bodies, perhaps not one part in 500 ; and yet no
one doubts that it is essential to the composition of
the bones. But the same salt is found in the ashes

74 FOOD OF THE VEGETATING PLANT. CHAP. II.

of all vegetables ;* and who will say that it is not
essential to their perfection ?

SECTION V.
Earths.

As most plants have been found by analysis to
contain a portion of alkaline or earthy salts, so most
plants have been found to contain also a portion of
earths : and as the two substances are » so nearly
related, and so foreign in their character to vege-
table substances in general, the same inquiry has
consequently been made with regard to their origin.
Whence are the earths derived that have been found
to exist in plants ?

Whether It seems to have been the opinion of Lampadius
the'pro-111 th^ the earths contained in plants are merely the
T«S'etaUon e^ect °^ vegetation, and altogether independant of
the soil in which they grow : and extravagant as
the opinion is, it has been made to assume the sem-
blance of resting upon experiment. Lampadius
prepared, in his garden, five small beds of four feet
square in surface by one in depth ; each bed con-
sisted of a pure earth mixed with eight pounds of
cow-dung. The earths were alumine, silica, lime,
magnesia, and garden mould. They were sown
with Rye, and the produce of each was separately
* Saus. sur la Veg. chap, viii. sect. iv.

SECT. V. EARTHS. 75

reduced to ashes. But the same principles were
found in them all ; amongst which was a portion of
silica ; — -whence Lampadius concluded that the silica
found in plants is merely the result of vegetation,
having no relation whatever to the soil in which the
plants grow.

But this conclusion was by much too hasty, and
has been since shown to be most palpably erroneous ;
because Lampadius does not take into the calcula-
tion the constituent principles of the cow-dung
with which his earths were mixed, the very sub-
stance from which his plants must have derived the
greater part of their nourishment. If this precau-
tion had been taken, his conclusion must have been
very different : for it has been ascertained by Ruc-
kert that dung does actually contain a portion of
silica ;* which in the case of cow-dung will appear
the less surprising if it is only recollected that the
plants which cows principally feed on do themselves
contain a portion of silica. To the cow-dung,
therefore, with which the different earths were
manured, the origin of silica may be traced. It was
thus of necessity found in them all, though not
perhaps in an equal proportion.

Saussnre, in adverting to the experiment ofTheopi-
Lampadius, exposes indeed the absurdity of his ™°£ ab~
conclusion ; but deduces from it another which is
perhaps equally exceptionable — namely, that plants
growing in calcareous and granitic sand, mixed with
* Sur. la Vcgct. chap. ix. sect. iij.

76 FOOD OF THE VEGETATING PLANT. CHAP. IT.

the same manure or mould, will produce equal
quantities of ashes. But this supposes manures to
have the same action upon all soils, which is surely
not the fact : and if there be any manure that acts
on a calcareous soil, without acting at all on a grani-
tic soil, then the quantity of ashes will be altered
in the former case, from that very circumstance;
because the plant is now nourished not only by the
manure that was committed to the soil, but from
the original soil itself, in its state of combination
\vith the manure.

Ab«orbed The earths, then, that are contained in vegetables
lion? U a**e derived chiefly from the soil : but in what
peculiar state of combination do they enter the
vessels of the plant ? The state most likely to faci-
litate their absorption is that of their solution in
water, in which all the earths hitherto found in
plants are known to be in a slight degree soluble.

Lime is soluble in water with the aid of a little
carbonic acid, in the proportion of about -5-1-5- part
of its weight ; but it is also soluble even without
the aid of the acid,* and the solution is known by
the name of lime-water. Clay is soluble in water
by means of the mineral acids ; and also, though
very sparingly, in pure water, from which even the
filtre cannot abstract it.-f- Silica is soluble in water
by means of carbonate of potass, as is evident from
Black's analysis of the waters of Geyser in Iceland.
It is soluble also in pure water according to the
* Scneb. Phys. Veg. vol. iii. p. 17, f Ibid.

SECT. V. EARTHS. 7f

analysis of Klaproth ; and in that state of division
in which it is precipitated from its solution in fixed
alkalies, it is perfectly soluble in 1000 parts of
water.* Magnesia is soluble in water by means of
the mineral acids, and even in pure water, in very
small quantities ; requiring about 2000 times its
weight to hold it in solution.

All the earths, then, found in plants are less or
more soluble in water. And if it be said that the
proportion in which they are soluble is so very small
that it scarcely deserves to be taken into the account,
it is to be recollected that the quantity of water
absorbed by the plant is great, while that of the
earth necessary to its health is but little, so that it
may easily be acquired in the progress of vegetation.

Such is the manner in which their absorption
seems practicable : but the following experiments
afford a presumption that they are actually absorbed
by the root. Woodward took three plants of Spear-
mint, one of which he made to vegetate in distilled
or pure water ; another in river water ; and a third, in
water mixed with mould. At the commencement
of the experiment the first plant weighed 114
grains ; at the end of the experiment it weighed
155 grains, being augmented by 41 grains. The
water expended was 8863 grains, and the increase
as 1-214 +. At the commencement of the ex-
periment, the second plant weighed 18 grains, at
the end 54 grains, being augmented by 26 grains.

* Kivwan's Miner, vol. 5. p. 10.

1

78 *OOD OF THE VEGETATING PLANT. CHAP. II.

The water expended was 2493 grains, and the in-
crease as 1 : 95 +• At the commencement of the
experiment the third plant weighed Q2 grains, at
the end 376 grains, being augmented by 284 grains.
The water expended was 14Q50 grains, and the
increase as ] : 52 + .*

From the greater proportional augmentation of
the plant to which the mould had access, we may
infer the beneficial effect of the earths as applied to
the root, and perhaps the absorption of a part ; par-
ticularly as it is known that the proportion of earths
contained in the ashes of vegetables depends upon
the nature of the soil in which they grow. The
ashes of leaves of the Rhododendron ferrugineum,
growing on Mount Jura, a calcareous mountain,
yielded 43*25 parts of earthy carbonate, and only
0'75 of silica. But the ashes of leaves of the same
plant, growing on Mount Breven, a granitic moun-
tain, yielded two parts of silica, and only 16*75 of
earthy carbonate.

It is probable, however, that plants are not in-
debted merely to the soil for the earthy particles
which they may contain. They may acquire them
partly from the atmosphere. Margray has shewn
that rain water contains silica in the proportion of a
grain to a pound; which, if it should not reach the
root, may possibly be absorbed along with the water
that adheres to the leaves.

But although the earths are thus to be regarded
* Phil. Trans, vol. xxi. p. 200. Saus. sur la Vcg. chap. ix. sect. iii.

SECT. VI. MANURES. 7Q

as constituting a small proportion of vegetable food, Whether
they are not of themselves sufficient to support the n'
plant, even with the assistance of water. Giobert
mixed together lime, alumine, silica, and magnesia,
in such proportions as are generally to be met with
in fertile soils, and moistened them with water.
Several different grains were then sown in this
artificial soil, which germinated indeed, but did not
thrive; and perished when the nourishment of the
cotyledons was exhausted. It is plain, therefore,
that the earths, though beneficial to the growth of
some vegetables, and perhaps necessary to the
health of others, are by no means capable of afford-
ing any considerable degree of nourishment to the
plant.

SECTION VI.

Manures.

As the object of the preceding sections has been
that of exhibiting a brief view of the different species
of vegetable food, whether it be regarded as derived
from the soil or the atmosphere ; so the object of the
present section will be that of showing how the food
necessary to the support of the vegetating plant may
be supplied when defective, or restored when ex-
hausted : but this unavoidably involves the subject
of manures, or artificial preparations of vegetable
food, so important to the advancement of agriculture,
and consequent interest of mankind.

4

SO FOOD OF THE VEGETATING PLANT. CHAP. IT.

What im- With regard to the food of plants derived from
pyins' the atmosphere, the supply is pretty regular; at least,
in as far as the gases are coneerned ; for they are
not found to vary materially in their proportions on
any part of the surface of the globe : hut the
quantity of moisture contained in the atmosphere is
continually varying, so that in the same season you
have not always the same quantity, though in the
course of the year the deficiency is perhaps made
up. From the atmosphere, therefore, there is a re-
gular supply of vegetable food kept up by nature
for the support of vegetable life, independent of the
aid of man : and if human aid were even wanted,
it does not appear that it could be of much avail.

But this is by no means the case with regard to
Composi- soils ; for if soils are less regular in their composi-
ti°n> tnej are at ^east niore within the reach of
human management. We have already seen the
materials of which soils are composed : but what
are the proportions of the materials in soils best
suited for culture ? According to the analysis of
Bergman, the soil best suited for culture contains
four parts of clay, three of sand, two of calcareous
earth, and one of magnesia : and, according to the
analysis of Fourcroy and Hassenbratz, 921 6 parts
of fertile soil contained 305 parts of carbon, together
with 2/9 parts of oil ; of which, according to the
calculations of Lavoisier, 220 parts may be regarded
as carbon : so that the whole of the carbon contained
in the soil in question may be estimated at about

SECT. VI. MANURES. 81

525 parts, exclusive of the roots of vegetable— or to
about T'T of its weight.

Mr. Young observed that equal weights of differ-
ent soils, when dried and reduced to powder, yielded
by distillation quantities of air somewhat corre-
sponding to the ratio of their values. The air was a
mixture of fixed and inflammable airs, proceeding
probably from decomposition of the water ; but
partly, I should presume, from its capacity of ab-
stracting a portion of air from the atmosphere, which
the soil at least is capable of doing.

The following is the analysis of a fertile soil, as
occurring in the neighbourhood of Bristol. In 400
grains, there were of

Water 52

Silicious sand - 240

Vegetable fibre 5

o

extract 3

Alumine 48

Magnesia 2

Oxide of iron 14

Calcareous earth 30

Loss ' 6

Total. . . 400*

But Mr. Kirwan has shown in his Geological Fertility
Essays, that the fertility of a soil depends in a great

city

* Agricultural Magazine, April, 1808.

VOL. II. G

r Of THE

82 FOOD OF THE VEGETATING PLANT. CHAP. II.

measure upon its capacity for retaining water : and
if so, soils containing the same ingredients must be
also equally fertile, all other circumstances being
the same ; though it is plain that their actual fertility
will depend ultimately upon the quantity of rain
that falls, because the quantity suited to a wet soil
cannot be the same that is suited to a dry soil. And
hence it often happens that the ingredients of the
soil do not correspond to the character of the cli-
mate. Silica exists in the soil under the modification
of sand, and alumine under the modification of clay.
But the one or the other is often to be met with in
excess or defect. Soils in which the sand prepon-
derates retain the least moisture ; arid soils in which
the clay preponderates retain the most : the former
are dry soils ; the latter are wet soils. But it may
happen that neither of them is sufficiently favour-
able to culture ; in which case their peculiar defect
or excess must be supplied or retrenched before they
can be brought to a state of fertility.

Poororex- But soils in a state of culture, though consisting
Boils'ame- originally of the due proportion of ingredients, may
horated, yet become exhausted of the principle of fertility by
means of 'too frequent cropping, whether by repeti-
tion or rotation of the same, or of different crops.
And in this case, it should be the object of the
phytologist, as well as of the practical cultivator, to
ascertain by what means fertility is to be restored to
an exhausted soil ; or communicated to a new one.
By drain- In the breaking up of new soils, if the ground has

ing, par-

SECT. VI. MANURES. 83

been wet or marshy, as is frequently the case, it is often ing, burn-
sufficient to prepare it merely by means of draining Ulgj
off the superfluous and stagnant water, and of paring
and burning the turf upon the surface. This mode of
preparation is at present much practised throughout
England, but particularly in Yorkshire and Lincoln-
shire, as being the best suited to the character of
the soil of these counties that remains to be taken
into cultivation.

If the soil has been exhausted by too frequent a
repetition of the same crop, it often happens that a
change of crop will answer the purpose of the culti-
vator; for although a soil may be exhausted for
one sort of grain, it does not necessarily follow that
it is also exhausted for another. And accordingly,
the practice of the farmer is to sow his crops in ro-
tation, having in the same field a crop, perhaps, of
wheat, barley, beans, and tares in succession ; each
species selecting in its turn some peculiar nutriment,
or requiring, perhaps, a smaller supply than the crop
that has preceded it. But even upon the plan of
rotation, the soil becomes at length exhausted, and
the cultivator obliged to have recourse to other means
of restoring its fertility.

In this case, an interval of repose is considerably Repose,
efficacious, as may be seen from the increased ferti-
lity of fields that have not been ploughed up for
many years, such as those used for pasture ; or even
from that of the walks and paths in gardens when
they are again broken up. Hence also the practice

02

84* FOOD OF THE VEGETATING PLANT. CHAP. II.

of fallowing, and of trenching or deep ploughing,
which must have nearly the same effect.

If any one asks how the fertility of a soil is
restored by the means now stated, it will be suffi-
cient for the object of the present section to reply
that, in the case of draining, the amelioration is
effected by means of its carrying off all such super-
fluous moisture as may be lodged in the soil, which is
well known to be prejudicial to plants not naturally
aquatics, as well as by rendering the soil more firm
and compact. In the case of burning, the ameliora-
tion is effected by means of the decomposition of
the vegetable substances contained in the turf, and
subjected to the action of the fire, which disperses
part also of the superfluous moisture, but leaves a
residue of ashes favourable to future vegetation. In
the case of the rotation of crops, the fertility is not
so much restored as more completely developed and
brought into action ; because the soil, though ex-
hausted for one species of grain, is yet found to be
sufficiently fertile for another, the food necessary to
each being different, or required in less abundance.
In the case of the repose of the soil, the restored
fertility may be owing to the decay of vegetable
substances that are not now carried off in the annual
crop, but left to augment the proportion of vegetable
mould ; or to the accumulation of fertilizing parti-
cles conveyed to the soil by rains; or to the con-
tinued abstraction of oxygen from the atmosphere.
In the case of fallows, it is owing undoubtedly to the

SECT. VI. MANURES. 85

action of the atmospheric air upon the soil, whether
in rendering it more friable, or in hastening the
putrefaction of noxious plants ; or, it is owing to the
abstraction and accumulation of oxygene. In the
case of trenching, it is owing to the increased facility
with which the roots can now penetrate to the pro-
per depth ; and in the case of deep ploughing, it is
owing, as it would appear, to the same cause.

But it often happens that the soil can no longer By the a p-
be ameliorated by any of the foregoing means, and manures.0
in this case there must be a direct and actual appli-
tion made to it of such substances as are fitted to
restore its fertility. And hence the indispensable
necessity of manures, which consist chiefly of ani-
mal and vegetable remains that are buried and
finally decomposed in the soil, from which they
are afterwards absorbed by the root of the plant, in
a state of solution.

But as carbon is the principal ingredient furnished
by manures as contributing to the nourishment of
the plant, and is not itself soluble in water, nor even
disengaged by fermentation in a state of purity ;
under what state of chemical combination is its
solution effected ? Is it effected in the state of char-
coal ? It has been thought, indeed, that carbon in
the state of charcoal is soluble in water; because
water from a dunghill, when evaporated, constantly
leaves a residuum of charcoal, as was first ascertained
by the experiments of Hassenfratz. But there seem
to be reasons for doubting the legitimacy of the

' 2

8 FOOD OF THE VEGETATING PLANT. CHAP. II.

conclusion that has been drawn from it ; for Sene-
bier found that plants whose roots were immersed in
water took up less of the fluid in proportion as it
was mixed with water from a dunghill.* Perhaps
then the charcoal of water from a dunghill is held
merely in suspension, and enters the plant under
some other modification.

But if carbon is not soluble in water in the state
of charcoal, in what other state is it soluble ? It is
soluble in the state of carbonic acid gas. But is
this the state in which it actually enters the root ?

Opinion of On this subject phytologists have been somewhat
Sencbier. ,..,,. J . . ^ *

divided m opinion. Senebier endeavours to prove

that carbonic acid gas, dissolved in water, supplies the
roots of plants with almost all their carbon, and
founds his arguments upon the following facts : —
In the first place it is known that carbonic acid gas
is soluble in water ; in the second place it is known
to be contained in the soil, and generated by the
fermentation of the materials composing manures ;-f~
and in the next place it is known to be beneficial
to vegetation when applied artificially to the roots,
at least in a certain degree. This is evident from
the following experiment of Ruckert, as well as from
several experiments of Saussure's, previously related.
Ruckert planted two beans in pots of equal dimen-
sions,filled with garden mould ; the one was moist-
ened with distilled water, and the other with water
impregnated with carbonic acid gas. But the latter

* Phys. Veg. vol. hi. p. 154-. f Ibid. vol. iii. p. 55,

SECT. VI. MANURES. 87

appeared above ground nine days sooner than the
former, and produced 25 beans ; while the former
produced only 15. Now the result of this experi-
ment, as well as the preceding facts, is evidently
favourable to the presumption of Senebier, and shows
that if carbonic acid is not the state in which carbon
enters the plant, it is at least a state preparatory to
it; and there are other circumstances tending to
corroborate the opinion, resulting from the analysis
of the ascending sap of plants. The tears of the
Vine, when analysed by Senebier, yielded a portion
of carbonic acid and earth ;* and as the ascending
sap could not be supposed to have yet undergone
much alteration, the carbonic acid, like the earth,
was probably taken up from the soil.

.But this opinion, which seems to be so firmly Contro-
established upon the basis of experiment, Hassen- Hassen-7
fratz strenuously controverts. According to experi- fratz<
ments which he had instituted with an express view
to the investigation of this subject, plants which
were raised in water impregnated with carbonic acid
differed in no respect from such as grew in pure
water, and contained no carbon that did not pre-
viously exist in the seed. Now if this were the
fact, it would be decisive of the point in question.
But it is plain from the experiments of Saussure, as
related in a preceding section, that Hassenfratz
must have been mistaken both with regard to the
utility of carbonic acid gas as furnishing a vegetable
* Seneb. Phys. Veg. vol. iii. p. 55.

88 FOOD OF THE VEGETATING PLANT. CHAP. II.

aliment, and with regard to the augmentation of
carbon in the plant. The opinion of Senebier, there-
fore, may still be correct.

Conjee- It must be acknowledged, however, that the subject
Thomson. ^s not 7et altogether satisfactorily cleared up ; and
that carbon may certainly enter the plant in some
state different from that, either of charcoal in solution,
or of carbonic acid gas. Is not the carbonic acid of
the soil decomposed before entering the plant ? This
is a conjecture of Dr. Thomson's, founded upon the
following facts : — The green oxide of iron is capable
of decomposing carbonic acid ; and many soils con-
tain that oxide. Most soils indeed contain iron,
either in the state of the brown or green oxide, and
it has been found that oils convert the brown oxide
into green.* But dung and rich soils contain a
quantity of oily substance. One effect of manures,
therefore, may be that of reducing the brown oxide
of iron to the green, thus rendering it capable of
decomposing carbonic acid gas, so as to prepare it
for some new combination, in which it may serve as
an aliment for plants. All this, however, is but a
conjecture ; and it is more probable that the carbonic
acid of the soil enters the root in combination with
some other substance, and is afterwards decomposed
within the plant itself.

* Thomson's Chemistry, vol. iv. p. 394-.

CHAPTER III.

OF THE PROCESS OF NUTRITION.

IN the foregoing chapter I have enumerated the
substances constituting the principal food of plants,
as deducible from the observations and experiments
of the best phytological chemists. But this enu-
meration serves only as a step to conduct us to
further inquiries. For it is necessary to know not
only in what the food of plants consists, but also by
what means that food, whether lodged in the soil or
wafted through the atmosphere, is taken up by the
plant, conveyed to its different parts, and elaborated
so as to prepare it for final assimilation. The inves-
tigation of these topics shall form the subject of the
several following sections.

SECTION I.
Intro-susception.

As plants have no organ analagous to the mouth Effected
of animals enabling them to take up the nourish- pjrese0f
ment necessary to their support, by what means do
they effect the intro-susception of their food ? In
our anatomical analysis of the vegetable structure,
it was found that the whole of the parts of the plant,
the root, stem, branches, leaves, flower, and fruit,

mis.

QO PROCESS OF NUTRITION. CHAP. III.

are covered with an epidermis, or fine and transpa-
rent pellicle, which has been described by some
phytologists as being of so close and compact a
texture that the eye, aided even by the best micro-
scopes, is unable to discover in it the slightest vestige
of pores or apertures. Hedwig and Decandolle
have, however, detected pores in the epidermis of
the leaves of many plants, and they may readily be
detected by any one who will be at the trouble of
employing the same means. It does not appear
that any pores have been yet detected in the epider-
mis of the root ; though we must not on that account
conclude that it is not porous. We must even, on
the contrary, admit that it is furnished also with
pores, as well as the epidermis of the leaf; because
the whole of the nourishment which the plant de-
rives from the soil must of necessity pass through it.
Absorbing But if the pores of the epidermis are so very fine
fl^idsf * lg as either to elude the sight, or to be discoverable
only by the application of the highest magnifying
powers, they can be permeable only to fluids ; and
if so, then the food of the plant can be taken up
only by absorption or inhalation, as the chyle into
the animal lacteals, or the air into the lungs. The
former term will be applied to the intro-susception
of non-elastic fluids ; the latter, to that of gaseous
fluids.

Non-elas- Of the fact of the absorption of non-elastic fluids

absorbed ^Y tne epidermis °f plants any one may easily

satisfy himself, merely by immersing in water a plant

SECT. I. INTRO-SUSCEPTION. 91

of almost any species of moss that has been some
time gathered, or long exposed to drought, so as to
have had its leaves shrivelled up. The moisture
will immediately begin to ooze through the epider-
mis, and the plant to resume its original form and
verdure.

But has any of the moisture thus absorbed passed By the
through the root ? If the bulb of a hyacinth is
placed on the orifice of a glass bottle filled with
water, so as that the radicles only shall be immersed,
the water is imperceptibly exhausted, and the plant
grows : the moisture must consequently have passed
through the root. The following experiment of
Hales proves not only the fact, but also the extra-
ordinary energy of the absorbent power of the root.
Having laid bare the root of a pear tree half an inch
in diameter, and luted to it a tube of glass, one
inch in diameter and eight inches long, to which
was luted also another tube a quarter of an inch in
diameter and 18 inches long, he filled both with
water, and immersed the extremity in a cistern of
mercury. The result was, that the absorption of
water by the root was so rapid that the mercury
rose eight inches in the space of six minutes.*

But moisture is absorbed also by the leaves as Bytheleaf.
well as root. Du Hamel cut off several branches
from several trees of different species, and covered
the surface of the section with mastic. The conse-
quence was that the branches soon began to exhibit
* Veg. Star. Exper. xxi.

92 PROCESS OF NUTRITION. CHAP. III.

a faded and sickly appearance. Some of them were
then removed to damp situations, and others to dry
situations, to know what the effect of such removal
might be. The former gave indications of recovery,
the latter of continued decay.* It is plain, there-
fore, that in the former case moisture must have been
absorbed from the atmosphere by means of the
epidermis of the leaf, or at least of the branch.
Mariotte cut off from a tree a branch terminating in
two boughs, which he suspended upon the edge of a
vessel filled with water, so as that the one was
within and the other without the vessel. The
former preserved its verdure for several days, but the
latter began almost immediately to wither.
Experi- But the most complete set of experiments upon
Bonnet, the absorbent power of leaves which has hitherto
appeared is that of M. Bonnet, of Geneva. Satisfied
that leaves are furnished with absorbent organs for
the purpose of the intro-susception of moisture,
as deducible from the experiments of Hales and
Guettard, his object was that of ascertaining whether
the absorbent power of both surfaces was alike.
With this view he filled several vessels with water,
on the top of which he placed a number of leaves,
some having the upper, and others the under surface
applied to the water, so as that they only floated in
it but were not immersed. If the leaf retained its
verdure longest with its upper surface applied to the
water, the absorbing power of the upper surface was
* Phy. des Arb. liv. ii. chop. iii.

SECT. I. INTRO-SUSCEPTION. Q3

to be regarded as the greatest ; but if it retained its
verdure longest with the under surface applied to
the water, then the absorbing power of the under
surface was to be regarded as the greatest. The
experiment was made in the spring and autumn, the
temperature being between five and ten of Reaumur;
and the leaves employed being such as were fully
expanded. The result was as follows : —

Out of fourteen herbs of different genera selected On the de-
forthe purpose of experiment, the leaves of six — the }^vees of
Arum maculatum. Kidney Bean, Sun-flower, Cab- herbs-
bage, Spinach, and small Mallow — were indifferent
to the mode in which they were applied to the water,
and were found to retain their verdure equally long
whether moistened by the upper or under surface.
The rest — the Plantain,, white Mullein, great Mallow,
the Nettle, Cockscomb, purple-leaved Amaranth,
Marvel of Peru, and Balm — were not indifferent to
the mode in which they were applied to the water,
but retained their verdure longest when moistened
by the upper surface.

The following are the most remarkable examples
of the relative capacity of their different surfaces : —
The leaf of the Nettle when moistened by the upper
surface lived two months, but when moistened by
the under surface only three weeks. The leaf of
the Amaranth when moistened by the upper surface
lived three months, and when moistened by the
under surface only seven or eight days. The leaf
of the Mullein when moistened by the upper surface

Q4 PROCESS OF NUTRITION. CHAP. III.

lived five weeks, and when moistened by the under
surface only five days. A leaflet of the French
Bean absorbed also a sufficient quantity of moisture
to nourish another leaflet that was still attached to
the same footstalk, though not touching the water.
Onthede- Out of sixteen trees or shrubs of different genera
tares of selected for the purpose of experiment, the leaves of
only two, the Lilac and Aspen, retained their ver-
dure equally long by whatever surface they were
moistened. But the leaves of the rest — the Vine,
Pear, Cherry, Prune, Apricot, Walnut, Mulberry,
Oak, Hazel, Rose, &c. — retained it longest when
moistened by the under surface. The following are
the most remarkable examples of relative capacity :
— The leaves of the white Mulberry when moistened
by the under surface retained their verdure for
nearly six months, but when moistened by the
upper surface they retained it for only five or six
days. The leaves of the Vine, Poplar, and Walnut
faded almost as soon when moistened by the upper
surface, as when left without water altogether. The
leaves of the Hazel and Rose when moistened by
the under surface absorbed a sufficient quantity of
moisture to nourish also other leaves on the same
branch, though not touching the water.*

Such was the result of the experiments of M.
Bonnet ; and the only thing to be regretted is that
he has not always been sufficiently accurate in spe-
cifying, beyond the chance of mistake, the plant on
* Recherches sur les Usages des Feuilles.
4

SECT. I. INTRO-SUSCEPTION. Q5

which his experiments were made ; which are on
this account the less satisfactory, as well as the less
valuable. And hence it is now impracticable to as-
certain what particular species of Mallow are in-
tended by the Great and Little Mallows ; or what
particular species of Poplar it is that differs so much
in its capacity of absorption from the Populus tre-
mula or Aspen. But the inference deducible from,
the whole, and deduced accordingly by Bonnet, is
that the leaves of herbs absorb moisture chiefly by
the upper surface, and the leaves of trees chiefly by
the under surface.

But what is the cause of this direct opposition Their dif-
between the absorbing surface of the leaf of the herb pYchiesac-
and of the tree ? The immediate cause must be, counted
that there exists a greater number of absorbents in
the upper surface of the one, and in the under sur-
face of the other. But what is the cause in the
economy of the vegetable subject, or state of sur-
rounding bodies, that requires this arrangement ?

Du Hamel thought the lower surface of the leaf By Du

TT 1

of the tree was endowed with the greater capacity
of absorbing moisture, chiefly for the purpose of
catching the ascending dews and exhalations that
must necessarily come into contact with it as they
rise, but which might possibly still escape if ab-
sorbabie only by the upper surface, as being now
considerably rarefied, as well as more rapid in their
ascent ; * presuming, as it appears, that absorption
* Phys. des Arbres, liv. ii. chap. iii.

g6 PROCESS OF NUTRITION. CHAP. HI

by the upper surface is all that is necessary to herbs,
being but low in stature, and near the surface of the
earth, where the dews and exhalations are yet so
much condensed and so slow of ascent, that absorp-
tion by the under surface of the leaf would but
drench and destroy them. There may possibly be
some truth in this conjecture, though it rests on a
foundation rather too slight to be much trusted to ;
as the same mode of argumentation would have
suited a reversed order of the absorbing capacity of
surfaces, if viewed with regard to the rains that
descend from the atmosphere.
Observa- But as the foregoing experiments upon leaves

living011 were ma(^e on such onty as were detached from the
plants. plant, it may be said that they are not well calcu-
lated to become the ground of any general conclu-
sion, and that they do not represent to us the actual
phenomena of vegetation. To the actual phenomena
of vegetation therefore let us now appeal, in as far at
least as they are applicable to the present subject.
They will be found fully to confirm the fact of the
absorption of moisture by the leaf. If, after a long
drought, a fog happens to take place before any rain
falls, so as to moisten the surface of the leaves, the
plant begins to revive and to resume its verdure long
before any moisture can have penetrated to the root.
Hence it follows incontestably that moisture has been
absorbed by the leaf: because it is impossible to
account-for the change that has been effected, except
by such absorption. But the efficacy of rains them-

SECT. I. INTRO-SUSCEPTION. Qf

selves and of artificial waterings may be accounted
for upon the same principle ; for they have not
always penetrated to the root when they are found
to have given freshness to the plant ; and indeed
many plants will thrive merely by having their
leaves kept moist, though no water should reach the
root at all. The same thing might be said of the
immersed Fuel, many of which being totally des-
titute of root, and constituting merely a sort of
frond or leaf, absorb the nourishment necessary to
their support by the whole of their surface. The
moisture then entering the plant as a food is taken
up by means of the absorbent pores of the epi-
dermis, not only of the root and leaf> but often, as
it is to be believed, of the other parts of the plant
also, at least when they are in a soit and succulent
state.

But by what means do the gaseous fluids enter Elastic

n . ,

the plant? From what has been already ascertained be inhaled
concerning the vegetable structure, it follows un-
avoidably that the gases which may be inhaled as
a food must enter the plant in a manner similar to
that of moisture, that is, they must also pass
through the pores of the epidermis. Perhaps the
pores by which moisture is absorbed are fitted also
for the inhalation of air; but this cannot be re-
garded as altogether certain ; if it is not rather
altogether certain that each of the two fluids enters
the plant by a peculiar set of pores. Or by dif-

Bonnet has shown that most leaves absorb mois-

VOL. II. H

gS PROCESS OF NUTRITION. CHAP. III.

ture better by the one surface than the other : and
it is known that some surfaces do actually repel it ;
as may be seen in the case of Cabbage-leaves in
the time of rains and dews, when the drops roll
along the upper surface without wetting it, or lodge
in its folds and hollows like globules of quicksilver,
conglomerated together without being absorbed.
This is the case also with all such plants as are
covered with bloom. It is probable therefore that
all such surfaces as repel moisture are fitted rather
for the inhalation of air which they have long been
regarded as capable of effecting; and in times in
which it was fashionable to look for analogies
between the plant and animal in every thing what-
ever, leaves were even regarded as being the lungs
Though of plants. The notion seems to have arisen as
noUungs. follows : Grew thought he had discovered in the
leaves a number of little bags or bladders filled
with air : the air was supposed to have entered by in-
halation ; and the bags or bladders were supposed to
be analogous in their office to the cells of the lungs
of animals. This was at the time a sufficiently
plausible conjecture, but was not enough to prove
that leaves are lungs. Accordingly it became ne-
cessary to look out for some further arguments in
defence of the doctrine, and one of the first that
was discovered was that of the experiment of M.
Papin, who, with a view to ascertain the point in
question, introduced into the receiver of an air-
pump an entire plant, root, stem, and leaf. The

IECT. I* iNf ROStrsCEPTION.

consequence was that it very soon died. He then
introduced a plant by the root and stem only,
while the leaves were still exposed to the influence
of the air. But in this case the plant lived much
longer than in the former, and warranted him, as
he thought, to conclude that leaves are the lungs
of plants. It is plain., however, that this conclusion
was by much too hasty ; because the life of the
plant might have been protracted merely by the
absorption of the moisture of the atmosphere
through the medium of the leaf, and not by the
inhalation of any gaseous principle. And before
venturing upon such a conclusion, the experiment
should have been also reversed, to show the result
of enclosing the leaves only in the receiver, and of
leaving out the stem and root : and if it had even
been proved that atmospheric air is actually inhaled
by the leaf and indispensable to the health of tlie
plant, still it would have been necessary to show
that it is again expired also, in order to make good
the analogy of leaves to lungs.

Another argument in support of the doctrine

was deduced from Du Hamel's experiment of

besmearing the surface of the leaf with oil, in

consequence of which treatment it soon died,

owing, as it appeared, to the exclusion of air.*

But this argument is also insufficient to establish

the fact, and is here introduced, together with that

of M. Papin, not merely for the purpose of show-

* Phys. des Arb. liv. ii. chap. iii.

H 2

100 PROCESS OF NUTRITION. CHAP. III.

ing its inadequacy, or of making it appear that
there is any absurdity in the doctrine it was in-
tended to support; but rather that the doctrine,
though founded in truth, could not have been satis-
factorily proved by any experiments that were prac-
ticable at the time.

Their in- It is to the modern improvements in pneumatic
proved by chemistry, and to them alone, that we are indebted
chemTcT for our knowledge of the real functions of the
experi- leaves of plants ; from which it is proved indispu-
tably, that the leaves not only contain air, but do
actually inhale it. It was the opinion of Priestley
that they inhale it chiefly by the upper surface.
Has this been confirmed ? And it has been
shown by Saussure that their inhaling power de-
pends entirely upon the organization. A bough
of the Cactus Opuntia, when placed, as it was de-
tached from the plant, in an atmosphere of common
air, inhaled in the course of a night four cubic
inches of oxygene ; but when it was placed in a
similar atmosphere after being cut to pieces and
pounded in a mortar so as to destroy the organiza-
tion of its parts, no inhalation took place. The
inhalation of air, therefore, is no doubt effected by
the pores of the epidermis of the leaf.

It has been a question, however, among phytolo-
gists, whether it is not also effected by the epidermis
of the other parts of the plant. We can scarcely
suppose it to be effected by the dry and indurated
epidermis of the bark of aged trunks, of which

SECT. II. ASCENT OF THE SAP. 1O1

the original organization is obliterated; nor by that
of the larger and more aged branches. But it has
been thought there are even some of the soft and
succulent parts of the plant by which it cannot be
effected, because no pores are visible in their epi-
dermis. M. Decandolle found no pores in the
epidermis of fleshy fruits, such as Pears, Peaches,
and Gooseberries ; nor in that of roots, or scales of
bulbs ; nor in any part not exposed to the influence
of air and light. It is known, however, that fruits
will not ripen, and that roots will not thrive, if
wholly deprived of air; and hence it is probable
that they inhale it by their epidermis, though the
pores by whjich it enters should not be visible. In
the root, indeed, it may possibly enter in combi-
nation with the moisture of the soil ; but in the
other parts of the plant it enters no doubt in the
state of gas. Herbs, therefore, and the soft parts
of woody plants, absorb moisture and inhale gases
from the soil or atmosphere by means of the pores
of their epidermis, and thus the plant effects the
intro-susception of its food,

SECTION II.
Ascent of the Sap.

IN tracing out the means by which the plant
effects the intro-susception of its food, it was found
to be chiefly that of absorption by the root. But

PROCESS OF NUTRITION. CHAP. III.

the fluids existing in the soil when absorbed by
the root, are designated by the appellation of sap
or lymph ; which, before it can be rendered sub-
servient to the purposes of vegetable nutrition, must
either be intermediately conveyed to some viscus
proper to give it elaboration, or immediately dis-
tributed throughout the whole body of the plant.
The object, therefore, of the present section will be
that of tracing out the progress of its distribution
or ascent.

Sap proved A very simple experiment will be sufficient to
show that the sap is in motion in one direction or
other, at least at occasional periods. If the branch,
or trunk, or even root of a tree, is laid open
or fractured in the course of spring, whether
by intentional incision or accidental wound, the
sap will immediately begin to flow, and will, in
some cases, continue to be copiously discharged
perhaps for several days, or at least till the wound is
cicatrized ; and if the wound is again opened the
sap will flow afresh. This is what is usually de-

Bythe nominated the bleeding of plants, and is well
exemplified in the Vine, Birch, Maple, and Walnut,
as affording a most copious discharge.

But what is the most to be wondered at in the case
of the bleeding of plants, is that the most copious
discharge does not seem to injure the individual in
any material degree. J)u Hamel selected several
strong and healthy Vines as the subject of experi*
jpent, some of ivhich were trimmed in the usual

SECT. II. ASCENT OF THE SAP. 103

way, and others made to bleed copiously ; but the
latter were afterwards as vigorous and productive as
the former. The American Maple will also con-
tinue to yield its usual quantity of sap in the spring
for many years ; though it requires now and then
an interval of rest.

The plant always bleeds most freely about the Which is
time of the opening of the bud ; for in proportion per
as the leaves expand the sap flows less copiously,
and when they are fully expanded it entirely ceases.
But this suspension is only temporary, for the plant
may be made to bleed again in the end of the
autumn, at least under certain conditions. If an
incision is now made into the body of the tree
after the occurrence of a short but sharp frost, when
the heat of the sun or mildness of the air begins to
produce a thaw, the sap will again flow. It will
flow even where the tree has been but partially
thawed, which sometimes happens on the south
side of a tree, when the heat of the sun is strong
and the wind northerly. At the seasons now speci-
fied, therefore, the sap is evidently in motion ; but
the plant will not bleed at any other season of the
year. Are we to conclude, therefore, that the Though
motion of the sap is at such other season wholly motion "is
suspended ; or that it only flows with diminished J^r
velocity ? It has been the opinion of some phyto- suspended,
logists, indeed, that the motion of the sap is wholly
suspended during the winter. But though the
great cold of winter, as well as the great heat of

104 PROCESS OF NUTRITION. CHAP. III.

summer, is by no means so favourable to vegetation
as the milder though more changeable temperature
of spring and autumn, yet it does not wholly
suspend the movement of the sap. Palms may be
made to bleed at any season of the year. And al-
though this is not the case with plants in general,
yet there is proof sufficient that the colds of winter
do not, even in this climate, entirely prevent the
sap from flowing. Buds exhibit a gradual develop-
ment of parts throughout the whole of the winter,
as may be seen by dissecting them at different
periods. So also do roots. Evergreens retain their
leaves ; and many of them, such as the Arbutus,
Laurustinus, and the beautiful tribe of the Mosses,
protrude also their blossoms, even in spite of the
rigour of the season. But all this could not pos-
sibly be accomplished if the motion of the sap were
wholly suspended.

Itsdirec- The sap then is in perpetual motion with a more
o'f ascent, accelerated or more diminished velocity throughout
the whole of the year: but still there is no decided
indication, exhibited in the mere circumstance of
the plant's bleeding, of the direction in which the
sap is moving at the time ; for the result might be
the same whether it was passing from the root to the
branches, or from the branches to the root. But as
the great influx of the sap is effected by means of
the pores of the epidermis of the root, it follows
that its motion must, at least in the first place, be
that of ascent ; and such is its direction at the sea-

SECT. II. ASCENT OF THE SAP. 105

son of the plant's bleeding, as may be proved by the
following experiment : — If the bore or incision that
has been made in the trunk is minutely inspected
while the plant yet bleeds, the sap will be found to
issue almost wholly from the inferior side. If
several bores are made in the same trunk one above
another, the sap will begin to flow first from the
lower bore, and ;then from those above it. If a
branch of a Vine be lopped, the sap will issue copi-
ously from the section terminating the part that
remains yet attached to the plant ; but not from the
section terminating the part that has been lopped
off. This proves indubitably that the direction of
tbe sap's motion, during the season of the plant's
bleeding, is that of ascent.

But if the sap flows so copiously during the sea-Itsvelo-
son of bleeding, it follows that it must ascend withciy*
a very considerable force ; which force has accord-
ingly been made the subject of calculation. To the
stem of a Vine cut off about two feet and a half
from the ground, Hales fixed a mercurial gauge
which he luted with mastic ; the gauge was in the
form of a syphon, so contrived that the mercury
might be made to rise in proportion to the pressure
of the ascending sap. The mercury rose accord-
ingly, and reached, as its maximum, to a height of
38 inches.* But this was equivalent to a column
of water of the height of 43 feet 34- inches ; demon-
strating a force in the motion of the sap that, without
*Veg. Stat. Exper.
1

106 PROCESS OF NUTRITION. CHAP. III.

the evidence of experiment, would have seemed
altogether incredible.

The sap then in ascending from the lower to the
upper extremity of the plant is propelled with a
very considerable force, at least in the bleeding
season. But is the ascending sap propelled indis-
criminately throughout the whole of the tubular
apparatus, or is it confined, in its course, to any
particular channel ? Before the anatomy of plants
had been studied with much accuracy, there was
a considerable diversity of opinion on the subject.
Channel Some thought it ascended by the bark ; others

of ascent.

thought it ascended by the bark, wood, and pith,
indiscriminately ; and others thought it ascended
between the bark and wood.

According The first opinion was maintained and supported
pighi. by Malpighi ; who seems to have taken it for
granted that the sap ascends by the bark, merely
because the fibres of the bark (which he describes
under the appellation of Jibrce lignea, seu vasa
tubulosa)* had been found to be tubular, and
hence permeable to fluids : but this is a very lame
argument indeed ; for although the bark is of
a vascular texture and permeable to fluids, yet
this is no proof that the sap in its natural course
ascends through it, because the vessels contained
in it may possibly be destined for purposes very
different from that of the transmission of the
sap. But it was said that when a horizontal in-

Anat. Plant, v.
fi

SECT* II. ASCENT OF THE SAP. 107

cision is made in the bark, a fluid is found to exude
from the lower lip, and that consequently the sap
ascends by it. But in order to make this argument
good, the fluid must first be proved to be sap, or at
least to afford the presumptive evidence of continu-
ing to flow for a considerable length of time ; as it
is known that the vessels of plants will empty
themselves at both ends when cut horizontally, as
any one may see merely by cutting in two the stem
of any species of Spurge ; so that the mere exuda-
tion of a fluid from the lower lip, is no proof that
it proceeds from the ascending sap since the vessels
might thus empty themselves if they but contained
even a fluid descending.

It was further contended that old Willows and
several other sorts of trees will still continue to
vegetate even when the whole of the woody part of
the trunk is decayed, and nothing but bark remain,
ing. But this is not exactly the fact ; for in the
case alluded to, there will always be found to be
more or less of wood immediately under the bark;
so that the ascent of the sap through the channel of
the bark is by no means established.

The second opinion does not seem to have ,been
entertained by any very distinguished phytologists
— namely, that of its ascending between the bark
and wood ; but it seems to have been entertained
by those who held it, because much juice is found
there ; because the wood is formed there ; and be*
cause the graft takes effect there.

108 PROCESS OF NUTRITION. CHAP. Ill,

According Grew has shown this opinion to be altogether er-
roneous, and has substituted a third in its place —
namely, that the sap ascends by the bark, wood, and
pith indiscriminately.* It ascends by the pith, as
he says, during the first year of the plant's growth,
and during the first year only ; because the pith is
always found succulent during that time., whether in
the sprout from a seed, or sucker from a root, or
scion from a branch ; but dry ever after. And it
ascends by the wood and bark, because upon cutting
a branch a liquid issues from both either spontane-
ously or by pressure. But we must not too hastily
conclude that any particular part of the plant serves
as the channel of the sap's ascent, merely because
it has been found to be moist, or to give out a liquid
by pressure ; for one might just as well say, because
the soil of a meadow situated bv the banks of a
river contains a great deal of moisture, that it is
therefore the channel of the descent of the water as
well as the bed of the river itself. The sap is no
doubt conveyed to all the parts of the plant, and is
consequently to be found in them all under one
modification or another, but still its ascent is con-
fined to a peculiar channel. Let us try to ascertain
by experiment what that channel is.

If a tree is to be subjected to the operation of

bleeding, there will be no notable discharge of sap

unless the bore or incision penetrates beyond the

bark ; and if the operation is performed on the

* Vcg. of Trunks, chop. i.

SECT. II. ASCENT OF THE SAP. iOQ

trunk of the Poplar-tree, there will be no notable
discharge till it penetrates almost to the centre.*
These facts afford a strong presumption that the sap
does not ascend by the bark ; but the following ex-
periments afford an indubitable proof.

Du Hamel stript several trees of their bark en- Experi-
tirely, which continued, notwithstanding, to HveDu
for many years, protruding new leaves and new Anight,
branches as before.-}- Mr. Knight stript the trunk of
a number of young Crab-trees of a ring of bark
half an inch in breadth, but the leaves were pro-
truded, and the branches elongated, as if the
operation had not been performed.^ It is evi-
dent, therefore, that the sap does not ascend by the
bark.

But it is equally evident that it does not ascend
by the pith, at least after the first year ; for then,
even upon Grew's own supposition, it becomes either
juiceless or wholly extinct : and even during the
first year it is not absolutely necessary, if at all
subservient to the ascent of the sap, as is proved
by an experiment of Mr. Knight's. Having contrived
to abstract from some annual shoots a portion of
their pith, so as to interrupt its continuity, but not
otherwise materially to injure the fabric of the
shoot, he found that the growth of the shoots
which had been made the subject of experiment
was not at all affected by it.

* Exper. par Coulomb. f Phys. cles Arb. lir. v. chap, ii.
Phil. Trans. ISOi.

110 PROCESS OF NUTRITION. CHAP. 111.

Proving The sap then ascends neither by the bark nor
through"1 pith, but by the wood only. , But the whole mass
ihe wood, Q£ tke wooc| throughout is not equally well adapted
for the purpose of conveying it. The interior and
central part, or part that has acquired its last de-
gree of solidity, does not in general afford it a pas-
sage. This is proved by what is called the girdling
of trees, which consists in making a circular gap
or incision quite round the stem, and to the depth
of two or three inches, so as to cut through both
the bark and alburnum. The operation is very
generally performed by the American farmer on
trees whose further growth might be prejudicial to
his crop, but which he does not yet find it conve-
nient to cut down : and indeed there are but few
trees that will long survive the operation, particu-
larly if performed early in the spring.* An Oak-tree
on which Mr. Knight had performed the operation
with a view to the very object in question, namely,
that of ascertaining the channel of the sap's ascent,
exhibited not the slightest mark of vegetation in
the spring following.-^- The sap then does not
ascend through the channel of the matured wood.
Or rather But if the sap ascends neither through the chan-
"' nel of the bark, nor pith, nor matured wood ;
through what other channel does it actually ascend?
The only remaining channel through which it can
possibly ascend is that of the alburnum. But
though the object of our inquiry has been thus so
* Barton's Elcm. of But. p. 15,5. f Phil. Trans. 1805.

SECT. II. ASCENT OF THE SAP. Ill

far obtained, another inquiry remains yet to be in-
stituted. In passing through the channel of the Vessels
alburnum, does the sap ascend promiscuously by ^hklfit
the whole of the tubes composing it, or is it con-ascends»
fined in its passage to any peculiar set ?

The earliest conjectures recorded on this subject
are those of Grew and Malpighi, who, though they
maintained that the sap ascends chiefly by the
bark, did not yet deny that it ascends also partly
by the alburnum or wood : but their opinions do
not at all coincide with regard lo the peculiar set
of vessels through which the sap ascends the al-
burnum. Malpighi thought it ascended through According
the channel of the tubes formed by the woody ^Md-
fibre, which he describes under the appellation of P5Shi-
fistula Ugnecz ;* regarding the tracheae, which he
represents as constituting also part of the wood,
as being confined merely to the function of con-
ducting air. But Grew thought it ascended the
alburnum only through the channel of the tra-
cheae,-j~ which he represents as being numerous
both in the stem and root, and capable of conduct-
ing not only air but sap. Such were the primitive
conjectures entertained on this subject, at a time
when phytological inquiry was but yet in its in-

* Sunt autem hae fistulce ejusdem naturae cum exaratis cor-
ticem compingentibus, et consimilcrn admittunt succum qui ex
natures legibus sursum pellitur. Anat. Plant, xi.

t In the wood the sap ascendeth only by the air vessels. Yog,
of Trunks, chap. i.

112 PROCESS OF NUTRITION. CHAP. III.

fancy ; and as the obscurity as well as importance
of the subject demanded, so it gave origin to fur-
ther investigations.

It occurred to succeeding phytologists that the
progress of the sap, and the vessels through which
it passes, might be traced or ascertained by means
of making plants to vegetate in coloured infusions;
and accordingly plants were made so to vegetate.
The earliest experiments on the subject seem to be
those of Magnol, instituted about the beginning of
the eighteenth century, though it does not appear
that his object was any thing beyond that of merely
demonstrating the ascent of the sap to the very
summit of the plant. The colouring matter he
made use of was the juice of Phytolacca ; and
when the extremity of a stem of the Tuberose was
moistened in an infusion of this juice, it was found
to mount up to the summit and to give a red colour
De la to the flower. M. De la Baisse, improving upon
this hint, instituted a number of experiments, with
the same juice, upon a great variety of different
plants, and found that the infusion always left
behind it some evident traces of its ascent in the
form of longitudinal streak? or threads. In the
root, it was found that the smaller divisions were
always tinged more deeply, and the larger divisions
more faintly ; the tinge being also deeper as it ap-
proached the centre. In stems of the Peach and
Elm, of from three to four feet in length, the
coloured tubes were traced to the extremity of the

SECT. II. ASCENT OF THE SAP. 113

branches pervading the wood only, but not the
pith or bark, the tinge being always deepest at the
origin of the leaf and branch. But in the im-
mersed portion of the stem, the bark was tinged
where the epidermis was wanting ; and in branches
of the Fig-tree, the medullary sheath, or sheath sur-
rounding the pith, was tinged also. On inspecting
the surface of a transverse section of a branch of
the Lime-tree that had been made the subject of
experiment, the wood was found to be variegated
with alternate zones of white and red ; but there
was no colouring in the bark or pith.

In herbaceous plants the case was nearly the
same, the streaks being found only in the bundles
of woody fibre, though in some examples the upper
part of the plant had assumed a reddish tinge, even
where no traces of fibre were perceptible. In the
leaves the infusion was found to have passed
through two different sets of vessels, the one large
and longitudinal, the other undulating and twisted ;
the former abounding chiefly in the under surface,
and the latter in the upper surface. In repeating
the experiment of Magnol, M. De la Baisse was
completely successful ; and in extending it to a
species of Antirrhinum, the infusion was found to
have tinged not only the corolla, but also all the
other parts of the fructification.

Bonnet instituted a set of similar experiments Bonnet,
on this subject also, in which he used for colouring
matter, ink, andx tincture of Madder-root The

VOL. II. I

114 PROCESS OF NUTRITION. CHAP. III.

central part of the root was, as in the foregoing
experiments, tinged the deepest ; but the wood of
a branch of the Apricot was tinged the deepest
towards the circumference, the pith and bark being
unaltered ; and in a case in which the branch was
stripped of a ring of bark, the wood was tinged as
before. On the surface of a transverse section of
a bud three black spots were distinguishable, indi-
cating the ascent of the coloured fluid ; and when
the experiment was made upon the stalk of French
Beans the tincture was found to have ascended only
by the bundles of woody fibre.

DuHameJ. Du Hamel, in pursuit of the same object, mixed
a quantity of powdered Madder-root with the earth
in which a plant vegetated, hoping he might thus
succeed in detecting and tracing out the sap vessels,
in the same manner as he had succeeded in colour-
ing the bones of some animals by means of mixing
Madder-root with their food. But the experiment
failed. He then adopted the plan of Bonnet,
namely, that of steeping the extremity of a branch
or stem in a coloured fluid* The fluid he used was
ink ; and the subject of experiment branches of
the Fig, Elder, Honeysuckle, and Filbert. In ex-
amining some branches of the two former after
being steeped for several days, the part immersed
was found to be black throughout, but the upper
part was tinged only in the wood, which was co-
loured for the length of a foot, but more fairjtly
and oartially in proportion to the height. The pith
*

SECT. II. ASCENT OF THE SAP. 115

indeed exhibited some traces of ink, but the bark
and buds none. In some other examples the ex-
ternal layers of the wood only were tinged. In
the Honeysuckle the deepest shade was about the
middle of the woody layers ; and in the Filbert
there was also observed a coloured circle surround-
ing the pith ; but none in the pith itself, nor in the
bark.

Such were the experiments of the earlier phyto-
logists with a view to discover the vessels conduct-
ing the sap in its ascent, which, though they do not
exactly determine the point in question, do yet very
much circumscribe the limits of inquiry, showing
that it ascends through the vessels of the longitu-
dinal fibre composing the alburnum of woody
plants, and through the vessels of the several
bundles of longitudinal fibre constituting the woody
part of herbaceous plants. But it has been already
shown that the vessels composing the woody fibre
are not all of the same species. There are simple
tubes, porous tubes, spiral tubes, mixed tubes, and
interrupted tubes. Through which of these, there-
fore, does the sap pass in its ascent ?

The best reply to this inquiry has been furnished Mirbeland
by Mr. Knight and M. Mirbel, whose experiments night*
on the subject are considerably more luminous than
the preceding. Mr. Knight prepared some annual
shoots of the Apple and Horse-chesnut, by means
of circular incisions, so as to leave detached rings
of bark with insulated leaves remaining on the

i 2

II 6 PROCESS OF NUTRITION. CHAP. III.

stem* He then placed them in coloured infusions
obtained by macerating the skins of very black
grapes in water ; and on examining the transverse
section at the end of the experiment, it was found
that the infusion had ascended by the wood beyond
his incisions, and also into the insulated leaves, but
had not coloured the pith nor bark, nor the sap
between the bark and wood.* From the above
experiment Mr. Knight concludes that the sap as-
cends through what are called the common tubes
of the wood and alburnum, at least till it reaches
the leaves. This is no doubt the fact, though still
it is but vaguely stated. M. Mirbel is somewhat
more explicit. From a variety of experiments
made by immersing branches of the Elder in co-
loured infusions, he finds himself entitled to con-
clude that the sap ascends through the medium of
what he calls the small tubes ; because they only
were found to be coloured with the infusion, while
the large tubes were not ; and because in the bleed-
ing season they are found to contain a limpid juice,
which the large tubes do not.

Who Thus the sap is conveyed to the summit of the

mTinto alburnum. But Mr. Knight's next object was to

the leaf, trace the vessels by which it is conveyed into the

leaf. The Apple-tree and Horse-chesnut were still

his subjects of experiment. In the former the

leaves are attached to the plant by three strong

fibres, or rather bundles of tubes, one in the middle

* Phil. Trans. 1801.

SECT. II. ASCENT OF THE SAP. 117

of the leaf-stalk, and one on each side. In the
latter they are attached by means of several such
bundles. Now the coloured fluid was found in each
case to have passed through the centre of the se-
veral bundles, and through the centre only, tinging
the tubes throughout almost the whole length of
the leaf-stalk. In tracing their direction from the
leaf-stalk upwards, they were found to extend to
the extremity of the leaves ; and in tracing their
direction from the leaf-stalk downwards, they were
found to penetrate the bark and alburnum, the
tubes of which they join, descending obliquely
till they reach the pith which they surround.*
From their position Mr. Knight calls them central
tubes, thus distinguishing them from the common
tubes of the wood and alburnum, and from the
spiral tubes with which they were every were ac-
companied as appendages ; as well as from a set
of other tubes which surrounded them, but were
not coloured, and which he designates by the ap-
pellation of external tubes.

The experiment was now transferred to the Flower
flower-stalk and fruit-stalk, which was done by
placing branches of the Apple, Pear, and Vine,
furnished with flowers not yet expanded, in a de-
coction of Logwood. The central vessels were
rendered apparent as in the leaf-stalk. When the
fruit of the two former was fully formed, the ex-
periment was then made upon the fruit-stalk, in
* Phil. Trans. 1805.

1J8 PROCESS OF NUTRITION. CHAP. III.

which the central vessels were detected as before ;
but the colouring matter was found to have pene-
trated into the fruit also, diverging round the core,
approaching again in the eye of the fruit, and ter-
minating at last in the stamens. It was by means
of a prolongation of the central vessels, which did
not however appear to be accompanied by the spiral
tubes beyond the fruit-stalk.

Such then are the parts of the plant through
which the sap ascends, and the vessels by which it
is conveyed. Entering by the pores of the epi-
dermis, it is received into the longitudinal vessels
of the root by which it is conducted to the collar.
Thence it is conveyed by the longitudinal vessels
of the alburnum, the small tubes of Mirbel, and
common tubes of Knight, to the base of the leaf-
stalk and peduncle ; from which it is further trans-
mitted by the central vessels of Knight to the ex-
tremity of the leaves, flower, and fruit. It is to be
regretted, however, that Mr. Knight's description
of the central vessels is not altogether so explicit
as could be wished. In trying to illustrate the
subject by synonym, he says indeed, that his cen-
tral vessels are M. Mirbel's tubular tissue.* But
this unhappily tends to obscure rather than to elu-
cidate the subject. For M. Mirbel's tubular tissue
consists of not less than five or six different species,
large tubes, small tubes, simple tubes, porous tubes,
spiral tubes, and mixed tubes. But to which of
* Phil. Trans. 1807-

SECT. II* ASCENT OF THE SAP. MQ

them do the central vessels correspond? If we
regard their respective functions they can corres-
pond only to the small tubes, as it is by them alone,
according to M. Mirbel, that the sap ascends.

And yet after all the elucidation that has been Function
thrown on the subject, the function of the spiral °ai tubST
tubes is as much involved in obscurity as ever. ^

Grew, who, together with Malpighi, regarded them a?d Mal-
originally as being destined to the transmission of
air, is known to have retracted his opinion, or at
least to have very much modified it; so that, instead
of regarding them as being solely air-vessels, he
afterwards regarded them as being also sap-vessels,
and as being even the sole sap-vessels of the wood
or alburnum. But this opinion is evidently con-
tradicted by the fact that no trachese are to be found
in the wood or alburnum, except in the annual
shoot immediately surrounding the pith ; for they
are not generated in the succeeding and annual
layers by which the stem and trunk are augmented
in width, and are obliterated by age in the vicinity
even of the pith itself. It is impossible, therefore,
that they should be the channel of the sap's as-
cent through the wood or alburnum of an aged
trunk.

And yet this opinion seems to have been adopted According
even by Dr. Smith, upon the authority as it appears Kni^hT,'"'
of Dr. Darwin and Mr. Knight, whom he repre-andSmith<
sents as having proved in the most satisfactory
manner that the spiral vessels are the channel

}2Q PROCESS OF NUTRITION. CHAP. III.

through which the sap ascends.* That this was
the conclusion deduced from Dr. Darwin's expe-
riment, there is no doubt. But it does not appear
that Mr. Knight has deduced any such conclusion
from any experiments of his own ; but certainly
not inasmuch as regards the ascent of the sap
through the alburnum, in which he denies the ex-
istence of the spiral tubes altogether, except as
already stated. And although his central tubes,
which conduct the sap through the leaf and leaf-
stalk of woody plants, as well as through the stem
of herbaceous plants, are accompanied with spiral
tubes as appendages ; yet these spiral appendages
are represented as conveying no fluid. How then
Dr. Smith came to regard it as Mr. Knight's opi-
nion that the sap ascends through the channel of
the spiral tubes, it is not easy to say, except from
Mr. Knight's occasional obscurity and perplexity
of expression, if not of thought, that so often
embarrass the reader, even in his most luminous
papers.

Which the But what is the office of the spiral tubes where

bable opt they are certainly known to exist ? The opinion of

Grew and Malpighi, as it is the most ancient, is

perhaps also tne most correct : at least we may

fairly regard Crew's reformed opinion in this light;

namely, that they transmit not only air but sap.

It is indeed the opinion of Knight that they are

altogether incapable of transmitting moisture : but

* Introduction, p. 4-9.

SECT. II. ASCENT OF THE SAP. 121

this can refer only to their uncoiled state, in which
they do not form a tube, but merely a loosely spiral
line ; for in the coiled up state in which they
exist in the living vegetable and in which the spires
are united, they form a perfect tube, which we
cannot regard as incapable of transmitting moisture
without some proof. On the contrary it seems to
have been ascertained that they do contain mois-
ture. Hedwig, who examined with great care, and
with a view to the very point in question, the stem
of the Cucurbita Pcpo, and Momordlca Elate-
rium, in which the spiral tubes are comparatively
large, affirms that the juices may be seen issuing
from their orifices, if the horizontal section is in-
spected immediately after the stem is divided.*
Senebier gives a similar account of their appearance
in the stem of the Sagus farimfera, which he
had chosen for the subject of his observations.-}-
And Hedwig appears to have succeeded even in
inspecting them by means of steeping a portion of
the stem in coloured infusions ; and also in mea-
suring their diameter, which he estimates at about
the -s-j-g- of a line. In these observations there
may certainly have been error; but from the known
accuracy of the observers we are warranted in re-
garding them as correct ; and consequently in con-
cluding that the tracheae or spiral tubes, where they
exist, do also conduct sap.

But still there remains a question to be asked
* Fund. Hist. Nat. Muse. p. 55. f Pfys. Veg, vol. i. p. 107.

122 PROCESS OF NUTRITION. CHAP. III.

Lateral intimately connected with the sap's ascent. Do
cation.Uni" ^e vessels conducting the sap communicate with
one another by inosculation or otherwise, so as that
a portion of their contents may be conveyed in a
lateral direction, and consequently to any part of
the plant ; or do they form distinct channels
throughout the whole of their extent, having no
sort of communication with any other set of tubes,
or with one another?

Denied. Each of the two opinions implied in the question
has had its advocates and defenders. At the head
of those embracing the former we find Malpighi ;
and at the head of those embracing the latter we
find Grew ; who, in speaking of what he calls the
succiferous and air vessels of the bark and wood
of the root, describes them as being no where in-
osculated or twisted one about another, but only
tangent or collateral.* This was regarded as a proof
that the vessels of plants do not communicate la-
terally, so as to distribute their sap in all directions,
but are destined merely to the nourishment of a
particular part. It was also urged in support of
the same opinion, that if a tree is planted so as to
have cultivated ground on the one side, and uncul-
tivated ground on the other, the roots and branches
will be the most vigorous and the most luxuriant
on the cultivated side; and that if a tree having
two or more principal branches, with the same
number of principal roots, has one of the roots
* Anatomy of Roots, Part II. chap. iii. and iv.

SECT. II. ASCENT OF THE SAP. J23

cut off, the branch corresponding to it will be con-
3iderably affected by the loss.

But a very little reflection will serve to show that Proved,
the above premises are by no means sufficient to
justify the conclusion that has been drawn from
them: for although the tracheae as they exist in
the living plant are not twisted one about another,
but only tangent or collateral, yet the longitudinal
film of which they are composed is itself perfo-
rated with pores, or interrupted with meshes, as
may be seen by inspecting those of the leaf-stalk
of the Artichoke ; so that it is very possible they
may be occasionally tangent, where the pores or
meshes shall meet. And the degeneration of the
root or branch in the cases above stated is just
what would have taken place, upon the supposition
that a lateral communication exists : for if by
default of nutriment in the direct line, any root
or branch is supposed to be nourished merely by
means of the sap that may be transmitted to it
through the lateral apertures, its growth will of
necessity be less luxuriant, because its supply is
now rendered both more scanty and more difficult
of access. So that we have in this argument a
refutation of the very doctrine it was meant to sup-
port ; for if the root or branch thus treated does
not absolutely die, it is a proof that lateral commu-
nication must exist.

But the existence of a lateral communication
between the vessels conducting the sap has been

124 PROCESS OF NUTRITION. CHAP. III.

also further elucidated by means of direct expe-
riment. Du Hamel having selected a tree for the
purpose of experiment, made two incisions at dif-
ferent heights and on opposite sides of the trunk,
each penetrating to the centre. He then closed up
the gaps with a mixture of wax and turpentine, in
order to prevent the action of the air from inter-
fering in the result ; and found accordingly that the
tree continued to vegetate as before the experiment.
Hales took two branches of equal size, in one of
which he made four incisions, answering to the
four cardinal points, and each penetrating to the
centre ; in the other he made no incision. He
then put the extremities of both into water, and
found that the branch that was cut with incisions
absorbed moisture as copiously as the one that was
not so cut. Knight has also shown that a branch
will still continue to live though the tubes leading
directly to it are cut in the trunk.* From all which
it follows that the sap, though flowing the most co-
piously in the direct line of ascent, is at the same
time also diffused in a transverse direction. But
this seems to have been acknowledged even by
Grew himself, in spite of all he has advanced in
support of a contrary opinion : for he says that
the sap vessels of the bark being the first year ad-
jacent to the pith, do all that time transfuse part
of their sap into it, and so keep it always succu-
lent;^ which, whether we regard as being the fact
* Phi). Trans. 1801. t Vcg. of Trunks, chap. i.

SECT. III. CAUSES OF THE SAP's ASCENT. 125

or not, is at any rate admitting a species of la-
teral communication.

SECTION III.

•

Causes of the Sap's Ascent.

FROM the evidence exhibited in the foregoing
section the ascent of the sap is demonstrated, and
the channel of its distribution ascertained. But
what is the cause of that ascent ; or by what power
is the sap propelled ?

The great and almost impenetrable obscurity in
which this subject is unavoidably involved has oc-
casioned much diversity of opinion among phyto-
logists. Grew states two hypotheses which he Hypmhe-
seems to have entertained at different periods, Grew.
though it is not quite certain to which of them he
finally gave the preference. In one of them he
attributes the ascent of the sap to its volatile nature
and magnetic tendency, aided by the agency of
fermentation.* But this hypothesis is by much
too fanciful to bear the test of serious investigation.
In the other he attributes the entrance and first
stage of the sap's ascent to the agency of capillary
attraction, and accounts for its progress as follows :
The portion of the tube that is now swelled with
sap, being surrounded with the vesiculae of the

* Anat. of Veg, chap, iii.

126 PROCESS OF NUTRITION. CHAP. III.

Parenchyma, swelled also with sap, which they
have taken up by suction or filtration, is conse-
quently so compressed, that the sap therein is
forced upwards a second stage, and so on till it
reaches the summit of the plant.* But if the
vesiculae of the Parenchyma receive their moisture
only by suction or filtration, it is plain that there
is a stage of ascent beyond which they cannot be
thus moistened, and cannot consequently act any
longer upon the longitudinal tubes. The supposed
cause, therefore, is inadequate to the production of
the effect.

Of Mai- Malpighi was of opinion that the sap ascends by
means of the contraction and dilatation of the air
contained in the air-vessels. This supposition is
perhaps somewhat more plausible than either of
Grew's ; but in order to render the cause efficient,
it was necessary that the tubes should be furnished
with valves, which were accordingly supposed ;-}-
but of which the existence has been totally dis-
proved by succeeding phytologists. If the stem or
branch of a plant is cut transversely in the bleed-
ing season, it will bleed a little from above, as well
as from below : and if the stem of any species of

* Veg. of Trunks, chap. i.

t Subintrans itaque humor, sursum asccndit et quasi suspen-
ditur; singula namque portio, quae invicem fibrarum frustula
unit, cum parum interius emineat, valvulae vices supplet, et ita
minima quaelibet guttula, veluti per funem, seu per gradus, ad
ingens deducitur fastigiuin. Anat. Plant, vol. v.

SECT, III. CAUSES OF THE SAP's ASCENT. 127

spurge is cut in two, a milky juice will exude from
both sections, in almost any season of the year.
Also if a plant is inverted, the stem will become a
root, and the root a stem and branches, the sap
ascending equally well in a contrary direction
through the same vessels ; as may readily be proved
by planting a willow twig in an inverted position.
But these facts are totally incompatible with the
existence of valves ; and the opinion of Malpighi
proved consequently to be groundless.

The next hypothesis is that of M. De la Hire, of De la
who seems to have attempted to account for the
phenomenon by combining together the theories
of Grew and Malpighi. Believing that the ab-
sorption of the sap was occasioned by the spongy
parenchyma which envelopes the longitudinal tubes,
he tried to illustrate the subject by means of the
experiment of making water to ascend in coarse
paper, which it did readily to the height of six
inches, and by particular management even to the
height of eighteen inches. But in order to com-
plete the theory, valves were also found to be ne*
cessary, and were accordingly summoned to its aid.
The sap which was thus absorbed by the root was
supposed to ascend through the woody fibre, by
the force of suction, to a certain height, that is, till
it got above the first set of valves, which prevented
its return backwards ; when it was again supposed
to be attracted as before, till it got to the second

128 PROCESS OF NUTRITION. CHAP. ill.

set of valves, and so on till it got to the top of the
plant.

BorelH. This theory was afterwards adopted by Borelli,
who endeavoured to render it more perfect by
bringing to its aid the influence of the condensation
and rarification of the air and juices of the plant
as a cause of the sap's ascent. And on this prin-
ciple he endeavoured also to account for the greater
force of vegetation in the spring and autumn ; be-
cause the changes of the atmosphere are then the
most frequent under a moderate temperature ; while
in the summer and winter the changes of the at-

o

mosphere are but few, and the air and juices either
too much rarified or too much condensed, so that
the movement of the sap is thus at least prejudi-
cially retarded, if not perhaps wholly suspended.
But as this theory, with all its additional modifica-
tions, is still but a combination of the theories of
Grew and Malpighi, it cannot be regarded as af-
fording a satisfactory solution of the phenomenon
of the sap's ascent.

DuHamel. With this impression upon his mind, and with
the best qualifications for the undertaking, Du
Hamel directed his efforts to the solution of the
difficulty, by endeavouring to account for the phe-
nomena from the agency of heat, and chiefly on
the following grounds : * Because the sap begins to
flow more copiously as the warmth of spring re-
* Phys. de* Arb. liv. v. chap. ii.

SECT. III. CAUSES OF THE SAP's ASCENT.

turns ; because the sap is sometimes found to flow
on the south side of a tree before it flows on the
north side, that is, on the side exposed to the in-
fluence of the sun's heat sooner than on the side
deprived of it ; because plants may be made to
vegetate even in the winter, by means of forcing
them in a hot-house ; and because plants raised
in a hot-house produce their fruit earlier than such
as vegetate in the open air.

There can be no doubt of the great utility of
heat in forwarding the progress of vegetation ; but
it will not therefore follow that the motion and
ascent of the sap are to be attributed to its agency.
On the contrary, it is very well known that if the
temperature exceeds a certain degree, it becomes
then prejudicial both to the ascent of the sap and
also to the growth of the plant. Hales found that
the sap flows less rapidly at mid-day than in the
morning ; * and every body knows that vegetation
is less luxuriant at mid-summer than in the spring.
So also in the case of forcing it happens but too
often that the produce of the hot-house is totally
destroyed by the unskilful application of heat ; and
if heat is actually the cause of the sap's ascent,
how comes it that the degree necessary to produce
the effect is so very variable even in the same cli-
mate. For there are many plants, such as the
Arbutus, Laurus Tinus, and the Mosses, that will
continue not only to vegetate, but to protrude their
* Veg. Stat. Exper, 36.

VOL, II. K

J3O PROCESS OF NUTRITION. CHAP. III.

blossoms and mature their fruit, even in the midst
of winter, when the temperature is at the lowest.
And in the case of submarine plants the temperature
can never be very high ; so that although heat does
no doubt facilitate the ascent of the sap by its ten-
dency to make the vessels expand, yet it cannot be
regarded as the efficient cause ; since the sap is
proved to be in motion even throughout the whole
of the winter. Du Hamel endeavours, however,
to strengthen the operation of heat by means of
the influence of humidity, as being also powerful
in promoting the ascent of the sap, whether as re-
lative to the season of the year or time of the day.
The influence of the humidity of the atmosphere
cannot be conceived to operate as a propelling cause,
though it may easily be conceived to operate as
affording a facility to the ascent of the sap in one
way or other; which under certain 'circumstances
is capable of most extraordinary acceleration, but
particularly in that state of the atmosphere which
forebodes or precedes a storm. In such a state a
stalk of Wheat was observed by Du Hamel to grow
three inches in three days ; a stalk of Barley six
inches ; and a shoot of a Vine almost two feet ; but
this is a state that occurs but seldom, and cannot be
of much service in the general propulsion of the sap.
Linnaeus. On this intricate but important subject Linnaeus
appears to have embraced the opinion of Du
Hamel, or an opinion very nearly allied to it ; but
does not seem to have strengthened it by any new

SECT. III. CAUSES OF THE SA?'s ASCENT. 131

accession of argument; so that none of the hitherto
alleged causes can be regarded as adequate to the
production of the effect.

Perhaps the only cause that has ever been sug- Saussure.
gested as appearing to be at all adequate to the
production of the effect, is that alleged by M»
Saussure. According to Saussure the cause of the
sap's ascent is to be found in a peculiar species of
irritability inherent in the sap vessels themselves,
and dependant upon vegetable life ; in consequence
of which they are rendered capable of a certain
degree of contraction, according as the internal
surface is affected by the application of stimuli, as
well as of subsequent dilatation according as the
action of the stimulus subsides ; thus admitting
and propelling the sap by alternate dilatation and
contraction. In order to give elucidation to the
subject let the tube be supposed to consist of an in-
definite number of hollow cylinders united one to
another, and let the sap be supposed to enter the
first cylinder by suction, or by capillary attraction,
or by any other adequate means ; then the first
cylinder being excited by the stimulus of the sap,
begins gradually to contract, and to propel the con-
tained fluid into the cylinder immediately above it.
But the cylinder immediately above it, when acted
on in the same manner, is affected in the same
manner ; and thus the fluid is propelled from cy-
linder to cylinder till it reaches the summit of the
plant. So also when the first cylinder has dis-

K 2

]32 PROCESS OF NUTRITION. CHAP. III.

eharged its contents into the second, and is no
longer acted upon by the stimulus of the sap, it-
begins again to be dilated to its original capacity,
and prepared for the introsusception of a new
portion of fluid. Thus a supply is constantly kept
up, and the sap continues to flow.

Knight. The above is by far the simplest as well as most
satisfactory of all theories accounting for the ascent
of the sap. But Mr. Knight has presented us with
another which, whatever may be its real value, merits
at least our particular notice, as coming from an
author who stands deservedly high in the list of
phytological writers. This theory rests upon the
principle of the contraction and dilatation, not of
the sap vessels themselves, as in the theory of Saus-
sure, but of what Mr. Knight denominates the
silver grain, assisted perhaps by heat and humidity,
expanding or condensing the fluids. The appella-
tion of the silver grain seems to be synonymous
with that of the medullary rays already explained.
On the transverse section of the trunk of woody
plants, particularly the Oak, they appear in the
form of the radii of a circle extending from the
pith to the bark, and on the longitudinal cleft or
fissure of the trunk of most trees, but particularly
the Elm ; they appear in the form of fragments of
thin and vertical lamina or plates, interlacing the
ascending tubes in a transverse direction, and touch-
ing them at short intervals, so as to form with them
a sort of irregular wicker work, or to exhibit the
7

SECT. III. CAUSES OF THE SAP's ASCENT. 133

resemblance of a sort of web. Such then being
the close and complicated union of the plates and
longitudinal tubes, the propulsion of the sap in
the latter may be easily accounted for, as it is
thought, by means of the alternate contractation and
dilatation of the former, if we will but allow them
to be susceptible to change of temperature ; which
susceptibility is proved, as it is also thought, from
the following facts : — On the surface of an oaken
plank that was exposed to the influence of the sun's
rays, the transverse layers were observed to be so
considerably affected by change of temperature as
to suggest a belief that organs which were still so
restless, now that the tree was dead, could not have
been formed to be altogether idle while it was
alive. Accordingly on the surface of the trunk of
an Oak deprived of part of its bark, the longitu-
dinal clefts and fissures which were perceptible
during the day were found to close during the night.
But in the act of dilating they must press unavoidably
on the longitudinal tubes, and consequently propel
the sap ; while in the act of contracting they again
allow the tubes to expand and take in a new supply.
This, as I think, is the substance of the theory.*

But in drawing this grand and sweeping conclu-
sion, it should have been recollected that change of
temperature cannot act upon the transverse layers
of a tree that is covered with its bark in the same
manner as it acts upon those of a tree that is stripped
* Phil. Trans. 1801.

134 PROCESS OF NUTRITION. CHAP. III.

Insuffi- of its bark, or upon those of a plank ; and if it were
even found to act equally upon both, still its action
would be but of little avail. For according to what
law is the machinery of the plates to be contracted
and dilated, so as to give impulse to the sap ? Ac-
cording to the alternate succession of heat and
humidity. But this is by much too precarious an
alternation to account for the constant, and often
rapid, propulsion of the sap, especially at the season
of bleeding. For there may be too long a conti-
nuance of heat, or there may be too long a con-
tinuance of humidity ; and what is to become of
the plant during this interval of alternation? If
we are to regard it as happening only once in the
space of four and twenty hours, as in the case of
the Oak, it can never be of much efficacy in aiding
the propulsion of the sap. But if we should even
grant more, and admit the alternate contraction and
dilatation of the vessels to be as frequent as you
please, still their effect would be extremely doubt-
ful, owing to a want of unity or co-operation in
the action of different plates, or of different portions
of the same plate. If heat, like humidity, entered
the plant by the root, and proceeded gradually up-
wards like the ascending sap, perhaps it might be
somewhat efficacious in carrying a portion of sap
along with it ; but as this is not the case, and as
the roots of plants are but little affected by change
of temperature, while the trunk and upper parts
may be affected considerably, it can scarcely be

SECT. IV. ELABORATION OF THE SAP. 135

supposed that the action of the plates will be uni-
form throughout the whole plant ; or rather, it must
be supposed that it will often be directly in oppo-
sition to that which is necessary to the propulsion
of the sap. But admitting that the sap is pro-
pelled by the agency of the plates in question, and
admitting that it has been thus raised to the ex-
tremity of the woody part of the plant, how are
we to account for its ascent in such parts as are
yet higher — the leaf-stalk and leaf, the flower-
stalk and flower ; as well as in the herb also, and
in the lofty Palm, in which no such plates exist ?
Here it .will be necessary to introduce the agency
of a new cause to complete the work that has been
thus begun, and of a new set of machinery to
supply the deficiency or absence of the machinery
that has been already invented. In short the theory
of Mr. Knight is beset with so many difficulties, and
the agency of the alleged cause so totally inadequate
to the production of the effect to be accomplished,
that of all theories on the subject it is perhaps the
least satisfactory,

SECTION IV.
Elaboration of the Sap,

THE moisture of the soil is no sooner absorbed Com-
into the plant than it begins to undergo a change, the root
This is proved by the experiment of making a bore OI
or incision in the trunk of a tree during the season

136 PROCESS OF NUTRITION. CHAP. III.

of bleeding; the sap that issues from the wound
possesses properties very different from the mere
moisture of the soil, as is indicated by means of
chemical analysis, and sometimes also by means
of a peculiar taste or flavour, as in the case of the
Birch-tree. Hence the sap has already undergone
a certain degree of elaboration ; either in passing
through the glands of the cellular tissue, which it
reaches through the medium of a lateral commu-
nication, or in mingling with the juices contained
in the cells, and thus carrying off a portion of them ;
in the same manner, we may suppose, that water by
filtering through a mineral vein becomes impreg-
nated with the mineral through which it passes.

But this primary and incipient stage of the
process of elaboration must always of necessity
remain a mystery to the phytologist, as being
wholly effected in the interior of the plant, and
consequently beyond the reach of observation.
All he can do, therefore, is to trace out its future
progress, and to watch its succeeding changes, in
which the rationale of the process of elaboration
may be more evident.

But is The next, and indeed the principal, part of the

fectecHn process of the elaboration of the sap is operated

*n ^e ^ea^ : *°r t^le saP no sooner reaches the leaf
than part of it is immediately carried off by means of
perspiration, perceptible or imperceptible ; effecting
a change in the proportion of its component parts,
and by consequence a change in its properties.

SECT. IV. ELABORATION OF THE SAP. 137

Imperceptible perspiration is an excretion of sap Impercep-
thrown off by the Epidermis of the leaf or other u
tender parts of the plant, in consequence of the
healthy action of the vegetable organs. It is not
discoverable by the external senses, as the name
indeed implies, but is legitimately inferred from
the following fact: — If the branch of a tree is lopped,
and the section of the part lopped off covered with
mastick, the branch will be found in the course of
a few days to have lost in weight. This was ori-^ .
ginally an experiment of Mariotte's, and the loss in
weight is to be accounted for only on the principle
of the perspiration of the sap escaping through the
pores of the epidermis. This conclusion may per-
haps be regarded as not altogether satisfactory, as
being founded on an experiment made only on a
lopped-off branch. But the same conclusion fol-
lows from experiments on the living plant : — Hales
reared a Sun-flower in a pot of earth till it grew to
the height of three feet and a half; he then covered
the mouth of the pot with a plate of lead, which
he cemented so as to prevent all evaporation from
the earth contained in it. In this plate he fixed
two tubes, the one nine inches in length and of but
small diameter, left open to serve as a medium of
communication with the external air; the other two
inches in length and one in diameter, for the pur-
pose of introducing a supply of water; but kept
always shut except at the time of watering. The
holes of the bottom of the pot were also shut, and

133 PROCESS OF NUTRITION. CHAP. III.

the pot and plant weighed for fifteen successive
days in the months of July and August ; hence he
ascertained, not only the fact of transpiration by
the leaves, from a comparison of the supply and
waste ; but also the quantity of moisture transpired
in a given time, by subtracting from the total waste
the amount of evaporation from the pot. In a dry
and hot day it transpired the most, and in a damp
and wet day it transpired the least ; the mean rate
of transpiration being 1 Ib. 4oz. — 17 times more in
proportion than that of the human body. In a hot
and dry night without dew it transpired 3oz. ; in
a dewy night it did not transpire at all ; and in a
rainy night, or night of much dew, its weight was
increased by 3oz.

Hales suspected that the quantity transpired was
in proportion to the extent of the surface of the
leaves, which he regarded as the principal organs
of transpiration ; and ascertained also the relative
proportion of the capacity of the leaves for trans-
piration as compared to the capacity of the root
for absorption. The surface of the leaves and stem
of the plant which was the subject of experiment
was found to be equal to about 56 1 6 square inches ;
and the surface of the root of the same plant, or
rather, as I believe, of a plant of nearly the same
size, was found to be about 2280 square inches, the
latter being to the former in the proportion of two
to five ; from which it follows that the absorbing
power of the root is greater than the transpiring

SECT. IV. ELABORATION OF THE SAP. 13Q

power of the leaves, in the proportion of five to two.
Similar experiments were also made upon some
species of cabbage, whose mean transpiration was
found to be lib. 3oz. per day; and on some species
of evergreens, which were found, however, to tran-
spire less than other plants. The same is the case
also with succulent plants, which transpire but little
in proportion to their mass, and which as they
become more firm transpire less. It is known,
however, that they absorb a great deal of moisture,
though they give it out thus sparingly ; which we
cannot but regard as a wise institution in nature for
the purpose of resisting the great droughts to which
they are generally exposed, inhabiting, as they do for
the most part, the sandy desert or the sunny rock.
Along with his own experiments Hales relates
also some others that were made by Mr. Millar,
of Chelsea ; the result of which was that, other cir-
cumstances being the same, transpiration is in pro-
portion to the transpiring surfaces ; and is affected
by the temperature of the air, sunshine, or drought
promoting it, and cold and wet diminishing or
suppressing it entirely. It is also greatest from
six o'clock in the morning till noon, and is least
during the night. But when transpiration becomes
too abundant owing to excess of heat or drought,
the plant immediately suffers and begins to lan-
guish ; and hence the leaves droop during the day,
though they are again revived during the night.
For the same or for a similar reason, transpiration

PROCESS OF NUTRITION. CHAP. III.

has been found also to increase as the heat of
summer advances ; being more abundant in July
than in June, and still more in August than in
either of the preceding months, from which last
period it begins again to decrease.

But the most remarkable instance of rapid tran-
spiration yet observed is that which is related by
Guettard, who found that a small sprig of the
Corneil-tree or Cornelian Cherry, Cornus mascula,
transpired in the course of a day 1 oz. 3£ drams,
a quantity almost double its own weight. He found
also in general that branches deprived of their
leaves afford but little transpired matter, and that
branches furnished with their leaves afford a great
deal ; it follows, therefore, of necessity that the
leaves, as Hales suspected, are the principal organs
of transpiration.

The substance thus transpired by the plant may
be obtained by enclosing a bough in a glass vessel
of proper dimensions luted to the branch. Its pro-
perties have not yet been very minutely investi-
gated ; Hales and Guettard could discover in it
nothing different from common water except that in
some cases it had the odour of the plant ; but Du
Hamel found that it became sooner putrid than water.
Or per- Such then are the facts that have been ascertained
with regard to the imperceptible perspiration of
plants, from which it unavoidably follows that the
sap undergoes a very considerable modification in
its passage through the leaf. But it often under-

SECT. iv. JELABORATION OF THE SAP. 141

goes also a further modification in consequence of
what may be called perceptible perspiration, which
is an exudation of sap too gross or too abundant
to be dissipated immediately, and which hence ac-
cumulates on the surface of the leaf. It is very
generally to be met with in the course of the
summer on the leaves of the Maple, Poplar, and
Lime-tree ; but particularly on the surface exposed
to the sun, which it sometimes wholly covers. Its
physical as well as chemical qualities are very dif-
ferent in different species of plants ; so that it is
not always merely an exudation of sap, but of
sap in a high state of elaboration, or mingled
with the peculiar juices or secretions of the plant.

Sometimes it is a clear and watery fluid conglo-
merating into large drops, such as are said to have
been observed by Mr. Millar, of Chelsea, exuding
from the leaves of the Musa arbor> or Plantain-
tree ; and such as are sometimes to be seen in hot
and calm weather, exuding from the leaves of the
Poplar, or Willow, and trickling down in such
abundance as to resemble a slight shower. This
Phenomenon was observed by Dr. Smith under a
grove of Willows, in Italy,* and is said to occur
sometimes even in England.-}- Sometimes it is
glutinous, as on the leaf of the Lime-tree ; some-
times it is waxy, as on the leaves of Rosemary;
sometimes it is saccharine, as on the Orange leaf,
according to the account of M. De la Hire, as re-
* Lectures at R. lust. + Introd. p. 188.

142 PROCESS OF NUTRITION. ^ CHAP. Ill,

lated by Du Hamel ; who having observed under
some Orange-trees a saccharine substance some-
what resembling Manna, found upon further invesj.
tigation that it had fallen from the leaves.* Some-
times it is resinous, as on the leaves of the Cistus
creticuSy from which the resin known by the name
of Labdanum is obtained, by means of beating it
gently with leathern thongs to which the exudation
adheres ;-f- as also on the leaves of the Populus
dilatata, or Lombardy Poplar, the exudation from
which Ovid in his metamorphosing flights regards as
the tears of Phaeton's sisters, whom he transforms,
as it is supposed, into this species of Poplar.^
Their tears were now gum.§ The leaves of Frax-
inella or Dictamnus albus are also said to be often
covered with a sort of resinous substance. And
after a hot day, if the air is calm, the plant is even
found to be surrounded with a resinous atmosphere,
which may be set on fire by the application of the
flame of a candle. This, as I think, was the dis-
covery of a daughter of the celebrated Linnaeus.

The cause of this excess of perspiration has
not yet been altogether satisfactorily ascertained ;
though it seems to be merely an effort and insti-
tution of nature to throw off all such redundant

* Phys. des Arb. vol. i. p. 130. f Voyage de Tournefort

I Smith's Introd. p. 189.

§ Inde flaunt lachrymae, stillataque sole rigescunt

De ramis elcctra novis, quse lucidus amnis

Excipit, et nuribus inittit gcstanda Latinis. Ovid. Met. ii.

SECT. IV. ELABORATION OF THE SAP. 143

juices as may have been absorbed, or secretions as
may have been formed, beyond what are necessary
to the due nourishment or composition of the plant,
or beyond what the plant is capable of assimilating
at the time. Hence the watery exudation is per-
haps nothing more than a redundancy of the fluid
thrown off by imperceptible perspiration,, and the
waxy and resinous exudations nothing more than
a redundancy of secreted juices ; all which may be
still perfectly consistent with a healthy state of the
plant. But there are cases in which the exudation
is to be regarded as an indication of disease, par-
ticularly in that of the exudation known by the
name of Honey-dew, a sweet and viscid substance
covering the leaves like a varnish, and sometimes
occasioning their decay, Such at least seems to be
the fact with regard to the honey-dew of the Hop,
which, according to the observations of Linnaeus,
is the consequence of the attacks of the caterpillar
of the ghost moth injuring the root. And such
seems also to be the fact with regard to the honey-
dew of the Beech-tree, which Dr. Smith regards
as the consequence of an unfavourable wind.* But
whether the honey-dew of the Oak is to be re-
garded as an indication of disease I cannot say, as
I have often met with it on trees and leaves that
seemed perfectly healthy. The sap then in the
progress of its ascent from the extremity of the
root to the extremity of the leaf undergoes a con-
* Introduction, p. 18y.

144 PROCESS OF NUTRITION. CHAP. III.

siderable change, first in its mixing with the juices
already contained in the plant, and then in its
throwing off a portion at the leaf. Perhaps it is
also further aifected by means of the gases entering
into the root along with the moisture of the soil,
but certainly, by means of the gases inhaled into
the leaf; the action and elaboration of which I
shall now proceed to elucidate.

SECTION V.
Elaboration of Carbonic Acid.

Carbonic THE utility of carbonic acid gas as a vegetable
inhalecTby f°°d nas heen already shown in the preceding

chapter, in which plants were found not only to
absorb it by the root along with the moisture of
the soil ; but also to inhale it by the leaves, at
least when vegetating in the sun or during the day.
But how is the elaboration of this gas effected? Is
it assimilated to the vegetable substance imme-
diately upon entering the plant, or is its assimilation
effected by means of intermediate steps ? The gas
thus inhaled or absorbed is not assimilated imme-
diately, or at least not wholly : for it is known
Evolved that plants do also evolve carbonic acid gas when
nigh".8 1 1C vegetating in the shade, or during the night. The
circumstance that led to this discovery was as fol-
lows : — About the year 1771, Priestley in his experi-
ments on air found that a cabbage leaf which was

SECT, V. ELABORATION OF CARBONIC ACID. J'15

placed under a glass vessel filled with common air
for the space of one night only, had so affected its
atmosphere by next morning that a candle would
not burn in it, and yet the leaf showed no symp-
toms of putrefaction.* This fact he did not at the
time attempt to account for ; so that it was not yet
known whether the change produced in the atmos-
phere of the leaf was occasioned by the abstraction
of any constituent part, or by the addition of any
extraneous substance. The true cause was after-
wards ascertained by Saussure : into a receiver con-
taining only atmospheric air, Saussure introduced
some plants of Vitia Faba, and placed the appa-
ratus in the shade ; but at the end of six days
when the experiment was stopped, the atmosphere
of the receiver was found by the application of
lime water to contain ^y^ of carbonic acid* Into
another receiver containing also atmospheric air he
introduced at the same time several other plants of
the same species, together with a small quantity of
lime, and placed the receiver over lime water,
leaving the apparatus in the shade. At the end of
the six days of experiment the atmosphere of the
feceiver contained --f-y- of carbonic acid, though a
great deal must have been abstracted also by the
lime ; but in both these experiments the excess of
Carbonic acid gas found in the atmosphere of the
plants, could have been derived only from the
plants themselves. Plants, then, vegetating in coii-

* Priestley on Air, vol. i. p. 51.
VOL, II. £

146 PROCESS OF NUTRITION. CHAP. III.

fined atmospheres evolve carbonic acid gas in the
shade, or during the night ; and the vitiated state
of their atmospheres after experiment is owing to
that evolution.

Process of But in this alternate inhalation and extrication
t!on.a *" of carbonic acid, is any part of it assimilated to the
plant? or is the quantity extricated always equal
to the quantity inhaled ? From the continual in-
crease of the carbon of the vegetating plant, the
assimilation of carbonic acid is unquestionable ;
and the supply inhaled by the leaves indispensable
to vegetation. For if the carbonic acid that is
evolved in the night is withdrawn from the artificial
atmosphere as soon as it is formed, the leaves
wither and the plant dies. Into a receiver con-
taining atmospheric air deprived of its carbonic
acid, in which a Pea had been made to vegetate,
Saussure introduced a small quantity of lime,
placing the receiver over lime water, and exposing
the apparatus to the sun. On the second day the
atmosphere of the plant had diminished in volume.
On the third day the lower leaves began to fade ;
and on the fifth or sixth day the stem was com-
pletely stript of its leaves ; the atmosphere when
examined was found to be vitiated, containing
only TVV °f oxygeue. But there had been an ab-
sorption of carbonic acid by the lime, and conse-
quently a formation of that acid, the component
parts of which could have been derived only
from the plant. The elaboration of carbonic acid

SECT. V. ELABORATION OF CARBONIC ACID. 147

gas, therefore, is essential to vegetation in the
sun.

But plants which were made to vegetate at the
same time in receivers filled with common air with-
out lime had effected no change in their atmosphere
either in purity or volume ; this seems to contradict
the necessity of the elaboration of carbonic acid.
But the process was here imperceptible only because
the plant again inhaled the gas in the same pro-
portion in which it had previously evolved it, or
formed it with the surrounding oxygene.

It should be added, however, that the action of
lime water did not produce the same destructive
effect upon the leaves of succulent plants, such as
the Cactus, when treated as above ; which, owing
to their very thick parenchyma and less porous
epidermis, thus seem to retain more obstinately the
carbonic acid which they form.

But the result of such experiments as were con-
ducted in the shade was very different ; for so far
were plants thus exposed from showing any symp-
toms of langour or decay when placed under re-
ceivers containing lime and lime water, that their
growth was even more vigorous than that of others
which were placed under receivers containing only
common air. The mean augmentation of each
plant in the receiver containing lime was seven
grains in the space of six days ; and the proportion
of carbonic acid remaining after the experi-
ment T-J-yj while the mean augmentation in the

J. 2

t48 PROCESS OF NUTRITION. CHAP. Ilk

receiver without lime was only five grains in the
same space of time, though it appeared by the
application of lime water that the proportion of
carbonic acid remaining after the experiment was
TyT. Saussure explains the phenomenon thus :
the great quantity of carbonic gas evolved by plants
in the shade is prejudicial to their vegetation at
least in confined atmospheres ; but a partial priva-
tion of the gas thus produced is beneficial to their
vegetation.*

The foregoing experiments were made upon
plants vegetating in pure water j but Saussure made
some experiments also on plants vegetating in the
earth, by means of enclosing part of a bough in a
large globe of glass. The results obtained were
upon the whole similar to the former; but in the
case of the decay of the leaves by their exposure
to the sun and to the action of lime, the effect was
produced more slowly. It should be recollected,
however, that the cases are not precisely similar ;
for though the plants were in both cases equally
deprived of the external action of carbonic acid ga*
upon their leaves ; yet there was a supply of that
gas communicated to the plant from the oil in the
one case that could not have been communicated to
it in the other.
By the as- The elaboration of carbonic acid then in plants

aimilation . . .

of its car- exposed to the sun is unquestionable: but in what
evolution state is '* actually assimilated to the plant ? Is it
Xy" 'Snr.laVeg.chap.*

SECT. V. ELABORATION OF CARBONIC ACID. 149

assimilated in the state in which it is inhaled ? or
is it previously decomposed ? It had been observed
by Ingenhoutz that the leaves of plants, if placed
in water and exposed to the action of the sun's rays,
will evolve a quantity of oxygene gas. It was af-
terwards ascertained by Senebier that this process
takes place only when the leaves are fresh and the
water impregnated with carbonic acid. For when
the water was deprived of its carbonic acid by
boiling, or in the course of experiment, there was
no more oxygene evolved. But when the water
was again impregnated with carbonic acid, the
extrication of oxygene recommenced as before ; the
conclusion, therefore, is obvious and the pheno-
menon satisfactorily accounted for. The carbonic
acid gas contained in the water is abstracted and
inhaled by the leaf, and immediately decomposed ;
the carbon being assimilated to the substance of the
plant, and the oxygene evolved.

Such was the important discovery of Senebier,
affording an undoubted proof of the decomposition
of carbonic acid. But the effects of that decompo-
sition had not yet been analysed ; nor was it yet
ascertained whether the quantity of oxygene evolved
was more or less than the quantity contained in
the composition of the carbonic acid, or equal to it.
The solution of the question was reserved for Saus-
sure, who after a variety of experiments obtained
the most satisfactory results.

In an artificial atmosphere composed of common

150 PROCESS OF NUTRITION. CHAP. III.

air and carbonic acid gas the eudiometer indicated
.jSjiy-of oxygene ; and lime water 7? of carbonic
acid gas. Into the receiver containing this at-
mosphere there were introduced several plants
of the Vinca minor ; the apparatus was exposed
during six days to the direct rays of the sun, from
five o'clock in the morning till eleven. On the
seventh day the plants were taken out ; they had
undergone no alteration, nor had their atmosphere
sustained any perceptible change of volume. But
the lime water gave no longer any indication of the
presence of carbonic acid gas, and the eudiometer
indicated 24- 5 parts in the hundred of oxygene.
The capacity of the receiver was 2QO cubic inches ;
it contained, therefore, before the experiment 31 1 '0,2
inches of nitrogene, 56*33 of oxygene, and 2175
of carbonic acid. But after the experiment it was
found to contain 218'95 cubic inches of nitrogene,
and 71*05 of oxygene, which were the whole of its
contents ; the carbonic acid gas had disappeared.
The plant then had decomposed or elaborated 21£
cubic inches of carbonic acid gas. Now, if in the
process of decomposition the whole of the oxygene
had been disengaged, there would have been also a
quantity of oxygene produced equal in volume to
the carbonic acid that had disappeared ; but the
quantity of oxygene disengaged was only 14-f- cubic
inches, The plants then had assimilated seven
cubic inches of oxygene in decomposing the car-
bonic acid ; and had at the same time produce^

SECT. V. ELABORATION OF CARBONIC ACID. 151

seven cubic inches of nitrogene. Several plants
of the same species were made to vegetate in a
similar apparatus, at the same time and in the same
exposure, in pure atmospheric air. Their atmos-
phere was not altered either in purity or volume,
but their carbon instead of augmenting had rather
diminished ; whilst the carbon of the others, as
was found by comparative analysis had augmented
very considerably. Experiments of the same Of which
kind were made upon Mentlia aquatica, Lythrum Js
Salicaria, Pinus genevensis, and Cactus Opuntia ; a part*
and the results were always similar, from which it
follows also that plants decomposing carbonic acid
gas assimilate at least a part of the oxygene which
it contains.

Such are the several results obtained from expe-
riments, concerning the accuracy of which there
can be no doubt. The decomposition of carbonic
acid gas takes place only during the light of day,
though Saussure has made it also probable that
plants decompose a part of the carbonic acid gas
which they form with the surrounding oxygene
even in the dark. But of this there does not yet
exist any satisfactory proof; how the light acts is
not certainly known. But the effect is operated
chiefly by means of the leaves and other green parts
of vegetables, that is, chiefly by the parenchyma ;
the wood, roots, petals, and leaves that have lost
their green colour not being found to exhale oxy-

PROCESS OF NUTRITION. CHAP. W.

gene gas. It may be observed, however, tbat tbe
green colour is not an absolutely essential character
of the parts decomposing carbonic acid ; because
the leaves of a peculiar variety of the d triplex
hortensis, in which all the green parts change to
red, do still exhale oxygene gas. But all leaves
have not the same facility in decomposing carbonic
acid; a plant tf Ly thrum Salicaria has been known
to decompose in one day seven or eight times its
volume, while many other plants cannot decon>
pose the one-fifth or even the one-tenth of that
quantity; though in general it may be observed
that the leaves and other green parts of the plant
decompose it in proportion to their surface, and not
in proportion to their volume. But how is the
formation of nitrogene to be accounted for, which
is always found to be extricated along with the
oxygene thus evolved by the leaves ? The subject
is yet enveloped in much obscurity, as well as the
means of giving it the elucidation to be desired ;
but perhaps it is abstracted from the interior of the
leaf through the medium of the evolved oxygene
for which it is known to have an affinity.

SECT. VI. ELABORATION OF OXYGENE. 153

SECTION VI.

Elaboration of Oxygene.

IN treating of the utility of the gases as a vege-
table food it has been already shown that the leaves
of plants abstract oxygene from confined atmos-
pheres, at least when placed in the shade, though
they do not inhale all the oxygene that disappears ;
but it has been further proved from experiment,
that the leaves of plants do also evolve a gas in the The leaves
sun. This phenomenon was first observed by disengage

Bonnet, who gave indeed a wrong explanation of it ;
belivingr it to be the extrication of the air that might shown by

Bonnet,

have entered the plant along with the sap, or be-
lieving it to come directly from the water. His
method was to expose the leaves to the sun, in an
inverted glass vessel filled with water; air bubbles
began immediately to disengage themselves from
the surface of the leaves, and to ascend to the sum-
mit of the water.

The next experiments on this subject are those of And
Priestley, who discovered that the leaves of plants
in a state of vegetation have the property of ameli-
orating vitiated air. On the 17th of August 1771>
he put a sprig of Mint into a quantity of atmo-
spheric air in which a candle had burnt out, and
found after confining it till the 27th of the same
month, that the air was again ameliorated and ca-

154 PROCESS OF NUTRITION. CHAP. III.

pable of supporting combustion : another candle
burned in it perfectly well.^ The experiment suc-
ceeded also with sprigs of Balm, and with plants of
Groundsel and Spinach, and the process seemed to
depend on the vegetating state of the plant; for
\vhendetached leaves only were introduced., they did
not ameliorate the air, though they were yet per-
fectly fresh. The ameliorating of a quantity of
vitiated air by means of confining a sprig of Winter
Savoury in it for five or six days was ascertained
also by the application of the eudiometer. Equal
measures of the confined atmosphere and nitrous
gas occupied a space equal only to 1 '275. Hence
the vitiated air was evidently ameliorated by the
plant. It does not, however, appear that Priestley
had yet discovered the rationale of the above ame-
lioration, whether it was by abstraction or extrica-
Who finds tion ; but he discovered some years afterwards that
pure or plants, when placed in water and exposed to the

'*Snt °f tne sun* £^ve out wnat was tnen called pure
or dephlogisticated air. In the course of his ex-
periments on the growth of plants in water impreg-
nated with fixed air, he had observed air-bubbles
issuing spontaneously from the stalks and roots of
several plants growing in water that was not so im-
pregnated ; believing that the air thus extracted had
percolated through the plant, he thought he had
now discovered the clue that was to lead him infal-
libly to the ascertaining of the fact of the ameliora-
* On Air, vol. i. p. 60.

SECT. VI. ELABORATION OF OXYGENE. 155

tion or contamination of the air of the atmosphere
effected by the vegetating plant. For if this air was
purer than that of the atmosphere, then it seemed
to afford a proof that the phlogiston of the atmos-
pheric air had heen retained by the plant as its true
food, and the pure part liberated, agreeable to the
hypothesis by which he supposed phlogiston to be
the pabulum of plants.

In order, therefore, to ascertain the fact he plung-
ed into water a number of phials containing sprigs
of Mint, so as that the air discharged might be re-
tained in them, the bottoms being a little elevated.
The sprigs thus placed continued to vegetate and also
to evolve air, so that in the course of a few days he
procured an ounce measure of it, which proved to
be so pure that when mixed with equal measures of
nitrous gas the mixture occupied but the space of
one measure. In repeating the experiment he
found that many of his phials became lined with a
green vegetable matter, Conferva minima, which also
gave out bubbles of pure air when exposed to the
light of the sun, but never except in such exposure.

From the above experiments, made in the month
of June 1788, Priestley inferred that the air of the
atmosphere is ameliorated through the process of
vegetation, and purged of the impurities with which
it is loaded by the putrefaction of vegetable and
animal substances, the noxious part being assimi-
lated to the substance of the plant, and the remain-
ing part evolved pure ; so that the atmosphere even

150 PROCESS OF NUTRITION. CHAP. III.

of bogs and marshes is purified, and rendered at
least less insalubrious by means of the plants that
grow in them, such as the Conferva and Duck-*
meat, which last thrives, as he says, better in in-
flammable than even in dephlogisticated air.
Oroxy- Whatever may be the legitimacy of this conclu-
provedby sion, upon the whole the facts from which it is
houtz; drawn prove incontrovertibly that plants vegetating
in the sun exhale an air purer than that of the at-
mosphere. But the air thus exhaled was afterwards
ascertained by Ingenhoutz to be pure oxygene gas ;
Which is plants then in the process of vegetation inhale
during the oxygene gas in the shade or during the night, and
d exhale it in the light of the sun or during the day.

during the $ut the detail and rationale of the different processes
remained yet to be inquired into, as also, whether
any part of the oxygene inhaled was assimilated to
the plant; or whether plants evolve in the day
exactly what they inhale in the night.

Experi- Jt was at first supposed that plants assimilate the

roents of

Saussure. whole, or at least the greater part, of the oxygene
they inhale in the night ; but this opinion was soon
found to be erroneous, as will appear from the ex-
periments of Saussure, whose view of the whole
process of the influence of oxygene on the vegetat-
ing plant is so full and satisfactory as to leave but
little unexplained ; of which view the following is an
abstract : — a Cactus of six cubic inches in volume,
which had inhaled during the night four cubic
inches of oxygene, was exposed on the following

SECT. VI. ELABORATION OF OXYGENE.

morning to the action of the sun's light in a receiver
containing 48 cubic inches of atmospheric air de-
prived of its carbonic acid. In the succeeding
evening its atmosphere was found to be augmented
by 4 -4 cubic inches, but without any accession of
carbonic acid ; 274- parts in the hundred being
oxygene, as indicated by the eudiometer, and the
remainder being nitrogene. Before the experiment
the receiver contained 10*1 cubic inches of oxygene,
and 3 7 '9 °f nitrogene ; after the experiment it con-
tained 14-28 of oxygene, and 38*1 of nitrogene.
The amount of the difference, then, or the quantity
of gas extricated was 4-18 cubic inches of oxygene,
and O*2 of nitrogene. The experiment was con-
tinued with the same plant during seven successive
days and nights. In the course of the second night
the quantity of oxygene inhaled was equal to 3%-
<?ubic inches ; and in the course of the following day
the quantity of gas evolved was equal to four cubic
inches of oxygene, and % cubic inch of nitrogene.
In short it was found during the seven days of ex-
periment, that the quantity of oxygene alternately
inhaled and evolved, during the night and day, was
always diminishing ; and the quantity of nitrogene
extricated, always increasing ; the quantity of oxy-
gene inhaled upon the whole being 21-f- cubic inches,
and the quantity of gas evolved upon the whole
being 29^- cubic inches, of which 23^- were oxygene
and 6^- nitrogene.

Saussure varied the experiment upon the extrica*

158 PROCESS OF NUTRITION. CHAP. III.

tion of oxygene gas, by means of immersing a plant
in distilled water during the day, which had been
placed under a receiver filled with atmospheric air
deprived of its carbonic acid during the night. The
general result was the same as in the foregoing ex-
periment ; but owing to the constrained and un-
natural situation of the plant the process did not go
on so rapidly, and the oxygene given out was con-
taminated by a considerable quantity of nitrogene.
Leaves sa- When the leaves were kept constantly in the
withoxy- shade and in a confined atmosphere, without being
gene* at all exposed to the light of day, they continued to
inhale oxygene slowly till they were saturated ;
when they refused to inhale any more. The quantity
necessary to their saturation was about l-^ their
volume ; and the time necessary to complete the
Still con- process from 36 to 4O hours. But still they con-
consume tinued to act upon the surrounding oxygene, with
which and with' the carbon they contained they
formed carbonic acid, consuming about ~ the oxy-
gene they consumed by inhalation, but not thus
altering the volume of their atmosphere. But
when they were again exposed to the sun, they
evolved, in the space of seven or eight hours, a much
greater quantity of oxygene than when they were
confined in the receiver only for one night. Six
cubic inches of the Cactus Opuntia which by re-
maining 36 successive hours under a receiver in the
dark had inhaled 7~ cubic inches, while in the
course of one night it inhaled only four ; evolved

1

SECT. VI. ELABORATION OF OXYGENE.

during the succeeding day, when exposed to the
light of the sun, 74- cubic inches also.

The quantity of oxygene, therefore, which isTh

,7 . ' tides aiter-

exhaled during the day is proportional and nearly nately in-
equal to the quantity inhaled during the night, or

during the time of the plant's confinement in the
shade up to its saturation. The former quantity is
generally indeed somewhat more than the latter,
which Saussure regards as being probably owing
to the decomposition of water in the plant. But
whatever may be the true explication of this par-
ticular phenomenon, it is evident that no permanent
assimilation of oxygene js effected in the alternate
process of its inhalation and extrication by the
leaves, so as to increase materially the quantity of
dried vegetable substance.

But as plants vegetating in the shade and in con- Saturation

occurs

nned atmospheres become so soon saturated with only in
oxygene and refuse to absorb more, one might be ^0?
apt to conclude that plants vegetating even in the$i>her""
open air, if situated in the shade, must become
saturated with it also, and refuse to absorb more
when placed in an Artificial atmosphere. This,
bowever, is not the fact. Saussure tried the ex-
periment repeatedly, and found that plants confined
in an artificial atmosphere, after having been ex-
posed to the open air in the shade, always inhaled
oxygene as in other cases ; so that by frequently
changing their exposure from the natural to the artifi-
cial atmosphere and the contrary, they were capable

160 PROCESS OF NUTRITION. CHAP. III.

of being made to inhale an unlimited quantity of
oxygene many times the size of their own volumes*
Why ? What is the cause of this apparent anomaly ?

Why are not leaves which are made to vegetate in
the dark, saturated with oxygene in the open air as
well as in confined atmospheres ? and why does their
alternate exposition in the receiver and in the open
air give them the property of inhaling an unlimited
quantity. The truth is, that the inhalation of this
unlimited quantity is a mere deception, produced by
the action of the atmospheric air upon the carbonic
acid contained in the leaves. The air of the atmos-
phere has a chemical affinity for carbonic acid gas,
as has been already shown upon the authority of
Bertholet,* and abstracts, by consequence, a portion
of it from the leaf which it thus prepares for com*
mencing anew the process of inhalation ; so that
however long the alternate change of exposition
may be continued, there is no accumulation of car-
bonic acid or of oxygene.

inhalation But the inhalation of oxygene seems to depend
onPtheant uPon tne structure and organization of the leaf; for
structure Saussure found with regard to the Cactus what

of the leaf.

Senebier found with regard to other leaves — that
when they were cut into pieces and pounded in a
mortar, so as to destroy their organization, and then
placed under a receiver filled with common air, no
inhalation took place ; though they formed carbonic
acid gas, by the combination of the carbon which
* Mem. tic rinst. Nat. torn. iii.

6

SECT. VI. ELABORATION OF OXYGENE. l6l

they contained with the oxygene of their atmos-
phere ; the juice of the plant was coagulated.
Hence the oxygene inhaled by the leaf of the vege-
tating plant seems also to form carbonic acid gas
with the carbon which the leaf already contains ;
and in this state it probably remains in the paren-
chyma, till exposed to the action of light. There is
not indeed any direct proof that this is the fact ; but
there is no other supposition that will explain the
phenomena of the process so well.

But if the oxygene inhaled by the plant is thus Affinityby
converted into carbonic acid, and condensed in the0xygeneis
parenchyma, by what affinity is it retained? Itretamed>
cannot be extricated by placing the plant in the
vacuum of an air pump. Six cubic inches of a
Cactus which had inhaled during one night four
cubic inches of oxygene, gave out in the vacuum
of an air pump only one cubic inch of air contain-
ing not more than Ty^ of oxygene gas. A heat,
without light, sufficiently moderate not to destroy
the vegetable, produced no better effect. It is re-
tained therefore by an affinity too strong to be over-
come by such means. It is overcome, however, by
means of the action of the sun's light, as is demon-
strated by the clearest evidence ; but how the light
acts is not known.

The property then which plants possess of in-
haling and evolving oxygene in the night and day
is analogous, and seems to be subordinate, to that by
which they decompose carbonic acid. The green

VOL. II. M

]g2 PROCESS OF NUTRITION. CHAP. III.

parts which effect the decomposition of the latter
effect also the alternate inhalation and extrication of
the former ; which two operations seem to be the
cause, the one of the other. When a leaf is put
into the shade immediately after having been ex-
posed to the light of the sun, it contains no carbonic
acid gas, because that gas has been decomposed by
Overcome the light ; but the oxygene of the atmospheric air
b7 l'6ht> which now penetrates and traverses the leaves, is
seized in its passage by the carbon of the plant.
And hence carbonic acid gas is again formed, which
loses its elasticity by its union with the water of
vegetation ; and which undergoes also a compression
by means of the vegetable structure, bounded how-
ever by certain limits, since plants which absorb the
most do not absorb more than TV of their volume.
They are now therefore saturated, and evolve by con-
sequence carbonic acid gas ; but the action of the
oxygene is in both cases the same — namely, that of
forming carbonic acid with the carbon of the plant.
But forms Before saturation the carbonic acid is condensed in
carbonic ^e p|ant ; but after saturation it is evolved, because
the plant can contain no more. Hence it follows
also that leaves do not immediately assimilate the
oxygene of the atmosphere which they inhale during
the night, unless they then decompose part of the
carbonic acid which is thus formed, and of which
experiment affords no proof. There can be no con-
clusion drawn from the phenomena produced in the
dark, in atmospheres deprived of oxygene ; because

SECT. VI. ELABORATION OF OXYGENfi. 163

in this case vegetation is altogether suspended. The
plant soon discovers a tendency to putrefaction,
furnishing from its own substance, and in conse-
quence of its decomposition, the two elements of
carbonic acid gas.

The foregoing results which were obtained from Condi-
experiments on Cactus Opuntia are equally appli- SUCeessful

cable to the leaves of other plants, though not in so
perceptible a degree. But the more succulent any the leaves-
leaf is the better it is fitted for experiment ; because
succulent leaves contain a great quantity of green
herbaceous matter within a small volume, while the
leaves of most other plants are so thin and fine, and
their surface so much extended that the experiment
is not only more difficult but the result less striking.
According to Saussure, the following conditions are
necessary in order to ensure success in experiment:
— the leaves must be perfectly sound and fresh, and
they must displace from about the TV to ~ part of
their volume of the air contained in the receiver, for if
they displace less, the effect is not sufficiently per-
ceptible, and if more, there is too little oxygene
left. When the apparatus is placed in the sun, the
leaves must not touch the sides of the receiver,
which is then so hot as to disorganize the structure
of the plant.

But although the quantity of oxygene extricated
in the day is proportional to the quantity inhaled in
the night, yet the specific quantity inhaled is very
different in the leaves of different plants. The leaves

M 2

PROCESS OF NUTRITION. CHAP. III.

of succulent plants consume less than most others,
but they retain it also more obstinately — that is, they
give out less carbonic acid — perhaps because they
present fewer points of contact to the surrounding
air, and are furnished with fewer pores in their
epidermis ; hence they lose but little of their carbon,
even when vegetating in the open air, and can live
for a long time under the privation of that part of
their nourishment: and hence also their peculiar
aptitude to the different sorts of soil in which they
naturally grow — sand, clay, or the barren rock, as
in the case of Sedum, Saxifrage Sempervivum.

Plants inhabiting marshes consume less oxygene
than other herbaceous plants, which proceeds no
doubt from an institution in nature fitting them for
the situation in which they vegetate, and in which
they are deprived of the free access of oxygene,
owing to the vapours that surround them ; hence the
herbaceous plants of the mountain, where the supply
of oxygene is but little, are often to be found in the
marshes of the plain.

The leaves of ever-greens consume also but little
oxygene gas, and are consequently found to thrive
in a barren soil, and in a rarefied atmosphere ; as in
the case of Pinus, Jitniperus, and Rhododendron.

But plants which shed their leaves in the winter
contain in general the most oxygene, and lose, by
consequence, the most carbon ; and hence they are
not to be met with in such lofty situations as herba-
ceous plants.

SECT. VI. ELABORATION OF OXYGENE. 105

The general conclusion to be drawn from these
observations is, that the quantity of oxygene con-
sumed by the leaves is relative to the situation in
which the plant naturally vegetates ; and that plants
vegetating in a barren soil, or in a rarefied at-
mosphere, or in a marshy situation, consume, in the
same circumstances, less oxygene than such as vege-
tate in a fertile soil with an abundant supply of
atmospheric air.

But in saying that any quantity of oxygene was
consumed, it is not meant that it was all inhaled by
the plant ; the greater part of it was often employed
in the formation of carbonic acid gas in the at-
mosphere of the receiver : for it does not appear
that the actual inhalation of oxygene had in any
instance perceptibly exceeded the volume of the
leaves. It was for the most part less.

Such then is the detail and rationale of the alternate
processes of the inhalation and extrication of oxygene
by the leaves of the vegetating plant. Do any of the
other parts of the plant perform similar functions?

If a sound and fresh root deprived of its stem is On the
put into a receiver filled with atmospheric air and r°
placed over mercury, it inhales indeed a small por-
tion of oxygene and hence diminishes the volume
of its atmosphere, but it consumes, and seems also
to inhale a much larger portion ; while the oxygene
that thus disappears is employed in the formation of
carbonic acid with carbon, which it abstracts from
the root. If the root is immediately removed into

166

PROCESS OF NUTRITION. CHAP. III.

another receiver, no futher change is produced in
the volume of its atmosphere ; and consequently no
further inhalation of oxygene. But if it is allowed
to remain some time in the open air it inhales
oxygene as before. But the quantity of oxygene thus
inhaled is always inferior to the volume of the root.
A Radish, which consumed in the space of 24 hours,
a quantity of oxygene equal to its own volume, in-
haled one-fourth part. But a Carrot, which con-
sumed in the same space of time, a quantity equal
to its own volume, inhaled only ^-fa part. And a
Potatoe, which consumed only O*04 of its own
volume, inhaled only O'OS.

This regular inhalation of a quantity less than the
root, with the faculty of inhaling oxygene anew after
a short exposure to the open air, seems to prove
that the root does not immediately assimilate the
oxygene which it inhales, but converts it into car-
bonic acid gas, which the atmospheric air again ab-
stracts. Thus the action of oxygene on the root,
whether in the sun or shade, resembles its action
upon leaves vegetating in the shade ; though in the
former case, the inhalation is less perceptible.
Roots therefore do not evolve oxygene at all.

But if the experiment is made upon roots to
which the stem is still attached, the result is very
different, at least if the root only is confined in the
receiver, while the stem and leaves are left exposed
to the open air. For, in this case, the root seems to
inhale more than its volume of oxygene gas ; though

SECf. VI. ELABORATION OF OXYGENE. 167

the gas thus inhaled is not yet assimilated to the
vegetable, but is given out to the atmosphere by
the leaves. Hence also, if an entire plant — root,
stem, and branch, is introduced into the receiver,
so as that the root shall be immersed in the water
by the extremity only, and in contact, for the most
part, with the atmosphere of the receiver, the
oxygene of this atmosphere is not diminished ; be-
cause the portion which is abstracted by the root is
restored again by the leaves. The oxygene inhaled
by the root, then, is not again evolved by it, nor im-
mediately assimilated to the vegetable substance;
but is conducted to the leaves in the state of car-
bonic acid, and there elaborated, or given out to the
atmosphere.

If the branch of a woody plant, taken and lopped On the
off in the spring immediately before the expansion
of the buds, is inclosed in a receiver filled with com-
mon air together with a small quantity of water to
supply it with nourishment, it will develope its
leaves as if vegetating in the open air. But it will
not effect this developement if it is placed in a
receiver filled with nitrogene or hydrogene gas ; in
which it will, on the contrary, soon exhibit symp-
toms of putrefaction, by giving out a quantity of
nitrogene and carbonic acid gas. The developement
then, in the former case, must consequently have
been effected by means of the inhalation of oxygerte,
which it thus appears that the stem and branches
are capable of effecting, even though stripped of

PROCESS OF NUTRITION. CHAP. III.

their leaves ; for they are then found to vitiate com-
mon atmospheric air, whether in the sun or shade,
without changing the volume of their atmosphere ;
replacing the oxygene which they consume by an
equal quantity of carbonic acid, and by consequence
not assimilating it immediately. Branches of Salia:
alba, Populus nigra, and Quercus Robur consumed
in the space of 24 hours, in the spring and summer,
at 15° of Reamur, a quantity of oxygene, equal to
more than half their volume ; while branches of the
Apple and Pear consumed, in equal circumstances,
two or three times their volume.

The oxygen which the stem and branches inhale
in the shade they give out again in the sun, in pro-
portion to the quantity of green vegetable substance
contained in their bark ; by means of which they
perhaps assimilate a small quantity of oxygene in
decomposing the carbonic acid which they form
with that of their atmosphere, though the effect is
not perceptible.

But if a portion of the stem remains in the re-
ceiver whilst the root remains in the soil, and the
leaves in the open ?:r, then the oxygene gas which
the stem consumes is not replaced by an equal
quantity of carbonic acid ; because the carbonic
acid, after being formed, follows the course of the
branch, and is decomposed by the leaves in the open
air. Into a glass tube, containing 6'3 cubic inches
of atmospheric air, Saussure introduced the extremity
of the branch of an Apple tree, stripped of its leaves,

SECT. VI. ELABORATION OF OXYGENE.

but still attached to the stem, which he luted to the
neck of the tube. The tube was then placed over
mercury. Two hours after sun-set the mercury rose
one and a half line within the tube, corresponding
to about half the volume of the Branch. On the
following morning the mercury was found to have de-
scended a little ; and about two hours after the rising
of the sun it was as at the commencement of the ex-
periment. The air contained — A_ of carbonic acid,
and -Jy»T of oxygene. The branch had then consumed
in the space of 24 hours more than five times its vo-
lume of oxygene, which it had replaced by scarcely
three times its volume of carbonic acid. Now
the disproportion between the quantity of oxygene
and carbonic acid remaining, was evidently owing to
the circumstances of the latter's being carried off to
the leaves by means of the branch. — But there was
formed also in the tube a very considerable quantity
of nitrogene, for the volume of its contained at-
mosphere was not changed, which Saussure accounts
for as follows : — As the branch inhales the oxygene
of its atmosphere a vacuum is formed in the tube, in
consequence of which the external atmospheric air
penetrates the porous substance of the branch, and
insinuates itself into the atmosphere within; the
oxygene of this new atmosphere is absorbed by the
branch, and its nitrogene left behind : and hence
the proportion of nitrogene in the atmosphere of the
tube is of necessity augmented.

If this experiment is made with water instead of

1

170 PROCESS OF NUTRITION. CHAP. III.

atmospheric air, and the water placed over mercury,
then the phenomenon occurs by which Hales was
deceived into the opinion that plants inhale air dur-
ing the day and give it out during the night.
Whilst the water is rapidly absorbed by the branch,
owing to the more copious perspiration of the leaves
during the day, the air is yet prevented from rushing
in by means of this very perspiration, although a
vacuum may be formed in the tube. The mercury
then ascends. But at night when the perspiration
and consequent absorption is but small, there is no
cause to counteract the intrusion of the atmospheric
air; the mercury again descends, and gives rise to
the apparently alternate inhalation and extrication
of air by day and by night, as understood by Hales.
But it is thus obvious, that the phenomenon is to
be ascribed to the nature of the apparatus.
On the The action and influence of oxygene are equally
conspicuous in the developement of the flower as in
the other parts of the plant. The flower-bud will
not expand if confined in an atmosphere of pure
nitrogene, and will fade much sooner than in an
atmosphere of common air. But in a confined at-
mosphere of common air, if placed in the shade, al-
though it does not alter the volume of its atmosphere,
at least in a perceptible degree, yet it replaces the
oxygene it absorbs by nearly an equal quantity of
nitrogene ; and in this respect the flower differs
from the other parts of vegetables, which when ve-
getating in the dark give out but little nitrogene,

SECT. VI. ELABORATION OF OXYGENE, 171

and consequently diminish for the most part the
volume of their atmosphere. Some flowers of Li-
lilt m album, which were introduced into a receiver
filled with common air, and placed over mercury in
the shade, consumed in the space of 24 hours a
quantity of oxygene equal to 1*1 of their own.
volume, of which they inhaled 0*15, replacing it by
O-15 of nitrogene. In a similar experiment on a
Rose it was found to have consumed 1*8 of its own
volume, inhaling 0*43 parts of oxygene, and giving
out at the same time 0*43 parts of nitrogene. There
seems then to be some ground for the commonly
received opinion of the unwholesomeness of sleeping
in an apartment which may happen to contain a
great many flowers ; for the nitrogene which they
give out will no doubt have some effect upon
the atmosphere of the apartment, if there is not a
free circulation of air in it, though the consequences
said to result from this circumstance have certainly
been much exaggerated.

The action and influence of oxygene are in like On the
manner essential to the maturity of the fruit.
Saussure introduced a bunch of grapes, not yet ripe3
into a globe of glass, which he luted by its orifice to
the bough and exposed to the rays of the sun ; the
bunch ripened without having effected any material
alteration in its atmosphere, except that it contained
rather more oxygene than at first. But when a bunch
was placed in the same circumstances, with the ad-
dition of a quantity of lime, the atmosphere was

PROCESS OF NUTRITION. CHAP. III.

contaminated, and the grapes did not ripen : hence
we may infer, that the elaboration of oxygene is ne-
cessary to the maturity of the fruit.

General From the whole then of the foregoing ex peri*
ment, as relative to the action and influence of
oxygene on the plant, and the contrary, the follow-
ing is the sum of the results.

The green parts of plants, but especially the
leaves, when exposed in atmospheric air to the suc-
cessive influence of the light and shade, inhale and
evolve alternately a portion of oxygene gas mixed
with carbonic acid. But the oygene is not imme-
diately assimilated to the vegetable substance ; it is
first converted into carbonic acid by means of com-
bining with the carbon of the plant, which withers
if this process is prevented by the application of
lime or potass. The leaves of aquatics, succulent
plants, and ever-greens consume, in equal circum-
stances, less oxygene than the leaves of other plants.

The roots, wood, and petals, and in short all parts
not green, with the exception of some coloured
leaves, do not effect the successive arid alternate in-
halation and extrication of oxygene ; they inhale it
indeed, though they do not again give it out, or as-
similate it immediately, but convey it under the
form of carbonic acid to the leaves, where it is
decomposed.

Oxygene is indeed assimilated to the plant, but
not directly, and only by means of the decomposi-
tion of carbonic acid ; when part of it, though in a

SECT. VI. ELABORATION OF OXYGENE. 173

very small proportion, is retained also and assimi-
lated along with the carbon.

Hence the most obvious influence of oxygene, as
applied to the leaves, is that of forming carbonic
acid gas, and thus presenting to the plant elements
which it may assimilate; and perhaps the carbon
of the extractive juices absorbed even by the root
is not assimilated to the plant till it is converted by
means of oxygene into carbonic acid.

But as an atmosphere composed of nitrogene and
carbonic acid gas only is not favourable to vegetation,
it is probable that oxygene performs also some other
function beyond that of merely presenting to the
plant, under the modification of~ carbonic acid, ele-
ments which it may assimilate. It may effect also
the disengagement of caloric by its union with the
carbon of the vegetable, which is the necessary re-
sult of such union.

But oxygene is also beneficial to the plant from Influence

-, i -i r i i ... ofoxvgene

its action on the soil; for when the extractive juices On soil,
contained in the soil have become exhausted, the
oxygene of the atmosphere, by penetrating into the
earth and abstracting from it a portion of its carbon,
forms a new extract to replace the first. Hence we
may account for a number of facts observed by the
earlier phytologists, but not well explained. Du
Hamel remarked that the lateral roots of plants are
always the more vigorous the nearer they are to the
surface,;* but it now appears that they are the
* Phys. <les,Arbres, liv, i. chap. v.

174 PROCESS OF NUTRITION. CHAP. III.

most vigorous at the surface because they have there
the easiest access to the oxygene of the atmosphere,
or to the extract which it may form. It was ob-
served also by the same phytologist that perpen-
dicular roots do not thrive so well, other circum-
stances being the same, in a stiff and wet soil as in a
friable and dry soil ; while plants with slender and
divided roots thrive equally well in both : but this
is no doubt owing to the obstacles that present
themselves to the passage of the oxygene in the for-
mer case, on account of the greater depth and
smaller surface of the root. It was further observed,
that roots which penetrate into dung or into pipes
conducting water divide into immense numbers of
fibres, and form what is called the fox-tail root ; but
it is because they cannot continue to vegetate, ex-
cept by increasing their points of contact, with the
small quantity of oxygene found in such mediums.
Lastly, it was observed that plants whose roots are
suddenly overflowed with water remaining after-
wards stagnant, suffer sooner than if the accident
had happened by means of a continued current. It
is because in the former case the oxygene contained
in the water is soon exhausted, while in the latter
it is not exhausted at all.

And hence also we may accounf for the pheno-
menon exhibited by plants vegetating in distilled
water under a receiver filled with atmospheric air,
which having no proper soil to supply the root with
nourishment, effect the developement of their parts

SECT. VI. ELABORATION OF OXYGENE.

only at the expence of their own proper substance ;
the interior of the stem, or a portion of the root, or
the lower leaves decaying and giving up their ex-
tractive juices to the other parts.

Thus it appears that oxygene gas, or that consti- Conclud-
tuent part of the atmospheric air which has been
found to be indispensable to the life of animals is
also indispensable to the life of vegetables ; on both
which accounts it seems to have well merited the
appellation of vital air, by which it was at one time
designated. But although the presence and action
of oxygene is absolutely necessary to the process of
vegetation, plants do not thrive so well in an at-
mosphere of pure oxygene, as in an atmosphere of
pure or common air. This was proved by an ex-
periment of Saussure's, who having introduced some
plants of Pisum sativum that were but just issuing
from the seed into a receiver containing pure
oxygene gas, found that in the space of six days
they had acquired only half the weight of such as
were introduced at the same time into a receiver
containing common air. From whence it follows
that oxygene, though the principal agent in the
process of vegetation is not yet the only agent ne-
cessary to the health and growth of the plant, and
that the proportion of the constituent parts of the
atmospheric air is just what it ought to be, as well
for the purposes of vegetable as of animal life ; being
at once an indication both of the wisdom and good-
ness of Him by whom it was established.

PROCESS OF NUTRITION. CHAP. III.

SECTION VII.
Decomposition of IVater.

Inferred ALTHOUGH the opinion was proved to be ground-
bfer Lr less, by which water had been supposed to be con-
vertible into all the different ingredients entering
into the composition of the vegetable substance by
means of the action of the vital energy of the plant ;
yet when water was ultimately proved to be a chemi-
cal compound, it was by no means absurd to suppose
that plants may possess the power of decomposing
part, at least, of what they absorb by the root, and
thus acquire the hydrogene as well as a portion of
the oxygene which, by analysis, they are found to
contain. This opinion was accordingly pretty gene-
rally adopted, but was not yet proved by any direct
experiment. Senebier pointed out several pheno-
mena from which he thought it was to be inferred,
but particularly that of the germination of some
seeds moistened merely with water, and so situated
as to have no apparent contact with oxygene. But
to this it was objected by Saussure that the seeds in
question might have germinated in consequence of
the action of the air contained in the water, inde-
pendent of that of its component principles.
And In- The decomposition of water was inferred also by
$en atz. ingennoutZj from the amelioration of an atmosphere
of common air into which he had introduced some
succulent plants vegetating in pure water ; but the

SECT. VII. DECOMPOSITION OF WATER. 177

degree of amelioration is not stated ; and on this
account Saussure is of opinion that no conclusion
should be founded on the fact, as he had never ob-
served any example in which a plant deprived of the
contact of carbonic acid had augmented the quantity
of oxygene contained in its atmosphere by a quantity
exceeding that of its own volume, which he regards
as being too little to establish the above conclusion.

It was next ascertained that plants vegetating in From in-

.1 . -i . sufficient

pure water augment their weight, at least in a green data.
state, even though confined in an atmosphere of
oxygene, or of common air deprived of us carbonic
acid. This was thought to be a fact of great im-
portance, but it does not yet prove the decomposi-
tion of water by the plant, nor the fixation of its
oxygene, or hydrogene ; because the augmentation
in weight may have been occasioned by the mere
introduction of the water into the sap vessels, or cel-
lular tissue : and hence the question can be deter-
mined only by the evidence of the augmentation of
the solid substance of the vegetable in a dried state.

The first experiments that were instituted with a Experi-
view to this object are those of Saussure ; his method
was as follows : — Having gathered a number of plants
of the same species, as nearly alike as possible in all
circumstances likely to be affected by the experiment,
he dried part of them to the temperature of the at-
mosphere, and ascertained their weight ; the rest he
made to vegetate in pure water, and in an at-
mosphere of pure oxygene, for a given period of time,

VOL. II. >'

178 PROCESS OF NUTRITION. CHAP. III.

at the end of which he dried them as before, and
ascertained their weight also, which it was thus only
necessary to compare with the weight of the former
in order to know whether the plants had increased
in solid vegetable substance or not. But after many
experiments on a variety of plants, the result always
was, that plants when made to vegetate in pure water
only, and in an atmosphere of pure oxygene, or of
common air deprived of its carbonic acid, scarcely ,
added any thing at all to their weight in a dried
state ; or if they did, the quantity was too small to
be appreciated. Particularly he made the experi-
ment on three plants of the Lysimachia vulgar is,
which he introduced into a receiver containing 250
cubic inches of common air deprived of its carbonic
acid, the roots were immersed in about one cubic
inch of distilled water, and the plants weighed in
their green state 129^ grains, displacing half a cubic
inch of their atmosphere ; three other plants of the
same species and weight when green, were found
to weigh when dried to a certain degree of the
thermometer and hygrometer 38J- grains: at the
end of eight days the plants which had been con-
fined in the receiver were taken out ; they had in-
creased considerably in length and were in a per-
fectly sound state, but had made no perceptible
change upon the atmosphere in which they vege-
tated either in purity or volume. They now
weighed in their green state J41 grains, but when
dried to the proper degree 40^- grains : they had thus

SECT. VII. DECOMPOSITION OF WATER. 179

augmented their solid vegetable substance by some-
what more than two grains, which could have been
acquired only by the assimilation of the oxygene and
hydrogene of the water, which they had consequently
decomposed. But when the experiment was pro-
longed to double or treble the time, the weight of
the dried vegetable substance of the plants was not
farther augmented ; for which reason, added to that
of the small amount of their augmentation, Saussure
did not regard the proof from these experiments as
being altogether complete, and began to suspect that
the oxygene and hydrogene of the plant cannot,
perhaps, be assimilated by the plant in any consi-
derable degree, unless the augmentation of its carbon
is effected in the same proportion.

The next thing to be done, therefore, was to place
his plants in a mixture of common air and carbonic
acid gas, that they might have the privilege of assi-
milating carbon at the same time ; the results were
now more perceptible and more decided, the solid
vegetable substance of the plant was evidently in-
creased in a greater proportion than could have
arisen from the mere presence of carbonic acid.
Seven plants of the Vinca minor, vegetating in pure
water in a receiver filled with common air and car-
bonic acid gas, assimilated in the space of six days
the carbon contained in 21-|- cubic inches, or a
quantity equal to 4'2 grains ; they assimilated at the
same time seven cubic inches of oxygene, but as

N 2

180 PROCESS OF NUTRITION. CHAP. III.

that was replaced by an equal quantity of nitrogenc,
it goes for nothing in the weight of the plants.

Before the experiment they weighed in their
green state 168*- grains, which were ascertained to be
equal to 5 1 grains of dried vegetable matter ; but
after the experiment the quantity of dried vegetable
matter was equal to 6l grains. There was conse-
quently an augmentation of weight of 10 grains, of
which 4'2 only can be attributed to the formation of
Who in- carbon ; hence it follows most evidently, that there
thedecom- na^ been a decomposition of the water, and an assi-
ofmilation °f 'ts component parts, by means of which
5*8 grains were added to the weight of the plant.

The decomposition then, and fixation of water by
the vegetating plant is thus, according to Saussure,
legitimately inferred ; but it does not appear that
plants do in any case decompose water directly —
that is, by appropriating its hydrogen e and at the
same time disengaging its oxygene in the form of
gas, which is extricated only by the decomposition
of carbonic acid. Plants vegetating in nitrogene
gas and exposed to the alternate influence of night
and day, do, indeed, extricate a quantity of oxygene
equal to many times their volume; but this is be-
cause being deprived of the contact of that gas in
the first period of experiment, they form of their
own substance a supply of carbonic acid gas, which
they afterwards decompose : and hence the origin
of the oxygene found in their atmosphere. They

SECT. VII. DECOMPOSITION OF WATER. 181

do not, however, by a similar exposure augment
the volume of oxygene when confined in an at-
mosphere of oxygene gas, or of common air deprived
of its carbonic acid, because the carbonic acid which
they now form is the result of the combination of
their carbon only with the oxygene that surrounds
them, and not the entire produce of their own sub-
stance : hence it is only in such atmospheres that
the experimenter can form any judgment concerning
the direct decomposition of water by the plant.

Succulent plants form indeed an exception with
regard to the augmentation of the volume of oxygene
when vegetating in an atmosphere of common air
deprived of its carbonic acid, but afford no proof of
the direct decomposition of water. Into a receiver
containing 41- cubic inches of atmospheric air pre-
viously deprived of its carbonic acid, a leaf or articu-
lation of the Cactus Opuntia was introduced, so as
that part of it was immersed in a glass containing dis-
tilled water, which was to serve as its nourishment ;
at the end of 31 days, when the experiment was
stopped, the leaf was still sound and vigorous ; it had
even formed roots of an inch in length, and aug-
mented its atmosphere 34- cubic inches. The eudio-
meter indicated the presence of 25 parts in the
hundred of oxygene, and the application of lime
water showed that it contained no carbonic acid;
hence the leaf had extricated in the space of a
month 3i- times its volume of oxygene, which could
be attributed to no other cause but that of the
1

PROCESS OF NUTRITION. CHAP. III.

composition of water. Still, however, there is no
proof that this decomposition was direct ; but rather
there is reason to suppose that the leaf formed in
the sun carbonic acid gas from its own substance,
and that the oxygene was extricated by the decom-
position of this gas : for in the progress of a similar
experiment, when a vessel filled with potass was
suspended in the receiver, the formation of oxygene
was stopped ; it is plain, therefore, that carbonic acid
gas was forming, and that the oxygene which ap-
peared was produced from its decomposition.

SECTION VIII.

Descent of the Proper Juice.

Itsanalogy WHEN the sap has been duly elaborated in the
Wood of leaf by means of the several processes that have just
animals, ^een described, it now assumes the appellation of
the Cambium, or Proper Juice of the plant. In this
ultimate state of elaboration it is found chiefly in
the bark, or rather between the bark and wood, and
may .very often be distinguished by a peculiar
colour, being sometimes white, as in the several
species of Spurge, and sometimes yellow, as in
Celandine. It is said to be the principal seat of the
medical virtues of plants ; and was regarded by
Malpighi as being to the plant what the blood is to
the animal body— the immediate principleof nourish-
ment, and grand support of life ; which opinions he

SECT.' VIII. DESCENT OF PROPER JUICE,

endeavours to establish by tbe following analogies :—
if the blood escapes from the vessels of the animal
body, it forms neither flesh nor bone, but tumors ; if
the proper juices of the plant are extravasated, they
form neither bark nor wood, but a lump of gum,
resin, or inspissated juice. The disruption of the
blood vessels and consequent loss of blood, injures
and often proves fatal to the animal. The extra-
vasation of the proper juice injures and often proves
fatal to vegetables, unless the evil is prevented by
the skill and management of the gardener. What-
ever may be the value of these remarks as tending
to establish the analogy in question, it cannot be
doubted that the cambium or proper juice consti-
tutes at least the grand principle of vegetable
organization ; generating and developing in succes-
sion the several organs of the plant, or furnishing
the vital principle with the immediate materials of
assimilation.

But how is the proper juice, which is thus so in- Anddis-
dispensable to the process of vegetation, conveyed Ihro^g
to the several parts or organs of the plant ? As the °}1atntthe
sap in its ascent to the summit of the leaf is con-
ducted by an appropriate set of vessels, so also is
the proper juice in its descent to the extremity of
the root. One of the earliest and most satisfactory
experiments on this subject, at least as far as regards
the return of the proper juice through the leaf and
leaf-stalk, is that of Dr. Darwin, which was con-
ducted as follows : — A stalk of the Euphorbia helis-

184 PROCESS OF NUTRITION. CHAP. III.

copia9 furnished with its leaves and seed-vessels,
was placed in a decoction of Madder-root, so as that
the lower portion of the stem and two of the in-
ferior leaves were immersed in it. After remaining
so for several days the colour of the decoction was
distinctly discerned passing along the midrib of each
leaf. On the upper side of the leaf many of the
ramifications, going from the midrib towards the
circumference, were observed to be tinged »vith red ;
Channel but on the under side there was observed a system
°f branching vessels, originated in the extremities
°^ tne *ea^ anc* carrvmg not a red but a Pa^

and leaf- fluid, which after uniting in two sets, one on each

cording to side the midrib, descended along with it into the

leaf-stalk. These were the vessels returning the

elaborated sap.* The vessels observable on the up-

per surface Darwin calls arteries, and those on the

under surface he calls veins ; the propriety of which

appellations is questionable, though the discovery of

the different sets of vessels conducting the sap and

proper juiceis important; because it points out the

intention of the peculiar structure of the leaf as dis-

coverable in the skeleton, which has been already

described as consisting of two, or, as in the case of

the Orange-leaf, of three layers of net-work.

According To this may be added the more recent discoveries

Knight. °f Mr. Knight who in his experiments, instituted

with a view to ascertain the course of the sap, de-

tected in the leaf-stalk, not only the vessels which

* Pbytologia, sect. iv.

SECT. VIII. DESCENT OF PROPER JUICE. 185

he calls central tubes through which the coloured
infusion ascended, together with their appendages,
the spiral tubes ; but also another set of vessels sur-
rounding the central tubes, which he distinguishes
by the appellation of external tubes, and which ap-
peared to be conveying in one direction or other a
fluid that was not coloured, but that proved upon
further investigation to be the descending proper
juice. In tracing them upwards they were found to
extend to the summit of the leaf; and in tracing
them downwards they were found to extend to the
base of the leaf-stalk, and to penetrate even into the
inner bark. According to Mr. Knight, then, there
are three sets of vessels in leaves, the central tubes,
the spiral tubes, and the external tubes. And yet Sir
J. E. Smith* represents him as meaning to speak of
two sets of vessels only, admitting that his language
seems to imply three, but cautioning the reader
against falling into the mistake.

But whatever Mr. Knight's meaning may have
been, he positively speaks of and specifies three
distinct sets of vessels, the central, the spiral, and
the external, as is plain from the circumstance of
his trying to ascertain the respective functions of
each. The first, he says, conducts the ascending
sap from the tubes of the alburnum to the leaf-stalk
and leaf; the second does not seem to conduct any
fluid ; the third contains the proper juice and con-

* Introduction, p. 51.

J S6 PROCESS OF NUTRITION. CHAP. III.

ducts it in its descent from the summit of the leaf

down to the base of the foot-stalk.*

Channel But by what means js the proper juice conducted
veyance from the base of the leaf-stalk to the extremity of

the°stem. the rOot ? This Was the cbief obJect °f the inquir7
of the earlier phytologists who had not yet begun to

trace its progress in the leaf and leaf-stalk ; but who
were acquainted with facts indicating at least the
descent of a fluid in the trunk. If the stem, or
branch, or even root of a woody plant is encircled
, by a strong ligature, a tumor is formed immediately

above the ligature, but no tumor is formed below
it.^ Hence they inferred the descent of a fluid
that was now stopped ; but this descending fluid was
proved also to be the Cambium or proper juice. If
a branch of any tree abounding in a conspicuous
proper juice, such as the Fig or Fir-tree, is cut
transversely in two, the proper juice will flow much
more copiously from the upper portion next the
leaves than from the under portion next the trunk,
even though their positions should be inverted. If
trees are stripped wholly of their bark, they will
often form new productions from the leaf down-
wards, but none or scarcely any from the root up-
wards. Du Hamel stript GO trees of their bark in
the course of the spring, laying them bare from the
upper extremity of the sap and branches to the
root ; the experiment proved indeed fatal to them,
as they all died in the course of three or four years.
* Phil. Trans. 1806. t Phys. des Arb. liv. v. chap, ii.

SECT. VIII. DESCENT OF PROPER JUICE. 187

But many of them had made new productions both
of wood and bark from the buds downwards, ex-
tending in some cases to the length of a foot ; though
very few of them had made any new productions
from the root upwards. Hence it is that the
proper juice not only descends from the extremity
of the leaf to the extremity of the root, but gene-
rates also in its descent new and additional parts.

But although the above experiments prove in
general the descent of the proper juice, yet they do
not decide in particular by what peculiar channel it
descends — that is, whether by the bark or wood.
It was the opinion of Du Hamel that it descends According
through the channel of the bark, in favour of which JJ
there is indeed an original presumption in the fact
of its being always found in the greatest abundance
in the bark when analysed ; or of its flowing the
most copiously from it when cut ; as well as a
direct and positive proof in the result of the follow-
ing experiments : — In the time of the flowing of the
sap Du Hamel stripped the trunk of a Cherry-tree of
a ring of bark, and covered the wound with a piece
of canvass to let nothing escape, wrapping it up at
the same time with an additional covering: of straw

o

to prevent its becoming dry : the result was that
the upper lip yielded a most copious exudation of
gum, while the lower lip yielded none ; but the tree
did not long survive the experiment. The proper
juice then descends through the channel of the bark,
and cannot be made to descend through the medium

188 PROCESS OF NUTRITION. CHAP. III.

of any other channel. But although such experi-
ments as the foregoing do generally prove fatal to
the life of the plant on account of the interruption
of the channel of the descent of the proper juice,
and consequent privation of nutriment ; yet there
are some plants to which the experiment even com-
municates a temporary and preternatural fertility.
If a ring of bark is detached in the spring from the
trunk of an Olive-tree, it will produce that year a
double quantity both of blossoms and of fruit,
though it will soon afterwards die ; * but the pheno-
menon is easily accounted for. The preternatural
fertility of the plant is owing to the unusual accu-
mulation of proper juice in the leaves and branches,
in consequence of the interruption of the descent
of the proper juice; and the subsequent death of
the plant is owing to the privation of nutriment
sustained by the root, in consequence of the same
cause.

According But Hales did not admit the bark to be the chan-
nel of the descent of the proper juice, alleging in sup-
port of his objections the evidence of the following
experiment: — Having stripped a trunk of its bark,
so as to leave a number of insulated rings still re-
maining, of which some were furnished with buds,
and some not, the trunk still lived, and the buds
protruded both leaves and branches ; the lower lips
of such rings as were furnished with buds producing
tumors, and the lips of such as were without buds
* La Nature Devoilce.

SECT. VIII. DESCENT OF PROPER JUICE. 1 »9

producing none. Hence he inferred that the bark
cannot be the channel of the descent of the sap
or proper juice, since the plant still lived in spite
even of the abstraction of several circular portions.
But if some plants are so very tenacious of life as to
survive even the violent operation of girdling, it will
not appear surprising if some plants should survive
also the gentler operation of a partial barking. For
in this case the proper juice may find a partial and
temporary channel even in the alburnum where it is
naturally of a very loose texture, and not too much in-
durated by exposure to air; and as the sap ascends,
at any rate by the alburnum, there is no difficulty in
accounting for the developement of the buds in the
above experiment. For wherever a bud is formed the
ascending juice will find its way to it, from which the
elaborated sap or proper juice will again descend
by the bark, its natural channel, at least till it meets
with some interruption ; where it will form tumors
as in the above case. And if no tumors were formed
on the lower lips of the rings without buds, it is
because there was no particular determination of sap
towards such rings on the very account of their want
of buds, and consequently no room for the process
of elaboration and return of proper juice. This was
accordingly Du Hamel's reply, and subsequent ex-
periment has shown it to be correct ; for the experi-
ments of Mr. Knight on this subject are, if possible, According
more convincing than even those of Du Hamel. toKmsht-
From the trunks of a number of young Crab-trees

PROCESS OF NUTRITION. CHAP* III,

Mr. Knight detached a ring of bark of half an
inch in breadth. The sap rose in them, and the
portion of the trunk above the ring augmented as
in other subjects that were not so treated, while the
portion below the ring scarcely augmented at all.
The upper lips of the wounds made considerable
advances downwards, while the lower lips made
scarcely any advances upwards ; but if a bud was
protruded under the ring, and the shoot arising
from it allowed to remain, then the portion of the
trunk below that bud began immediately to aug-
ment in size, while the portion between the bud and
incision remained nearly as before. When two
circular incisions were made in the trunk so as to
leave a ring of bark between them with a leaf
growing from it, the portion above the leaf died,
while the portion below the leaf lived ; and when
the upper part of a branch was stripped of its leaves
the bark withered as far as it was stript. Whence
it is evident that the sap which has been elaborated
in the leaves and converted into proper juice, de-
scends as air through the channel of the bark, or
rather between the bark and alburnum to the ex-
tremity of the root, effecting the developement of
new and additional parts. *

But not only is the bark thus ascertained to be

the channel of the descent of the proper juice, after

Vessels entering the trunk ; the peculiar vessels through

iii's it!0' which it immediately passes, have been ascertained

* Phil. Trans. 1803.

SECT. IX. CAUSES OF DESCENT.

also. In the language of Mr. Knight they are
merely a continuation of the external tubes already
noticed, which after quitting the base of the foot-
stalk he describes as not only penetrating the inner
bark, but descending along with it and conducting-
the proper juice to the very extremity of the root.
In the language of M. Mirbel they are the large or
rather simple tubes so abundant in the bark of
woody plants, though not altogether confined to it ;
and so well adapted by the width of their diameter
to afford a passage to the proper j uice.

SECTION IX.
Causes of Descent.

THE proper juice then, or sap elaborated in the
leaf, descends by the returning vessels of the leaf-
stalk, and by the longitudinal vessels of the inner
bark, the large tubes of Mirbel and external tubes
of Knight, down to the extremity of the root.
What is the cause of its descent ? It appears that According
the descent of the proper juice was regarded by the earlier
earlier phytologists as resulting from the agency
of gravitation, owing perhaps more to the readiness
with which the conjecture suggests itself than to
the satisfaction which it gives. But the insufficiency
of this cause was clearly pointed out by Du Hamcl,
who observed in his experiments with ligatures that
the tumor was always formed on the side next to

4

PROCESS OF NUTRITION. CHAP. III.

the leaves, even when the branch was bent down
whether by nature or art, so as to point to the
earth,* in which case the power propelling the
proper juice is acting not only in opposition to that
of gravitation, hut with such force as to overcome
it. This is an unanswerable argument ; and yet it
seems to have been altogether overlooked, or at
Accord- least undervalued in its importance by Mr. Knight,
Knight. wh° nas more recently investigated the subject of
the descent of the proper juice; but without
having been able to offer any thing that can be at
all regarded as satisfactory. He endeavours, how-
ever, to account for the effect by ascribing it to the
joint operation of the four following causes : — gra-
vitation, capillary attraction, the waving motion of
of the tree, and the structure of the conducting
vessels ; but, like charity among the virtues, the
greatest of these is gravitation.

Gravita- Gravitation. — A vertical shoot of a Vine was
forcibly bent down in nearly a perpendicular di-
rection, and its succulent extremity introduced into
a pot as a layer, without wounding the stem or
depriving it of any of its leaves. Two circular
incisions were made in the bark of the inverted
part and the intervening portion of bark was stript
off. But there was more wood formed at the lip
now uppermost, than at the lip opposite to it ;
which in the opinion of Mr. Knight was owing to
the force of gravitation, since the result would have

* Phys. des Arb. iiv. iv. chap. v.

SECT. IX. CAUSES OF DESCENT. 1Q3

been quite the contrary if the shoot had been al-
lowed to remain in its natural position. This con-
clusion seems at first sight to be plausible enough ;
but was afterwards acknowledged even by Mr.
Knight himself to be rather too hastily drawn; as
it occurred to him upon further reflection that the
proper juice which in other cases would have gene-
rated the greatest quantity of wood at the lip now
undermost, was, in the present case, employed in
the formation of roots. But although the argument
drawn from the above fact is thus rendered invalid,
the opinion of the efficacy of gravitation is by no
means given up by Mr. Knight, as is evident from
a subsequent attempt to account for the descent of
the radicle upon the same principle as stated in a
foregoing chapter.

Capillary attraction.-— This though enumerated Capillary
by Mr. Knight as a cause of the descent of the attraction'
proper juice, is not much insisted on. And indeed
it is plain from the known laws by which this
species of attraction is regulated, that it could be
but of little avail in operating the alleged effect;
if indeed, it is at all applicable to the case in
question.

The waving motion of the plant. — Part of the Waving
stem of a number of young seedling Apple-trees
was bound by means of stakes and bandages of
hay, so as to prevent all motion from the action of
winds to the height of three feet. The upper part
of the stem which was kept in motion by the winds

VOL. TI. O

>*::

PROCESS OF NUTRITION. CHAP. HI.

increased in size very considerably ; but the under
part which remained motionless increased very
little. A plant which was compelled to move in a
circle was found to have the greatest diameter of its
trunk in the direction of its motion. Hence Mr.
Knight inferred that the motion communicated to
plants by the action of the winds facilitates the
descent of the proper juice and consequently growth
of the plant; and that plants deprived of that
motion do not thrive so well, as in the case of
trees nailed to walls. It seems probable, however,
that the small degree of augmentation in the under
part of the stem of the seedling Apple-trees was
as much owing to its exclusion from air and light,
as to its want of motion ; as in the case of what is
termed the etiolation of plants, exemplified in the
slender stem of potatoes that may happen to pro-
trude their shoots in cellars or other dark places.
And trees nailed to walls are often as healthy as
standards, particularly Vines.

To the waving motion of the plant Mr. Knight
also attributes the facility with which plants adapt
themselves to the habitats in which they grow. In
lofty and exposed habitats they will increase most
near the root, owing to the accelerated descent of
the proper juice ; they will send out many lateral
branches and diminish gradually towards the top ;
they will be low and sturdy. In groves and vallies,
where they are crowded and less exposed they will
extend in length without extending proportionally

SECT. IX. CAUSES OF DESCENT. JQ5

in breadth, owing to the retarded descent of the
proper juice from want of motion. But this re-
mark though founded on the general aspect of plants
affecting the habitats in question is not without its
exceptions. For the Pine though inhabiting the
most lofty mountains is still a lofty tree ; and the
Oak though inhabiting the recesses of the grove may
still, even in respect of diameter, be the monarch
of the wood. In aged subjects the descent of the
proper juice, or at least the augmentation of the
plant is sometimes promoted by means of paring
off the lifeless part of the bark, owing, as Mr.
Knight thinks to the increased pliancy or flexibility
which is thus communicated to the stem ; and the
excision of any decayed part is always of benefit to
the plant. But the operations in question will com-
municate but little flexibility to a stiff and aged
trunk where the mass of wood has become already
firm and indurated ; so that the good effect pro-
duced is perhaps more properly ascribed to the
facility which is thus given merely to the access
of air.

Structure of the vessels. — Mr. Knight is of Structure
opinion that the vessels of the bark are better fitted vessels.
by their conformation to convey the proper juice
towards the root than in any other direction, which
opinion he founds upon the following experiment :
« — Four strong shoots of a Vine were selected and
converted into layers; and were in the end of the
autumn disengaged from their parent stock, at the

o 2

PROCESS OF NUTRITION. CHAP. III.

distance of five inches from the layer corresponding
to the length of wood left on the opposite side.
The buds on each end were by previous manage-
ment made to stand at equal distances from the
root, and an inch of wood was left at each end
beyond the buds. If Mr. Knight's hypothesis
was true it was to be expected that the proper juice
would be impelled less forcibly towards the extre-
mities that had originally formed the summit of
the shoots than towards the opposite extremities,
beyond which it was presumed that new wood
might even be formed. The result was as follows :
—At the proper and natural extremities the wood
above the buds became dry and lifeless, while the
wood below increased as usual. But at the in-
verted extremities the result was also inverted, new
wood being accumulated above the buds, and even
numerous roots protruded, while no sensible aug-
mentation took place between them. Inverted
cuttings of Gooseberries and Currants were also
made the subject of experiment ; the former not
succeeding at all ; but the latter succeeding for the
most part, and exhibiting phenomena similar to that
of the inverted ends of the layers, with the ex-
ception of their not emitting roots. Whence Mr.
Knight concludes that the vessels of the bark
through which the proper juice descends are better
adapted by their structure to transmit their content*
towards the original root, than in any other direc-
tion ; by which means the motion of the returning

SECT. IX. CAUSES OF DESCENT.

fluid in the pendant branches of the Weeping
Willow, and other such plants, is enabled to coun-
teract the power of gravitation, though not wholly
to destroy it ; as its agency is still discernible in
the pliancy and feebleness of the pendant shoot,
and in the occasional success of inverted cuttings.

This is certainly as complete a jumble as could
well have been made if it had even been attempted
on purpose ; and a notable example of the unphi-
losophical practice of multiplying causes without
necessity. First we are told of the paramount
influence of gravitation, and then we are introduced
to a cause which is capable of counteracting it, if
the branch happens to be pendant. And what is
this transcendant cause that overcomes even the
agency of gravitation ? It is the supposed existence
of valves in the tubes of the bark ; an opinion en-
tertained with regard to the sap vessels, at least by
some of the earlier phytologists, but long ago ex-
ploded, as has been already seen upon the almost
uniform evidence of the success of inverted cuttings
of the Willow and Poplar. But the same argu-
ments are applicable to the tubes of the bark, in
which if valves even existed they could seldom be
of any use, as the motion of the proper juice is
almost always downwards. Would not Mr. Knight
have found a cause better calculated to account for
the phenomenon of the inverted layer in the force
of habit, on which he lays so much stress, in a
variety of other cases ? as for example in that of

108 PROCESS OF NUTRITION. CHAP. III.

the susceptibility of the plant to the action of heat
as necessary to the protrusion of the bud, accord-
ing to the temperature in which it has formerly
been kept. And should it not have been also re-
collected that the phenomenon might have been
owing merely to the difficulty attending the ad-
mission of the proper juice into any vessels capable
of conveying it in the inverted direction ? there
being no set of vessels leading from the bud di-
rectly upwards, as there are vessels leading from it
directly downwards, in the original position of the
shoot. So that the entrance of the proper juice
could be effected only by lateral communication,
which in this case the structure of the vessels may
very possibly not admit of.

Insuffi- Such are the causes assigned by Mr. Knight
account f°r tne descent of the proper juice. They are each
perhaps of some efficacy ; and yet even when taken
altogether they are not adequate to the production
of the effect. The greatest stress is laid upon gra-
vitation ; but its agency is obviously over-rated, as
is evident from the case of the pendant shoot ; and
if gravitation is so very efficacious in facilitating
the descent of the proper juice, how comes its
influence to be suspended in the case of the ascend-
ing sap. The action of the Silver grain will
scarcely be sufficient to overcome it ; and if it
should be said that the sap ascends through the
tubes of the alburnum by means of the agency of the
vital principle, why may not the same vital principle

SECT. IX. CAUSES OF DESCENT.

conduct also the proper juice through the returning
vessels of the bark. In short if, with Saussure, we
admit the existence of a contracting power in the
former case sufficient to propel the sap from ring to
ring, it will be absolutely necessary to admit it also
inthe latter. Thus we assign a cause adequate to the
production of the effect, and avoid at the same
time the transgression of that most fundamental
principle of all sound philosophy which forbids us
to multiply causes without necessity.

CHAPTER IV.

PROCESS OF VEGETABLE DEVELOPEMENT.

WHEN the sap has been elaborated in the leaf, and Different
converted into proper juice, it is now finally prepared d^eTo?
for immediate assimilation, and for the production Plants-
of such parts and organs as are peculiar to the
species, or necessary to the perfection of the in-
dividual. The next object of our inquiry, therefore,
will be that of tracing out the order of the deve-
lopement of the several parts, together with the
peculiar mode of operation adopted by the vital
principle. But this mode of operation is not
exactly the same in herbaceous and annual plants,
as in woody and perennial plants. In the former,
the process of developement comprises as it were

20O PROCESS OF BEVELOPEMENT. CHAP. IV.

but one act of the vital principle, the parts being
all unfolded in immediate succession and without
any perceptible interruption till the plant is com-
plete. In the latter, the process is carried on by
gradual and definite stages easily cognizable to the
senses, commencing with the approach of spring,
and terminating with the approach of winter ;
during which, the functions of the vital principle
seem to be altogether suspended, till it is aroused
again into action by the warmth of the succeeding
spring. The illustration of the latter, however,
involves also that of the former; because the growth
of the 6rst year exemplifies at the same time the
growth of annuals, while the growth of succeeding
years exemplifies whatever is peculiar to perennials,

SECTION I.
Elementary Organs.

IF the embryo, on its escape from the seed and
conversion into a plant, is taken and minutely in-
spected, it will be found to consist of a root, plume-
let, and incipient stem, which have been developed
in consecutive order ; and if the plant is taken and
dissected at this period of its growth it will be found
to be composed merely of an epidermis enveloping
a soft and pulpy substance, that forms the mass of
the individual ; or it may be furnished also with a
central and longitudinal fibre ; or with bundles of

SECT. I. ELEMENTARY ORGAN'S. 201

longitudinal fibres giving tenacity to the whole.
These parts have been developed no doubt by means Formed

r . . , • • i ' • out of th»

of the agency of the vital principle operating on pr0per
the proper juice ; but what have been the several Juice'
steps of operation ?

Some phytologists have attempted to account for Which
the formation of the above parts by supposing the SUpp0sed
proper juice to consist of multitudes of organic 0°
fibres, which being united together by the vege-fibres-
table gluten constitute the cellular and tubular
tissue, and thus form the mass of the plant. But this
supposition leaves us just where we were before,
For if it were even proved to be the fact, the next
question would be, how are the organic fibres
themselves formed ? But as it is an assumption
founded on no proof, it merits of course no fur-
ther consideration. Perhaps no satisfactory expli-
cation of the phenomenon has yet been offered,
though M. Mirbel, in the want of all plausible con*
jecture, submits the following: — He supposes the Or to b
proper juice to be at first converted into a fine mem- b"e
brane, which he calls the membranous tissue, from
which the cellular tissue of the pulp is afterwards sue
formed, by means of the foldings and doublings of
the original membrane, so as to present an hexa-
gonal appearance similar to that of the cells of the
Bee. The tubular tissue he supposes to be in like From
manner formed out of the cellular tissue, by means
of such openings and perforations as may be acci-
dentally effected in the tissue itself, from the

"lnto"

202 PROCESS OF DEVELOPEMENT; CHAP. IV%

bursting of the vertical partitions of the cells, the
tubes having no existence till the membrane is
lacerated.*

But if the tubes are generated in the manner
here supposed, that is by the accidental bursting
of the partitions of the cells, it will be difficult to
account for the known regularity with which they
are formed. The only circumstance giving plausi-
bility to the conjecture is that of the occasional
occurrence of a transverse membrane interrupting
the continuity of the small tubes, which M. Mirbel
The sup- regards as a proof of their cellular origin. But
beset with allowing this to be a sufficient proof of the truth
difficulties. Qf 1|le SUppOSition, which few will be disposed to
admit ; how is the formation of the tracheae to be
accounted for, which retain no traces of a cellular
origin, and are besides twisted spirally throughout
the whole of their extent ? They cannot be sup-
posed to be merely the result of the accidental
bursting of the cells of the pulp ; because there is
too much of regularity both in their form and dis-
tribution to be the result of accident. If M. Mirbel
had even contended that the cells burst open in a
regular and determinate manner, and thus give to
the tube its spiral or vertical direction, his hypo-
thesis would still have been clogged with difficul-
ties ; but on the position he assumes the difficulties
arc doubled. The most that can be said for it is.
that it is perhaps not impossible ; but it cannot

* Traite d'Anat. ct clc Phys. Ve$ef. 1JV. k

SECT. I. ELEMENTARY ORGANS. 20-8

certainly be said to be founded on any known
facts.

It is much more likely, however, that the rudi-
ments of all the different parts of the plant do
already exist in the embryo in such specific order
of arrangement as shall best fit them for future
developement, by the intro-susception of new and
additional particles, than that the vital principle
should first manufacture a membrane which it then
converts into cells, which are afterwards partially
and accidentally converted into tubes, and the plant
so patched up. For if this were the fact, there
would be no such thing as saying what species of
plant any particular seed might produce when com-
mitted to the soil.

The only portion of the infant plant now re- Formation
maining is the epidermis, which although it is in dermf«.Cpl
some cases to be regarded as a composite organ, in
consequence of its consisting of more than one
layer ; yet as it cannot in the incipient stages of
vegetation be divided into distinct layers, it may
with sufficient propriety be introduced into the pre-
sent section. How then is the epidermis generated,
in which the body of the infant plant is invested
as in a sheath ?

The pellicle constituting the vegetable epidermis According
has generally been regarded as a membrane essen- ^ ^\,
tially distinct from the parts which it covers, and as p'ghl>
generated with a view to the discharge of some par-
ticular function. Some phytologists, however, have

204 PROCESS OF DEVELOPEMENT. CHAP. IV.

viewed it in a light altogether different, and have
regarded it as being merely the effect of accident,
and nothing more than a scurf formed on the ex-
terior and pulply surface of the parenchyma indu-
rated by the action of the air. This was the opinion
of Grew and Malpighi, which, though it does not
seem to have ever met with any very general recep-
tion, has been, however, revived of late by M.
According Mirbel ; who, professing to be dissatisfied with the

to Mirbel.

analogy that has generally been thought to exist
between the epidermis of the animal and vegetable,
contends that the latter is nothing more than the indu-
rated surface of the parenchyma, from which it differs
only in such circumstances as are occasioned by posi-
tion. If it is more or less transparent — if it is tougher
end firmer in its texture than the parenchyma or
any of its parts, it is only because it is constantly
exposed to the influence of light and air, and to the
contact of such bodies as float in the atmosphere ;
but it is not to be regarded as constituting a distinct
organ or membrane, or as exhibiting any proof of
its being analogous to the epidermis of animals.*
Such is the substance of M. MirbeFs opinion, to
which he is aware that objections may still be
urged. For it may be said, if this is the true origin
of the epidermis, how comes it to separate so easily
from the interior parts in the spring? To this ob*
jection M. Mirbel furnishes the following reply-
namely, that its facility of detachment is owing to the
* Traitc d'Anut. ct de Phys. Veg. torn. i. p. 87.

2

>ECT. I. ELEMENTARY ORGANS. 205

disorganization occasioned in the epidermis by means
of its exposed position, which has even the effectof ulti-
mately detaching it from the plant altogether, as may
be seen in the instances in which it bursts and exfo-
liates when it is not able to expand in proportion to
the internal parts. And thus M. Mirbel presumes he
has established his position. But this is by no
means the most formidable objection to which his
hypothesis is liable ; for if it be true that the epider-
mis is nothing more than the pellicle formed on the
external surface of the parenchyma, indurated by the
action of the air, then it will follow that an epider-
mis can never be completely formed till such time
as it has been exposed to that action. But it is
known that the epidermis exists in a state of com-
plete perfection in cases where it could not possibly
have been affected by the external air. If you take
a rose-bud, or bud of any other flower, before it ex-
pands, and strip it of its external covering, you will
find that the petals and other inclosed parts of the
fructification are as completely furnished with their
epidermis as any other parts of the plant, and yet
they have never been exposed to the action of the
air. The same may be said of the epidermis of the
seed while yet in the seed vessel, or of the root, or
of the paper birch, which still continues to form
and to detach itself, though defended from the
action of the air by the exterior layers. In herbs
and in the annual parts of woody plants, such as the
leaves and flowers, the epidermis never detaches

206 PROCESS OF DEVKLOPEMENT. CttAP. IV.

itself at all ; which circumstance M. Mirbel adduces
as an additional argument in favour of his hypothe-
sis, though to me it seems an argument against it.
For if the air produces such violent effects upon the
trunk and branches of woody plants, why should it
not produce similar effects upon other plants, or upon
other parts of the same plant ? and why is the epi-
dermis of the leaf and fruit incapable of being again
regenerated if accidentally destroyed ? Till a satis-
Whose factory answer can be given to these questions it is
^P^iJ! impossible to admit the hypothesis of M. Mirbel.
sible. But so far is the action of the external air from
being the cause and origin of the epidermis, that it
is even detrimental to its formation. For the repro-
duction of a part that has been destroyed, in cases
capable of reproduction, is always more easily
effected if the wound is covered closely up. And
hence it is extremely improbable that the epidermis
is merely a modification of the external surface of
the parenchyma effected by the influence and action
of the air; if rather it is not evidently an organ
formed by the agency of the vital principle, even
while the plant is yet in embryo, for the very pur-
pose of protecting it from injury when it shall have
been exposed to the air in the process of vegetation.
Its growth or dcvelopement is accordingly found to
keep pace with that of the plant which it invests as a
sheath, extending in all its dimensions and accom-
modating itself with wonderful facility to the ex-
pansion of the interior parts ; as may be seen in large

SECT. I. ELEMENTARY ORGANS. 207

trees, and fruits of rapid growth. Its expansion,
however, is circumscribed by certain bounds or
limits which it cannot pass ; for when vegetation is
too rapid, or when the parts have become indurated
with age, it refuses or is unable to expand further,
and consequently cracks, as in the bark of aged trees,
or in Melons of luxuriant growth ; the fissure being
for the most part perpendicular, though sometimes,
as in the Cherry-tree, horizontal. It is also much
more capable of expansion in some trees than others,
and remains longer smooth ; and where it does not
expand freely it is thought to retard in some degree
the developement of the interior parts, as in the case
of the Cherry-tree, the epidermis of which the gar-
dener is often obliged to lay open by a longitudinal
incision, in order to facilitate the growth of the
plant.

With regard to the disavowed analogy between
the animal and vegetable epidermis, it is of no con-
sequence to the above argument whether it holds
good or not. But there are several respects in
which an analogy between the two cuticles is suffi*
ciently striking : they are both capable of great ex-
pansion in the growth of the subject ; they are both
easily regenerated when injured (with the exceptions
already stated), and seemingly in the same manner ;
they are both subject, in certain cases, to a constant
decay and repair ; and they both protect from injury
the parts enclosed.

2O8 PROCESS OF DEVELOPEMENT. CHAP. IV.

SECTION II.
Composite Organs.

THE elucidation of the developement of the Com-
posite Organs involves the discussion of the two
following topics t— the formation of the annual plant,
and of the original shoot of the perennial ; and the
formation of the subsequent layers that are annually
added to tho perennial.

SUBSECTION I.

Annuals and Annual Shoots. — If a perennial of a
year's growth is taken up in the beginning of winter
when the leaves, which are only temporary organs,
have fallen, it will be found to consist of a root and
trunk, surmounted by one or more buds. The root
is the radicle expanded into the form peculiar to the
species, but the trunk and buds have been generated
Section of in the process of vegetation. Let the root or trunk be
ex' now taken and cut into two by means of a transverse
section, and it will be found to consist already of
bark, wood, and pith. The pith is spongy and succu-
lent, being an assemblage of hexagonal cells filled
with a limpid juice. The wood is tender and brittle,
being an assemblage of longitudinal tubes, or fibres,
forming in the aggregate a cylinder or circular layer
that invests the pith. The bark is soft and flexible,
being also an assemblage of tubes that form in their

SECT. II* COMPOSITE ORGANS. 2OQ

aggregate a cylinder or circular layer closely invest-
ing the wood. If the root or trunk of an annual is
taken and treated in the same manner, it will be
found to consist of an epidermis, pulp, and inter-
spersed fibre. Here then is the termination of the
growth of the annual, and of the first stage of the
growth of the perennial : how have their several
parts or organs been formed ?

As the pith seems only a modification of the ori- Formation
ginal pulp, the same hypothesis that accounts for the of theplU
formation of the one will account also for the forma-
tion of the other, at least in a*> far as they are found to
consist of cellular tissue; the cells and membrane
composing them being in both cases alike, though
somewhat modified by situation. If the cells of the
pith are the largest, it is perhaps because being lodged
in the centre they are there the farthest removed from
the compression and action of the air : and if the cells
of the exterior pulp are the smallest, it is perhaps be-
cause being situated towards the circumference they
are there the most exposed to the influence of the
same causes. But their character is also affected by
the character of the juices they contain; the pulp
containing a resinous juice, as being mingled from its
position with the proper juice of the plant ; and the
pith containing a watery juice, as having more com-
munication with the ascending sap. Hence the pith
and pulp, or parenchyma, are ultimately converted
into organs essentially distinct from one another;
though phytologists have been much puzzled to Function,
assign to each its respective functions.

VOL. II. p

210 PROCESS OF DEVKLOPEMENT. CHAP. IV.

According In the earlier ages of phytological inquiry, or
!?erhph*£. rather in ages in which phytological opinions were
legists, formed without inquiry, one of the vulgar errors of
the time seems to have been an opinion by which
the function of the pith was supposed to be that of
generating the stone of fruit, and by which it was
thought that a tree deprived of its pith would pro-
duce fruit without a stone.* But this opinion is by
much too absurd to merit a serious refutation.
Another early opinion, exhibiting however indica-
tions of legitimate inquiry, is that by which the pith
was regarded as being analogous to the heart and
Malpighi, brain of animals,-^ as related by Malpighi; who did
not himself adopt it, but believed the pith to be
like the cellular tissue, the viscera in which the sap
is elaborated for the nourishment of the plant, and
Magnol, for the protusion of future buds. % Magnol thought
that it produces the flower and fruit, but not the
DuHa- wood. Du Hamel regarded it as being merely an
mel> extension of the pulp or cellular tissue, without
being destined to perform any important function in
Linn<eus. the process of vegetation. § But Linnaeus was of
opinion that it produces even the wood ; regarding it
not only as the source of vegetable nourishment,

* Phys. des Arb. liv. i. chap. iii.

f Medullae usus olim insignis cordi et cerebro analogus crede-
batar. Anat. Plant. 13.

J Concoquitur itaque in horizontalibus utriculis, et medulla
ipsa succus, ut futuris et proximo erupturis gemmis, et tenellis
foliis praesto sit. Anat. Plant. 13.

§ Phys. des Arb. liv. i. chap. iii.

SECT. It, COMPOSITE ORGANSi 21 1

but as being also to the vegetable what the brain
and spinal marrow are to animals, the source and
seat of life. In these opinions there may be some-
thing of truth, but they have all the common fault
of ascribing to the pith either too little or too
much.

Mr. Lindsay, of Jamaica, suggested a new opinion Lindsay,
on the subject, regarding it as being the seat of the
irritability of the leaves of the Mimosa, and Sir J.
E. Smith says he can see nothing to invalidate the
arguments on which this opinion is founded. Plenk Plenk,anfti
in his Physiologia Plantarum, and Mr. Knight in Knight,
one of his papers published in the Philosophical
Transactions, regard it as destined by nature to be a
reservoir of moisture to supply the leaves when ex-
hausted by excess of perspiration ; which opinion
Sir J. E. Smith combats, contending that the cause
assigned is wholly inadequate to the effect, as the
moisture of the pith would in many cases be insuf-
ficient to supply one hour's perspiration of a single
leaf, and as it is not found to be affected even when
the leaves are flaccid by drought. The objections
thus alleged are fatal to Mr. Knight's hypothesis,
which is regarded however as deriving considerable
support from the phenomena of the roots of some
of the Grasses, as from that of Phleum pratense,
which in moist situations has a fibrous root, while
in dry situations it has a bulbous root, the interior
of which is moist and spongy like the pith of the •
young shoot. But this, instead of proving the pith

p 2

212 PROCESS OF DEVELOPEMENT. CHAP. IV.

to be a reservoir of moisture, proves rather the capa-
city inherent in plants of adapting themselves to
their situation, by means of an extraordinary exer-
tion of their vital energies.

And Sir J. Sir J. E. Smith professes to hold an intermediate
E. Smith. Opmion between that of Du Hamel, who ascribes to it
no peculiar function at all, and that of Linnaeus, who
ascribes to it almost every thing important in vege-
tation— regarding it not as a source of nourishment,
but as a reservoir of vital energy or life, analogous
to the spinal marrow and nerves in animals, which
do not nourish the individual, but give life and
vigour to the whole by being diffused throughout
the whole of its parts.* But in thus adopting the
golden mean, through which, while he guards against
ascribing to it too much, he avoids also at the same
time the opposite extreme of ascribing to it too little,
and steers equally clear both of Charybdis and Scylla,
there does not seem to have been much gained in
the present instance. The analogy between the
pith of vegetables and spinal marrow of animals is
not very well made out : if the spinal marrow is
injured the parts are immediately paralyzed, and if
it is broken the animal dies; but Mr. Knight has
shown that a portion of the pith may be abstracted
from the shoot so as to effect a disruption of con-
tinuity without occasioning any material injury to
the plant. It should be recollected, however, in
justice to the phytology of ancient Greece, that this
* Introduction, p. 40.

SECT. II. COMPOSITE ORGANS. 213

experiment had been performed, and the result as-
certained, even in the time of Theophrastus.* The
pith cannot therefore be regarded as correspond-
ing to the spinal marrow of animals, in any thing at
all essential.

Hence it appears that the peculiar function of the
pith has not yet been altogether satisfactorily ascer-
tained ; and the difficulty of ascertaining it has been
thought to be increased from the circumstance of its
seeming to be only of a temporary use in the pro-
cess of vegetation, by its disappearing altogether in
the aged trunk. But although it is thus only tem-
porary as relative to the body of the trunk, yet it
is by no means temporary as relative to the process
of vegetation ; the central part of the aged trunk
being now no longer in a vegetating state, and the
pith being always present in one shape or other in the
annual plant, or in the new additions that are an-
nually made to perennials. The pith then is essential
to vegetation in all its stages : and from the analogy
of its structure to that of the pulp or parenchyma
which is known to be an organ of elaboration, as in
the leaf, the function of the pith is most probably
that of giving some peculiar elaboration to the sap,
according to the hypothesis of Malpighi ; which
seems to me to be the best founded of all the fore-
going, with the exception of that part of it by

* *H $t pvTp
tyvrav &ITKM. TO. E.

214 PROCESS OF DEVELOPEMENT. C#AP, IV.

which the pith is supposed to be also peculiarly
destined to give origin to the future buds.
Origin and The next topic of inquiry is that of the genera-
of the a tion of the layer of wood in our example of woody
layers or plants> or of the parts analogous to wood in the case
otherwise. of herbaceous plants ; a topic that has been hitherto
but little attended to. Phytologists have indeed of-
fered many conjectures concerning the origin of the
annual layer that is added to perennials; but they do
not seem to have taken up the subject at the proper
point. They have generally made their observations
on trees of considerable age and magnitude, a.nd have
contended, some that the wood is formed from the pith,,
others that it is formed from the bark, and others
that it is formed from the alburnum of the former
year ; thus evading the subject of the formation of
the original layer altogether, which is the foundation
of all the rest, and the most essential step in the
process of vegetation ; though it is a step concern-
ing which there can be but little said that is at all
satisfactory. If we suppose the rudiments of all
the different parts to exist already in the embryo,
then we have only to account for their developement
by means of the intro-susception and assimilation
of sap and proper juice; but if we suppose them
to be generated in the course of vegetation, then the
difficulty of the case is augmented : and at the best
we can only state the result of operations that have
been so long continued as to present an effect cog-

SECT. II. COMPOSITE ORGANS. '215

nizable to the sense of sight, though the detail of
the process is often so very minute as to escape even
the nicest observation. All,, then, that can be said on
the subject is merely that the tubes, however formed,
do, by virtue of the agency of the vital principle
operating on the proper juice, always make their
appearance at last in an uniform and determinate
manner, according to the tribe or species to which
the plant belongs, uniting and coalescing so as to
form either a circular layer investing the pith, as in
woody plants ; or a number of divergent layers in-
tersecting the pith, as in some herbaceous plants ;
or bundles of longitudinal and woody fibre inter-
spersed throughout the pith, as in others ; though
in some of the less perfect plants no longitudinal
fibres are at all discernible, and consequently
no part analogous to wood.

In the same manner we may account for the form- And bark,
ation of the layer of bark, either by supposing
that it is merely the developement of some original
elements existing in the embryo, or that it is gene-
rated by means of the agency of the vital principle
in the process of vegetation and out of the proper
juice, so as to form an exterior layer distinct in its
character and properties, and separate or easily
separable from the wood or interior part of the
plant.

Such is a slight sketch of the process of the de^
velopement of the elementary and composite organs
of annuals, or of perennials of a year's growth.

2J6 PROCESS OF DEVELOPEMENT. CHAP. IV.

SUBSECTION II.

Formation Perennials, and their Annual Layers. — If a pe-
ers of the rennial is taken at the end of the second year and
year,nd dissected as in the example of the first year, it will
be found to have increased in height hy the addition
of a perpendicular shoot consisting of bark, wood,
and pith, as in the shoot of the former year ; and in
diameter by the addition of a new layer of wood, and
of bark generated between the wood and bark of the
former year, and covering the original cone of wood,
like the paper that covers a sugar-loaf: this is the
fact of the mode of augmentation about which phy-
tologists have not differed, though they have differed
widely with regard to the origin of the additional
layer by which the trunk is increased in diameter.
According Malpighi was of opinion that the new layer of
ghi ancT~ wood is formed from the liber of the former year ;
Grew- the layer of liber being by degrees assimilated to the
woody substance, and ultimately converted into
a layer of wood,, which attaches itself to the layer
that was previously formed.* But the defect of this
hypothesis is, that it does not account for the forma-
tion of the new layer of liber itself. Grew was of
opinion that a new ring of sap vessels is first gene-
rated on the inner furface of the liber of the former
year, which is gradually converted into a new layer
of liber that ultimately splits into two portions,

* Anat. Plant. 11.

SECT. II. COMPOSITE ORGANS.

taking contrary directions ; the outer portion extend-
ing towards the circumference of the plant, and
forming the new layer of bark ; and the inner por-
tion receding towards the centre and forming the
new layer of wood. This hypothesis is preferable to
Malpighi's, inasmuch as it accounts for the new layer
both of wood and bark ; and perhaps no hypothesis
whatever is more conformable to fact. Hales was of
opinion that the new layer of wood is formed from,
the layer of the preceding year, both by means of the
dilatation of the horizontal vessels of the former layer,
and also of the extension of the longitudinal tubes.
The opinion was founded upon the phenomena of a
tumor that seemed evidently formed from the wood ;
whence he inferred that the new layer is also formed
from the wood. But as it could never have been
deemed logical from the phenomena of the diseased
action of a part to infer the mode of procedure in
the sound action of the whole, the hypothesis does
not appear to have met with many advocates. Lin- According
naeus thought the new layer of wood was formed ^s?"
from the pith, which is absurd, because the opinion
goes to the inversion of the very order in which the
layer is formed, the new layer being always exterior
to the old one. But according to the most general
opinion, the layer was thought to be formed from a
substance oozing out. of the wood or bark — first, a
limpid fluid, then a viscid pulp, and then a thin
layer attaching itself to the former ; the substance
thus exuding from the wood or bark was generally

218 PROCESS OF DEVELOPEMENT. CHAP. IV.

regarded as being merely an extravasated mucilage,
which was somehow or other converted into wood
Du Ham- and hark : but Du Hamel regarded it as being
already an organized substance, consisting of both
cellular and tubular tissue, which he designated by
the appellation of the Cambium) or Proper Juice.
This opinion seems to have been entertained also by
Grew, though it does not appear to rest on any very
convincing evidence ; the fact, however, of its exu-
dation was evident, though it was not yet ascertained
whether it exuded from the wood or from bark of
the former year ; and whether the new layer, when
formed, separated into two, as Grew had conjectured.
This inquiry was undertaken by Du Hamel,* whose
experiments on the subject are indeed most lumi-
nous, and are, though seldom quoted, an anticipation
of almost every thing that has been done by the
most distinguished of our modern phytologists.
Who as- 1° order to ascertain whether the new layer of
thathYs wo°d is formed from the former layer of wood or of
formed bark, his first experiment was that of a graft par
Fecusson ;-f- which is done by means of detaching a
portion of bark from the trunk of a tree and supply-
ing its place exactly by means of a portion of bark
detached from the trunk of another tree, that shall
contain a bud. In this way he grafted the Peach on
the Prune tree, because the appearance of the wood
which they respectively form is so very different that
it could easily be ascertained whether the new layer

* Phys. dcs Arb. liv. iv. chap. «ii. f Ibid. chap. 4.

SECT. II. COMPOSITE ORGANS.

was produced from the stock or from the graft.
Accordingly at the end of four or five months after
the time of grafting the tree was cut down, and as
the season of the flowing of the sap was past, a por-
tion of the trunk including the graft was now boiled
to make it part more easily with its bark ; in the
stripping off of which there was found to be formed
under the graft a thin plate of the wood of the Peach,
united to the Prune by its sides, but not by its
inner surface, although it had been applied to the
stock as closely as possible : hence Du Hamel can- From the
eluded that the new layer of wood is formed from the
bark, and not from the wood of the preceding year. 7ear-
The same experiment was repeated with the same
result upon the* Willow and Poplar; when it was
also found that if a portion of wood is left on the
graft it dies, and the new wood formed by the
bark is exterior to it. The above conclusion, there-
fore, is perfectly legitimate, which Du Hamel also
strengthens by the following experiment : — Having
detached a cylinder of bark from its trunk, and
covered the wood below it with a thin plate of tin-
foil, he then replaced the bark as before^ reducing
the case to the following dilemma ; if the new layer
of wood was formed from the old layer of wood, then
it was plain that the new layer would be deposited
within the tin-foil ; and if it was formed from the
bark, it was also equally plain that it would be de-
posited without the tin-foil : the result accordingly
was, that a new layer of wood was deposited between

220 PROCESS OF DEVELOPEMENT. CHAP. IV.

the bark and tin-foil, but none between the tin-foil

and the interior layer. This experiment was com-

pletely decisive of the point in question ; and yet

there is an experiment of Dr. Hope's on the same

subject, which is, if possible, still more convincing : —

Having made a longitudinal incision in the trunk of

a Willow of three or four years old so as to penetrate

through the bark, he laid bare a portion of the stem

by slipping the bark to the one side, which was,

however, still attached to the stem at the upper and

lower extremities of the decorticated part ; the de-

tached portion of bark was then bent into the form

of a hollow cylinder, by uniting its edges as closely

as possible, and the whole well secured from the

action of the atmosphere.3* The plant was then

allowed to remain undisturbed for several years,

when the result of dissection was, that new layers

of wood were generated within the lateral cylinder

of bark, while the decorticated portion of the stem re-

mained unaugmented; the portions above and below

being augmented, as in other ordinary cases of vege-

tation. It is evident, therefore, that the additional

layer by which the plant increases in diameter is

generated from the bark.

Not by But it was not yet accurately ascertained whether
version'of tne newly formed layer of wood was merely in-

Tnto ^uratec* liber, as was the opinion of Malpighi; or a
wood, production formed from it, as was the opinion of
Grew. This Du Hamel thought he might ascertain

* Smith's Introduction, p. 35.

SECT. II. COMPOSITE ORGANS. 221

by means of passing through the bark of a tree
several small threads of silver in a horizontal di-
rection, so as to penetrate the liber.* If the liber was
converted into wood, the threads, it was to be pre-
sumed, would be found ultimately imbedded in
the wood ; and if it was not converted into wood,
they would be found still in the bark. Accordingly
when a trunk which had been so treated was at the
end of several years opened up and inspected, the
threads were found to be deeply imbedded in wood :
it is plain, therefore, that the new layer of wood
forms originally a layer of liber 9 according to the
common acceptation of the term. But to try also
the value of Grew's conjecture with regard to the
separation of the liber into two parts, the one ex-
panding towards the circumference and forming
new bark, and the other condensing towards the
centre, and forming new wood, Du Hamel varied
the above experiment so as that some of the threads
were passed through the outer part of the bark, near
the epidermis; others through the inner part of it,
near the liber; others through the liber itself; and
others between the liber and wood. At the end of
several years, when the trunk was opened up and
inspected, the threads that were originally placed in
the outer bark and near the epidermis were now
covered only with a thin and decayed crust, which
broke readily _in to pieces ; those that were originally
placed in the outer bark, but near the liber, were
* Phys. des Arbres, liv. iv. chap. iii.

7

222 PROCESS OF DEVELOPMENT. CHAP. IV.

now among the external cortical layers ; those that
were originally passed through the liber were now
imbedded in wood ; and those that were orginally
passed between the liber and wood were still more
deeply imbedded. The conjecture of Grew, there-
fore, is confirmed, at least in substance. For either
the layer that is formed separates into two distinct
portions, the one tending towards the circumference
and forming bark, and the other tending towards
the centre and forming wood ; or, two distinct layers
are originally generated receding in opposite di-
rections, and forming respectively wood and bark :
which last part of the alternative is the most likely
to be the fact ; because we can scarcely refer two
substances so distinct in their character and proper-
ties as the wood and bark, precisely to the same
origin.

Buttyim- But although the above experiments are correct

metiiate j • • i j 11 r

generation and convincing, beyond all controversy, as far as

proper * tne7 g°> 7et tney ^° not include the whole of the
•Jutce; case ; for the annual layer, which seejns thus to be
formed merely from the bark, is in fact formed only
from the proper juice descending from the leaf
through the tubes of the liber. The bark then is not
to be regarded as the generating cause of the new
layer, but merely as the medium of the transmission
of the materials from which it is formed. For the
proof of this most important fact we are chiefly
indebted to the well-known experiments of Mr.
Knight, by which he has thrown the highest degree

SECT. II. COMPOSITE ORGANS. 223

of elucidation on one of the most obscure and intri-
cate processes of the vegetable economy, in having
shown that the sap is elaborated, so to render it fit As elab»-
for the formation of new parts, in the leaf only. If the6 leaf,
a leaf or branch of the vine is grafted even on the
fruit-stalk or tendril, the graft will still succeed ;*
but if the upper part of a branch is stripped of its
leaves the bark will wither as far it is stripped ; and
if a portion of bark furnished with a leaf is insulated
by means of detaching a ring of bark above and below
it, the wood of the insulated portion that is above
the leaf is not augmented :-f~ this shows evidently
that the leaf gives the elaboration necessary to the
formation of new parts, and that without the agency
of the leaf no new part is generated.

There seems indeed to be an exception to this Or even
law in one of Mr. Knight's own experiments, in
which he found that when the fruit-stalk was grafted
on the leaf-stalk, the graft succeeded also ; and in
which case the wood was deposited on the external
sides of his central vessels, having oozed, no doubt,
from the external tubes by which the proper juice
descends. Now this seems to prove that the parts
of the flower are capable of generating wood as well
as the leaf: but it should be recollected that flowers
in general are furnished with a calyx, which is cer-
tainly very nearly allied to the leaf, and that some
parts of the flower are even convertible into leaves ;
* Phil. Trans. 1803. f Ibid, 1801.

5

224 PROCESS OF DEVELOPEMENT. CHAP. IV.

as may be seen in the case of the common Cherry
when the blossom becomes double, the stamens
being converted into petals, and the pistil not un-
frequently into a leaf. A similar phenomenon may
be sometimes observed also in the fruit of the Pear-
tree. In the summer of 180Q, I observed in the
garden of Rendlesham Parsonage two Pears, of
nearly the size of the rest on the same tree, having
each several leaves growing out of it, with the
insertion about half way between the base and
apex of the fruit : I do not know what particular
variety of Pear it was, but it was a large and dusky-
coloured winter Pear, perhaps the winter rousselet.
The same thing may be also observed in the fruit of
the Medlar ; and hence the success of Mr. Knight's
graft of the fruit-stalk on the leaf-stalk is the less
surprising. The fact then is that the new layer
Andde- l8 formed not absolutely from the bark, as the
experiments of Du Hamel might seem to indicate,

the return- kut from the proper juice descending through the
returning vessels of the leaf, leaf-stalk, and inner
bark, from the summit to the lower extremity of
the plant ; in tracing which vessels Mr. Knight
thought he could even discover two distinct sets, one
for forming the new layer of wood, and another for
forming the new layer of liber. This is a very nice
distinction indeed, and a fact, if it is the fact, diffi-
cult to ascertain. It is certain, however, that either
two layers are originally generated ; or that the ori-

SECT. II. COMPOSITE ORGANS. 225

ginal layer separates into two parts, as Grew sup-
posed ; because the bark is augmented by a new
layer as well as the wood.

Such is the final result of the experiments of Peculiar
Du Hamel, Hope, and Knight. And yet Mr. Knight,
Knight, who has done so much to elucidate the
subject, entertains at the same time some minor
opinions that are altogether incompatible with his
general theory. He is of opinion that the new
bark, as well as the leaf, possesses also the power of
preparing proper juice and of generating new wood;
because it was observed that a small quantity of
wood was generated even at the lower extremity of
an insulated portion of bark on which there was
neither bud nor leaf.* But is it not possible to
account for this small production from the quantity
of proper juice that might exist in the bark at the
time it was left in its insulated state ? He is also of
opinion that the wood or alburnum already formed
extends itself laterally without any radicles as he
calls them, descending from the leaves and shoots
above ; because trees of different species, when
grafted on one another, preserve their wood distinct
in quality immediately above and below the graft.
But if the wood extends itself laterally, why did it
not so extend itself above his insulated leaf, where
we are told it made no augmentation? And is it not
also possible that the proper juice may receive its
final degree of modification in the bark itself?

* Phil. Trans. 1803.
VOL. II. 0,

'226 PROCESS OF DEVELOPEMENT. CHAP. IV.

This is much more likely to be the case than that
the alburnum should extend itself laterally, which
is contrary to the experiments of Du Hamel, and
also to the scope of Mr. Knight's general con-
clusion ; namely, that the sap after being exposed
to the action of the light in the leaves, and con-
verted into proper juice, is again carried back by
the returning vessels of the leaf and leaf-stalk to
the bark, by which it is conveyed throughout the
whole extent of the plant, to add new matter and
to compose the different organs for the succeeding
year.*

Augment- Such then is the mode of the augmentation of
succeeding the plant in the second year of its growth. It ex-
tends in width by a new layer of wood and of
bark insinuated between the wood and bark of the
former year ; and in height by the addition of a
perpendicular shoot or of branches, generated as
in the shoot of the first year. But if the plant is
taken and dissected at the end of the third year, it
will be found to have augmented in the same
manner ; and so also at the end of the succeeding
year as long as it shall continue to live ; so that the
outermost layer of bark, and innermost layer of
wood, must have been originally tangent in the first
year of the plant's growth ; the second layer of
bark, and second layer of wood, in the second
year ; and so on in the order of succession till you
come to the layer of the present year, which will

* Phil. Trans. 1805.

SECT. II. COMPOSITE ORGANS. 22?

in like manner divide into two portions, the outer
forming one or more layers of bark, and the inner
forming one or more layers of wood. And hence
the origin of the concentric layers of wood and of
bark of which the trunk was found to be composed
in treating of the anatomy or internal structure of the
plant ; where it was shown that the layers of wood
are by no means regularly developed, being often
thicker on the one side of the stem than on the
other, and often also more in number ; owing, as it
appeared, to a superabundance of sap flowing from
a large root, or to a large branch, or to sudden
changes of temperature. And even where the in-
dividual layers are of equal thickness throughout,
they are not always equal in thickness to one
another ; owing no doubt to the age and vigour
of the plant; for the larger the diameter of the
tree, the thinner the layer, even if the same quan-
tity of wood should be formed. But the layers of
wood are always thicker than the layers of bark ;
though the bark of sickly trees is thicker in pro-
portion to the wood than that of healthy trees.
But how are the different layers united together so
as to form but one body in the aggregate? Malpighi
thought the layers of liber, as formed by the lon-
gitudinal tubes, are united or cemented together by
means of a plate of cellular tissue interposed be-
tween them. In the formation of the layers it is
true that tubes and utricles are always conjoined,

a 2

228 PROCESS OF DEVELOPEMENT. CHAP. IV.

the former being apparently united together by
the latter. But it does not appear that an inter-
vening layer of cellular tissue is always to be found
distinct. There are some plants, however, which do
exhibit the layer in question distinctly enough ac-
cording to the description of Malpighi. Between
every two layers of the bark of the Fir-tree, there is a
thin layer of a substance evidently different in tex-
ture, which might have been the ground of Mal-
pighi's remark. And even in the body of the
trunk there is alternately a layer of wood that is
hard and white, and a layer that is brown and re-
sinous, from which the resinous drops exude when
the trunk is cut.

Formation But how are we to account for the formation of
vergent the divergent layers, which Du Hamel erroneously
cordingCto supposed to proceed from the pith ? If Du Hamel
•UuHamel, na(j j^ happened to attend to the phenomena re-
lative to the point in question, which some of his
own experiments were the best calculated to exhibit,
he would readily have found the true solution of
the difficulty. This,, however, has been furnished
by Mr. Knight, who, in tracing the result of the
operation of budding, observed that the wood
formed under the bark of the inserted bud unites
indeed confusedly with the stock, though still pos-
sessing the character and properties of the wood
from which it was taken, and exhibiting divergent
layers of new formation which originate evidently

• '

SECT. II. COMPOSITE ORGANS. '220

in the bark, and terminate at the line of union
between the graft and stock. * Also, if a portion
of the stem of a tree is decorticated so as to leave
the surface of the alburnum exposed to the air for
any considerable length of time, there is no farther
vegetation on that part of the alburnum. But if
the wound is not very large it will again close up,
first by means of the production of a new bark
issuing from the edges, and gradually narrowing
the extent of the wound ; and then by the pro-
duction of new layers of wood formed under the
bark as before. The new wood will not indeed
unite with the portion of alburnum that had been
exposed to the air ; but it will exhibit on a horizontal
section, the same traces of divergent layers as
before, extending from the bark in which they
originate to the lifeless surface of the old wood
within. It is evident, therefore, that the divergent whose

layers are formed, not from the pith, but from the °Pinion i§

erroneous.

proper juice descending through the channel of the
bark, and are synchronous in their formation with
that of the concentric layers through which they
pass.

It seems indeed impossible that the divergent
layers should be an extension of the pith, at least
beyond the first or second year of the plant's
growth, whether on account of the gradual indu-
ration of the wood, or of its own natural diminu-
tion. For as the trunk increases in size the pith
* Phil. Trans. 1803.

330 PROCESS OF PEVELOPEMENT. CHAP. IV.

gradually diminishes in diameter, till it is at length
totally obliterated, and its place supplied with
wood, as in the case of the aged trunk ; existing
only in the smaller branches, or in the annual
shoot.

Conver- But how is the formation of the wood to be
pith into C accounted for, that now occupies the place of the
wood. p^h ? In the chapter on the anatomy of the plant
it was observed that the pith of the young shoot is
surrounded by a set of longitudinal tubes, forming
in the aggregate a cylinder, in which it is invested
as in a sheath, which M. Mirbel designates by the
appellation of the Tubular sheath; but which I
have thought to be better designated by the ap-
pellation of the Medullary sheath; inasmuch as
the latter term suggests the use of the organ in
question, which the former term does not. But
by whatever appellation it may be designated, it
appears that the tubes of which it is composed do,
in the process of vegetation, deposit a Cambium,
which forms an interior layer that is afterwards
converted into wood for the purpose of filling up
the medullary canal. Such is the account given
by M. Mirbel,* of the origin of the wood occupying
the place of the pith in the aged trunk, which is
countenanced by the fact of the developement and
existence of longitudinal tubes that are to be found
even within the body of the pith, as stated also in
the above-mentioned chapter.

* Traite d'Anat. et de Phys. Veg. liv. iii.

SECT. II. COMPOSITE ORGANS. 231

But in consequence of the increase of the trunk Conver-
by means of the regular and gradual addition of burnum
an annual layer, the layers whether of wood or of mtowood'
bark are necessarily of different degrees of solidity
in proportion to their age ; the inner layer of bark,
and the outer layer of wood, being the softest; and
the other layers increasing in their degree of soli-
dity till you reach the centre on the one hand, and
the circumference on the other, where they are re-
spectively the hardest, forming perfect wood or
highly indurated bark, which sloughs or splits into
chinks, and falls off in thick crusts, as in the Plane-
tree, Fir, and Birch. What length of time then
is requisite to convert the alburnum into perfect
wood, or the liber into indurated bark ; and by what
means are they so converted ?

There is no fixed and definite period of time
that can be positively assigned as necessary to the
complete induration of the wood or bark, though
it seems to require a period of a good many years
before any particular layer is converted from the
state of alburnum to that of perfect wood ; and
perhaps no layer has received its final degree of
induration till such time as the tree has arrived at
its full growth. But this is not a subject of any
peculiar importance. It is a subject of some im-
portance, however, to trace the cause of the indu-
ration of the wood, concerning which there seems
to have existed, or to exist now, some diversity of
opinion.
4

PROCESS OF DEVELOPEMENT. CHAP. IV.

Attributed An opinion pretty generally entertained was that
sap. by which the induration of the alburnum, and its
consequent durability, are attributed to the loss of
sap which the layer sustains after the period of its
complete developement ; when the supply from the
root diminishes, and the waste by evaporation or
otherwise is still kept up, inducing a contraction
or condensation of its elementary principles that
augments the solidity of the layer, in the first
degree, and begins the process that future years
finish.

Theory But Mr. Knight believes the induration of the
Knight, alburnum as distinguishable in the winter to be
owing rather to some substance deposited in it in
the course of the preceding summer, which he re-
gards as being the proper juice in a concrete or
inspissated state, but which is carried off again by
the sap as it ascends in the spring. This was ori-
ginally a conjecture which he thinks he has proved
to be also the truth. The first argument is founded
on the fact that the sap as it ascends becomes gra-
dually more and more mixed with the proper juice
of the plant, as may be seen in the case of the
Maple, and Birch, the sap of which last when ex-
tracted near the root, being almost without taste ;
but when extracted at the height of seven or eight
feet, or less, being sensibly sweet. The second ar-
gument is founded on the fact that the specific
gravity of the sap in the bleeding season increases
according to the height at which it is extracted.

SECT. II. COMPOSITE ORGANS. 133

The specific gravity of the sap of the Sycamore*
tree extracted close to the ground was 1 '004 ; at
the height of seven feet, 1-008; and at the height
of twelve feet, 1-012. The same proportion was
also observed in the sap of the Birch ; but after the
sap had flowed for some days from the same incision
the specific gravity was reduced to 1'002 ; which
shows that the matter carried off from the alburnum
had diminished at least in the vicinity of the in-
cision. The third argument is founded on the
fact that the specific gravity of the alburnum is
greater in the winter than it is either in the pre-
ceding or following summer. Two equal portions
were taken from two poles that had sprung from
the same shoot, the one having been felled in De-
cember, and the other in the May following. They
were kept for the space of seven weeks near a warm
fire, at the end of which period they both ap-
peared to be perfectly dry. The specific gravity of
the winter felled wood was 0*679 » while that of
the summer felled wood was only 0-609. Still it
was possible that the apparent difference of specific
gravity might have proceeded merely from a greater
degree of contraction in the winter felled wood ;
in consequence of which doubt it was thought that
the comparison of their respective quantities of ex-
tractive matter would be the best means of avoiding
all mistake. Accordingly six ounces of boiling
water were poured on 100O grains of each, reduced
to small fragments ; and at the end of twenty-four

'134 PROCESS OF DEVELOPEMENT. CHAP. IV.

hours it was found that the winter felled wood had
communicated a much deeper tinge to the water,
and raised its specific gravity to T002, the specific
gravity of the other being only 1-001. Whence
Mr. Knight concludes that the cause of the su-
perior quality of winter felled timber, and of the
conversion of the alburnum into wood, is attribu-
table to the matter deposited in the alburnum
during the preceding summer, and partially,
though not totally, carried off in the succeeding
spring.*

Throws But after all this parade of experiment, it must
light on still be confessed that there is but little elucidation
ject.8U thrown on the subject. For the truth of the facts
may be admitted, and yet the legitimacy of the
ultimate conclusion deduced from them may be
denied. It may be true that an extraordinary
quantity of proper juice is deposited in the al-
burnum in the course of the summer, which is
again partly carried off in the succeeding spring ;
and this will no doubt account for its superior
quality in the intervening winter. But how is it
to account for its final conversion into wood, a
change that is effected only by slow degrees, the
layer becoming every year more and more indu-
rated till it acquires in >the end its last degree of
solidity. For if the matter deposited in the sum-
mer is almost wholly carried off again in the suc-
ceeding spring, no progress has been made in the
* Phil. Tram. 1805.

SECT. II. COMPOSITE ORGANS. 235

process of induration ; unless you suppose that the
matter carried off from the alburnum in the spring,
by means of the ascending sap, is again deposited
in it in the course of the summer. And this is
indeed what Mr. Knight supposes ; for he thinks
that the proper juice in descending from the leaf is
expended not only in forming a new epidermis,
where that is wanted, and a new layer of liber and
of alburnum, but partly also in entering the pores
of the former alburnum and mingling again with
the ascending sap. But if this second accession
of proper juice were even allowed, its effect could
be but very trifling. For if it mingles again with
the ascending sap, it must also be again for the
most part carried off, and can consequently be of
no great advantage to the induration of the wood.
And if it should even leave behind it a considerable
deposit, now, in the second year, still you have
to account for its further induration in the third
and fourth and subsequent years, when it will
hardly be contended that the descending proper
juice enters it. It cannot, therefore, be admitted
upon Mr. Knight's principles that the alburnum is
converted into wood by means of any matter de-
posited in it during the summer ; because the
matter thus deposited is again carried off in the
succeeding spring; and is not proved, but con-
jectured, to be again restored in the summer fol-
lowing : on which very slender foundation Mr.
Knight has, however, thought proper to erect the

236 PROCESS OF DEVELOPEMENT. CHAP. IV.

superstructure of the doctrine of the circulation of
the vegetable juices.

SECTION III.
Circulation of Vegetable Juices.

According AFTER the discovery of the circulation of the
earlie^ blood of animals, phytologists, who were fond of
gists010" tnnnrig analogies between the animal and vegetable
kingdoms, began to think that there perhaps existed
in plants also, a circulation of fluids. There was
not indeed any visible apparatus corresponding
respectively to the stomach, intestines, lacteals, and
heart of animals, the main spring of the circulation
of the blood ; but the defect was supplied in the
best way possible. The root was regarded as cor-
responding both to the mouth and stomach of
animals, and as effecting some peculiar change
upon the fluid absorbed, that fitted it for the direct
nourishment of the plant ; as well as possessing
also the power of propelling the digested fluid,
impregnated with the principles of nutrition,
growth, and developement, to the very summit of
the leaf, from which it was again returned to the
root, where, mingling with the newly digested fluid,
it was again propelled to the summit as before, and
a circulation thus kept up. The vessels in which
it was propelled to the summit of the plant were
denominated arteries ; and the vessels in which

SECT. HI. CIRCULATION OF JUICES.

it is again returned to the root were denominated
veins.

Such was the original theory of the circulation of
the vegetable fluids, which was soon found to rest
on a very slender basis, and to stand in need of the
support and sanction of some substantial argument.
Accordingly the best arguments that could be ob-
tained were mustered up in defence of the doctrine.

In proof of the digestive power of the root it
was said that if a tree is cut down level with the
earth, it will still continue to live and to send out
new shoots ; which it could scarcely be thought
capable of doing, except upon the supposition that
the sap is elaborated in the root, and not in the
upper part of the plant. But the Fir-tree uni-
formly dies under this operation; and although
most trees do indeed survive it, yet it is only by
virtue of new buds which are formed on the upper
part of the root, or remaining part of the stem,
and in which the process of elaboration is con-
tinued. For if you constantly destroy the buds as
they make their appearance the root will to a cer-
tainty die. It was urged, however, that the root
is the organ of elaboration, because, in plants having
a conspicuous proper juice, it may be readily per-
ceived by means of a transverse section oozing
from the very extremity of the root. But so also
it may be observed to ooze even from the extremity
of the stem. The argument then proves nothing ;

238 PROCESS OF DEVEXOPEMENT. CHAP. IV.

and if it does prove the root to be the organ of
elaboration, why does the sap in general ascend the
stem unaltered ?

In proof of the fact of the circulation of the
sap it was said that it is impossible to conceive how
the important and complicated operations of the
secretion of the peculiar juices of the plant could
be effected all at once ; and that, therefore, it was
reasonable to suppose them to be effected by re-
peated efforts, which the circulation of the sap, as
of the blood in the animal system, was the best
fitted to produce. But this is obviously an argu-
ment of convenience, which proves nothing. For
if the cause of vegetable developement should
remain unexplained, we are not to assume that of
the process of circulation without any adequate
proo£ merely because it seems to account for it
the most easily. But it was added that different
sorts of vessels are distinguishable in the structure
of the plant, some for conducting trie sap in its
ascent, and others for conducting it in its return.
This it was admitted might be the fact, without
proving the one set to be arteries and the other
veins. It was then said that they must still be
supposed to exist, though we should not be able to
distinguish or ascertain them ; in the same manner
as we must suppose their existence in the wing of
a butterfly without being able to distinguish them.
This is no doubt possible; but it is contradicted

SECT. III. CIRCULATION OF JUICES. 23Q

by the fact that an inverted plant grows. It was
also added that a malignant humour has been some-
times found to pervade the whole of the vascular
system ; which could not have happened, as it was
thought, except upon the supposition of a circulation
of fluids. But it is also known that diseases of the
trunk do not always affect the root ; and that if a
tree diseased in the trunk or branches is cut down
to the root, it will send up new shoots as sound and
vigorous as at first. Finally, it was said that para-
sitical plants are injurious to the tree on which
they grow, by throwing into the circulation some
noxious principle. But it is not proved that para-
sitical plants are always injurious to the tree on
which they grow; and if they are so sometimes,
the effect may be very well accounted for by attri-
buting it to the privation of a part of its due nou-
rishment, rather than by the introducing of some
noxious principle into an assumed circulation.

Such are the principal arguments that were ad-
vanced by the earlier phytologists in support of the
circulation of the sap, as stated and refuted by Du
Hamel,* who, while he admits the ascent of the sap,
and descent of the proper juice, each in peculiar and
appropriate vessels, does not however admit the doc-
trine of a circulation ; which seems, about the mid-
dle of the last century, to have fallen into disrepute.
For Hales, who contended for an alternate ascent and
descent of fluids in the day and night, and in the same
vessels, or for a sort of vibratory motion as he also

* Phys. des Arbres, liv, v. chap. ii.

24O PROCESS OF DEVELOPEMENT. CHAP. IV,

describes it, gave no countenance whatever to the

doctrine of a circulation of juices.

According But the doctrine, as it appears, has been again
CortCi,Tngd revived, and has met with the support of some

of the most distinguished of modern phytologists.

now

Hedwig is said to have declared himself to be of
opinion that plants have a circulation of fluids si-
milar to that of animals. But as I am not ac-
quainted with the arguments on which his opinion
is founded, I can say nothing with regard to them.
Corti is said to have discovered a species of circu-
lation in the stern of the Chara, confined as I
believe, within the limits of the internodia. But
perhaps it was nothing more tban a sort of vibra-
tory motion of the contained fluids, similar to that
which I observed in the peduncle of the Mar-
chantia, as related in the Analysis of the Internal
Structure. Willdenow has also introduced the sub-
ject, and defended the doctrine, in his Principles of
Botany ; * but only by saying he believes a circu-
lation to exist, and that it is impossible for the
leafless tree to resist the cold if there be not a circu-
lation of fluids ; which, as it is no argument, merits
no particular reply.

According But as Mr. Knight has given his reasons sorne-

to Knight, wj)at more in detail, we will also be somewhat more

particular in endeavouring to ascertain their value.

The experiments by which Mr. Knight accounts for

the conversion of the alburnum into wood have

been already stated in detail. But he is of opinion

* English Trans, p. 285.

SECT. III. CIRCULATION OF JUICES. 241

that they prove at the same time the circulation of
the vegetable fluids. For if it is admitted that the ^

descending proper juice forms not only a new epi-
dermis where wanted, and a new layer of liber and of
alburnum, but enters also, partly, the alburnum of
the preceeding year, where it mingles and is again
carried up with the ascending sap, it is obvious that
a sort of circulation is completed. But this last
and most essential part of the process rests merely
on the foundation of conjecture ; for there is no
proof offered in support of the fact : it is only said
that you cannot conceive how in a body so porous
as wood, the several fluids should remain unmixed.
It is, however, no proof of the truth of any opinion
to say that you cannot conceive the thing to be
otherwise, as the same thing has been said in sup-
port of ten thousand absurdities which have still
continued to be absurdities. It is no doubt difficult
to conceive how the fluids should remain unmixed ;
but what if they should remain unmixed after all ?
The alburnum of the former year being now con-
siderably condensed, will not afford that ready
reception to the proper juice which is here alledged :
in the same manner we shall suppose that the re-
turning vessels of the leaves do not admit coloured
infusions ; but if the vessels of the alburnum should
admit some part of the descending proper juice by
means of lateral communication as is here supposed,
can any one be certain that it is the juice which was
formerly carried up, and nat rather part of that

VOL. II. R

242 PROCESS OF DEVELOPEMENT. CHAP. IV.

which has been newly generated ? And if the cir-
culation is completed only by the entrance of the
descending fluid into the alburnum of the former
year, what becomes of the circulation of juices
during the first year of the plant's growth, when
there is yet no alburnum of a former year to enter ?
which if it does enter in future years, why is it carried
up again ? It does not seem necessary to complete
the circulation, and upon Mr. Knight's principles it
ought rather to remain for the purpose of effecting
the induration of the wood. In short there seems
to be a great deal of confusion and contradiction in
Mr. Knight's hypothesis. For first he supposes
that the superior specific gravity and superior
quality of winter felled wood depends upon a sub-
stance deposited in the alburnum during the pre-
ceeding summer and autumn, and yet he abstracts
the major part of it in the succeeding spring without
replacing it by a quantity sufficient to account for
its increased solidity in the subsequent winter, or at
least, without replacing it by any quantity which is
to remain permanent
Whose Mr. Knight's hypothesis, therefore, cannot be

hypothesis . .

is inde- true in its whole extent ; for if the supposed circu-
0 e* lation exists, then the superior quality of winter
felled wood does not ultimately depend upon any
substance deposited in the alburnum in summer,
because it is all or in great part carried off in the
succeeding spring and not absolutely proved to be
replaced in the subsequent summer; and if the

SECT. III. CIRCULATION OF JUICES. 243

matter supposed to be deposited in the alburnum is
the true cause of the wood's superior quality, then
the circulation cannot take place ; because on the
supposition in question the matter that is thus de-
posited ought not to be again abstracted. Indeed
it seems to be doubtful whether the hypothesis is
good in any of its parts ; for as on the one hand the
circulation rests on no admissible proof, so on the
other the superior quality of the winter felled wood
is well enough accounted for by its becoming more
condensed.

It is no proof of the circulation of the vegetable
fluids to say that the proper juice may even be seen
in the alburnum of some plants, as in the example
of the Fig. For since the alburnum is itself ori-
ginally formed of the proper juice, it cannot during
the first year be otherwise than mixed with it ; and
if it should occasionally be found even in the
matured wood, it may be nothing more than the
portion that was originally deposited, now in an
inspissated state. Nor is the induration of the
wood to be regarded as proceeding from the intro-
susception of some additional substance into the
alburnum, rather than from its condensation, owing
to the mere change of colour which takes place in
that process from a white to a dark brown ; or to its
increased durability, as supposed by Mr. Knight,*
because the effects in question may be easily ac-
counted for, even upon the principle of condensa-
*Phil. Tran. 1806,
R 2

244 PROCESS OF DEVELOPEMENT. CHAP. IV.

tion. The leaf changes its colour in the autumn,
and wood when felled not only changes its colour,
but becomes also more durable without the intro-
susception of any new substance.

Though But although the doctrine of a circulation as
JfeEST1 maintained by Mr. Knight should be felse, yet the
luminous. account which he gives of the progress and agency
of the sap and proper juice, short of circulation,
may be true. The sum of the account is as fol-
lows : — When the seed is deposited in the ground
under proper conditions, moisture is absorbed and
modified by the cotyledons, and conducted directly
to the radicle, which is by consequence first de-
developed. But the fluid which has been thus
conducted to the radicle, mingling no doubt with the
fluid which is now also absorbed from the soil,
ascends afterwards to the plumelet through the
medium of the tubes of the alburnum. The plume-
let now expands and gives the due preparation to
the ascending sap, returning it also in its elaborated
state to the tubes of the bark, through which it
again descends to the extremity of the root, forming
in its progress new bark and new alburnum ; but
mixing also, as Mr. Knight thinks, with the albur-
num of the former year, where such alburnum
exists, and so completing the circulation.

But in this account of the process of vegetation,
though sufficiently perspicuous, one or two links of
the chain are obviously omitted ; no conjecture
being offered with regard to the origin of the tubes

SECT. IV. DECOMPOSITE ORGANS. 245

of the alburnum and bark. Their existence is as-
sumed but not accounted for. We are told, indeed,
that the tubes of the alburnum arc not discoverable
at a very early period of vegetation, as coloured in-
fusions are not absorbed by the plant till it is some
weeks old, even when part of the root is cut off, at
least in the case of the Horse-chesnut,* though
they begin to be discoverable soon after that period.
But we are not favoured even with a conjecture with
regard to the probability of their actual origin ;
whether as being wholly generated in the progress
of vegetation, or as being merely developed by the
intro-susception of nutriment into some primordial
and duly organized element pre existing in the
embryo.

SECTION IV.

Decomposite Organs.

To the above brief sketch of the agency of the
vital principle in the generation or growth of the
elementary and composite organs, there now re-
mains to be added that of the progress and mode of
the growth of the decomposite organs, or organs im-
mediately constituting the plant, as finishing the
process of the vegetable developement. This will
include the phenomena of the ultimate develope-
ment of the root, stem, branch, bud, leaf, flower,
and fruit.

* Phil. Trans. 1806.

246 PROCESS OF DEVELQPEMENT. CHAP. IV.

SUBSECTION I.

The Root. The Root. — From the foregoing observations and
experiments it appears that the roots of plants, or at
least of woody plants, are augmented in their width by
the addition of an annual layer, and in their length
by the additon of an annual shoot, bursting from
the terminating fibre. But how is the developement
of the shoot effected ? Is it by the intro-susception of
additional particles throughout the whole of its ex-
tent ; or only by additions deposited at the ex-
tremity ? In order to ascertain the fact, with regard
Elongated to the elongation of the root, Du Hamel instituted
tremity6*" ^e ^°^ow^ng experiment :• — Having passed several
only« threads of silver transversely through the root of a
plant, and noted the distances, he then immersed
the root in water. The upper threads retained
always their relative and original situation, and the
lowest thread which was placed within a few lines
of the end was the only one that was carried down.
Hence he concluded that the root is elongated
merely by the extremity.* Mr. Knight who from
a similar experiment obtained the same result de-
duced from it also the same conclusion.-}- We may
regard it then as certain that the mode of the elon-
gation of the root is such as is here represented,
though in the progress of its developement it may
affect a variety of directions.

* Phys. des Arb. liv. i. chap. v. | Phil. Trans. 180&

SECT. IV. DECOMPOSITE ORGANS. 247

The original direction of the root is generally Its direc-
perpendicular, in which it descends to a consider- ll<
able depth if not interrupted by some obstacle. In
taking up some young Oak-trees that had been
planted in a poor soil, Du Hamel found that the
root had descended almost four feet, while the
height of the trunk was not more than six inches.
If the root meets with an obstacle it then takes a
horizontal direction, not by the bending of the
original shoot, but by the sending out of lateral
shoots. The same effect also follows if the ex-
tremity of the root is cut off. It grows in length no
longer. Du Hamel made some Cherry-stones,
Almonds, and Acorns to germinate in wet sponges ;
and when the roots had grown to the length of two
inches, he then placed them in glasses as bulbous
roots are placed, so as that the extremity of the root
only touched the water. Some were previously
shortened by the cutting off of a small bit from the
point ; others were put in entire. The former im-
mediately sent out lateral shoots, but elongated no
farther in a perpendicular direction; the latter de-
scended perpendicularly to the bottom of the glass.
He cut off also the tips of some roots vegetating in
the earth, and had the same result ; the wound
citatrized, and the root sent out lateral divisions.

When a root ceases of its own accord to elongate, Lateral
it sends out also lateral fibres, though less vigorously fibrcs°
and with less rapidity than in the above cases.
The lateral branches of perpendicular roots are

248 PROCESS OF DEVELOPEMENT. CHAP. IV.

always the more vigorous the nearer they are to the
trunk, but the lateral branches of horizontal roots
are the less vigorous the nearer they are to the
trunk. In the former case the increased luxuriance
is perhaps owing to the easy access of oxygene in
the upper divisions; but in the latter case the in-
creased luxuriance of the more distant divisions is
not so easily accounted for, if it is not to be at-
tributed to the more ample supply of nutriment
which the fibres meet with as they recede from the
trunk, particularly if you suppose a number of them
lying horizontally and diverging like the radii of
a circle.

Accidental But the direction of roots is so liable to be affected
' by accidental causes, that there is often but little
uniformity even in roots of the same species. If
plants were to be sown in a soil of the same density
throughout, perhaps there might be at least as much
uniformity in the figure and direction of their roots,
as of their branches ; but this will seldom happen.
For if the root is injured by the attacks of insects,
or interrupted by stones, or earth of too dense a
quality, it then sends out lateral branches, as in the
above cases ; sometimes extending also in length by
following the direction of the obstacle, and some-
times ceasing to elongate, and forming a knot at
the extremity. But where the soil has been loosened
by digging or otherwise, the root generally ex-
tends itself to an unusual length. This Du Hamel
has illustrated by the following cases : — If a trench

SECT. IV. DECOMPOSITE ORGANS* 24Q

is opened at a small distance from a young tree and
immediately filled up again with loose earth, the
roots which enter the trench will continue to follow its
direction, and will send out but few lateral branches.
And if part of the trench is filled up with earth of
a superior quality, or with earth mixed with manure,
the greater number of divisions will be directed to
that quarter. Trees also that are planted by the
banks of a river extend their branches chiefly in the
directiou of the river without sending out many
lateral b ranees ; where the earth is very loose the
roots are generally weak, because having no obstacle
to overcome they have extended to an undue length.
Hence the roots of plants vegetating in pots,, but
especially in water, are the weakest ; but where
roots have some considerable obstacle to overcome
they will often acquire a strength proportioned to
the difficulty : sometimes they will penetrate through
the hardest soil to get at a soil more nutritive, and
sometimes they will insinuate their fibres into the
crevices even of walls and rocks which they will
burst or overturn. This of course requires much
time, and does much injury to the plant. Roots
consequently thrive best in a soil that is neither too
loose nor too dense ; but as the nourishment which
the root absorbs is chiefly taken up by the ex-
tremity, so the soil is often more exhausted at some
distance from the trunk than immediately around it.

Du Hamel regards the small fibres of the root Terminal
which absorb the moisture of the soil as being compared

250 PROCESS OF DEVELOPEMENT. CHAP. IV.

to the lac- analogous to the lacteals of the animal system,
™imals. which absorb the food digested by the stomach.
But at this rate we must also regard the earth as
being the stomach of plants, which analogy, as I
think, will not hold good. For the root is rather to
be regarded as the mouth of the plant, selecting
what is useful to nourishment and rejecting what is
yet in a crude and indigestible state ; the larger por-
tions of it serving also to fix the plant in the soil and
to convey to the trunk the nourishment absorbed
by the smaller fibres, which ascending by the tubes
of the alburnum, is thus conveyed to the leaves,
the digestive organs of plants.
Said to die Du Hamel thinks that the roots of plants are

11

likcUthey furnished with preorganized germes by which they
are enabied to send out lateral branches when cut,
though the existence of such germes is not proved ;
and affirms that the extremities of the fibres of the
root die annually like the leaves of the trunk and
branches, and are again annually renewed ; which
last peculiarity Professor Wildenow affirms also to
be the fact,* but without adducing any evidence by
which it appears to be satisfactorily substantiated.
On the contrary Mr. Knight, who has also made
some observations on this subject, says, it does not
appear that the terminating fibres of the roots of
woody plants die annually, though those of bulbous
roots are found to do so.-}-

* Princ. of Bot. Eng. Trans. 262. i Phil. Trans. 1809.
4

SECT. IV. DECOMPOSITE ORGANS. 251

SUBSECTION II.

The Stem. — The stem, like the root, or at least Mode of

. . augmenta-

the stem of woody plants, is also augmented in tion.
width by the addition of an annual layer, and in
length by the addition of an annual shoot bursting
from the terminating bud. Is the developement of
the shoot issuing from the stem effected in the same
manner also ? The developement of the shoot from The new

shoots aug-

the stem is not effected in the same manner as that mented by
of the root — by additions to the extremity only — susceptkm

but by the intro-susception of additional particles
throughout its whole extent, at least in its soft and out its

. whole ex-

SUCCulent state: the longitudinal extension dimi-tent;

nishing in proportion as the shoot acquires solidity,

and ceasing entirely when the wood is perfectly

formed ; though often continuing at the summit

after it has ceased at the base. Du Hamel divided

a shoot of the Horse-chesnut into several equal

parts, distinguished by coloured varnish ; and on

inspecting it some time afterwards, found that all the

marks were removed from one another to a greater

distance than at first ; but on inspecting it after a

second interval, he found that the upper marks only

had continued to increase in distance. Hales made

a number of similar experiments on shoots of the

Vine, and obtained similar results ; from which it

seems to follow, as Du Hamel had observed, that

the extension of the shoot is inversely as the indura-

252 PROCESS OF DEVELOPEMENT. CHAP. IV,

tion, rapid while it remains herbaceous, but slow in
proportion as it is converted into wood. Hence
moisture and shade are the most favourable to its
elongation, because they prevent or retard its in-
duration ; and hence the small cone of wood which
is formed during the first year of the plant's growth
increases no more after the approach of winter,
In length neither in height nor thickness. But the plant is
shoot, augmented in height by the addition of a new cone
protruded from the terminating bud in the succeed-
ing spring, that rises to a certain height above the
former cone, which it invests entirely with a new
layer of wood originating in the descending proper
juice, and augmenting the width of the trunk, and
is at last terminated by a bud which sends out a
new shoot in the spring following, and so on till the
tree ceases to vegetate ; so that at the end of a
hundred years the tree has been augmented in
length by a hundred longitudinal shoots, and at the
base by a hundred layers of wood, diminishing in
number as you ascend ; and yet the trunk is some-
times augmented in thickness by the addition of a
new layer, after the shoot has ceased to elongate.*
In thick- The trunk then is annually augmented in length
twk^he ty tne length of the terminating shoot; and in
annual diameter by twice the thickness of the layer. If the
induration of the trunk is effected slowly, then the
growth of the plant is rapid ; and if it is effected
rapidly, then the growth of the plant is slow, as in

* Phys. des Arb. liv. iv. chap. iii.
3

SECT. IV. DECOMPOSITE ORGANS. 253

the respective examples of the Horse-chesnut and
Box, though the growth and induration of the plant
are also liable to be affected both by soil and ex-
posure.

Sometimes the one side of a shoot will remain in
a state capable of extension longer than the other ;
and hence the tree is liable to become deformed.
But gardeners correct or prevent the deformity by
making a number of oblique incisions in the bark
of the shoot on the side to which it is inclined,
which, by occasioning an irruption of the cellular
tissue, forces it back again to an erect posture.

At the junction of the root and stem, which I Thecollar.
have denominated the collar, there is generally to
be observed a sort of irregular and circular pro-
tuberance, similar to that which is occasioned by the
operation of grafting. This is owing — first, to
its being the point of the insertion of the seed
leaves — secondly, to its being the point in which
the divisions of the roots often originate, causing a
deflection of the longitudinal fibres — and lastly, by
the different degrees of augmentation which take
place in the root and stern, the latter augmenting
more than the former, and consequently occasion-
ing a bulge.

Such is the mode of the growth and develope- Growth of
ment of the trunk of perennial and woody plants, Ofpaimg.
to which there exists indeed a striking exception in
the growth of the trunk of Palms. Their internal
structure has been already taken notice of as pre-

254 PROCESS OF DEVELOPEMENT. GHAP. IV.

seating no concentric or divergent layers, and no
medullary canal but merely an assemblage of large
and woody fibres, interspersed without order in a
pulp or parenchyma, softer at the centre and
gradually becoming harder as it approaches the cir-
cumference ; which structure they possess indeed in
common with many animals. But the grand and
peculiar feature by which they are distinguished
from all other plants is that of the origin and mode
of the annual augmentation of their stem.

When the seed of the Palm-tree germinates it
protrudes a circular row of leaves, or of fronds,
which crowns the radicle, and is succeeded in the
following year by a similar row issuing from the
centre or bosom of the former leaves, which ulti-
mately die down to the base. This process is con-
tinued for four or five years successively without
exhibiting as yet any appearance of a stem, the
remaining bases of the leaves or frond forming by
their union merely a sort of knob or bulb. At last,
however, they constitute by their union an incipient
stem, as thick the first year as it ever is after;
which in the following year is augmented in height
as before, and so on in succession as long as the
plant lives, the leaves always issuing from the sum-
mit and crowning the stem which is a regular
column, but decaying at the end of the year, and
leaving circular marks at their points of insertion,
which furrow the surface of the plant, and indicate
the years of its growth.

I

SECT. IV. DECOMPOSITE ORGANS. 25 §

SUBSECTION III.

The Branches. — The Branches, in their mode of Their
growth and developement, exhibit nearly the same
appearances as the trunk from which they issue.
They originate in a bud, and form also a cone that
consists of pith, wood, and bark; or rather they
form a double cone. For the insertion of the
branch into the trunk resembles also a cone whose
base is at the circumference, and whose apex is at
the centre, at least if it is formed in the first year of
the plant's growth, or on the shoot of the present
year ; but falling short of the centre in proportion
to the lateness of its formation, and number of in-
tervening layers.

Like the trunk and root it increases also in width They in
by the accession of new layers, and in length by
the addition of new shoots, at least in as much as
regards its external portion; exhibiting however
some slight peculiarities in as far as regards its in-
sertion, the apex being never carried nearer to the
centre than at the period of its first formation, and
the inserted portion elongating only in consequence
of the accumulation of the new layers by which the
diameter of the trunk is increased. In its width,
however, it increases like the external portion by
the addition of new layers pervading the alburnum
of the trunk, to which it is intimately united by the
interplexus of their respective fibres, forming a firm

256 PROCESS OF rJEVELOPEMENT. CHAP. iv.

and compact knot, as may be seen by truncating a
stem immediately above or below a small branch,
but particularly in the case of the Fir-tree. For
the branches are not formed merely by means of a
horizontal extension of the longitudinal tubes of the
trunk, but are each as it were a distinct individual,
of which the external cone is the trunk, and the in-
ternal cone the root. Hence the trunk is to the
branch what the soil is to the plant, the source of its
nourishment and stability. The branches in their
developement assume almost all varieties of position
from the reflected to the horizontal and upright ;
but the lower branches of trees are said to be
Theirposi- generally parallel to the surface of the soil on which
they grow, even though that surface should be the
sloping side of a hill — owing, as it has been thought,
to the evolution of a greater number of buds on the
side that forms the obtuse angle with the soil, in
consequence of its being exposed to the action of a
greater mass of air.*

SUBSECTION IV.

The Bud. — The Bud which in the beginning of
spring is so very conspicous on the trees of this
country as to be obvious to the most careless ob-
Not com- server, is by no means common to all plants, nor to
plants.°a p'ants of all climates ; shrubs in general, and an-
nuals universally, are destitute of buds as well as
* La Nature Dcvoilec. Dialog, xiv

SECT. IV. DECOMPOSITE ORGANS. 257

all plants whatever growing within the tropics, the
leaf being in them immediately protruded from the
bark. It is only in the woody plants of cold cli-
mates therefore that we are to look for buds, and in
them no new part is added, whether proper to the
leaf or flower, without the intervention of a bud.
For when the young shoot is produced, it is at the
same time furnished with new buds which are again
extended into new shoots in the following spring ;
and thus the bud is to be regarded as forming not
only the cradle but also the winter quarters of the
shoot, for which its coat of tiled and glutinous
scales seems admirably well adapted. It is found Where
chiefly in the extremity, or on the surface of the Sl'
young shoot or branch and but rarely on the
stem, except it be at the collar where it produces
suckers. It is also generated for the most part in
the axil of the leaves, as may be seen by inspecting
the annual shoot of almost any tree at rani u^,
though not universally so ; for to this rule there
exists a curious and singular exception in the bud of
the Plane-tree, which is generated in the very centre
of the base of the foot-stalk, and is not discoverable
till after the fall of the leaf.

But how are the buds formed which are thus Their ori-
developed? Pliny thought they were formed from ^rdtng to
the pith, but without ^adducing any substantial rea- riil,iy.a??

Malpighi.

son.* Malpighi thought they were formed from

* Medulla, sive ilia vitalis anima, ante se tendit longitudi-
nem irnpellens, quamdiu nodi pervia patet fistula, cum vero
VOL. II, S

258 PROCESS OF DEVELOPEMENT. CHAP. IV.

the pith or cellular tissue which he regarded as viscera
destined for the elaboration of the sap and protru-
sion of future buds ;* but this opinion has not been
supported by subsequent observation. Du Hamel
thinks the exterior scales of the bud originate in the
interior part of the bark, of which they seem to be
only a prolongation, and that the young branch or
flower contained within the scales seems to be a
prolongation of the wood and pith of the former
year. And yet this opinion seems to be altogether
inconsistent with an opinion which he also ad-
vances, and by which he supposes the buds of the
plant to originate in what he denominates pre-
organized germes, existing in the proper juice, and
deposited by it in its descent so as to pervade the
whole of the plant. If these germes are understood
to be the result of the agency of the vital principle,
their existence is not impossible ; though it must, at
the same time, be acknowledged that it is by no
means proved. Perhaps the opinion arose from the
facility with which buds are protruded in given cir-
cumstances, in almost any part of the, plant. If a
branch is lopped, or if the stem is truncated, new
buds containing the rudiments of new shoots will
soon after make their appearance near the sec->
tion ; so that they seem to be dispersed without
number throughout the whole extent of the plant.

repcrcussa juxta nodos, hoc vocatur in vite gemma. Nat, Mist,
liv. xvii. chap. 21.
* Anat. Plant. 13.

SECT. IV. DECOMPOSITE ORGANS,* 15Q

But the Fir-tree will send out no bud at all if cut
down near to the root. It may be said that this is
merely the exception to the rule ; but we cannot,
after all, place much reliance on the doctrine of pre-
organized germes.

Mr. Knight relates an experiment from which he According
thinks it follows that the buds are formed from the Knight.
descending proper juice. He intersected the run-
ners connecting the tubers of a potatoe witb the
stem, and immersed both portions in a decoction of
logwood. The decoction passed along in both di-
rections, but did not enter the stem, because in that
direction the communication is kept up only by
the bark through which the proper juice descends
from the leaves, and which admits not coloured in-
fusions : but in the opposite direction it was found
that the infusion had passed through an elaborate
assemblage of vessels between the bark and albur-
num, the ramifications of which were seen to ap*
proach the skin at the base of the buds, to which
they were thought to convey nourishment.* But
allowing the experiment to be correct, it does not
prove that buds are formed from the proper juice but
only nourished by it; as the experiment must have
given precisely the same result if the buds had pro-
ceeded from the pre-organized germes of Du Hameh

But whatever may be the actual origin of the bud,
it is evident that its developement does not take
place except through the medium of the proper

* Phil. Trans. 1SC3.
S 2

26O PROCESS OF DEVELOPEMENT. CHAP. IV.

juice, which has been elaborated in the leaves of
preceding buds, and originally in those of the plume-
let ; as the young bud does not make its appearance
till the leaves df the preceding buds have expanded,
and will not ultimately succeed if deprived of them
too soon.

But from the period of its first formation during
the course of that summer to that of its final expan-
sion in the following spring it continues gradually
and constantly to augment in size ; its progress
being visible by dissection even in the course of the
winter, and accelerated as the spring advances, till
at last its bonds are loosened and the scales ex-
panded, protruding both leaf and flower.
Bulbs. Bulbs are so very similar to buds both in their

origin and developement as to require no specific
investigation. The parent bulb produces an offset
analogous to the bud, which attains to maturity about
the time of the maturity of the flower, and which
finally detaches itself and forms a new individual ;
in which last property it differs essentially from the
bud, which does not detach itself spontaneously,
and can but rarely be made to vegetate if detached
by art.

SUBSECTION V.

How aug- The Leaf. — When the leaves burst from the ex-
panding bud, and even Jong before that period, as may
be seen by the dissection of the bud in the winter,

SECT. IV. DECOMPOSITE ORGANS. 26l

they are complete in all their parts — all the nerves,
and all the indentations of the margin, being dis-
tinctly perceptible, at least by the assistance of a
good glass, together with the fibres, or bundles of
fibres connecting the branch and foot-stalk, and
thus presenting in the aggregate a miniature repre-
sentation of the future leaf. Hence it is obvious that
the leaf, like the young shoot, effects its final deve-
lopement by means of the intro-susception of new
particles throughout the whole of its dimensions :
and yet this law of developement is not common to
all leaves whatever, for the leaves of liliaceous plants
extend chiefly at the point of their junction with
the bulb. This fact was ascertained by Du Hamel
by means of graduating the leaves of the Hyacinth
with transverse lines of coloured varnish ; the lines
near the point of the leaf maintained their original and
relative distances, but the lines below were removed
to a considerable distance, and the nearer the bulb the
distance was the greater. Perhaps this peculiarity
of developement is the effect of their peculiarity of
structure, in being formed of parallel tubes which
extend throughout their whole length, without those
transverse and branching fibres that constitute what
are called the nerves of the leaves of woody plants.

SUBSECTION VI.

The Flower and Fruit.— When the flower bursts Com
from the expanding bud, and even long before that

PROCESS OF DEVELOPEMENT. CHAP. IV.

before its period, it is already complete in all its parts, as may
be seen also by the dissection of the bud in winter.
Du Hamel, who dissected the bud of a Pear-tree in
the month of January describes it as follows : — The
scales were from twenty-five to thirty in number,
enveloping from eight to ten flowers, attached to a
common foot-stalk of half a line in length ; the
flowers resembled rose-buds set with hairs ; the
stamens were distinguished with ease, together
with their anthers which were white ; the petals
were distinguished with some difficulty ; but the
pistils were not yet to be discerned. In the month
following the pistils were now discernible, and the
anthers had begun to assume a reddish tinge ; the
ovary was not perceptible at this early period, but it
was perceptible before the evolution of the bud.*
Hence, as Grew had before observed, the flowers
which are protuded in the spring have been actually
formed in the preceding year, being generally of a
whitish colour till toward the time of their expan-
sion, when the several parts begin to assume their
own peculiar shade, and to exhibit their essential
traits of character. The calyx and corolla exhibit a
structure similar to that of the leaf. The stamens
consist merely of a parenchyma enveloped by a fine
epidermis, but the filaments are sometimes tubular,
as in the Tulip, and sometimes furnished with spiral
threads, according to Senebier ;-j~ though I have not

* Phys. dcs Arb. liv. iii. chap. i.
}- Phys. Vcg. vol. ii. p. 6'0.

SECT. IV. DECOMPOSITE ORGANS. 2()3

been able to discover them in any specimens I have
yet examined. The pollen is now capable of being
distinguished into three parts, according to the de-
scription of Gaertner — a cuticle, a cellular tissue,
and a parenchyma ; — and the pistil, which is at first
merely a gelatinous mass, begins now to be distin-
guishable into germen, style, and stigma, the ger-
men being the Linnaean name for what Malpighi
calls the uterus, and Gaertner the ovarium.

The ovary in its first stage of growth exhibits also Develops
the appearance of a homogeneous mass of paren-
chyma, without any division into distinct parts ; but
in a more advanced state it exhibits also the rudi-
ments of distinct organs, and finally the embryo
occupying the centre.

The style, which is not a constant part of the Style,
pistil, originates generally in the substance of the
ovary, and sometimes though rarely in the recep-
tacle ; as in leguminous, malvaceous, and rough-
leaved plants. It agrees in its fabric and texture
with the ovary or receptacle, being merely an ex-
tension of the one or the other ; its vessels commu-
nicating with the ovary from which it ascends, and
containing a fluid which occasionally exudes and
moistens the surface of the stigma.

The stigma, which according to Gaertner is pre- Stigma.
sent in the flower of all plants except Aphrodites,
originates in the style if the style is present, and if
not, in the upper extremity of the ovary ; assuming
generally some peculiar figure, and being sometimes

264 PROCESS OF DEVELOPEMENT. CHAP. IV.

smooth and sometimes hispid, but always beset with
a number of pores or papillae through which the
moistening fluid exudes.
Origin of Such is the order of the developement of the

the several r . n . . . c

parts ac- several parts ot the nower, concerning the origin or

Linnaeus*0 wnicri there have been several different opinions.
Linnaeus represents the pistil as originating in the
pith, the stamens in the wood, and the corolla and
calyx in the inner and outer bark respectively : but
this account of their origin though extremely plau-
sible at first sight, will not bear the test of minute
examination, being contradicted by the anatomy of
the parts themselves ; particularly in the case of
compound flowers. But with all its imperfections
it seems to have obtained at least a partial and tem-
porary celebrity, and to have been adopted in sub-
stance by Hill, who refined upon it indeed very
considerably, describing the flower-cup as origi-
nating in the outer bark ; the petals in the rind and
blea (alburnum) ; the nectaries in the vascular series ;
the filaments in the flesh ; the receptacle in the
conic clusters; and the seeds and capsule in the pith ;
and thus amusing the reader with the arrangements
of his own fancy instead of the arrangements of the
Divine Mind.

Gaertner, Gaertner regards the ovary as proceeding from the
wood and bark, in superior flowers ; and from the
receptacle in inferior flowers.

Knight. Mr. Knight in investigating the organization of
the Apple and Pear endeavoured to ascertain the

SECT. IV. DECOMPOSITE ORGANS.

origin of the several parts by tracing the several
parts of the fruit-stalk to their termination. In the
fruit-stalk he thought he could discover the pith,
the central tubes, spiral tubes, and tubes of the
bark, together with its epidermis : and in tracing
them to their termination he thought the pith
seemed to end in the pistils ; the central vessels in
the stamens, after diverging round the core and ap-
proaching again in the eye of the fruit ; and the
bark and epidermis, in the two external skins.*
Hence he infers that the flower is a prolongation of
the pith, wood, and bark in nearly the same way as
Linnaeus, though he adduces arguments from dis-
section with which Linnaeus was not acquainted.
But although central vessels are found in the stamens,
it is no proof that the stamens are a prolongation of
the wood, unless the central vessels of the fruit-stalk
and common tubes of the alburnum are proved to be
one and the same, which remains yet to be done.
It seems also doubtful whether the fruit-stalk con-
tains any thing that can be absolutely regarded as
pith ; and it is evident from a very little inspection
-that the two external skins of the Apple are not verv
well accounted for by deriving them from the bark
and epidermis of the fruit-stalk.

But another question of some considerable im- Nourish-
portance has arisen out of this subject : does the ^"flowe
flower or fruit elaborate sap for its own developement, and fruit*
or is it supplied with nourishment from the leaf?
* Phil. Trans. 1801.

266 PROCESS OF DEVELOPEMENT. CHAP. IV.

By placing small branches of the Apple, Pear, and
Vine with blossoms not expanded in a decoction of
logwood, Mr. Knight found that the central vessels
were coloured by the decoction. By means of a
similar experiment on the same subjects after the
fruit was formed, the colouring matter was traced
through the mass of the fruit to the base of the
stamina.* And hence it appears to me that the
flower and fruit do possess the power of elaborating
sap for their own developement ; since it seems that
the sap ascends to them only in an unelaborated
state, as is to be inferred from the ascent of the
coloured decoction, which tubes conveying elaborated
sap do not seern capable of admitting.

Inferences Mr. Knight infers, however, from the foregoing
Knight, data that the blossom is nourished from the albur-
num,-f~ by means, .as I should suppose, of the
mingling of the proper juice which the alburnum
may be supposed to contain with the sap in its
ascent. There may perhaps be something of truth
in this remark ; but it is to be observed that most
blossoms are accompanied with a calyx, which
may be supposed from its similarity to the leaf to
perform to the flower or fructification similar
functions : and so are the petals themselves similar
in structure to the leaves, and may perhaps be capa-
ble of performing similar functions. It may be
objected, however, to this opinion that when the
leaves are by any accident stripped off or destroyed,

* Phil, Trans. JS05, f Ibid. 1805.

SECT. IV. DECOMPOSITE ORGANS. 267

the fruit does not come to maturity ; but still the
calyx or corolla may perform some peculiar and in-
dispensable function to such flowers as are furnished
with them : and there are also plants in which the
flower is completely developed before ever the leaves
expand ; as in the case of Daphne Mezereon and
the Apricot, which seems to imply that they are
capable of elaborating the sap necessary to their own
developement.

But the office of the tubes of the bark does not
seem to have been ascertained in the fruit-stalk,
though Mr. Knight thinks it cannot be the same with
that of the tubes of the leaf-stalk — namely, the con-
ducting of the returning proper juice for the purpose
of forming new parts below ; and this he thinks he
has proved by the following experiment : — When
the end of a shoot of the Vine immediately above a
bunch of grapes was pinched off as soon as it had
made its appearance, and the leaf opposite allowed
to remain, the wood below increased as usual ; but
when the leaf opposite was taken off also, then the
wood below ceased to elongate, and remained in
form and substance similar to the fruit-stalk. Hence
Mr. Knight concludes that the tubes of the bark do
not in the fruit-stalk conduct a fluid downwards that
is capable of forming wood ; and yet, as it is likely
that the motion of the tubes of the bark is in all
cases retrograde, he supposes that the function of the
tubes of the bark of the fruit-stalk may be that of
carrying oft' from the fruit any superfluous humours

ANOMALIES OF DEVELOPMENT. CHAP. V.

formed in it from excess of humidity, or other
causes.* It must be confessed that this is but a
very clumsy contrivance for the carrying off of super-
fluous humours, which might be much more easily
got rid of by means of transpiration ; though it
must, at the same time, be admitted that we are but
bad judges of the facility with which nature effects
her operations. But it appears from an experiment
of Mr. Knight's that the fruit and fruit-stalk do
actually generate wood in certain circumstances, for
lie says expressly that he succeeded at last in graft-
ing the fruit-stalk of the Vine on the leaf-stalk ; in
which case the fruit or fruit-stalk must have formed
wood.-f~

But how are these two contradictory experiments
to be reconciled ? Perhaps in the natural process of
vegetation there is but little juice returned by the
bark of the fruit-stalk ; while in the case of the graft
it might have been an extraordinary effort of the
vital principle by which the part grafted was adapt-
ing itself to the circumstances in which it was placed,

CHAPTER V.

ANOMALIES OF VEGETABLE DEVELOPEMENT.

IN the growth of the vegetable subject as well as
in that of the animal, it often happens that a devia-
tion from the general laws of developement is occa-

* Phil. Trans. 1801. f Ibid. 1803.

SECT. I. THE ROOT. 269

sioned by the intervention of some accidental cause ;
or of some cause operating permanently in certain
subjects. Hence the anomaly may regard the deve-
lopement either of an individual or a species, and
may occur either in the root, stem, branch, leaf,
bud, flower, or fruit, according to the circumstances
in which it is placed ; or it may aifect the habit,
duration or physical virtues of the plant

SECTION I.
The Root.

ACCORDING to the general laws of vegetable de-
velopement, plants of the same species are furnished
with the same species of root — not producing at one
time a woody or fibrous root, and at another time a
bulbous root. And yet it is found that there are
cases in which changes of this kind do occur.

If part of the root of a tree planted by a pond or The fox-
river is accidentally laid bare on the side next the tai1 root"
water, or if in the regular course of its growth it
protrudes beyond the bank, so as to be now partially
immersed, the future developement of the part is
considerably affected ; for the root which was for-
merly firm and woody instead of augmenting in the
regular way — that is, by the accession of new layers
insinuated between the wood and bark enlarging
the individual mass, divides now at the extremity
into innumerable ramifications, or sends out innu-

4

270 ANOMALIES OF DEVELOPEMENT. CHAP. V.

merable fibres from the surface, which become
again subdivided into fibres still more minute, and
give to the whole an appearance something re-
sembling that of the tail of a fox ; which has accord-
ingly been denominated by Du Hamel the fox-tail
root. (PI. IX. Fig. 5.) This anomaly I have fre-
quently observed in the root of Willows growing
by ponds, of which the main offset has been about
eighteen inches in length, and the terminal and
lateral subdivisions six or eight inches. Du Hamel
relates an example of the same anomaly, which he
had observed in the case of a root that had insi-
nuated itself into a water-pipe, where it increased by
the sending out of a prodigious number of small
fibres, till at last it occupied the whole diameter
of the pipe and stopped the current of the water.*
Perhaps the above anomaly is merely the result of
an extraordinary effort of the vital principle to adapt
itself to the circumstances in which it is placed, by
extending the surface and multiplying the subdivi-
sions of the root, for the purpose of the more easy
abstraction of the oxygene of the water.
Roots that But sometimes an anomaly takes place which is
fftrousTJ directly the reverse of the above. The Phleum
bulbous pratense when growing in a moist soil, which it natu-
rally affects, is uniformly furnished with a fibrous
root ; but when growing in a dry soil, where it is
also often to be found, it is furnished with a bulbous
root. The same is the case also with the Alope-

* Phys. ties Arb. liv. i. chap, v.

6

SECT. I.

THE ROOT. 271

curus gemculatus; which, when growing in its
native marshes, protrudes a fibrous root, though
when growing in a very dry situation, as on the
top of a dry wall, it is found to be furnished with
an ovate and juicy bulb.* This anomaly also
seems to be merely the result of a provision of
nature by which the plant is endowed with the ca-
pacity of collecting a supply of moisture suited to
existing circumstances, and hence of adapting itself
to the soil in which it grows.

The roots of Utricularla minor, which consist Bladder,
of a number of slender and hair-like filaments roots. *
exhibit the singular anomaly of being furnished
with a multitude of small and membraneous
bladders, each containing a transparent and watery
fluid, and a small bubble of air, by means of
which the plant is kept floating in the water.

Some perennials present the anomaly of what The
has been called the descending root, which is at
first spindle-shaped and perpendicular sending out
some lateral fibres ; but dying at the lower extre-
mity in the course of the succeeding winter, and
protruding new fibres from the remaining portion,
and even from the lower portion of the stem, in
the course of the following spring, which by des-
cending into the soil, draw down the plant with
them, so that part of what was formerly stem is
now converted into root. This process is repeated
every year, and by consequence a portion of the,
* Smith's Introduction, p. 113.

ANOMALIES OF DEVELOPEMENT. CHAP. r.

stem is made to descend every year into the earth.
The anomaly may be exemplified in the roots of
Vahriana dioica, Tanacetum vulgare, and Oxalis
acetosella ; and will also account for the bitten
and truncated appearance of Scabiosa succisa or
Devil's-bit.

Anomaly The Beet root, a biennial plant, if dissected
root. when about a year old, presents the singular anomaly
of being already furnished with from five to eight
distinct and concentric circles of longitudinal tubes
or sap vessels, imbedded at regular intervals in its
pulp ; whereas other biennial roots form only an
individual circle each year, and are, consequently
at no time furnished with more than two.*
Migratory There are also some roots that may be called
migratory, upon a principle similar to the fore-
going. If the stem of a descending root happens
to be creeping or procumbent instead of being erect,
then the lateral shoots from above are carried for-
ward in the direction of that piocumbency, so that
in the course of a. few years the plant has actually
changed its place by so much as the stem has been
converted into a root. This is well exemplified in
the genus Iris. But the migratory plant is perhaps
best exemplified in the case of some aquatics, which
have actually no fixed habitat, but float about on
the surface of the water as they happen to be driven
by the winds, as in the case of the genus Lenina
and some marine plants.

* Willdenow, p. 260.

SECT. I. THE ROOT. 27 S

But one of the most curious and singular ano- Inverted
malies throughout the whole of the vegetable king-
dom is that by which a plant may be made to
grow though inverted, the root being transformed
into a stem and branches ; and the stem and
branches into a root. If the stem of a young
Plum or Cherry-tree, but particularly of a Willow,
is taken in the autumn and bent so as that one half
of the top may be laid in the earth, one half of the
root being at the same time taken carefully out,
but sheltered at first from the cold and then gra-
dually exposed to it, and the remaining part of the
top and root subjected to the same process in the
following year; the branches of the top will be-
come roots, and the ramifications of the root will
become branches, protruding leaves, flowers, and
fruit in due season.

But it has been already seen in treating of the
germination of the seed, that no power or art is
capable of converting the radicle into the plumelet ;
or the plumelet into the radicle. How then is the
anomaly of the inversion of the plant to be ac-
counted for, at a future stage of its growth ? Per-
haps it may be accounted for thus. The embryo
of the seed is an individual germe, whose develope-
ment is necessarily effected in a determinate man-
ner, owing to its peculiar structure and organization,
But that happens to be by the descent of the ra-
dicle into the earth, and ascent of the plumelet
into the air. It could not, therefore, succeed by

$74 ANOMALIES OF DEVELOPEMENT. CHAP. V.

being inverted, because the plumelet contains as
yet no vegetative principle whose developement
could be effected by being placed in the earth. But
this is not the case with the inverted plant ; because
its leaves or branches contain buds or germes that
have been acquired in the process of vegetation. But
these germes are plants in miniature, containing
the rudiments of every thing necessary to the per-
fection of the species. Consequently they contain
a part equivalent to the radicle of the embryo, and
capable of being converted into a root when placed
in a proper situation. Now the earth affords them
that situation, and the inverted plant grows.

SECTION II.
The Stem.

The radi- IF the stem of a tree planted by a pond or river
is so bent in its growth as to come near to the sur-
face of the water and to be occasionally immersed
in it, it will sometimes send out from the under
surface a multitude of shoots that will descend into
the water and develope themselves in the manner
of the Fox-tail-root. They are often rendered con-
spicuous in the summer by means of the subsiding
of the water from the under surface of a stem that
may have been partially immersed in the winter,
such as that of Willows overhanging ponds or

eating
stem.

SECT. II. THE STEM. 275

ditches, and are produced, no doubt, by the agency
of the same cause that gives a similar figure to the
root.

Sometimes it happens that a stem instead of as- The flat-
suming the cylindrical form common to the species, stem.
assumes a compressed and flattened form similar
to the herbage of the Cactus. Of this anomaly
I have occasionally observed a specimen in the
stem of the Tamus communis, which from a cy-
linder of about a quarter of an inch in diameter,
its natural size and shape, was converted into a
flattened and oblong production of about an inch
in breadth. But the best specimen of the anomaly
I have ever met with, was in the case of the stem
of an Ash -tree (PI. IX. Fig. 6). The tree stood
in a hedge row in the parish of Stow Upland,
Suffolk, and in the autumn of ) 80Q, seemed to be
about twelve or fifteen years of age, or at any rate
to be about twelve or fifteen feet in height. Of this
tree the top and perpendicular shoot which had in
the preceding summer extended to the length of
twenty inches, was compressed into a flattened and
oblong production, fluted on both sides as well as
furnished with some buds, and of about an inch in
breadth, but expanding at the summit to the
breadth of nearly two inches, and surmounted with
a row of buds of between twenty and thirty in
number ; the shoot of the preceding year having
been cylindrical and now measuring about half an
inch in diameter.

27(5 ANOMALIES OF DEVELOPEMENT. CHAP. V.

Accounted Du Hamel accounts for the anomaly of the flat-
tened stem by supposing that an unnatural graft
must have taken place in the leaf bud ; and so
united shoots that would otherwise have been dis-
tinct. But if shoots should be thus united by
means of an unnatural graft, why should they be
compressed or flattened in their aggregate growth.
Affected Sometimes the stem is disfigured by accidental
o/bunches! tumors or bunches projecting from the surface, and
forming ultimately what are called knots in the
wood. They are very common in the Oak and
Elm, and are produced perhaps by means of some
obstruction in the channel of the sap's motion, by
which the vessels become convoluted and swell up
into a bunch.

But bunches are also to be met with on the stem
of herbaceous plants, as on that of the Carduus
pr at crisis ; of which you will often find a portion
near the top swollen out into an egg-shaped or egg
oblong bunch extending from an inch to two inches
in length and about an inch across. If this bunch
is cut open in the month of August, it will be
found to contain several large and white maggots.
It has consequently been occasioned by the punc-
ture of the parent insect depositing its eggs ; but
it does not seem to affect the general health of the
plant. Sometimes a number of trees growing
together are affected with a longitudinal protu-
berance all on the same side. This Du Hamel
attributes to a Coup de soldi vif, or to .frost. Some-

SECT. II. THE STEM. 277

times the bark of the stem becomes rough and
scabby and the wood underneath full of knots and
inequalities, this Du Hamel attributes to frost also.

Sometimes two or more contiguous stems, extend- The fasci-
ing in the process of their growth till they meet stem.
and press against one another, become incorporated
at length into one, and form a sort of bundle. This
is what may be termed a natural graft, in opposition
to an artificial graft, of which it is the model and
prototype, the whole of the art of grafting being
founded upon the capacity inherent in plants of
uniting together by the stem, in given circum-
stances, and in a given mode. But the natural
graft is always affected by means of the union of
the liber of the respective stems composing it ; so
that the perfection of the art of grafting consists in
applying the liber of the graft and stock together
in such a manner as shall the most facilitate their
incorporation. And hence the graft will not suc-
ceed unless the two libers are brought into contact,
and closely bound together. Nor will it succeed
well unless the plants ingrafted have some natural
affinity to one another, such as that subsisting be-
tween the Plum, and Cherry ; in which, and in all
other cases, the union is effected by means of a
granular and herbaceous substance exuding from
between the wood and bark, and binding and ce-
menting together the stock and graft ; though not
uniting the former layers of wood. But after the
graft has been effected, the new layers of wood arc

'278 ANOMALIES OF DEV ELOPEMENT. CHAP. V.

produced entire as before so that it is sometimes
difficult to point out the place of the graft, which
is generally discoverable, however, by means of a
tumor that is formed round it.

SECTION III.

The Branch.

Producing IF the branch of a tree is situated as in the fore-
likeshoots. gomg ca§e of the stem, so as to be partially or pe-
riodically immersed in water, it will send out also
the same sort of brush-like shoots. Like the stem
it is also liable to be disfigured by bunches or
knots ; exhibiting, however, an occasional variety
of structure which I have not observed in those of
the stem. The variety to which I allude seems as
if formed from a plexus of young shoots issuing
from nearly the same point, and crossing in all
directions, and finally incorporating together by
means of a sort of natural graft. Or perhaps the
knot is first formed, and then sends out a multitude
of shoots all over its surface, forming a batch inter-
woven all together, and exhibiting at a little dis-
tance something like the appearance of a pigeon's
With nest. These bunches are frequently to be met with
knots.** on tne branches of the Birch-tree, rarely on the
Slow-thorn (PL IX. Fig. 7), and are known
among the peasantry of Scotland by the name of
witches' knots. They are occasioned, like the

SECT. III. THE BRANCH. 270

bunches of the stem,, by some obstruction in the
channel of the sap or proper juice. A peculiar sort With
of knot or bunch is also often formed on the bunches.*
branches of the Dog-rose (PL IX. Fig. 9). The
nucleus, which is generally from an inch to an inch
and a half in diameter, is covered with a long and
winged shag, first of a green and then of a purple
colour, presenting the appearance of a small bunch
of moss. It has been occasioned like that of the
stem of the thistle, by the puncture of an insect
depositing its eggs in the tender shoot ; for if it is
cut open about the month of August, it contains
maggots.

SECTION IV.
The Bud.

THE regular developement of the bud is also Forming
often prevented by means of the puncture of in-0
sects, and converted into a large globular tumor. -
This is very often effected by a species of Cynips
that lances its piercer into the heart of the bud
while yet tender, and penetrates with its saw into
the very pith ; injecting at the same time a drop of
the corroding liquor contained in its bag, and then
laying its egg. The bud being. thus wounded, and
the juices corrupted by the injected poison, the
circulation is not only impeded, but a fermentation
is induced which burns the contiguous parts and
changes their colour. The extravasated juice flow*

'28O ANOMALIES OF DEVELOPEMENT. CHAP. V.

round the egg and is there accumulated and con-
verted into a sort of spongy lump which vegetates
and augments till it forms what is called a gall.
The gall thus formed affords both shelter and nou-
rishment to the young maggot, which after being
converted into a fly pierces its enclosure and launches
into the open air.

Oakap- The most remarkable of such galls are those
produced on the Oak-tree, and known in this
country by the vulgar name of Oak-apples ; of the
origin and growth of which I think Malpighi gives
a detailed account, but of which I cannot now
offer any abstract to the reader, not being at present
furnished with a copy of his works. The following
are some observations which may in the mean time
serve as a substitute. About the end of May, 1808,
having observed upon an Oak-tree some of the galls
in question (PL IX. Fig. 8.) I had some of them
gathered for the purpose of examination. The
largest was then about the size of a Golden Pippin,
soft and spongy to the touch, and covered with a
fine and glossy epidermis of a white colour, but
changing in some places to red, and hence not
much belying in appearance its vulgar name. At
its base it was furnished with a number of scales
or leaves resembling a calyx, which proved upon
examination to be the outer scales of the original
bud. On cutting the gall open whether by a lon-
gitudinal or transverse section, a number of oval
or cylindrical bodies of a whitish colour were found
2

SECT. IV. THE BUD. 281

to be imbedded in its centre. They were the eggs
of the insect by which the bud had been punc-
tured. But on some trees of the same species
there was found a gall of a very different aspect,
which; though nearly of the same size, was covered
with a long and white shag, and did not exhibit
the same fleshy texture when cut open. It was
occasioned^ however, in the same manner ; the eggs
of the insect, which was no doubt of a different
species, being crowded together in the centre like
a cluster of small seeds, united by the lower ex-
tremity, and covered with the wool. Having cut
open some of both sorts about the end of the month
of June following, the maggots were now distin-
guishable in the former by the aid of the micrp-
scope, complete in all their parts ; and in the latter
each egg was found to contain a fly. On the ex-
tremity of some of the branches a few fragments
of galls of the former sort were still to be found,
which seemed to have stood from the preceding
summer, and in which the holes or perforations
were still to be seen through which the maggots
or flies had escaped. The fragments were quite
charred by means of the action of the atmosphere.

The bud of the Willow, particularly Saliv Deformi-
HelLv,* is apt also to be punctured by insects and wn
converted into a gall. But the conversion is not
always complete; and in this case the shoot remains
dwarfish, anc1 the leaves which are now protruded
* Smith's Introduction, p, 346.

282 ANOMALIES OF DEVELOPEMENT. CHAP. V.

from nearly the same point assume something of
the figure of a rose. Hence it has obtained the
common name of the Rose Willow ; and so also in
the case of the Lime-tree ; the bud is often punc-
tured, and the egg deposited,, and the gall formed
into a round and fleshy substance about the size of
a garden Pea, with a good deal of complexion on
the side exposed to the sun, while the apex is yet
crowned with the rudiments of a leaf or leaves.

The galls of the Salma pomifera formed in the
above manner are said to be of a very pleasant
flavour, and are esteemed a great delicacy in eastern
countries.*

SECTION V.
The Leaf.

Nut galls, THE leaves, like the buds, are also frequently
chosen for the nidus of insects, and disfigured with
galls or excrescences. But the most remarkable
gall produced on the leaf, and indeed the most re-
markable and important of all galls, is that which
is so extremely useful in the arts of dyeing and
making ink, the nut-gall of the shops. It is ge-
nerated on the leaf of a species of Oak that grows
plentifully in the Levant, and is so well known
in commerce as to require no particular description.
It is occasioned by the puncture of the Cynips
querci folii, which deposits its egg in the substance
* Willdenow, p. 346.

SECT. V. THE LEAF. 283

of the leaf, by making- a small perforation on the
under surface.* So also various other excrescences
are generated on the leaves of Oaks of other species.
If the leaves of Quercus Robur, or the common
Oak of this country, are inspected in the beginning
of summer they will often be found to be disfigured
by a small purple coloured excrescence, about the
size of a Whortle-berry, partly imbedded in the
parenchyma, but chiefly swelling above the surface.
Having cut open one of these excrescences in the
month of May I found it to consist of a white and
glary fluid. And on inspecting some others in the
month of June following, nothing now remained
but the shrunk and withered bag in which the fluid
was contained. I had not an opportunity of ob-
serving the intermediate stages ; but it had un-
doubtedly been the nidus of some species of
4nsect.

On the leaf of SalLv alba there is often also to be Gall* of
found about the month of June an oblong and i0*v-ieaf?
glandular tumor, sometimes at the apex, and some-
times about the middle region, of about the size of
a Pea, assuming a reddish appearance with age,
and a villous exterior, which if cut open is found to
envelope a single maggot.

On the leaf of the Clinopodium vulgar e I have And cii

also found in the month of June a sort of gall or

excrescence of about the size of a Kidney Bean,

but larger at the one end, of a deep purple, and

* Withering, vol.. ii. p. 388.

284 ANOMALIES OF DEVELOPEMENT. CHAP. V.

covered with a hoary down. The skin was easily
separated from the nucleus, which when cut open
was found to be of a firm and solid consistence
containing a maggot.

Almost all leaves indeed are liable to similar de-
formities arising from similar causes, giving them
a blistered, wrinkled, or curled appearance ; and
often producing disease. But sometimes the ano-
maly consists in the excess or deficiency of the
usual number of leaves protruded in a group. Thus
in the case of the Trefoils, in which the leaves are
regularly protruded in trees, you will often find
them protruded in sets of four, five, or even six.
This anomaly is often to be met with at least in the
case of the commonly cultivated Clover, in which
you will sometimes find also a set consisting but of
a single pair.

Anomalies But the anomaly may also consist even in the
of figure. naturaj figure Of the leaf itself. Most leaves ex-
hibit in their general aspect a sort of compressed
and flattened surface, whatever may be their specific
figure ; but to this rule there exists a variety of ex-
ceptions. The leaves of Asparagus offitinalis are
bristle-shaped ; the leaves of Salsola Kali are awl-
shaped ; and the leaves of A Ilium Cepa are tu-
bular, tapering to a point. But one of the most
Sar- remarkable anomalies of figure is that which occurs
jn the ]caves of the genus Sarracenia, of which
the lower portion is tubular, ascending and ap-
proaching to funnel-shaped, or rather pitcher-

racema.

SECT. V. tHE LEAF. 285

shaped reversed, with a flattened and concave limb
attached by the one side to the orifice of the tube,
and constituting the upper portion of the leaf.
Linnaeus, who was acquainted with this singularity
of structure, accounted for it by supposing that it
was an institution of nature, meant for the purpose
of furnishing the plant with a supply of water,
which it could thus catch and retain in the leaf.
But as some species of the genus do not readily
admit water notwithstanding their capacity to retain
it, this hypothesis is regarded by Dr. Smith as
being extremely doubtful, who accordingly offers a
different solution founded upon the following facts.

An insect of the Sphex or Ichneumon kind had
been observed by one of the gardeners of the
botanic garden at Liverpool, to drag several large
flies to a leaf of Sarracenia adunca, and to force
them into the tubular part of it On examination
the leaf was found to be about half filled with
water, in which the flies were now struggling ; the
other leaves were also examined, and were found
crammed with dead or drowning flies. The leaves
of Sarracenia purpurea are said to exhibit also the
same phenomena, and seem peculiarly well adapted
to entrap and confine flies, by having the margin
beset with inverted hairs rendering the escape of
such insects as may have accidentally fallen into
the watery tube, or are intentionally forced into it,
impracticable ; so that the putrid exhalation from
the dead insects contained in the leaf often offends

286 ANOMALIES OF DEVELOPEMENT. CHAP. V,

the nostrils, even in passing near the plant. Hence
Sir J. E. Smith infers that the growth of the plant
is perhaps benefited by means of the air evolved by
the dead flies, which the water has been intended
to tempt, and the leaves to entrap and retain.* This
ingenious conjecture is no doubt sufficiently plau-
sible as far as the plant may be affected; but cannot
be regarded as quite satisfactory till such time as it
shall have been shown that the health of the plant
is injured when insects are prevented from approach-
ing it.

AndNe- The celebrated Nepenthes distillatoria exhibits
Sistiiiato- also an anomaly similar to that of Sarracenia, but
more striking if possible. The leaf, which is itself
lanceolate, terminates at the summit in a thread-
shaped pedicle supporting a pitcher-shaped process,
surmounted with a lid, and holding an ounce or two
of a fluid which appears to be secreted from the
leaf, and to be intended as a lure to insects, which
gain admission either by the spontaneous opening of
the lid, or by forcibly raising it themselves. The
consequence is that they fall into the fluid and are
drowned, no insect being capable of living in it
except a certain small squilla or shrimp with a pro-
tuberant back, which, according to Rumphius,
sometimes crawls into it and can live there.-}- To
this phenomenon Sir J. E. Smith applies the same
explication as above, which is of course liable to the
same objection.

* Smith's Introduction, p. 196". f Ibid. p. 197.

4

SECT. VI. THE FLOWER. 38?

But the figure of the leaf, however singular, is
generally the same throughout the same individual,
except in the case of accidental deformity, and yet
there are exceptions even to this rule. For some-
times the lower leaves of a plant are entire while
the upper leaves are divided, as occurs in a variety
of mountainous plants, such as Barnet, Saxifrage,
Anise, Coriander ; and sometimes the lower leaves
are divided while the upper leaves are entire, as in
the case of a variety of aquatics, particularly Ra-
nunculus aquaticus, in which the lower leaves are
capillary and immersed, and the upper leaves flat
and circular, floating on the surface of the water.
But sometimes the dissimilitude of the leaves is still
more remarkable. The Chinese Mulberry has not
two leaves alike in form on the whole plant. And
lastly, there are some plants, as in the case of the
Fungi, that are wholly destitute of leaves, and hence
called aphyllous ; while there are others, as in the
case of the Fuci, that seem to be wholly leaf.

SECTION VI.
The Flower.

THE principal anomaly relative to the flower is
that by which one of its parts is unduly augmented,
to the exclusion or diminution of some of the rest.
The flower is then said to be luxuriant, and com-

288 ANOMALIES OF DEVELOPEMENT. CHAP. V.

prises the three following varieties : — the multipli-
cate, the full, and the proliferous flower.
TheMul- The multiplicate flower is sometimes, though
flower, rarely, accasioned by an unusual multiplication of
the divisions of the calyx, as exemplified by Linnaeus
in Dianthus Caryophyllus and some of the Alpine
Grasses.* But the anomaly most generally con-
sists in the undue multiplication of the divisions of
the corolla, by the conversion of part of the stamens
into petals, which is occasionally to be met with
both in monopetalous and polypetalous flowers. It
occurs but seldom however in flowers growing in
their natural state and habitat, though you will now
and then meet with a double flower even in such
circumstances. I have met with several specimens of
the Ranunculus Acris in which the corolla consisted
of a double row of petals, even when growing wild
in the fields ; but double flowers are for the most
part the effect, and often also, the object of culti-
vation.

The following is a species of multiplicate flower
that does not come under any of the foregoing cases,
though it is perhaps not altogether a solitary ex*
ample; it is that of an individual flower of Pri-
mula veris, containing two ovaries, two styles, two
stigmas, and eight anthers complete, with the
rudiments of a ninth, and the calyx and corolla
divided into nine segments. It was gathered by
* Phil. Bof. 80.

SECT. VI. THE FLOWER. 28Q

Mrs. Keith in the church-yard of Stow Maries, near
Maldon, Essex, on the 10th of May, 1812.

The full flower is generally described to be that The full
in which the divisions of the corolla are so multi-
plied as to exclude the stamens and pistils wholly,
by means of their conversion into petals ; which
conversion is most readily effected in polypetalous
flowers, such as the Tulip, Poppy, Pink, and Ra-
nunculus ; monopetalous flowers seldom being
found full. This complete metamorphose is, I
believe, always the effect of cultivation, and is in-
deed, one of the principal objects of the art of the
florist ; the beauty of the flower, according to
general estimation, being thus much augmented. In
the full flower the stamens are always converted into
petals, whence we should perhaps infer their iden-
tity of origin. But the pistil is often converted into a
leaf, as may be seen by inspecting the flower of
the double blossomed Cherry, which generally pro-
trudes from the centre, a leaf in miniature. But a
flower may become full also by the multiplication of
the parts of the nectary, as is sometimes the case
in the genus Aquilegia, which produces full flowers
in three different ways,* by the multiplication of the
petals to the exclusion of the nectaries, by the mul-
tiplication of the nectaries to the exclusion of the
petals, and by the multiplication of the nectaries
while the proper petals remain. There are also
some peculiarities in the manner in which com-

* Phil. Bot. 80.
VOL. II. U

2QO ANOMALIES OF DEVELOPEMENT. CHAP. V.

pound flowers become full. Radiated flowers become
full sometimes by the multiplication of the floscules of
the ray to the exclusion of the floscules of the disk, as
in HelianthiiS) Anthemis, and Centaurea ; and some-
times by the multiplication of the floscules of the
disk to the exclusion of those of the ray, as in Ma-
tricaria and Bellis.*
The proli- The proliferous flower is that out of which another

fefous

flower. flower or another shoot is produced. It is seldom
found but in flowers already full ; from the centre
of which, that is, from the ovary or pistil, it some-
times happens that a new flower and foot-stalk is
produced if the flower is simple, as in the Ranun-
culus, Anemone, and Pink ; or several flowers and
foot-stalks, issuing from the common calyx, if the
flower is compound, as in the Daisy (PI. IX.
Fig. 11.), Hawkweed and Marigold; or a nevr
umbel issuing from the centre of the original umbel,
if the flower is umbellate, as in Cornus. Sometimes
the proliferous issue of the full flower is not itself a
flower, but a shoot furnished with leaves, as has
been sometimes, though rarely, observed in the case
of the Anemone and Rose.*f~ And hence we should
perhaps infer, with Du Hamel, the identity of the
origin of the pistil and woody shoot, of which he
thinks the bundles of woody fibres found in the
fruit of the Pear is also a presumptive proof. £

Such are the several varieties of luxuriant flowers,
constituting anomalies of excess ; but it sometimes
* Phil. Bat. 84, f Ibid. 82. % Phys. de* Arb. liv. iii. chap. ii.

SECT. VI. THE FLOWER. 2Q1

happens that there is also in the flower an anomaly Anomalies
of defect in the absence of one of its parts. Ex- °
amples of this sort are occasionally to be met with
in the flowers of Campanula pentagonia and Tus-
silago Anandria, in which the corolla is altogether
wanting, though proper to the species ; and in this
case the flower is said to be mutilated.

Sometimes the anomaly consists in the situation
of the flower, which is generally protruded from
the extremity or sides of the branches. But the
flower of the Ruscus is protruded from the surface of
the leaf; or it may consist in the relative situation of
the several parts of the flower. In simple flowers
the pistil is invariably central with regard to the
stamens ; but in compound flowers the pistils are
often situated in the circumference and the stamens
in the centre. This seems to be the case a*so with
some monoscious plants having their flowers on the
same peduncle, as in the examples of the Carex and
Arum, in which the stamens are more central than
the pistils.

Sometimes the anomaly consists in the colour of Of colour,
the corolla, which will often deviate even in the
same species. The general colour of the common
Cowslip, Primula veris, is a bright yellow ; but an
individual is occasionally to be met with, though
very rarely, in which the limb or expansion of the
corolla is purple with a line of yellow around the
border. A Cowslip answering to this description
was gathered by the Lady Francis Douglas, at

u 3

202 ANOMALIES OF DEVELOPEMENT. CHAP. V.

Gold sborough' Hall near Knaresborough, Yorkshire,
in the spring of 1800. I have met also with a simi-
lar anomaly in the flower of the Oxlip, and in
various other flowers.

In the sea- Sometimes the anomaly consists in the time of
flowering, flowering. The season proper for the flowering of
the Apple and Pear-tree is the month of May ; but
trees of that sort have been known to protrude both
bud and blossom even in the month of November.
Some plants, however, blow only in the winter, as
is the case of the Laurus Tinus and Arbutus
Unedo ; while others blow only in the night, and
refuse to expand their petals to the light of the sun.
Such is the case of the Cactus Grandiflorus that pro-
duces one of the most magnificent of flowers, but
blows only in the night ; and is hence known also
by the appellation of the Night-blowing Cereus.

Some plants, such as the Ferns, Algce, and Fungi,
are altogether destitute of conspicuous flowers ; and
Cryptoga- are hence called Cryptogamous : but in this respect
flowers, the Fig is perhaps the most singular. The flowers
which in other cases uniformly precede the fruit, are
in this case concealed within what is generally de-
nominated the fruit; as may be proved by cutting
open a ripe Fig by means of a longitudinal section
passing through its axis. Great numbers of flowers
are then discovered lining a sort of cavity in the
axis of the fruit ; and hence what is called the Fig
in common language is rather the receptacle of the
flower than any thing else.

1

SECT. VII. THE FRUIT.

Most plants have their flowers furnished both with Dioecious
stamens and pistils, and are hence hermaphrodites ;
but there are also many genera that have the stamens
in one flower and the pistils in another, both on the
same individual. These are denominated Monoeci-
ous plants, and are exemplified in the Oak and
Hazel. Other genera have the flowers with stamens
on one plant, and the flowers with pistils on another ;
these are denominated Dioecious, and are exempli-
fied in the Hop and Willow. Others have flowers
of all the previous kinds on one and the same plant;
these are denominated Polygamous, and are exem-
plified in the genus Atripkx.

SECTION VII.

The Fruit.

THE anomalies of the fruit may affect either its Multipli-
number, figure, colour, or appendages. The com- ca
mon Hazle-nut produces in general but one kernel
in one shell ; but in the course of opening up a
considerable number, you will now and then meet
with one containing two or three kernels in a shell.
This is perhaps best accounted for by supposing,
with Du Hamel, that it is the result of an un-
natural graft effected in the bud ; though, I think,
the fact is that the shell does always contain the
rudiments of two or more kernels, although it rarely
happens that more than one is developed. But if

ANOMALIES OF DEVELOPEMENT. CHAP. V-

two Apples or Pears are developed in an incorpo-
rated state, which is a case that now and then oc-
curs, it is no doubt best accounted for by the graft
of Du Hamel.
Anomalies Sometimes the anomaly consists in the figure of

of figure.

the fruit which is deformed by the tumours or ex-
crescences, in consequence of the bite of insects or
injuries of weather producing warts, moles, or
specks.

Colour. Sometimes it consists in the colour, producing
green Melons and white Cucumbers.*

Append- Sometimes it consists in an appendage of leaves,
as in the following examples : — In the autumn of
180Q, when gathering some fruit in the garden of
Rendlesham parsonage, I observed some Pears of
rather an unusual appearance ; they had grown to
nearly the size of the species, and were nearly of
the usual shape. But the anomaly consisted in
their being each furnished with several leaves resem-
bling the proper leaves of the tree, but not so large,
having their insertion about half way between the
base and apex of the fruit, and growing directly
out of the fleshy part of it. This anomaly, which I
have not found to be mentioned by any botanist
except Du Hamel,-^ may with propriety be desig-

Thc fbliat- nated by the name of the Foliated fruit* (PI-
Fig. 12.)

* Phil. Bot. 212. f Mem. de 1'Acad. Royal, 1755.

SECT. VIII. HABIT.

SECTION VIII.
Habit.

SOME plants which, when placed in a rich soil
grow to a great height, and affect the habit of a
tree, are when placed in a poor soil, converted into
dwarfish shrubs. This may be exemplified in the
case of the Box-tree ; and so also in the case of her-
baceous plants, as in that of Myosotis, which in
dry situations is but short and dwarfish, while in
moist situations it grows to such a size as to seem
to be altogether a different plant. The habit of the
plant is sometimes totally altered by means of cul-
tivation^ the Pyrus sativa when growing in a
wild and uncultivated state is furnished with
strong thorns ; but when transferred to a rich and
cultivated soil the thorns disappear. This phenome-
non, which was observed by Linnaeus, was regarded
as being equivalent to the taming of animals. But
this explication is, like some others of the same
great botanist, much more plausible than profound,
in place of which Professor Willdenow substitutes
the following : — The thorns protruded in the uncul-
tivated state of the plant, are buds rendered abortive
from want of nourishment, which when supplied
with a sufficiency of nourishment, are converted
into leaves and branches.

ANOMALIES OF DEVELOPEMENT. CHAP. V.

SECTION IX.

Physical Virtues.

WHEN plants are removed from their native soil
and taken into a state of culture, it alters not only
their habit but their physical virtues. Thus the
sour Grape is rendered sweet, the bitter Pear
pleasant, the dry Apricot pulpy, the prickly Lettuce
smooth, and the acrid Celery wholesome. Pot-
herbs are also rendered more tender by means of
cultivation, and better fitted for the use of man ;
and so also are all our fine varieties of fruit.

SECTION X.
Duration.

PLANTS are either annuals, biennials, or peren-
nials, and the species is uniformly of the same class.
But it has been found that some plants which are
annuals in a cold climate, such as that of Sweden,
will become perennials in a hot climate, such as that
of the West Indies. This anomaly has been ex-
emplified in Tropceolum, Beet- root, and Malva
arborica ; and on the contrary some plants, which
are perennials in hot climates, are reduced to annuals
when transplanted into a cold climate ; this has
been exemplified in Mirabilis and Ricinus.*

* Phil. Trans. 216.

CHAPTER VI.

OF THE SEXUALITY OF VEGETABLES.

THE doctrine of the sexuality of vegetables and
foundation of the Linnsean system, though but
lately established upon the basis of logical induc-
tion, is by no means a novel doctrine. It cannot,
however, be said that the original notion of a sexual
distinction as existing in vegetables was at all cor-
rect. It was a conjecture formed at random, rather
than an opinion founded upon the evidence of fact ;
which maintained its ground, however, for a period
of many ages, though wholly unsupported by any
convincing argument, till at last the elucidations of
Linnaeus established it beyond a doubt. The fol-
lowing brief sketch of the origin^ progress, and
proofs of the doctrine, from the earliest notices re-
corded in history down to the present times, will
furnish the reader with the evidence on which the
above remarks are founded.

SECTION I.

Anticipations of the Ancients.

IT cannot now be ascertained with whom or at
what particular period the notion of vegetable sexu-

2Q8 SEXUALITY OF VEGETABLES. CHAP. VI.

Empcdo- alky originated. But its antiquity is unquestion-
ably great ; as it appears to have been entertained
even among the original Greeks, from the antiquity
of their mode of cultivating Figs ; and to have been
made the subject of the speculations of some of
their earliest philosophers, from the fact of its having
been a doctrine taught by Empedocles, that the
sexes are united in plants ; a doctrine involved
indeed in that of Anaxagoras by which the desires
and passions of animals are attributed to vegeta-
Herodo- bles.* It was evidently a prevalent notion through-
out Greece, and the nations to the east of Greece,
in the time of Herodotus, who recognises it in his
account of the cultivation of the PhcenLr dacty-
lifera or Babylonian Palm ; which he represents as
being cultivated in the country around Babylon in
the manner of Figs, the cultivator taking the
flower of that Palm which the Greeks call the male
Palm, and binding it around the flowers of the
fruit-bearing Palm, that the fruit may not fall im-
mature.-^ Whether the beneficial effect resulting
from this practice was produced by the agency of
insects, generated in the male plant, as Herodotus
asserts, it is not our object at present to inquire.
It is enough to have ascertained that the notion of

* Arist. Hspi <PVTCDV. TO. A.

f Tows tpoivixs; GUK&UV rponov btpomtvwcri r«, rt «AA«, KM tpowlxuv,
?vXrjv££ xotoEOMft, TOVTOV vov xapnov Tre
TWV foivixuv, wa. nsTrdivy TE <r<pi o4/riv TW
v, Kcti jw,rj «7roppe» 6 xa^Troj o rou <poiv/xoj. Herodot. Porsoni
Clio, 193.

SECT. I. ANTICIPATIONS OF THE ANCIENTS.

a sexual distinction in plants existed, or rather was
a general and prevalent notion in the age of Hero-
dotus, that is at least 400 years before the Chris-
tian aera.

Our next authority is that of Aristotle, who Aristotle,
maintains the doctrine of a distinction of sex in
plants as well as in animals,* though he admits
that some plants are altogether without sex ; and
represents the beneficial effect of the practice
adopted in the cultivation of the Palm, as resulting
from the action of the dust of the male flower,
quickening the maturity of the fruit, which it is
said to effect also equally well if it is but wafted to
the female flower by means of the wind.

Theophrastus, the disciple and successor of Aris- Theo-
totle, who pursued his phytological investigations
to a much greater length than his master, maintains
also the doctrine of the sexuality of vegetables,
which he illustrates with more of detail, and exem-
plifies not only in the case of the Palm-tree, but in
that also of the Fig, and a variety of others. The
barren Palm he calls the male, and the fruit-bearing
Palm, the female; pointing out, at the same time,
the ground of this distinction as consisting in the
indispensable necessity of the co-operation of the
flower of the barren Palm, to the ripening of the
fruit of the fertile Palm ; the fruit of the fertile
Palm being otherwise extremely apt to fall off' before
it becomes ripe. But if the spathe of the male

Zwwv. To. A.

300 SEXUALITY OF VEGETABLES. CHAP. VI.

plant containing the male flowers is cut off, and
shook over the flowers of the female plant, the fruit
does not fall, but is preserved till it is mature ; in
which case, he adds, there is a sort of coitus of the
male and female.*

But beyond the example of the Date Palm and
such other plants as produce barren and fertile
flowers on distinct individuals, Theophrastus does
not seem to have entertained any correct notions of
vegetable sexuality. For although he institutes
the distinction of sex in other genera also, yet it is
by no means on the same principle, but rather upon
that of the habit or aspect of the plant, or upon
the quality of the timber when felled ; the male
being represented as shorter and stouter, and the
female as taller and more slender, as erroneously
exemplified in the case of the Pinus Larix^ which
is well known to produce no individuals that are
exclusively male or female ; ^ as well as in the case
of the Lime-tree, of which it is also added that
the male plant is not only barren, but destitute even

»j TO uppEV aTTOTfju-vovrsj ryv o~7fa^Vj a<p >?c TO

Ivfos UffKSp E;£ej TOV T£ XVOQV XOU TO «V00f5 XOit TOV XOV/OpTOV, «aT«CT£<-

ov<ri Kara, TOV xapTrov T>JJ 9eXgia; ; *av TO WTO Trdfy, ft*Pty0 xa\ ovx
5 q>oiiv£Toti J* «ju,^o<v afro dppsvo$ T0t£ 3>iA£o*
yap noihwo-i TOV xoLpnoQQpov) aXX* TI plv oiov

HOLT aXXoV TpOTTCV. '^sp^ QVTW l<TTOplOtC. TO. B.

f 4>a<7< ^ ci TripiMaxsfroviotv xai oincapTrov TI ycvoj oAwj eivou

Tspov. Rep i <PVTUV icrTopiotc, TO. F.

SECT. I- ANTICIPATION OF THE ANCIENTS. 301

of flowers.* And to complete the mystery in
which the doctrine was yet involved, the male plant
is, in some cases, said to bear fruit as well as the
female.-^ From all which it follows that the doc-
trine of vegetable sexuality was but very imper-
fectly understood in the time of Theophrastus.

After a long blank in the annals of phytological Pliny, Di-
research, the next traces of inquiry relative to the andGalen.
sexuality of vegetables, are such as occur in the
works of Pliny, Dioscorides, and Galen, who also
adopted the division by which plants were then dis-
tributed into male and female ; but chiefly upon
the erroneous principle of habit or aspect, and
without any reference to a distinction absolutely
sexual ; the fertile plant being sometimes denomi-
nated the male, and the barren plant the female,
as in the example of male and female mercury, in
which the true notion of vegetable sexuality was
altogether reversed. Pliny seems, however, to
admit the distinction of sex in all plants whatever,
and quotes the cas/s of the Palm-tree as exhibiting
the most striking example.^

* Tot$ de <pi\upot$, YI /w£V appet eVTiv YI SE S^eia ; TO psv 5s rrjf
oippevos |yXov euudeFTEpov ra: Trig §riteixst xa-i « jxev aKtipTfo^ KCX.I
YI dt $^£ia xoii av$o$ £%£(, xou KotpTrov. TIepi tyuruv i

•J- Aia^opat TrAcioy; sfcny9 YI ftlv mwi\ 'zzafiv y haipoutriv TO
TO appsy, «v TO /AEV xapTrfyopov, TO ds axxpTtov em TIVUV; sv vi$ 5k oip<pu
xapTPO^opa, TO SijAy xa\>.i#ap7rorepov. Ibid.

J Arboribus imo potius omnibus quse terra gignit herbisque
etiain utrumque sexum esse diligentissimi naturx tradunt. Lib.
?iii. p. 4.

302 SEXUALITY OF VEGETABLES. CHAT. VI.

SECTION II.

Discoveries of the Moderns.

Caesalpi- Caesalpinus, who follows next in order, though
not till after an interval of many centuries, enters
more into the detail of the doctrine, and speaks
with more confidence on the subject than any pre-
ceding phytologist. Trees which produce fruit only
he denominates females ; and trees of the same
kind which are barren, he denominates males ;
adding that the fruit is found to be more abundant
and of a better quality where the males grow in
the neighbourhood of the females, which is, as he
says, occasioned by certain exhalations from the
males dispersing themselves all over the females,
and by an operation not to be explained, disposing
them to produce more perfect seed. Still it seems
doubtful whether any conjecture had been yet
formed with regard to the peculiar and appropriate
organs by which the sexual intercourse is con-

Zeluzi- ducted. Zeluzianski, a native of Poland, who lived
about the end of the sixteenth century, is said to
have made some considerable discoveries with regard
to the sexuality of vegetables. But as his book,
if he ever published one, is not now to be met
with, no one seems able to say what his discoveries
were, if rather they are not a transcript of the dis-
coveries of Caesalpinus.*

* Pultene/s Sketches, p. 335.

SECT. II. DISCOVERIES OF THE MODERNS. 303

At last, however* about the middle of the seven- Opinion of
teenth century, when the improved philosophy of a p's ''
Bacon had begun to be adopted even in phytology,
and phytologists to be directed by observation and
experiment rather than by hypothesis and con-
jecture, the doctrine of the sexes of plants began
also to assume a more fixed and determinate
character, and to exhibit the legitimate evidence of
being founded upon fact. Still it is difficult to say
who first discovered and pointed out the peculiar
organs by which the sexes are respectively charac-
terized ; not that these organs had been overlooked
in the description of the flower, but that their func-
tions had been misunderstood. Malpighi, who
describes not only the stamens and anthers but
also the pollen contained in them, regards the for-
mer as excretory organs contributing to the per-
fection of the seed, and the latter as the substance
excreted.* The true use of the pollen, therefore,
was not yet discovered ; but the merit of suggesting
its true use seems to be between Sir T. Millington, Of Sir T.
Savilian Professor at Oxford, and the celebrated Dr. f™^"
Grew, who represents the suggestion as originating Grew-
with the Professor, and consisting in the expression
of an opinion that the stamens serve as the male

* Vegetantium igitur, uteri gratia, reliquae floris partes, folia
scilicet, stamina et calyx circumlocantur in faecundis floribus,
Anat. Plant. 55.

Ita determifiata succi portio per stamina et floris folia exceiv
nitur. Ibid. 5fr

4

304 SEXUALITY OF VEGETABLES. CHAP. VI.

organs of the vegetable for the purpose of the
generation of the seed ; which opinion he seems
himself to have previously entertained, or at the
least to have acquiesced in as soon as it was sug-
gested.* This we may regard as the first glimpse
that was ever caught of the true and proper use of
the stamens, and may date at ahout the year 1676.
Published. But the opinion, if not first suggested, was at
least first published by Dr. Grew, in his Anatomy of
Plants, together with the grounds on which he had
adopted it, and the illustrations which its novelty
demanded or his researches had furnished ; so that
he does not merely ascribe a peculiar function to the
stamens, but points out also the mode in which he
thinks that function is discharged, and which is re-
presented to be as follows :— When the summits of
the stamens, or anthers surmounting the filaments,
burst open in the process of vegetation, the inclosed
pollen falls upon the pistil and impregnates the
embryo ; not by actually entering the pistil, but by
J means of a subtle and vivific effluvium : hence the
stamens are the male, and the pistil or pistils the
female organs of vegetable impregnation. But this
was the very discovery that furnished the clue for

* Our learned Savilian Professor Sir T. Millington told me
that he conceived the attire (stamens) doth serve as the male for
the generation of the seed. J immediately replied that I was of
the same opinion, gave him some reasons for it, and answered
some objections which might oppose them. — Grtw's Anat. b. iv.
chap. 5.

SECT. II. DISCOVERIES OF THE MODERNS. 305

the unravelling of the whole of the mystery over-
hanging the subject, because it is equally applicable
to all sorts of vegetables whatever, whether pro-
ducing the organs in question in separate flowers
and on separate plants, as in the case of the Palm-
tree ; or in separate flowers and on the same plant,
as in the case of the Hazel-nut-tree ; or lastly,
in the same flower, as in the case of the Lily,
which is by far the most general mode of vegetable
sexuality.

The opinion of Grew was adopted also by Ray, Adopted
at first with some appearances of doubt, but finally y ay'
without any sort of reservation, as being founded
on evidence which appeared to him sufficiently
convincing, and which he was even induced to
illustrate.*

Hitherto the doctrine of the sexuality of vege-
tables had been supported chiefly upon the ground
of its probability as arising from careful observation,
or upon that of the necessity of the case, and had
not yet been confirmed by the evidence of actual
experiment: but this confirmation which was so
devoutly to be wished, and without which all
other arguments must have remained insufficient,
was at length also happily undertaken. The first
example of experiment recorded on this subject is
that of Camerarius, Professor of Botany at Tubingen,
who having adopted the opinions of Grew and Ray,
though without perhaps regarding their arguments rius>
* Sylloge Stirpium Europsearum Pragf. 1694.

VOL. II. X

306 SEXUALITY OF VEGETABLES. CHAP. VI.

as the best that could be adduced, conceived that
the subject might be still further illustrated by
means of depriving the plant of its male flowers
altogether, or of removing the individuals of different
sex to a distance from one another. Accordingly
having selected some plants of Mercurialis, Morus,
Zea Mays, and Ricinus, and stripped them of their
stameniferous flowers, or removed the male plant to
a great distance from the female, he found that the
fruit did not now ripen ; the inference from which
was that the generation of plants is analogous to
that of animals, and that the stamens of the flowers
of the former correspond to the sexual organs of the
males of the latter.*

But though the fact of the sexuality of vegetables
seemed thus unequivocally ascertained, the peculiar
mode of their fecundation was still left undeter-
mined. Some conjectures had been offered with
respect to it by Caesalpinus and Grew, the former
regarding it as being effected by means of an exhala-
tion from the male flower ; and the latter, by means
of an effluvium from the pollen : but Morland, who
published a paper on the subject in the Philosophi-
cal Transactions for 1703, in which he adopts indeed
the opinion of Grew with regard to the functions of
the stamens, contends, however, that the pollen is a
congeries of seminal plants, one of which at least
must be conveyed through the style into the ovary,
before it can become prolific. This conjecture
* L?,pistola de Sexu Plantarum, 1695.

SECT. II. DISCOVERIES OF THE MODERNS. 307

seems to have arisen out of the theory of Leuwen*
hoeck on animal generation, which was then popular,
but it is not corroborated by any experiments. It
seems, however, to have had the effect of keeping
alive the discussion of the subject; for Geoffrey, in OfGeofr-
his memoir presented to the Royal Academy of roy>
Sciences in 17 Hj on the structure and use of the
principal parts of flowers, endeavours, as it appears,
to reconcile the discordant theories of Grew and
Morland ; and maintains that the germ is never
visible in the seed till the anthers have shed their
pollen : adding, that if the stamens are cut off before
the anthers burst, the seeds remain barren. In this
we have a step in advance beyond the point that had
been gained by means of the experiments of Came*
rarius, which relate only to monoecious and dioecious
plants, in which the proof is less difficult than in
hermaphrodites, to which Geoffroy's experiments
apply.

From the spirit of inquiry that was thus excited
new discoveries could not but be expected to follow ;
for although the doctrine was discountenanced and
rejected by some of the leading botanists of the time,
and even by the illustrious Tournefort, yet it was too
well established in fact to be overthrown by any ar-
gument or any authority. Accordingly its evidence
was becoming every day more irresistible, and its
advocates more confident. Vaillant, in a dissertation of Vail-
the structure of flowers read at the opening of the lant
x 2

308 SEXUALITY OF VEGETABLES. CHAP. VI.

Royal Garden at Paris in 3717, supports the
doctrine of the sexes of vegetables by new accessions
of experiment, and throws additional elucidation
both on the structure of the pollen and manner of
its explosion ; which he represents indeed in terms
too glowing for the style of sober narrative, but by
which he appears according to the remarks of a co-
temporary author, to have been the first eye-witness
of that secret operation of nature — the sport that
passes between the flowers of plants in the mys-
terious process of vegetable generation.

But the doctrine of the sexes of vegetables, which
was thus daily acquiring new accessions of proof,
was destined to receive its last degree of elucidation
Of Lin- from the pen of Linnaeus. This great and illustrious
botanist, reviewing with his usual sagacity the evi-
dence on which the doctrine rested, and perceiving
that it was supported by a multiplicy of the most
incontrovertible facts, resolved to devote his labours
peculiarly to the investigation of the subject, and
to prosecute his inquiries throughout the whole
extent of the vegetable kingdom ; which great and
arduous enterprize he not only undertook but ac-
complished with a success equal to the unexampled
industry with which he pursued it. So that by
collecting into one body all the evidence of former
discovery or experiment, and by adding much that
was original of his own, he found himself at length
authorized to draw the important conclusion — that

SECT. III. INDUCTION OF PARTICULAR PROOFS. 30Q

no seed is perfected without the previous agency of
the pollen, and the doctrine of the sexes of plants is
consequently founded in fact.

SECTION III.

Induction of Particular Proofs.

THE evidence on which the above conclusion de-
pends is substantially comprised in the following
brief induction of particulars — first, as resulting
from observation ; and secondly, as resulting from1
experiment.

SUBSECTION I.

Observation 1 . — In all plants hitherto discovered From the
it has been observed that the fruit is uniformly
preceded by the blossom ; and that without blossom
there is no fruit. This is a remark that can scarcely
fail to be made even by the most inattentive observer,
at least with regard to such plants as come within
the sphere of his notice ; as every school-boy knows
that unless the Cherry-tree blossoms in the spring,
he will gather no fruit from it in the summer. This
proves that the organs necessary to the production
of the fruit exist in the flower ; and is one step at
least towards the general conclusion. But to this
rule there exists a seeming exception in the case of
the Colchicum autumnale, which produces, its fruit

310 SEXUALITY OF VEGETABLES. CHAP. VI.

in the spring and its flower in the autumn, so that
the former has the appearance of being the cause of
the latter; but the truth is that the fruit, which
ripens in the spring, is the natural result of the
flower of the preceding autumn, and not the cause
of the flower of the following autumn : for if the
flower is cut off in the autumn, before its expansion,
you will have no fruit in the succeeding spring ;
and yet if the fruit is cut off any time in the
spring, you will still have blossom in the following
autumn.

There exists also another seeming exception in
the case of the Pine apple, in which the part that is
commonly called the fruit is formed before the flower
expands : but when it is recollected that this alleged
fruit is merely a fleshy receptacle, and that the seed,
the only essential part of the fruit, is not developed
till after the expansion of the flower, the seeming
exception vanishes.

From the Obs. 2. — The fruit bearing individuals of such
tion of species as have their barren and fertile flowers on
diants°US distinct plants do not perfect their fruit except where
individuals of both sorts are sustained in the vicinity
of one another. This observation is confirmed not
only by the testimony of the ancients, and their
manner of cultivating the Palm and Fig-tree, but
also by the additional observations of the moderns.
Father Labat, a French ecclesiastic, who had under-
taken a voyage to the West Indian islands about
the year \*J\ 5, says that when he was in the island

SECT. III. INDUCTION OF PARTICULAR PROOFS. 311

of Martinique there was then growing near the
monastery of the order to which he belonged, a
female Date-tree, which bore fruit though single,
there being no other tree of the same species within
two leagues of it ; but he adds that the stones of the
Dates it produced did not germinate : it is plain,
therefore, that the fruit was not perfect, though it
might have been externally complete. A female
plant of the Cycas revoluta, in the possession of the
Bishop of Winchester, produced also fruit though
single ; but the drupe, which was externally and
apparently complete, was found when dissected by
Sir J. E. Smith to be internally very defective : for in
place of the embryo, the most important part of the
whole, all that could be discovered was only a
minute cavity, which defect Sir J. E. Smith rightly
attributes to the want of the vicinity of a plant fur-
nished with male flowers ; which he adds was, per-
haps, not to be found nearer than Japan. *

The fruit then is perfected by means of some
substance conveyed from the barren to the fertile
flower, and capable, as it appears, of being trans-
mitted through the medium of the atmosphere, if
the respective plants are situated in the vicinity of
each other.

But in the case of the Fig-tree vicinity is not
even enough, the structure of the fruit being such as
to require a peculiar mode of transmission ; for the
* Trans. Lin. Soc. vol. vi.

312 SEXUALITY OF VEGETABLES. CHAP. VI.

fruit of the Fig is not, as in most other cases, a peri-
carp enveloping the seed, but a common calyx or
receptacle enclosing the flowers : this may be readily
seen by means of cutting a fig in two in the direction
of the longitudinal axis of the fruit, in the centre of
which there will be found a cavity lined with a
jpultitude of flowers, the male and female blossoms
being generally in different Figs and on distinct
plants, and the medium of communication between
them being only a small aperture at the summit of
the receptacle. Hence the access of the substance
necessary to impregnation is rendered impracticable
jfl the ordinary mode of transmission. But nature
is not without a resource even in this difficulty ; for
tfi Greece and Italy, and the islands belonging to
them, the native country of Figs, a species of insect
of the genus Cynips, which is continually fluttering
about from Fig to Fig for the purpose of depositing
its eggs in the cavity, carries the substance necessary
to impregnation from the male to the female flower.
But the substance which it carries is the pollen of
the anthers, with which it becomes covered all over
in rummaging through a variety of receptacles till it
finds one to please it. The pollen then is the sub-
stance by which the impregnation of the female
flower is effected ; and the whole of the phenomena
of the growth and economy of flowers tends to cor-
roborate the fact. In Italy and the Levant, where
the Fig is much cultivated, the cultivator ensures or

SECT. III. INDUCTION OF PARTICULAR PROOFS. 313

facilitates the agency of the insect by presenting it
to the Fig at the time proper for impregnation ; and
the service he thus performs is called Caprification,

Obs. 3. — If the stamens or pistils are obliterated
by cultivation, or injured by rain or frost, or by the
operation of any other natural cause, the process of im-
pregnation is interrupted or prevented, and the fruit
deteriorated or diminished in quantity or quality.

Sometimes they are wholly obliterated by means From in-
of cultivation, as in the case of double flowers ; Ul^onctothe
which the stamens degenerate into petals, and the J3ens OI
pistil not unfrequently into a leaf: but in this case
it is well known that no flower produces perfect
seed. Sometimes they are injured by accidents
arising from weather, and even in such vegetables as
are the most serviceable for the food of man, parti-
cularly in crops of grain ; but some sorts of grain
are much more liable to be injured by such acci-
dents than others : — Crops of rye, for example, are
much more liable to be injured by heavy and con-
tinued rains than crops of Barley, because the
anthers are better sheltered by the husks of the
latter than of the former. But shrubs and trees are
affected in the same manner as the plants now men-
tioned. It was observed by Linnaeus that the
Juniper produces few or no berries in Sweden if the
flowering season is wet ; and that the Cherry-tree is
much less liable to come short of its annual crop
than the Pear-tree, because in the latter the blos-
soms are unfolded and the stamens and pistils

2

314 SEXUALITY OF VEGETABLES. CHAP. VI.

matured all about the same period, so that the whole
of them might be blasted by the dews or frosts of a
single night ; whereas in the former the blossoms
are unfolded, and the stamens and pistils matured,
by gradual and successive steps, so that if part of
them should happen to be destroyed by the occur-
rence of a frosty morning, the rest may escape.
But the fruit is equally blasted whether the injury
is done to the stamens or to the pistil ; the stamens
being the organs in which the impregnating sub-
stance is contained, and the pistil being the channel
through which it is conveyed to the ovary. Hence
we may account for the peculiar care with which
these organs have been guarded by the hand of
nature from external injury: sometimes this is effected
by means of a nodding or pendant flower, as in the
case of the Crown Imperial and Cowslip, in which
the intention of nature is the more evident in that
the flower-stalk after the time of flowering becomes
gradually erect, even though loaded with fruit ;
sometimes it is effected by means of a capacity in-
herent in the petals of folding themselves together
in the night and opening themselves out again in
the morning, as in the case of many of the Papi-
lionaceous and Compound flowers, particularly the
Pea and Dandelion. But one of the best examples
of this capacity is that of the Nymphcza alba of
Linnaeus, which closing its petals as the sun begins
to get low, and shrinking into itself, reposes its
lovely blossom upon the surface of the water till the

5

SECT. III. INDUCTION OF PARTICULAR PROOFS. 315

morning, when it again rears its head, sometimes to
the height of several inches, and presents its ex-
panded petals to the culminating sun. A pheno-
menon still more singular is related by Theo-
phrastus as occurring in what he calls the Lotus,
perhaps the NymphcEa Lotus of Linnaeus ; of which
he says, though only on report, that in the
Euphrates the flower keeps sinking till midnight,
when it again begins to ascend, but more rapidly as
day advances, elevating itself to the surface about
sun-rise, and afterwards expanding and rearing its
head high above the water. * Some flowers are so
very susceptible to changes of atmosphere as to shut
up their petals even upon the approach of rain.
One of the most remarkable examples of this sort is
that of the Anagallis arvensis, or Poor Man's
Weather-glass, which appellation it seems to have
obtained from its peculiar susceptibility, always
shutting up its blossoms even upon the slightest
symptoms of approaching rain, except in the case
of a sudden thunder-storm, when it happens to be
taken by surprise : but Sir J. E. Smith says he has
reason to think that its susceptibility is apt to be
impaired, and sometimes totally destroyed by long
continued wet;-}- and Linnaeus remarks that flowers
in general lose this susceptibility when the anthers
have discharged their pollen.

Obs. 4. — -The pollen is generally discharged from From the
the anther in such a manner as to ensure its dis-

Theoph. 106, Aldi, -f Introduction, p. 32p. len'

316 SEXUALITY OF VEGETABLES. CHAP. VI.

persion, at least to any pistil that is near it, and at
such a time as pistils of the same species are best
fitted to receive it. When the anther has given in-
dications of maturity by the distended appearance
of its cells ; the valves of which the cells consist
become daily more and more indurated till at last
they fly open with a sudden jerk, and discharge the
contained pollen as if by the force of an elastic
spring. The phenomenon exhibited in this case by
the Cypress-tree affords a good example, in which
the pollen is thrown out with such force and in
such abundance as to resemble a little cloud of
smoke ; but the same phenomenon may be observed
in the discharge of the pollen from the male catkins
of the Birch arjd Willow, particularly if they
arc suddenly shaken or agitated by the wind ; in
which cases a portion of the pollen can scarcely
fail to alight upon the pistil-bearing and contiguous
flowers, or to be wafted to them if even at some
distance.

But at the season of the discharge of the mature
pollen, the pistil is also peculiarly adapted to re-
ceive it, as is evident from the state of the stigma.
Sometimes this adaptation consists in the stigma's
then assuming a peculiar form or shape, as may be
exemplified in the case of the Gratiola, Martynia,
and Viola tricolor or Pansy, all of which are fur-
nished with what botanists call a gaping stigjna,
opening as if to receive the pollen, yet not in the
early stage of its growth, nor during its decline ; but

SECT. III. INDUCTION OF PARTICULAR PROOFS. 217

in the intermediate stage only, when the pollen is
ripe. But the adaptation generally consists in the
stigmas being then moistened with an exuding and
viscous fluid ; except in the case of a hispid stigma
in which no such exudation is discoverable, as is
peculiarly well exemplified in the case of the
Amaryllis for mosissima. This beautiful flower,
which when fully expanded is pendulous, exhibits
the curious phenomenon of the exuding of a fine
and limpid fluid from the surface of the stigma
every morning, which augments as the day advances,
and forms about noon a drop so large that one
would think it in danger of falling to the ground.
It is re-absorbed, however, by the style about three
or four o'clock in the afternoon, and again pro-
truded about ten o'clock on the following morning.
This limpid drop, which is thus regularly exuded
and absorbed, is intended no doubt in the economy
of the flower to facilitate the process of impregna-
tion, by catching a portion of the pollen as it is dis- -
charged from the anther, and conducting it to the
ovary. It is at least certain that the pollen reaches
it, and is detained by it ; as a number of drenched
and disfigured particles may generally be seen ad-
hering to the surface of the stigma, after the drop
has been absorbed. Perhaps it may even have some
effect in forwarding the explosion of the pollen,
which is known to be also strongly effected by
moisture.

As the stamens and pistils grow and come to

318 SEXUALITY OF VEGETABLES. CHAP, Vt.

maturity together, so they also decay together ; the
stamens shrinking and withering immediately after
the anthers have discharged their pollen, and
the stigma withering also and falling off much about
the same time, even when the style remains an ap-
pendage to the fruit.

From the Obs. 5. — The relative proportion, situation, and
Sf°Sietl0n mutual sympathies, of the stamens and pistils are
stamens of gych as seem expressly calculated to facilitate the

the pistils. r m J

process of impregnation. In pendulous flowers the
pistil is generally longest, as in the case of the Lily ;
but in upright flowers the stamens are generally the
longest, as in the case of the Ranunculus. In simple
and hermaphrodite flowers the situation of the pistil
is invariably central with regard to that of the
stamens,, as may be seen by inspecting almost any
flower at random. In plants of the class Moncecia,
the barren blossoms stand generally above the fertile
blossoms, even when situated on the same foot-stalk,
as may be seen in the case of the Car ex and Arum.
And in plants that have their barren and fertile
flowers on distinct individuals, the blossom is gene-
rally protruded before the leaves expand. But a
very little reflection will serve to show that all the
above arguments are institutions of nature, by which
the pollen, when it explodes from its envelopes,
shall possess the best possible chance of coming into
contact with the pistil or stigma.

And where such means are wanting, nature dis-
plays a variety of other contrivances to effect the

SECT. III. INDUCTION OF PARTICULAR PROOFS. 3 1 $

same end. The style 6f the Gloriosa superba is
bent towards the stamens at a right angle even from
the very base, and for no other conceivable purpose
but that of throwing itself in the way of the pollen
when discharged. The stamens of the genus Saxi-
fraga bend down to the pistil, one or two at a time;
if two, the two opposite, and discharge their pollen
directly over the stigma, returning afterwards to
their former position and giving place to one or two
others successively, which also retire in their turns,
till all of them have discharged their pollen.*
Similar phenomena have been observed in the
flowers of Parnassia, Celosia, garden Rue, and
others.

But the most singular phenomenon of this kind
is that which is exhibited in the stamens of the
flower of the Berberry Bush ; the stamens which
are six in number lie sheltered under the concave
tips of the petals as long as they are allowed to re-
main undisturbed; but if any extraneous body,
whether by accident or design, is made to touch a
stamen at the base of the filament, it immediately
collapses with a sudded jerk and bends inward till
the anther strikes against the summit of the pistil,
discharging its pollen if ripe, and again retiring.
This curious and singular fact seems to have been
first discovered by Sir J.E. Smith,f of the truth ofwhich
any one may easily satisfy himself by applying the
point of any instrument sufficiently deli<sate to the
* Withering, vol. i. p. 239. t Phil. Trans. 1788.

326 SEXUALITY OF VEGETABLES. CHAP. VI,

inner side of the base of a stamefc ; it will im-
mediately spring forward till it strikes against the
pistil. Whence it is to be presumed that the effect
is often produced in the natural order of things, by
means of the feet or trunks of insects rummaging
the flower in quest of honey.

From the Obs. 6. — The economy of many of the aquatics
ofaquatics. seems also expressly intended to facilitate the process
of impregnation. Many plants of this class that
vegetate for the most part wholly immersed in water,
and often at a considerable depth, gradually begin
to elevate their stems as the season of flowering
advances when they at last rear their heads above
the surface of the water, and present their opening
blossoms to the sun, till the petals have begun to
fade, when they again gradually sink down to the
bottom to ripen and to sow their seeds. This very
peculiar economy may be exemplified ia the case
of Ruppia maritima, and several species of Pota-
mogeton, common in our ponds and ditches ; from
which we may fairly infer that the flowers rise thus
to the surface merely to give the pollen an opportu-
nity of reaching the stigma uninjured.

But the most remarkable example of this kind
is that of the Valismria spiralis, a plant that grows
in the ditches of Italy. The plant is of the class
Dicecia, producing its fertile flowers on the extre-
mity of a long and slender stalk twisted spirally
like a cork-screw, which uncoiling of its own ac-
cord, about the time of the opening of the blossom,

SECT. III. INDUCTION OF PARTICULAR PROOFS* 321

elevates the flowers to the surface of the water, and
leaves them to expand in the open air. The barren
flowers are produced in great numbers upon short
upright stalks issuing from a different root, from
which they detach themselves about the time of
the expansion of the female blossom, mounting up
like little air bubbles, and suddenly expanding
when they reach the surface, where they float about
in great numbers among the female blossoms, and
often cling to them in clusters so as to cover them
entirely ; thus bringing the stamens and pistils into
immediate contact, and giving the anthers an op
portunity of discharging their pollen immediately
over the stigma. When this operation has been
performed, the now uncoiled stalk of the female
plant begins again to resume its original and spiral
form, and gradually sinks down as it gradually rose, '
to ripen its fruit at the bottom of the water.

SUBSECTION II.

Experiments. — The above are the proofs of the
sexuality of vegetables, arising from the observation
of the natural phenomena exhibited in the economy
of flowers. It remains now to exhibit such proofs
as arise from experiment.

Experiment !.< — If the anthers of an herma-Thean-
phrodite flower, or the stameniferous flowers of a{|^^
monoecious plant, are cut off before they shed their Phrodites

' cut off,

pollen, and care taken to prevent the access of the

VOL. II. Y

322 SEXUALITY OF VEGETABLES. CHAP. VI-

pollen of any other plant of the same species, the
fruit will prove abortive. From a flower of the
Chdidonum corniculatum, or red-horned Poppy,
which was detached from all other individuals of
the same species, Linnaeus removed all the anthers
upon the first opening of the blossom, and stripped
off at the same time all the rest of the flowers ; but
the result of the experiment was that the flower pro-
duced no seed.

A gardener who cultivated Melons and Cucum-
bers, but was no botanist, thinking that the sta-
meniferous flowers of the plant only exhausted the
nourishment due to the other flowers without being
of any utility in themselves, fancied that his plants
would be rendered more vigorous and his fruit of
superior flavour, and his profits consequently in-
creased, by means of tearing them off* altogether. But,
like the boy who cut open his goose that laid golden
eggs in the hope of getting rich all at once, he soon
found cause to repent of his rash experiment ; for
the consequence was that his plants produced no
fruit.

Supplied Evper. 2. — If after the anthers have been re-
flhnt8°ofer moved> as m tne foregoing experiment, the pollen
the same of another plant of the same species is shook over
the pistil, then the fruit will still ripen. This Lin-
naeus proved by first treating a flower of the Cheli*
donum corniculatum as in the foregoing experiment,
and then sprinkling over the pistil pollen borrowed
from another plant of the same species. The flower

SECT. III. INDUCTION OF PARTICULAR PROOFS. 323

produced perfect seeds. Upon this principle gar-
deners now assist the impregnation, or what they
call the setting of the fruit, at least in the case of
their Melons and Cucumbers, by means of sprink-
ling the pollen of the male flowers over the pistils
of the females. But if a plant has more than one
pistil, and you apply the pollen only to that one,
then that one only will ripen seed.

Evper. 3. — If the stigma of the pistil is cut off The stig-
before the discharge of the pollen, no fecundation m
ensues ; and the fruit is inferior both in quantity and
quality. Of this experiment I have not been able
to procure the proper examples : but it shows that it
is by no means a matter of indifference to what part
of the pistil the pollen is applied ; for unless it
enters by the stigma it cannot be conveyed to the
ovary.

Exper. 4. — If the stigma of a flower that has Sprinkled
been stripped of its stamens before the bursting of ^ from"
the anthers is sprinkled with the pollen of a plant J^^*
of a different species, then the seeds will not only species,
ripen arid produce perfect plants when sown, but
these plants will partake of the qualities both of the
fecundating and fecundated species. The pollen of
the Tragopogon pratensis, whose petals are yellow,
when sprinkled on the stigmas of the flower of the
Tragopogon purpureus, whose petals are purple,
yielded seeds that produced plants with both purple
and yellow flowers. Hence botanists account for
the existence of what are called spurious plants, at-

Y 2

524 SEXUALITY OF VEGETABLES. CHAP. VI.

tributing them to the accidental intermixture or
access of the pollen of a different species. Thus
Veronica spur la is thought to have sprung from
Veronica maritirna, impregnated by the pollen of
Verbena officinalis ; agreeing in its fructification
with the former, and in its leaves with the latter.
So also Delphinum hybridum is thought to have
sprung from Delphinum elatum and Aconitum Na-
pellus, by its combining together the features of
both. But this spurious" impregnation seems to be
confined within very narrow limits, and takes place
only among plants that are nearly related by natural
affinity.

A. male Exper. 5. — If a male plant is placed in the vici-
trodnced mty °f a female plant which, from its having been
or P? JJe|^ formerly insulated, had produced no perfect seed ;
a distance, or if the pollen of a male plant of the same species
is conveyed to it from a distance and sprinkled over
the stigma, it will now produce perfect seed. A plant
of the DatiscaCannabina, which came up in the gar-
den of Linnaeus from seed about the year 1750, and
which produced afterwards many flowers, yielded
however no perfect seed, as the flowers happened to
be all female ; a few perfect seeds were now pro-
cured and sown with a view to raise some male
plants, but still they were all female. At last,
however, in 1757 a parcel of seed was procured,
from which a few male plants were obtained that
flowered in the following year. They were removed
to a distance from the females, and when their

SECT. III. INDUCTION OF PARTICULAR PROOFS. 325

flowers were ready to discharge the pollen, it was
collected by means of shaking the panicle with the
finger over a piece of paper, till the paper was
covered with a fine yellow powder. The pollen
thus obtained was immediately carried to the female
plants, which were growing in another part of the
garden, and sprinkled over them ; in consequence of
which they now produced perfect seeds.

But the best example of this kind yet exhibited
is that of the famous experiment of Linnaeus upon
the Berlin and Leipsic Palms. About the period of
the foregoing experiment, or rather a few years prior
to it, there grew at Berlin an individual female
Palm-tree which had never perfected any fruit, so as
that the seeds would germinate ; while there grew
at the same time, at Leipsic, a male plant of the
same species. Hence it occurred to Linnaeus that
the impregnation of the female flowers of the former
was still practicable, even by means of the pollen that
might be procured and carried from the male flowers
of the latter. Accordingly a flowering branch of the
male plant was dispatched by post from Leipsic to
Berlin, a distance of twenty German miles, and
shook or suspended over the flowers of the female
plant. The consequence was that the fruit was
ripened and the embryo perfected, and young plants
raised from the seed.

Exper. 6. — If the male plant is again removed The male
from the vicinity of the female plant to which it jJ^J.
had given fecundity, the fruit of the female plant is drawn*

326 SEXUALITY OF VEGETABLES. CHAP. VI.

again produced imperfect as before. About the
year 1755, there grew in the garden of M. De la
Serre, at Paris, a female Pistachio-tree which blos-
somed every summer, but without producing any
fruit capable of germinating ; as M. De la Serre had
frequently sown the seeds it yielded in the hope of
raising more plants, though without success. At
last, however, he was advised by Bernard De
Jussieu and Du Hamel to endeavour to procure a
male plant and place it near it : accordingly a male
plant was procured in the following year, full of
flowers, and placed near the female ; the result being,
as in other cases of a similar kind, that the seed now
produced was capable of germinating when sown.
But when the male plant was afterwards removed,
the fruit of the female plant was found to be again
incapable of germinating as before.*

In the month of April, ]752, Linnaeus sowed a
few grains of Hemp-seed in two different pots, in
both of which it came up very well. In the one pot he
left the male and female plants together, which flower-
ed and produced fruit that was ripe in July ; from the
other pot he removed all the male plants as soon as
they could be distinguished from the females, which
grew indeed very well and presented their long pis-
tils in great abundance, as if in expectation of their
mates. But when the calyxes were afterwards in-
spected, about the time that the pistils began to
decay through age, though they were large indeed

* Phys. dcs Arb. liv. iii. chap. Hi.

SECT. III. INDUCTION OF PARTICULAR PROOFS. 327

and luxuriant, yet the seed-buds were brown, com-
pressed, and membranaceous, without exhibiting
any appearance of cotyledons or pulp.

Two plants of Clutia tenella were, in like manner,
kept growing in a window of Linnaeus's house or
apartments during the months of June and July
o^ 1753, the male plant being in one pot and the
female plant in another. The latter abounded with
flowers, not one of which proved abortive ; the pot
containing the male plants was after some time re-
moved to a different window in the same apart-
ment, and still the flowers that were protruded
under such circumstances were found to be fruitful.
The pot containing the male plant was at last re-
moved into a different apartment, and the female
plant left alone, after being stripped of all the flowers
already expanded. It continued indeed to produce
new flowers every day from the axils of every leaf,
but they proved to be all abortive. For after remain-
ing on the plant for the space of eight or ten days,
till the foot- stalks began to turn yellow, they all
fell barren to the ground.

Such is the amount of the great body of evidence^
whether resulting from observation or experiment,
on which Linnaeus has established the doctrine of
the sexes of vegetables, and on which the import-
ant and irresistible conclusion depends— namely,
that no seed is perfected without the previous agency
of the pollen.

328 SEXUALITY OF VEGETABLES. CHAP. VI.

SECTION IV.
Objections.

ALTHOUGH the proofs contained in tne foregoing
section seem to be altogether irresistible when taken
in their aggregate effect, yet it will readily be ad-
mitted with regard to several of them that they do
not amount to much in their individual weight.
And hence we can easily account for the doubts that
were entertained on the subject, and the opposition
that was given to the doctrine of vegetable sexuality,
at a time when the preceding proofs were not yet all
discovered nor collected into a body.

Anticipat- Camerarius, who had inferred the truth of the
inerarhis" doctrine from the result of actual experiment, which
he was indeed the first to institute on the subject,
seems after all to have found cause to doubt the
legitimacy of his conclusion, in observing that some of
the female plants on which his experiments were made
— namely, Hemp, Mercury, and Spinach, produced
also ripe and perfect seeds even when placed altogether
beyond the reach of the influence of the male plant.
This fact looked no doubt extremely hostile to the
doctrine he was endeavouring to establish, and per-
haps remained with him to be an insuperable
objection ; but the fact has been now accounted
for, and the objection done away. For it has been
ascertained, by means of more minute and accurate
6

SECT. IV. OBJECTIONS. 32Q

observation, that the fertile plants of the genera in
question have often some latent male flowers inter-
spersed among their female flowers, so that the
former, though difficult of detection, are sufficient
to secure the impregnation of the latter, even when
the individual producing them is solitary.

Tournefort, who denied the doctrine of the sexes Advano
altogether, though I do not know upon what precise Town*,
grounds, admitted, however, the utility of the sta- fort>
mens in the economy of fructification, regarding
them as organs both of secretion and excretion —
the substance excreted being the pollen, and the
substance secreted being a peculiar fluid that was
conducted by the filaments to the germen. But if Answered,
the pollen is merely an excrement, how comes it
to be so very curiously organized ? And if the
stamens secrete a fluid which they afterwards con-
duct to the germen, by what means do they conduct
it when placed on a different plant ?

Pontedera, who was one of the most zealous dis- Urged by
ciplcs of Tournefort, and willing to defend him Pontedera'
even where least defensible, not only adopted the
opinions of his master on this subject, but en-
deavoured to establish them by additional argument;
contending that if the stamens and pistils were
even destined to the discharge of the functions
ascribed to them by the sexualist, yet there are
many cases of perfect fructification in which they
could not possibly co-operate to the production of
the effect ; adducing the example of the Umbelliferce,

UNIVFDQITV

33O SEXUALITY OF VEGETABLES. CHAP. VI.

in which the style, as he rightly remarked, does
often not appear till after the stamens have fallen.
But although the styles remain often inconspicuous
till the period assigned by Pontedera, yet the stigma
is previously mature, and consequently capable of
the necessary co-operation.

Answered. But if the fact had been precisely what it appears
to be in the objection, still it would have afforded
no formidable argument against the doctrine of the
sexes. For as the several flowers of the same plant,
and much more the flowers of different plants, do
not all come to maturity precisely at the same time,
the flower whose stamens have fallen before the ma-
turity of its pistil, may still be impregnated by the
pollen of another flower or plant with which the
period of its maturity is identical, and to which it
may be contiguous. And in this way, we may
believe, the impregnation of many flowers is effected,
particularly in the case of Zea Mays or India Corn,
the barren flowers of which upon the same plants
have generally quite decayed before the fertile
flowers have burst from the bosom of the leaves, at
least as it grows in this country ; as also in the case
of the Jatropha urens> the barren floweres of which
are generally protruded either several weeks sooner
or several weeks later than the fertile flowers, and
are consequently either decayed or not yet come to
maturity at the time the style is perfect.

But if the fertile flower or plant should not be
contiguous to the barren flower or plant, the pollen

5

SECT. IV* OBJECTIONS. 331

may yet be wafted to it by means of the wind,
which curious phenomenon may sometimes be dis-
tinctly seen. On the 14th of June 1808, as I was
accidently looking at a field of Rye-grass situated
to the south of the spot on which I then stood, the
atmosphere being clear, and the wind blowing gently
from the west, I was surprized to observe a thin and
sudden cloud, as if of smoke or fine dust, sweeping
briskly along the surface of the Grass, and gradually .
disappearing. This cloud was soon followed by a
second from a different quarter of the field, and that
by a third, and so on in succession for several
minutes. It was a general discharge of pollen from
thousands of anthers bursting at the same moment, so
that no stigma ready to receive the pollen could possi-
bly fail of being supplied, either from the anthers pro-
per to the flower of which it formed a part, or from
those of some other flower discharging their con-
tents into the general mass. The distance to which
the pollen may be conveyed, on a short exposure to
the action of a fine atmosphere, is not likely to do
it any damage. Linnseus kept some of the pollen
of the Jatropha urens in paper for more than a
month, which even then fertilized the pistils it was
shook over.

The foregoing doubts or objections were enter- Insisted on
tained by the scrupulous or sceptical prior to the
elucidations of Linnaeus ; and indeed they arose al-
most naturally out of the darkness in which the
subject was then involved. But as the elucidations

332 SEXUALITY OF VEGETABLES. CHAP. VI.

of Linnaeus, though capable of affording conviction
to the mind of the impartial inquirer, were not able
to subdue passions, or to eradicate prejudices im-
imbibed by education or excited by comparison,
the doctrine of the sexes of vegetables met also
with many opponents even in the time of Linnaeus.
The most zealous and redoubtable of these was Dr.
Alston of Edinburgh ; who, professing to be dis-
satisfied with every thing that had been said or done
in support of the doctrine, made a show of refuting
it by means of counter experiments, of which the
most formidable are the following : — Admitting the
result of the experiment of the cutting off of the
anthers before the ripening of the pollen to be what
Linnaeus and others affirm, the abortion of the seed ;
he will not allow that it authorizes any conclusion
in favour of the sexes of plants, because he thinks
it is to be expected that a wound in any essential
part of the plant, together with consequent loss of
juice issuing from it, will occasion abortion in the
seeds : and in confirmation of the presumption he
quotes an experiment of Malpighi, who found that
the ripening of the seeds of a Tulip was prevented
by means of the pulling oft' of the petals before
their expansion. But the two experiments are not at
all of the same kind. In the latter there was a mate-
rial injury done to the flower, in consequence of its
being prematurely stripped of the covering of the co-
rolla; in the former there was no material injury done
to the flower, because the anthers were not cut off till

SECT. IV. OBJECTIONS. 333

after the natural expansion of the petals ; in which
case it is very well known that if the pistil is im-
pregnated even with the pollen of another flower
the seeds will still ripen. But Alston does not
even admit the fact that the stripping of a plant of
its stamens will render the seed abortive ; alleging
in support of his opinion Geoffrey's experiments on
Maze, in which it was found that some of the ears
ripened a few seeds, even when the stamens were
entirely cut off before the bursting of the anthers ;
together with a similar experiment of his own
upon a solitary Tulip, by which the ovary suffered
nothing, but increased and came to maturity quite
full of seeds. Now the defect of the argument is
that we are not told whether the seeds were put to
the proper test ; that is, whether they were sown and
found capable of germination.

The next counter experiment was made upon
Dioeceous plants. Three plants of common Spinach,
which were removed before it could be told
whether they were to be fertile or barren to a dis-
tance of at least eighty yards from the bed in which
they were raised, and from which also they were
separated by several intervening hedges, proved in
the end to be all fertile, and ripened plenty of seeds
that germinated again when sown. A solitary plant
of Hemp also that sprang up in Dr. Alston's garden,
having no other plant of the species within a mile
of it to his knowledge, grew luxuriantly, and pro-
duced seeds that germinated also when sown.

334 SEXUALITY OF VEGETABLES. CHAP. VL

Answered. These experiments are contradictory, no doubt, to
the experiments of Linnaeus ; but they afford no
argument against the doctrine of the sexes : for in
the first place it cannot be proved that some of the
pollen from the Spinach bed, or from a neighbour-
ing male plant of Hemp, might not have reached
the insulated plants by means of a favourable com-
bination of circumstances ; and in the next place it
is not certain that the plants in question were
not furnished with some minute and latent male
flowers, by which the impregnation might have been
effected.

Addue- But the most truly formidable, as well as the
most philosophical, opponent of the doctrine of the
sexes was the celebrated Spallanzani, who, having
an hypothesis to support which that doctrine stood
directly in the way of, found it necessary by all
means to overthrow it if possible. It is the less
surprising, therefore, that his experiments gave ge-
nerally the result he wished for; though I do not
introduce the remark with a view to detract from
the degree of accuracy and of credit that is due to
him, as he is well known to have been a most
able and masterly experimenter, and to have ex-
hibited a degree of candour and ingenuousness that
must have been sufficient to prevent him from any
intentional misstatement, in his giving also those
results which were the most unfavourable to his
own hypothesis.

Spallanzani's first experiment was made upon

SECT. IV. OBJECTIONS. 335

the Ocymum basilicum^ an hermaphrodite plant ;
the anthers of several flowers being all cut off
before the pollen was ripe, and the stigmas care-
fully secured from the access of the pollen of other
flowers : in which case it was found that most of
the seeds produced were evidently imperfect;
though there were also a few that seemed to be
completely matured, by their exhibiting on dis-
section the same appearances as others that had
been exposed to the action of the pollen. But
when these apparently perfect seeds were put to the
proper test, they were found to be in reality imper-
fect ; they did not germinate when sown.*

This result was discouraging enough, but was not
sufficient to deter the Signior from further ex-
periment, who now directed his attention to plants
of the class Moncecia, to try whether he could not
obtain from them a result more favourable to his
hypothesis. The subject of his experiment was the
Cucurbit a Citrullus, the male flowers of which were
destroyed as soon as they made their appearance ;
and the female flowers, in order to prevent all
suspicion of the access of pollen, were inclosed in
bottles luted to the stem by the neck, so as to
exclude even the external air. The seeds which
were procured in this way germinated and produced
plants.

This result was as favourable to his hypothesis as
could be wished ; but to give to the argument
* Dissert, vol. iii. chap. i. Eng, Trims.

336 SEXUALITY OF VEGETABLES. CHAP. VI.

against the sexes all the weight he could, he now
directed his attention to the class Dicecia, selecting
as the subject of experiment some plants of the
Cannabis sativa and Sp'macia oleracia, from which
he obtained also results equally favourable to his
views. For after taking every precaution to secure
the female plants from the access of pollen, as in the
above example I suppose, seeds were still procured
that germinated when sown.

From the above experiments, which appear in-
deed to have been made with great accuracy, Spal-
lanzani seems inclined to conclude that the pollen is
not in any case essential to fecundation ; and rails
much against the Linnaeans for drawing general
conclusions from particular premises, insisting that
they should never go beyond the extent of their
own experiments. But if the philosopher is not
allowed to infer a general conclusion from a fair and
legitimate induction of particulars, then our know-
ledge of the works of nature must remain very
limited indeed, and a great many of Spallanzani's
conclusions would not be what they are ; for although
he utterly disclaims all such procedure in principle,
as being wholly illogical, yet he is by no means
ashamed to resort to it in practice. And yet after
all the parade of argument and experiment which
he produces, the doctrine of the sexes of plants has
suffered but little from his attack ; for, in spite of his
most desperate efforts, still he is obliged to admit it
in part, that is in the case of hermaphrodite plants,

SECT. IV. OBJECTIONS. 33?

which according, to his own experiments, form an
obstacle that cannot be surmounted. And even with
regard to monoecious and dioecious plants perhaps
his experiments are not altogether free from error,
as we can oppose to them the experiments of Lin-
naeus on the very same species ; who will be allowed
to have been as attentive, and accurate, and success-
ful an observer, as Spallanzani. The necessity of
aiding the impregnation of Melons and Cucumbers,
as practised by gardeners, is against his conclusions
in the one case ; and the possibility of the existence
of some latent and undetected male flower lurking
among the females is against it in the other.

But although Spallanzani is extremely anxious
to disprove the doctrine of the sexes of plants, and
although his experiments turned out to be rather
favourable to his views, he does not seem after all to
lay a great deal of stress upon them ; thinking that
the doctrine may still be true, and that the ripening of
the seeds that were perfected without the aid of the
male flowers might have been effected by means of
a power, inherent in the female flowers, of propagat-
ing to a certain number of generations without the
assistance of the male ; as in the case of the Aphis
among insects, according to the observations of
Bonnet ; and as in the case of some plants which he
had himself observed to be propagated in this way
to three generations. But there does not seem to be
any very good ground for this supposition, nor does
it seem to be much supported by the observations of
VOL. n. z

S3 8 SEXUALITY OF VEGETABLES. CHAP. VI

Bonnet on the Aphis; from which it does not
follow that it had the power of propagating without
the male to ten generations and no more, but rather
that his observations were not pursued farther.

Spallanzani suggests also the possibility of the
fecundation of the ovary, by means of some seminal
principle residing in the pistil, and capable of sup-
plying the place of the pollen, as well as necessary
in the case of Monoecious and Dioecious plants, to
ensure the perfection of the seed. This conjecture
is perhaps countenanced in some degree by Koel-
reuter's account of the chemical properties of the
moisture exuding from the stigma when ripe, which
he represents as being precisely the same with the
chemical properties of the pollen. But this is leaving
the matter precisely as it was taken up ; for, if the
suggestion of Spallanzani is true, then there exists
at least a virtual sexuality in vegetables, to all in-
tents and purposes.

Reiterated The last and least formidable adversary of the
bySme ic. (joctrjne of tne sexes of vegetables whose opposition

J shall take any particular notice of at present is
Mr. Smellie, author of the Philosophy of Natural
History. Violent in proportion to his want of ar-
gument, he pushes his opposition to a greater length
than any of his predecessors, though with less effect.
Spallanzani had admitted that fecundation cannot be
effected in hermaphrodites without the aid of the
pollen, and that it may possibly be so effected in
monoecious and dioecious plants also ; contending

SECT. IV. OBJECTIONS.

only in fact for the establishment of the principle,
that nature in extraordinary cases may have recourse
to extraordinary means. But this is a concession
which Mr. Smellie is by no means inclined to
make, not admitting the existence of sexes, or the
efficacy of the pollen, in any case whatever ; to coun-
tenance which opposition one would think he must
have been able to produce a variety of the most de-
licate and decisive experiments that ever were made
on the subject, and that they had all succeeded to
his wish. But what must be the surprise and disap-
pointment of the reader when he is informed that
all Mr. Smellie's dogmatism and pertinacity rests
only on the very slender and narrow foundation of
one poor experiment made upon the Lychnis
dioica, which, by the by, is not his own experiment
after all.

But in order to account for the very sweeping
and decided conclusion of Mr. Smellie, it is to be
recollected that he began his reasonings on the sub-
ject with a wishthatthe doctrineof vegetable sexuality
might prove to be false, as well as with the hope of
showing some little ingenuity in refuting a doctrine
that was supported by the great Linnaeus, and thus
avowedly contending for victory rather than for truth.
Like Spallanzani he begins by complaining of the in-
sufficiency of the arguments drawn from analogy, by
which the doctrine of the sexes had been occasion^
ally illustrated ; and, like Spallanzani also, is guilty
of committing the very identical sin he condemns,

z 2

34O SEXUALITY OF VEGETABLES. CHAP. VI.

employing such arguments wherever it suits his
purpose, in all cases excepting that of sex. Witness
his very first chapter on the analogies between the
plant and animal ; in which he exhibits, no doubt,
an example of the most meritorious self-denial in
forbearing to pursue the analogy throughout the se-
veral sexual organs, to which he certainly had a
strong temptation, though he affects to regard the
doctrine as an absurdity.

But if plants, like animals, are found to produce
a new individual arising from a germe, seed, or egg,
why should it be thought strange if they are fur-
nished with analogous organs of generation ? The
alleged impregnation, says Mr. Smellie, is impossi-
ble : because if the doctrine were even true, the seed
could be impregnated by the pollen only in a gela-
tinous state ; and yet in most hermaphrodites, it has
acquired considerable solidity before the pollen is
shed. But this assumption, which is founded on
the already refuted arguments of Pontedera, is good
for nothing ; because Mr. Smellie cannot tell when
impregnation is and is not practicable merely from
the state of the seed ; and because it is not necessary
that a seed should be impregnated by the pollen of
its own flower. The experiment of the Leipsic and
Berlin Palms is regarded as defective, because it was
not continued for several successive years with and
without pollen ; and because it is possible it might
have produced fertile seeds, in the year of the ex-
periment at any rate. The futility of this objection

SECT. IV.

OBJECTIONS. 341

requires no reply, and proves only that the objector
was much in want of argument. It is said to be
ridiculous to suppose that the pollen should be
wafted by the winds, or carried by insects to im-
pregnate the germe ; but if it can be proved that the
pollen retains its fecundating property for some con-
siderable length of time after it is shed, which Lin-
naeus has actually done, there is no absurdity in
supposing that it may in some cases be conveyed to
the pistil by the wind. The wind must necessarily
waft it along, and it may certainly fall upon the
stigma of the female plant : and, if insects should
occasionally be the carriers of it, still it is far less
wonderful than the feats of Spallanzani, in a case
which I need not specify.

Varieties which have been proved to proceed, at
least occasionally, from the intermixture of the pol-
len of plants of different species or varieties, Mr.
Smellie ascribes wholly to soil and culture ; dismiss-
ing the experiments on the subject by saying that
the same results might have happened if the con-
ditions had been reversed, and finally contending
that the doctrine of the sexes is disproved by the
fact of the propagation of plants from slips and layers
in which new individuals are formed without the
intervention of sexual organs. But if this is at all
an argument, it is one from which the sexualist has
but little to fear; as in the case of slips and layers
there is in fact no production of a new individual,
but merely a prolongation of the old ; or at best a

342 SEXUALITY OF VEGETABLES. CHAP. VI.

multiplication by means of division, as in the case
of the Polypi : and although plants are capable of
being multiplied in this manner, it is no proof that
they may not be propagated by means of sexual
intercourse also.

Refuted. Such is the futility of Mr. Smellie's reasoning on
this interesting and important subject, in which the
reader will perceive that every thing is hypothetical.
But at length we come to the boasted and long ex-
pected experiment which is to outweigh the whole
body of evidence for the doctrine of the sexes,
whether as adduced by Linnaeus or others. And
what is this boasted experiment ? It is that of a
female plant of the Lychnis dioica, which was placed
by Mr. Smellie in a spot so situated that no male
plant of the same species was known to grow within
a mile of it, and which yet produced seeds. It is to
be recollected, however, that the experiment did not
succeed with Mr. Smellie himself; but when the
plant was removed to the garden of Dr. Rutherford
at Edinburgh, it succeeded after a year or two of ex-
pectation. But where is the proof that there was
no male plant within a mile of it during the whole
time of experiment ; which, if it could be produced,
would be but of little avail, as we are not told after
all whether the seed was capable of germination.
By the op- Lastly, the doctrine of the sexes of plants has been

ponents of , .

Crypto- objected to as altogether unfounded, upon the pre-

gamy' sumption that plants destitute of conspicuous flowers

are destitute of flowers altogether, and consequently of

SECT. IV. OBJECTIONS. 343

sexual organs, which if not necessary in some cases are
not necessary in any. Plants of the class Cryptogamia
are, as their name imports, destitute of conspicuous
flowers, and hence they have been regarded by many
botanists as being destitute of flowers altogether ; as
may be seen from the title by which they are cha-
racterized in the method of Tournefort and others :
but it is now very well known that plants may pos-
sess all that is necessary to constitute a flower,
without being furnished with a gaudy and conspi-
cuous corolla.

If the stamens and pistils are but present under
whatever shape, they constitute to all intents and pur-
poses an effective flower, because they are by them-
selves capable of producing perfect seed ; as in the
case of Hippuris, Salicornia, and Lemna, which are
indeed destitute of petals, but are furnished with
stamens and pistils that produce seeds. But in plants
that are strictly cryptogamous many botanists have
denied the existence of stamens and pistils under any
form whatever, regarding it as absurd even to suppose
their existence ; and either contending that they are
propagated without seeds, or inferring that seeds
may be formed without the intervention of sexual
organs, which if not necessary to the reproduction
of what are called cryptogamous plants are not ne-
cessary to the reproduction of any, and consequently
do not exist. But a contrary inference would have
been the more logical, and might have been de
duced thus : — The organs of fructification have been

844 SEXUALITY OF VEGETABLES. CHAP. VI.

detected in most plants, and the peculiar functions
of the several organs. There are, however, some
plants producing fruit, in which the organs of fructi-
fication have not yet been detected, but we con-
clude, from analogy, that such organs exist in them,
and discharge similar functions : and this inference
has been accordingly confirmed by means of the
actual discoveries to which the aid of the micro-
scope has led. The first minute portion that ever
Refuted by was removed of the veil concealing the fructification
very ofthe °f cryptogamous plants was removed by the hand of
tionlafthe MichelH9 in his detecting of the stamens and pistils
mosses. of Mosses, though he does not seem to have enter-
tained any correct notion of their respective func-
tions :'* and to the meritorious example of minute
investigation which he thus exhibited we are per-
haps indebted for the succeeding illustrations of
Dillenius and Linnaeus, who detected indeed the
parts of the fructification of the Mosses, but unfortu-
nately mistook the capsule for the anthers, and con-
sequently the seeds for the pollen. At length,
however, the task of investigation was undertaken
by the illustrious Hedwig, who detecting the errors
of his predecessors, and penetrating into the very
recesses ofthe mystery, exhibited a view ofthe sub-
ject so correct and so well supported by fact as to
leave but little doubtful, and to authorise a conclu-
sion directly the reverse of that of Linnaeus — the
anthers of Linnaeus being proved to be in fact the
* Nova Plantarum Genera,

SECT. IV. OBJECTIONS. 345

the fruit, and the cones and stars being presumed to
be the male organs.

The legitimacy of this conclusion seems now to
be almost universally admitted ; and yet it has been
lately suspected that the Mosses are hermaphrodites,
containing in the urn both the germe and pollen.
Such at least is the opinion of M. Palisot Beauvois, a
French botanist of some considerable celebrity ;*
who regards the column as constituting an individual
viscus, and containing a sort of granular and powdery
substance as well as the urn — the powder of the
latter, according to M. Beauvois, being the pollen ;
and that of the former being the seed. This
opinion is certainly plausible, and may perhaps prove
to be the truth. In the month of November, 1805,
I examined some capsules of Bryum argenteum
before the operculum had fallen, but not till it had
become a little brownish with age, and found that
the column actually contained within it a quantity
of fine granules imbedded in a pulpy and viscid
substance ; the granules of the capsule being in
nearly the same state at the same time. The granules
of the column were easily distinguished from those
of the capsule both in size and colour, the former
being by much the smallest and almost perfectly
transparent ; and the latter being comparatively
large, as well as opaque and green.

Such are the two sets of granules on which M.
Beauvois founds his opinion of the sexual organs
* Prodrome cks Mousses et des Lycopodes,

346 SEXUALITY OF VEGETABLES. CHAP. VI.

of the Mosses ; and it claims at least a fair and im-
partial consideration, as the cones and stars of Hed-
wig are by no means universal. I begin, however,
to suspect that M. Beauvois has, like Dillenius and
Linnaeus, misapprehended the true and natural cha-
racter of the two containing organs respectively ;
and that the powder of the column is the pollen,
and the powder of the urn the seed. My reasons
are the following: — 1st, Because the granules of
the column are much smaller than the granules of
the capsule, and therefore more analogous to the
character of pollen in general. 2dly, Because like
the pollen they are observable only at a certain
period of the plant's growth ; that is about the time
of the fall of the operculum, or a little before it,
so that if you look for them sooner you tind only
a gelatinous mass, and if later, they are gone.
3dly, Because the column after discharging its
contained granules becomes, like the anthers of
other plants, shrunk and shrivelled up long before
the granules of the capsule are ejected.

Perhaps an objector may say that the stamens are
on this supposition contained within the pistils,
which is contrary to all analogy. But why may
not the Mosses be allowed to form an exception, if
no other plants do, as they are in almost all other
respects confessedly anomalous. And if the urn
contains the pollen, and the column the seed, then
do the Mosses present an anomaly much more
wonderful than the eccentric position of the fruit ;

SECT. IV. OBJECTIONS. 347

namely, that of ripening and discharging their
seeds before the discharge of the pollen, which is
an absurdity.

I know it is the opinion of Mr. Brown,* that
M. Beauvois has been led into a mistake with re-
gard to the source of the central grains, which he
believes to have been pushed into the substance of
the column by the pressure necessary to cut it up,
or to have been carried over the surface of the
section by the cutting instrument. This, it must be
confessed, is giving M. Beauvois very little credit
for the accuracy of his observations ; although I
am satisfied there are but few botanists better qua-
lified than Mr. Brown to judge of that accuracy.
It is not for me to attempt to decide any thing
where such authorities have differed ; nor am I pos-
sessed of a sufficient induction of particulars to
form any decision ; but I will venture to add that
I am quite confident of the existence of two sets of
granules in the individuals of the species I exa-
mined ; as well as positive that the granules of the
urn were not forced into the substance of the
column by means of the dissecting instrument.

But the Mosses are not the only tribe of plants And pre-
that has been proved to be furnished with organs
of fructification after having been supposed to be

totally destitute of them. The Ferns, Algae, and A'g86* an(*
Fungi, according to the illustrations of Hedvyig?

* Lin. Trans, vol. x. part ii.

348 SEXUALITY OF VEGETABLES. CHAP. Vt,

As Hlus- have been found to exhibit similar proofs of sexu-

trated by . . _.

Hedwig, ahty also, so that Cryptogamy can now be scarcely
said to exist ; and much less any thing like equi-
vocal generation ; whence it seems indeed to follow,
according to the favourite maxim of that great na-
turalist, that all plants spring from seed.

At the same time it must be admitted that there
still exists some considerable diversity of opinion
on this subject, notwithstanding all that has been
done by Hedwig and others to prove that all plants
are furnished with distinct sexual organs, capable
of producing perfect seeds. Gaertner, a most able
and accurate observer of nature, controverts the
opinion of Hedwig, and contends that many of
the plants called Cryptogamous, instead of being
thus completely furnished with stamens and pistils,
are either defective in some part of their sexual ap-
paratus, so as not to exhibit the male and female
organs distinct; or are destitute of a sexual ap-
paratus altogether, and propagated not by seeds,
but by gems. In the former class he ranks the
Ferns, Mosses, and Fuci, discarding the alleged
stamens of Hedwig and others altogether, and con-
tending that the ovary is also the organ of fecun-
dation, absorbing and elaborating a mucous sub-
stance with which it is found to be surrounded,
particularly in the Fuci, and thus effecting its fe-
cundation, as in the Aphrodites of Adanson.* But

* Famil. dcs Plantcs, vol. i. p. 264.

SECT. IV. OBJECTIONS.

if the mucous substance is that by which impreg-
nation is effected, it is to all intents and purposes
a pollen, which in the case of the Fuel is neces-
sarily mucous as being suited to the nature of the
element in which the plant vegetates.* In the
latter class he ranks the Fungi, Confervce, and
Ulvce, contending that they are wholly without
seed as without sex, and propagated merely by
gems. But on the contrary, M. Correa De Serra
contends that they are in all respects similar to the
grains of the Fuci, and equally entitled to the ap-
pellation of seeds. So that if Gaertner has erred
on the one hand in denying the universality of the
sexes, and degrading the grains in question from
the rank of seeds, Hedwig has erred on the
other, in elevating a variety of substances, rather
too hastily, to the rank of stamens and pistils.

But if Gaertner's theory should even be un-AndGsert-
founded, it exhibits at least a' view of the compa- n<
rative perfection of plants as connected with the
perfection of their sexual apparatus, which should
not be omitted. When the species is propagated
by gems only, without seed, as in the lowest orders
of vegetable beings, no sexual organs are percepti-
ble. When the seed is inconspicuous and seemingly
nothing but an embryo, then the female organs
are perceptible but not the male organs, and the
plants are called Aphrodites. When the radicle

* M. Correa De Serra Fruct. of Submersed Algae,

350 IMPREGNATION OF THE SEED. CHAP* VII.

of the embryo, constituting a nucleus, is perceptible
in the seed, then also the pollen appears, but the
flower has no beauty. And when the embryo is
found no longer constituting a mere nucleus, but
surrounded with its cotyledons, then there is to be
seen both the apparatus of flower and of sexual
organs. The first class includes plants without
sex, the Conferva, Ulv<z, Fungi. The second
class includes the Approdites, the Filices, Musci,
Fuel. The third class includes what are called
ambiguous plants, such as Zostera, Zamia, Cycas.
And the fourth class includes all plants whatever
with conspicuous flowers. This gradation, if not
true, is at least beautiful ; and will perhaps be ad-
mitted to be also useful ; from which we may infer
the truth of the observation — that even the very
errors of a great mind are edifying.

CHAPTER VII.

OF THE IMPREGNATION OF THE SEED.

ADMITTING that the stamens and pistils are the
male and female organs of vegetable generation,
and that the pollen is the substance by which the
impregnation of the seed is eiFected, how is it
conveyed to the ovary ? and what is the amount
of its action ?

SECT. I. ACCESS OF THE POLLEN. 351

SECTION I.

Access of the Pollen.
WHEN the stamens and pistils are situated near By the

each other, as in the case whether of Hermaphro- °

dite or Monoecious flowers, the elastic spring with
which the anther flies open will generally be suffi-
cient to disperse the pollen, so as that part of it
must infallibly reach the stigma. The facilities
tending to ensure the access of the pollen as re-
sulting from the relative proportion, situation, and
mutual sympathies of the stamens and pistils have
been already noticed ; as well as the possible action
of winds wafting the pollen to a distance, and
hence including the case of Dioecious plants also.
But with all the above facilities the impregnation
of the seed would still in many cases be impracti-
cable even in Hermaphrodite flowers, without
further aid ; particularly in such as do not perfect
their stamens and pistils at the same time. For
although the action of the wind cannot but be
efficacious in some such cases ; yet it will, in some
others, naturally give to the flower a direction cal-
culated rather to prevent than to aid the access of
the pollen, by causing the corolla to veer round like
a vane according to the quarter from which it may
happen to blow ; or the very figure of the corolla
may operate as a bar to the entrance of the pollen

352 IMPREGNATION OF THE SEED. CHAP. VII,

which must be surmounted by extraordinary
means.

Or insects What then are the means instituted by nature for
byThe6 effecting the impregnation of Hermaphrodites so
nectar. circumstanced ? The true reply to this inquiry
seems to have been first suggested by Koelreuter,
namely, the agency of insects ; and has been since
confirmed by the more leisurely observations of
Spregnel, who found that the pollen in the above
case is very generally conveyed from the anther to
the stigma through the instrumentality of Bees,
though sometimes through that of insects peculiar
to a species. The object of the insect is the dis-
covery of honey, in quest of which, whilst it roves
from flower to flower and rummages the recesses of
the corolla, it unintentionally covers its body with
pollen, which it conveys to the next flower it visits,
and brushes off as it acquired it by rummaging for
honey; so that part of it is almost unavoidably
deposited on the stigma, and impregnation thus
effected. Nor is this altogether so much a work of
random as it at first appears. For it has been ob-
served that «ven insects, which do not upon the
whole confine themselves to one species of flower,
will yet very often remain during the whole day
upon the species they happen first to alight on in
the morning. And their agency is also completely
secured, from the necessity they are under of pro-
curing food ; though nature in her care for the im-
pregnation of the vegetable has not only lodged a

7

SECT. I. ACCESS OF THE POLLEN. 353

honey in the flower to tempt the taste of insects,
but seems to have furnished also the means of at-
tracting even the eye. This is thought to be done Or colour,
by mean* of the coloured spots with which many
flowers secreting a honied fluid are marked, which
Spregnel calls macula indicantes, as indicating the
treasure that is contained in the flower, and thus
attracting the attention of the insect. But the
very figure of the flower seems often intended to
produce the same effect. Spregnel has enumerated Or figure
several hundreds of flowers which in their figure as flower,
well as colour resemble insects, and hence attract
the notice of the plunderers of their honied stores.
The beautiful example of the Bee Orchis is known
to almost every body.

Such then are the means by which the notice of InHerma-
the insect is attracted ; and such also is the struc- p J
ture of the internal parts of the flower, that it must
of necessity pass across the stamens and pistils in
procuring the honey it is in quest of, which passage
is often a work of considerable difficulty, particu-
larly when the tubular part of the corolla is beset
with hairs, as in many flowers of the class Pentan-
drla arid Didynamia. But one of the most difficult
and singular cases of Hermaphrodite impregnation
as aided by the agency of insects is that of the
Aristolochia Clematitis. The corolla of this flower,
tvhich is tubular, but terminating upwards in a
ligulate limb, is inflated into a globular figure at
the base. The tubular part is internally beset with

VOL. II. 2 A

354 IMPREGNATION OF THE SEED. CHAP. VII.

stiff hairs pointing downwards. The globular part
contains the pistil, which consists merely of a
germen and stigma together with the surrounding
stamens. But the stamens being shorter than even
the germen, cannot discharge the pollen so as to
throw it upon the stigma, as the flower stands
always upright, till after impregnation. And hence
without some additional and peculiar aid the pollen
must necessarily fall down to the bottom of the
flower. Now the aid that nature has furnished in
this case is that of the agency of the Tipula penni-
cornis, a small insect, which, entering the tube of
the corolla in quest of honey, descends to the
bottom and rummages about till it becomes quite
covered with pollen ; but not being able to force its
way out again owing to the downward position of
the hairs, which converge to a point like the wires
of a mouse-trap, and being somewhat impatient of
its confinement, it brushes backwards and forwards
trying every corner till after repeatedly traversing
the stigma it covers it with pollen sufficient for its
impregnation ; in consequence of which the flower
soon begins to droop, and the hairs to shrink to the
side of the tube, effecting an easy passage for the
escape of the insect.*

In monoe- Monoecious plants are, according to Spregnel,

mostly impregnated by insects also, excepting such

as are destitute of nectaries. But many of them

do not require that aid, in which case the male arid

* Wilklcnow, p. 317.

SECT. I. ACCESS OF THE POLLEN. 855

female flowers stand close together, as in Typha,
Coix, Carex ; the females being lowest, and their
petals being deeply or minutely laciniated so as not
to interrupt the pollen in its fall, as in the genus
Pinns.

The impregnation of Dioecious plants is often And dice-
effected by insects also, as has been already see
in the case of the Fig, and their flowers are said
to be always furnished with nectaries ; the male
flowers being larger than the female flowers, that the
insect, as it has been thought, may have the better
opportunity of loading itself with pollen.*

From the fact of the agency of insects in con-
veying the pollen to the stigma it will follow that
no plant requiring such aid can possibly perfect its
seed unless the specific insect has access to it, or
unless some such aid is given to it by the cultivator.
And hence botanists attribute the imperfection of
the seeds of hot-house plants to the want of the
insect by which the species may be impregnated
in its native climate. This conjecture is counte-
nanced by the following experiment, as related by
Willdenow : — A plant of Abroma august a had
flowered for many years in a hot-house at Berlin
without producing any fruit; but when the gardener
by means of a hair pencil placed a little of the
pollen upon the stigma of several of the flowers,
perfect fruit was produced from which new plants
were raised.

* Willdenow, p. 3QQ.
2 A 2

IMPREGNATION OF THE SEED, CHAP. VII.

Passage of But admitting that the pollen is conveyed to the
through stigma by the means above stated, how is it thence
the style. conductec| to the ovary ? It was at one time gene-
rally supposed that the pollen is conducted from
the stigma to the ovary by means of a longitudinal
canal perforating the style. This canal is distin-
guishable in many of the liliaceous plants in which
it seems indeed to constitute the passage of the
pollen particularly from the phenomenon of the
Amaryllis formosissima, the fluid exuding from
the stigma of which returns again through the per-
foration of the style tinged with yellow, the colour
of the pollen. But the existence of the canal in
question, though distinguishable in the Amaryllis
formosissima, and other liliaceous plants, cannot
be admitted as a universal property of the style, at
least it cannot be detected. And if it is so very
fine as to escape all observation, then it could not
admit the particles of pollen, which are in some
cases comparatively large, as in Marvel of Peru ; the
pollen of which exceeds the style itself in diameter,
and could not consequently be admitted by a cen-
tral canal.

But in order to effect the impregnation of the
seed it is not necessary that the particles of pollen
should enter the style entire. The finer part of
their contents is sufficient, and is indeed the only
effective part in the act of fecundation : so that
whether we regard it as a subtle and elastic vapour
with Grew, and Adanson ; or merely as an oily

. I. ACCESS OF THE POLLEN. f$f

and gelatinous fluid exuding or exploding from the
globule ; still it will admit of being conducted
through the channel of the tubes of the style, al-
though no central canal should exist in it.

But another question has also arisen out of the Quantity
subject with regard to the quantity of pollen neces- necessary,
sary to effect impregnation. Adanson was of opi-
nion that the smallest possible particle, if conveyed
to the ovary is sufficient. But this opinion is sup-
ported by no proof, and is even contradicted by later
observation ; the merit of having ascertained the
fact seems due to Koelreuter, whose experiments
are decisive of the question. The globules of
pollen contained in all the anthers of an individual
flower of Hibiscus syriacus, were 4803, of which
5O or 60 at least were necessary to effect a complete
impregnation. For when the attempt was made
with a smaller number the seeds were not all
ripened, though those that were ripened were per-
fect. Ten globules were the least by which the
impregnation even of a single seed could be effected
in this plant.* But in the Mirabilis Jalappa and
longiflora, the flowers of which contained about
30O globules of pollen, two or three were found
sufficient for impregnation, as the seed was not im-
proved by the application of more. It was also
found that the impregnation of flowers having two
or more styles was completely effected, even when

* Willdenow, p. 323.
5

358 IMPREGNATION OF THE SEED. CHAP. VII.

the pollen was applied but to one of them ; which
shows that there is a communication between all
the styles, and consequently between all the
germens.

SECTION II.
Agency of the Pollen.

ADMITTING that the pollen is conducted to the
ovary through the channel of the tubes of the style,
how after all is the ovary fecundated ; or the seed
rendered fertile ? On this subject naturalists have
been much divided ; and according to their several
opinions have been classed under the respective ap-
pellations of ovaristfc, animalculists, and epigene-
sists.

SUBSECTION I.

Theory of the Ovarist. — According to the opi-
nion of the first class, the embryo pre-exists in the
ovary, and is fecundated by the agency of the
pollen as transmitted to it through the style. This
As main- seems to have been the opinion of Grew, who says
Grew, y expressly in his Anatomy of Plants, that when the
summits of the stamens open, and the pollen is
discharged upon the pistil, some subtile and vivifying
effluvium escapes ; which, descending through the
medium of the style, impregnates the embryo.
Bonnet and Haller seem to have been of the' same

SECT. II. AGENCY OF THE POLLEN. 3p0

opinion also, as well as many other eminent natu-
ralists. But the most convincing evidence in sup-
port of the opinion of the ovarists is that which has
been produced by Spallanzani, as founded on aSpallan-
series of observations on the flowers of the Spartium™
junceum. This plant was chosen on account of its
producing at the same time flowers in all the dif-
ferent stages of progress. His first observations
were made upon flower buds not yet expanded:
they seemed to form a compact and solid body;
but upon being dexterously opened, the petals,
which were yet green, were with some difficulty
discovered, then the stamens, and then the pistil.
The powder of the anthers was even perceived im-
bedded in a glutinous substance ; when the pistil
was freed from the surrounding integuments, and
attentively viewed with a good glass, the pod was also
discovered of about 1TV line in length. Several pro-
tuberances were seen upon its sides; which, upon
opening it longitudinally, were found to be occasioned
by the seeds, which though but small globules were
already discoverable, arranged in their natural order,
and attached by filaments to the interior of the Pod.
Upon dissection, they did not exhibit any appear-
ance of the several parts and membranes into which
the mature seed may be divided ; but a spongy,
homogenous mass. Flowers in the same state of
forwardness were not fully expanded till twenty
days after. On dissecting buds of a larger size the
petals were found to be somewhat yellowish and

30O IMPREGNATION OF THE SEED. CHAP. VII.

less compact ; and the powder of the anthers was
thrown out by the slightest agitation ; but the
lobes and plantlet were not yet perceptible in the
seeds.

On the eleventh day after the flowers had fallen,
that is, after impregnation had taken place, the
seeds which were formerly globular began to as-
sume the figure of an heart, attached to the pod by
the basis, and exhibiting the appearance of a white
point towards the apex. And when the heart was
cut open longitudinally, the white point proved to
be a small cavity enclosing a drop of liquid.

On the twenty-fifth day after the flowers had
fallen, the cavity was much enlarged towards the
base ; but was still full of the liquid, in the midst
of which there appeared a small and semi-transpa-
rent body, of a yellowish colour and gelatinous
consistence, fixed by its two extremities to the op-
posite sides of the cavity.

Jn a month after the flower had fallen, the heart-
shaped seeds became kidney-shaped.

In forty days after the flower had fallen, the
cavity was quite filled up with the body that had
been generated within it; and which was now
found to consist of a thin and tender membrane en-
velopjng the two seed-lobes, between which the
plantlet attached to the lower extremity was also
perceptible. And hence the seed was now visibly
complete in all its parts.

From these and a variety of other observations

SECT. II. AGENCY OF THE POLLEN. 36 L

on a variety of other species, all of which exhibited
similar appearances in the generation of the seed,
Spalknzani concludes that the seeds pre-exist in the
ovary before the access of the pollen, by which
they are merely rendered fertile ; and contends that
the embryo, though not previously perceptible, may
yet previously exist.*

The theory of the ovarists is supported also by Gaertaer*
Gsertner, who describes the vegetable egg as pre-
existing in the ovary, where, furnished with its
proper integuments, it waits the fecundating in-
fluence of the pollen which is necessary to its com-
plete developement ; so that it requires in fact the
exertion of two distinct energies to bring it to per-
fection, the vital principle, and the seminal ; the
former generating and organizing the different parts
of which the egg consists in common with the
other parts of the plant ; and the latter communi-
cating to the egg thus formed a distinct vegetable
life.f

SUBSECTION II.

Theory of the Animalculist. — But the theory of
the ovarists is not without its difficulties ; for as the
embryo is never found to make its appearance till
after fecundation, it has been thought that it must
necessarily pre-exist in the pollen of the anther ;
from which it is conveyed to the ovary through the

* Spal. Dissert, vol. iii. chap. i. Eng, Trans.
f Gcert. Jntrod,

362 IMPREGNATION OF THE SEED. CHAP. VII.

As origi- medium of the style, and afterwards matured. This
the^pecu- theory was founded upon that of Leuwenhoeck,
Leuwenf w^ rcSar^ to annua^ generation ; which supposes
hoeck, the pre-existence of animalcula in the seminal prin-
ciple of the male ; the animalcula being conveyed
in coitu to the ovary of the female where alone
they are capable of developement.* Hence it has
And been denominated the theory of the animalculists,
b/Jvior- and transferred to the case of vegetables by Mor-
land. jand, Needham, Gleichen, and others, who regard
the pollen as being a congeries of seminal plants,
one of which at least must be conveyed to the
ovary entire before it can become prolific.

But if the embryo pre-exists in the pollen may
it not be detected by inspection before impregnation
takes place ? Spallanzani examined the pollen in
its ripe and perfect state, with great care, and
under glasses of the highest magnifying powers,
but could distinguish nothing exhibiting the ap-
pearance of an embryo. It may be said, however,
that the embryo must still be supposed to pre-exist
in the pollen, though not visible, as Spallanzani has
said of its pre-existence in the ovary ; and that its
invisibility is no proof of its non-existence. The
animalculists have no doubt a right to offer this
reply ; but as the embryo is not visible whether in
the ovary or pollen, till after fecundation has taken
place, no conclusion can be drawn on either side
from the circumstance of its invisibility.
* Phil. Trans. No. 145, p. 74.

SECT. II. AGENCY OF THE POLLEN. 303

But admitting that the invisibility of the embryo
is no proof of its non-existence in the pollen, the
total want of a passage, in most styles, fit to con-
duct the particles of pollen entire, exposes this
theory to the most serious objections, if it does not
rather render the alleged mode of impregnation al-
together impracticable. And if a passage of suf-
ficient width were found to exist even in all styles,
still the probabilities of the two cases are in favour
of the ovarist. For if the embryo is to pre-exist
at all, is it not more likely that it should pre-exist
in the ovary where it is to be brought to maturity ;
than that it should first be generated in one organ
or plant, and then transferred to another to be deve-
loped ? Is it not also most extraordinary that the
embryo should so invariably assume the same po-
sition in the same species of seed,, if it is merely
conducted to the ovary from a different organ or
plant, and introduced as it were at random ? And
is not the doctrine of the ovarist countenanced from
the analogy of the process for which he contends
to that of the generation of the animal egg, which
is produced complete in all its integral and distinct
parts even without the co-operation of the male,
though still destitute of the principle of fertility ?
And finally is it not further countenanced from the
fact of the apparent and numerical perfection of
parts often observable in the fruit of insulated
female plants, in which the embryo is not always
wanting, but only not fecundated? For which

2

304 IMPREGNATION OF THE SEED. CHAF. VII.

reasons the theory of the ovarist seems to me to be
much more consonant to truth than that of the
animalculist.

SUBSECTION in.

Theory of the Epigenisist. — But the difficulties
inseparable from both theories, together with the
phenomenon of hybrid productions, have given
rise also to a third ; this is the theory of the epige-
nisists, who maintain that the embryo pre-exists
neither in the ovary nor pollen, but is generated by
the union of the fecundating principles of the male
and female organs ; the former being the fluid is-
suing from the pollen when it explodes ; and the
latter, the fluid that exudes from the surface of the
Asde- stigma when mature. As applicable to the case of
plants? tnis theory has been stoutly defended by
Koelreuter, who adduces in support of it a variety
of experiments instituted with a view to ascertain
the fact by means of impregnating the ovary of
one species with pollen taken from another, in
which cases the plant obtained from the seed uni-
formly exhibited a combination of the characters
of both species. The following is a most promi-
nent example, being the result of his experiments
on Nicotiana rusiica and paniculata ; the former
having egg-shaped leaves, with a short and yellow
corolla approaching to green ; and the latter having
roundish or cordate leaves, with a green corolla
approaching to yellow, and a stem longer by onfc

SECT. II. AGENCY OF THE POLLEN. 365

half. A flower of the former species was accord-
ingly deprived of all its stamens, and fecundated
with pollen from a plant of the same species. The
plant raised from the seed thus obtained was an
hybrid, exhibiting in all its parts an intermediate
character betwixt the two species from which it
sprang. The stamens of this hybrid, as well as
of all others he ever raised, were imperfect ; but
when its pistils were impregnated with pollen from
the paniculata as before, the new hybrid obtained
from the seeds now produced was more like a pa-
niculata than formerly ; and when the experiment
was continued through several successive gene-
rations, it was at last converted into a perfect pa-
nkulata.*

This is thought to be an infallible demonstration
of the truth of the doctrine of the epigenisists.
But why may not the pollen of one species of plant
be allowed to produce some particular change upon
the developement of the embryo of another species,
although that embryo should be supposed to have
pre-existed in the ovary ? The action of the pollen
thus introduced must amount to something; and
it is just as difficult to conceive how an individual
whether proper or hybrid should be generated from
the union of the seminal principles of two plants
of the same or of a different species, as from the
peculiar effect of the pollen of the same or of a
different species, upon an embryo already existing^
* Willdenow, p, 323.

366 IMPREGNATION OF THE SEED. t'HAP. VII.

But the doctrine is yet liable to a much more se-
rious objection ; for if the seed is generated from
the union of two fecundating principles which form
an intermediate offspring, then female plants of the
class Dicecia ought occasionally to produce seeds
whose offspring shall be Hermaphrodite^ or at least
Monoecious, which was never yet known to happen.

SECTION III.
Hybrids.

Asiilus- ALTHOUGH the arguments of the epigenisists are
STexpe- by no means satisfactory, yet it cannot be denied
Bradlfey ° ^at hybrid productions partake of the properties
and Mr. fc^ of faQ male an(J female from which they

Knight,

spring. This was long ago proved to be the fact
by Bradley,* and more recently confirmed by the
experiments of Mr. Knight; as well as happily
converted to the advantage of the cultivator. Ob-
serving that farmers who rear cattle improve the
progeny by means of crossing the breed, he pre-
sumed from analogy that the same improvement
might be introduced into vegetables. His prin-
cipal object was that of procuring new and im-
proved varieties of the Apple and Pear to supply
the place of such as had become diseased and im-
productive, by being cultivated beyond the period

* New Impr. of Plant, and Garden. Lond. 1717.

SECT. III. HYBRIDS.

which nature seems to have assigned to their per-
fection. But as the necessary slowness of all ex-
periments of the kind, with regard to the fruit in
question, did not keep pace with the ardour of his
desire to obtain information on the subject, he was
induced to institute some tentative experiments
upon the common Pea, a plant well suited to his
purpose, both from its quickness of growth, and
from the many varieties in form, size, and colour,
which it afforded. In 17§7> a degenerate sort of
Pea was growing in his garden which had not re-
covered its former vigour even when removed to a
better soil. Being thus a good subject of expe-
riment, the male organs of a dozen of its immature
blossoms were destroyed, and the female organs
left entire. When the blossoms had attained their
mature state, the pollen of a very large and luxu-
riant grey Pea was introduced into the one half
of them, but not into the other. The pods of
both grew equally ; but the seeds of the half that
were nnimpregnated withered away, without having
augmented beyond the size to which they had at-
tained before the blossoms expanded. The seeds
of the other half were augmented and matured as
in the ordinary process of impregnation ; and ex-
hibited no perceptible difference from those of
other plants of the same variety, perhaps, because
the external covering of the seed was furnished en-
tirely by the female. But when they were made
to vegetate in the succeeding spring the effect of the

3fl8 IMPREGNATION OF THE SEED. CHAP. VII.

experiment was obvious. The plants rose with
great luxuriance, indicating in their stem, leaves,
and fruit, the influence of this artificial impreg-
nation ; the seeds produced were of a dark grey,
By impregnating the flowers of this variety with
the pollen of others, the colour was agairi changed,
and new varieties obtained superior in every respect
to the original on which the experiment was first
made, and attaining, in some cases, to a height of
more than twelve feet. In these experiments it
was observed that the plant had a stronger tendency
to produce coloured blossoms and seeds than white
ones. For when the pollen of a coloured blossom
was introduced into a white one, the whole of the
future seeds were coloured. But when the pollen of
a white blossom was introduced into a coloured
one, the whole of the future seeds were not
white. *
Superfc. Mr. Knight thinks his experiments on this sub-

tation.

ject afford examples of superfetation, a phenomenon
the existence of which has been admitted amongst
animals, but of which the proof amongst vegetables
is not yet quite satisfactory. Of one species of
superfetatiou Mr. Knight has certainly produced
examples ; that is, when, by impregnating a white
Pea blossom with the pollen both of a white and
grey Pea, white and grey seeds were obtained,
But of the other species of superfetation in which
one seed is supposed to be the joint issue of two
* Phil. Trans.

&ECT. 111= HYBRIDS. 30Q

males, the example is not quite satisfactory. Such
a production is perhaps possible, and further expe-
riments may probably ascertain the fact^ but it
seems to be a matter of mere curiosity, and not
apparently connected with any views of utility.
But the utility of the experiments, in as far as they
show the practicability of improving the species, is
very obvious. And the ameliorating effect is the
same whether by the male or female ; as was ascer-
tained by impregnating the largest and most luxu-
riant plants with the pollen of the most diminutive
and dwarfish, or the contrary. By which means
any number of varieties rnay be obtained, accord-
ing to the will of the experimenter, amongst whiqh
some will no doubt be suited to all soils and situ-
ations. Mr. Knight's experiments of this kind
were extended also to wheat ; but not with equal
success. For though some very good varieties
were obtained, yet they were found not to be per-
manent.

But the success of his experiments on the Apple- Improve-
tree were equal to his hopes. This was indeed his fruits.
principal object, and no means of obtaining a suc-
cessful issue were left untried. The plants which
were obtained in this case were found to possess the
good qualities of both of the varieties employed,
uniting the greatest health and luxuriance, with
the finest and best flavoured1 fruit.*

* Phil. Trans. 17.0J.J.
VOL. II. 2 B

37O IMPREGNATION OF THE SEED. CHAP. VII.

Many experiments of a similar nature were tried
on other plants also ; from which it appeared that
improved varieties of every fruit and esculent plant
may be obtained by means of artificial impregna-
tion, as they were obtained in the cases already
stated. Whence Mr. Knight thinks that this pro-
miscuous impregnation of species has been intended
by nature to take place, and that it does in fact
often take place, for the purpose of correcting
such accidental varieties as arise from seed, and of
confining them within narrower limits. All which
is thought to be countenanced from the considera-
tion of the variety of methods which nature em-
ploys to disperse the pollen, whether by the elastic
spring of the anthers, the aid of the winds, or the
instrumentality of insects.

But although he admits the existence of vegetable
hybrids, that is, of varieties obtained from the in-
termixture of different species of the same genus,
yet he does not admit the existence of vegetable
mules, that is of varieties obtained from the inter-
mixture of the species of different genera ; in at-
tempting to obtain which he could never succeed,
in spite of all his efforts. Hence he suspects that
where such varieties have been supposed to take
place, the former must have been mistaken for the
latter. It may be said, indeed, that if the case
exists in the animal kingdom, why not in the ve-
getable kingdom ? to which it is perhaps difficult to

SECT. I. EXTERNAL CHANGES* 3?1

give a satisfactory reply. But from the narrow
limits within which this intercourse is in all cases
circumscribed, it scarcely seems to have been the
intention of nature that it should succeed even
among animals.

CHAPTER VIII.

OF THE CHANGES CONSEQUENT UPON IMPREGNATION.

WHATEVER may be thought of the different
opinons of the ovarist, animalculist, and epigenesist,
and whichsoever of them may be adopted by the
phytological inquirer, it is at all events an object of
the first importance to trace out the peculiar changes
consequent upon impregnation, as effected, whether
in the flowers or fruit.

SECTION I.

External Changes,

AT the period of the impregnation of the ovary t)ecay of
the flower has attained to its ultimate stage of per-
fection, and displayed its utmost beauty of colouring
and richness of perfume. But as it is now no
longer wanted, so it is no longer provided for in the
economy of vegetation. Its period of decline has

CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII,

commenced ; as is indicated first by the decay of the
stamens, then of the petals, and then of the calyx,
which wither and shrink up, and finally detach
themselves from the fruit altogether, except in some
particular cases in which one or other of them be-
comes permanent and falls only with the fruit. The
stigma exhibits also similar symptoms of decay and
the style itself often perishes. The parts contigu-
ous to the flower, such as the bractes and floral
leaves, are sometimes also affected ; and finally the
whole plant, at least in the case of annuals, begins
to exhibit indications of decay. But while the
Augmen- flower withers and falls, the ovary is advancing to
th£nva°ry. perfection, swelling and augmenting in size, and re-
ceiving now all the nutriment by which the decayed
parts were formerly supported. Its colour begins
to assume a deeper and richer tinge ; its figure is
also often altered, and new parts are even occasion-
ally added — wings, crests, prickles, hooks, bloom,
down. The common receptacle of the fruit under-
goes also similar changes, becoming sometimes large
and succulent, as in the Fig and Strawberry ; and
sometimes juiceless arid indurated, as in compound
flowers. Such are the external changes consequent
upon impregnation as effecting the flower and fruit,

SECT. II. INTERNAL CHANGES. 3?3

i
SECTION II.

Internal Changes.
If the ovary is cut open as soon as it is first dis- Ovary di-

. , visible into

coverable m the flower, it presents to the eye merely distinct
a pulpy and homogeneous mass. But if it is al- or§an*
lowed to remain till immediately before the period
of its impregnation, it will now be found to be di-
visible into several distinct parts, exhibiting an ap-
paratus of cells, valves, and membranes, constituting
the pericarp, and sometimes the external coats of
the seed. In this case the umbilical cord is also to
be distinguished ; but the embryo is not yet visible.
These changes therefore are to be attributed merely
to the operation of the ordinary laws of vegetable
developement, and are not at all dependant upon
impregnation.

But impregnation has no sooner taken place than Umbilical
its influence begins to be visible ; the umbilical cord, cc
which was formerly short and distended, is now
generally converted into a long and slender thread.
Sometimes the position of the seed is altered. Before
impregnation the seeds of Caryophyllus aromaticus
and Metrosideros gummifera are horizontal ; after
impregnation they become vertical. Before im-
pregnation the seeds of Magnolia are erect ; after
impregnation they become inverted and pendulous,*

* Gaert. De Seminibus.

374 CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII.

Position The figure of the seed is often also altered in pass-

oftheseed. f •. •• i

ing from its young to its mature state; changing

from smooth to angular, from tapering to oval, from
oval to round, and from round to kidney-shaped.
But all seeds are not brought to maturity of which
the rudiments may exist in the ovary. Lagcecia
and Hasselquestia produce uniformly the rudiments
of two seeds, of which they mature but one.*

But the principal changes resulting from im-
pregnation are operated in the seed itself, which,
though previously a homogeneous and gelatinous
mass, is now converted into an organized body, com*
posed of different membranes enveloping,, or en-
veloped by, one another,

The testa. The Testa, which is the external coat of the seed,
is formed from the original cuticle of the nucleus,
and augmented by means of the juices conveyed to
it through the umbilical cord. Hence it is some-
times formed, but never capable of being detached
from the mass of the nucleus, previous to fecunda-
tion ; after which it is easily, though not spontane-
ously separated, till the maturity of the fruit.

Subtesta. The Subtestci, which is the inner coat of the seed
and lies immediately under the testa, originates in
the interior vessels of the umbilical cord, which are
prolonged in a multiplicity of ramifications through-
out the whole membrane, is soft and pulpy till the
embryo is matured; as the juices by which the embryo
is nourished pass through it. It is seldom distin-

* Gaert, De Seminibus.

SECT. II. INTERNAL CHANGES.

guishable before impregnation ; but when the
seed is ripe it is easily detached from the interior
parts, though not always easily from the testa.

With these two integuments the enclosed nucleus
of the seed is in its young state almost always fur-
nished, and is generally found to consist of the four
following parts : — the Chorion, the Amnios, the
Sacculus colliquamenti, and the Embryo; all, ex-
cept the chorion, being the uniform product of fe-
cundation, and all, except the embryo, often dis-
appearing in the mature state of the seed.

The Chorion, so named by Malpighi,* is the soft The cho»
and pulpy substance of the primitive nucleus of
the seed, forming at first its principalAmass ; but
finally disappearing and leaving no trace of its ex-
istence behind, being gradually converted into the
nourishment of the other parts.

The Amnios is a clear and transparent fluid, the The am-
product of fecundation, sometimes thin and some-
times gelatinous, generated and contained within
the chorion, but at last absorbed by the embryo, or
converted into a solid substance called the albumen.

The Sacculus colliquamenti is a thin, white, and The sac-
pellucid membrane, originating in the vessels of the

internal umbilical cord, and being a proper integu-
ment with which the amnios is sometimes invested,

Last of all the Embryo is produced, the principal The em?
object of fecundation, and end of all the genital
apparatus occupying the centre of the nucleus, but
* Opera Omnia, p. 7 1 •

376 CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII.

appearing first in that region where the umbilical
vessels perforate the internal membrane, and where
the sacculus colliquamenti originates ; not where
the umbilical cord enters the testa. Its first for-
mation eludes the search of the keenest eye aided
by the best glasses. But, by and by, as it aug-
ments in size and solidity, it becomes at length
visible, in some plants sooner and in others later,
after impregnation. In Hdianthus it is perceptible
on the third day after impregnation, but in Colchi-
cum not till after several months. Its figure is at
first globular, its contexture pulpy, and its colour
white. It swims in the liquor amnii, from which it
derives its nourishment, seemingly unconnected
with either the seed or plant ; but immersing itself
deeper and deeper every day, and always in such a
position as to turn the radicle towards the exterior
of the seed, and the opposite extremity towards the
centre ; which extremity divides itself into lobes
called cotyledons, through which the nourishment
of the plantlet passes, or in which it is elabo-
rated. At length the chorion is exhausted, and the
amnios absorbed or converted into albumen^ and the
embryo with its integuments transformed into a per-
fect seed.
Fecunda- Such are the phenomena, according to the de-

tion spuri- . . .

ous or in- scnption or Gaertner,* accompanying or following
the impregnation of all flowers producing seeds,
except where the fecundation is spurious or incom-

* De Seaninibus. Jntrod,

SECT. III. SPECIFIC EXAMPLES. 377

plete. The fecundation is spurious when the ovary
swells but exhibits no traces of perfect seed within.
This often happens in the case of plants producing
berries, as in that of the Vine and Tamus. It is in-
complete when barren and fertile seeds are inter-
mingled together in the same ovary. This proceeds
from some defect either in the quantity or quality
of the pollen ; but rather in the quality, as it is not
always plants having the most pollen that produce
the most seeds. The two stamens of the Orchidea
fecundate 800O seeds, and the five stamens of
Tobacco fecundate QOO : while the 50 stamens of
Barringtonia, the 230 of Thea, and the 80 of the
Caryophylli, fecundate only two or three ovaries.

SECTION III.

Specific Examples.

As the exhibition of specific examples is always
the most edifying, as well as generally the most
pleasing, mode of instruction, I shall subjoin the
following observations upon the changes succeeding
impregnation in the seed and fruit of several of our
most common plants ; that the reader may have it
in his power to refer to the individual case, if he is
inclined to repeat the observation.

378 CHANGES SUCCEEDING IMPREGNATION. CHAP. V11I.

SUBSECTION I.

The Cherry.— On the 4th of May 1808, the first
blossoms of a Cherry-tree had just expanded. The
ovary was externally egg-shaped and smooth, but
marked with a longitudinal ridge on the side to
which the pistil bends ; internally it was a pulpy
and homogeneous mass, not yet exhibiting any
traces of organization.

On the 8th, a cavity was discoverable in the cen-
tre of the ovary by means of a longitudinal section,
occupied by two small vesicles, containing a trans-
parent and jelly-like substance.

On the 12th, one of the vesicles had begun to
exhibit symptoms of decay. The other had in-
creased considerably, and formed now the nucleus of
the seed.

On the ] 6th, the petals were now falling, and the
stamens withering away after having discharged
their pollen ; but the pistil was yet pretty entire, and
the ovary was about one fourth of an inch in length.
The external part or pericarp, which was still green
and pulpy, contained in its cavity the nucleus of the
future seed, of a white and gelatinous appearance,
considerably increased, together with the shrunk
vesicle lying between the nucleus and pericarp. The
tubes and spiral vessels, forming the umbilical cord
and conducting the sap from the fruit-stalk to the
nucleus, were seen by the assistance of a microscope

SECT. III. SPECIFIC EXAMPLES.

upon the longitudinal section of the ovary. The
nucleus was not easily separated from the pericarp
without injuring it, but its surface was seen to con-
sist of a net-work of fibres, being the ramifications,
no doubt, of the umbilical cord.

On the 17th, the nucleus was found to be separa-
ble from the pericarp. Its form was egg-shaped,
its colour was white, and its surface was marked
with a scar towards the upper extremity where it
had been detached from the umbilical cord. Upon
dissection it was still found to consist of a net-like
cuticle, and a pulpy, colourless, and transparent
mass contained within it. The cuticle is no doubt
the testa of Gsertner, or secundina exterior of Mai-
pighi, and the contained substance the chorion.

On the J 8th, there began to be formed on the inner
surface of the pericarp a sort of fibrous substance,
or rather a net-like plexus of fibres immediately in-
vesting the nucleus. This was the commencement
of the formation of the pyrena. The cup, stamens,
and pistil, had now fallen.

On the IQth, the pyrena had acquired a consider-
able degree of compactness, and was in some indivi-
duals distinguishable from the rest of the parts on the
horizontal section, which now exhibited four dis-
tinct and concentric circles ; the first and interior
circle being the line bounding the gelatinous mass
of the chorlon which occupied the centre ; the
second being the coats of the nucleus^ which were

379

38Q CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII.

now easily separated from the chorion ; the third
being the pyrena; and the fourth being the pulpy
pericarp.

On the 20th, the four concentric circles of the
transverse section were still distinctly visible, but less
easily separated.

On the 22d, the longitudinal section exhibited
similar appearances, but no traces of the amnios or
embryo were yet perceptible.

On the 24 th, the parts were considerably enlarged,
but still soft and pulpy. The two middle circles
were the firmest ; but it was now more difficult to
detach the envelope of the nucleus from the in-
terior mass.

On the 1 st of June, the exterior pulp was con-
siderably augmented in size, and the pyrena, in
some individuals, pretty hard. JThe sap vessels of
the foot-stalk were seen to enter the pyrena at the
lower extremity, and afterwards to emerge from its
interior surface rather above the middle, forming
the external umbilical cord and testa, or secundina
exterior of Malpighi, from the inner surface of
which they were again seen to emerge at the lower
extremity and to form the internal umbilical cord ;
which, entering the chorion at the base and passing
on in the direction of its longitudinal axis, termi-
nated ultimately in the sacculus colliquamenti and
amnios, now visible for the first time in the apex of
the chorion ; the sacculus being apparently a pro-

2

SECT. III. SPECIFIC EXAMPLES. 381

longation of the umbilical cord into the figure of an
inverted cone, as described by Malpighi.*

On the 2d, the induration of the pyrena was con-
siderably augmented ; and the sacculus colliqua-
menti and amnios, though not distinguishable on the
longitudinal or transverse section of the nucleus, were
yet separable from the chorion by means of a little
manipulation. The embryo was not yet perceptible.

On the 4th, the umbilical cord, or sacculus, ex-
tending throughout the length of the chorion, was
now visible on the longitudinal section for the first
time ; together with the embryo occupying the upper
region of the amnios, and measuring about the -j-i-g.
part of an inch. The seed lobes were perfectly dis-
tinct, resembling a pear cleft half way down from
the apex, but swelling a little where they unite, and
then terminating in a small point directed to the
circumference. This point was the radicle, which
began to assume a yellowish tinge immediately
upon being exposed to the air. The envelope of
the nucleus seemed as if about to separate into two
portions — the testa and subtesta, or exterior and
interior integuments of Gaertner.

On the 5th, the chorion was somewhat shrunk,
and the umbilical cord passing through it had as-
sumed a curvilinear position, as described by Mal-
pighi. The embryo measured about T1T inch.

On the 9th, the embryo measured about ~T inch,
but was flatter in its appearance than before. The
* Opera' Omnia. DC S'em. Gener,

3£2 CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII.

lobes had not yet separated at the top ; but the
umbilicus was less distinct.

On the 10th, the umbilicus was considerably
shrunk, and the plantlet now separable from the
cotyledons, measuring about -^of an inch in length.
The amnlos occupied about half the cavity of the
nucleus.

On the loth the chorion was much shrunk and
the cotyledons proportion ably enlarged. They were
now pouch-shaped, circular, but individually plano-
convex with the flat sides laid close together.

On the 20th, the fruit had begun to assume a
reddish hue, the embryo measured about TV of an inch
in length ; the amnlos being now much firmer than
before, and the chorion almost entirely absorbed.

On the 26th, the fruit was ripe ; and the embryo,
having exhausted the whole of the chorion and
amnios, was now complete, occupying the whole
extent of the cavity of its envelopes.

SUBSECTION n.

The Pea.— On the 4th of June, 1808, when the
legume of a flower fully expanded was opened, and
the nucleus of a seed cut asunder, it was found to
consist merely of a homogeneous mass of pulp,
measuring about ^ of an inch in diameter.

On the 8th, when a legume was opened of which
the petals had just fallen, a small speck was ap-
parent on the longitudinal section of the nucleus^

SECT. III. SPECIFIC EXAMPLES.

which proved to be a cavity generated in the centre,
the nucleus now measuring — of an inch. In some in-
dividuals two cavities were perceptible, the one cen-
tral, the other towards the circumference.

On the 10th, when the nucleus of a seed measur-
ing about TV of an inch in diameter was cut open, the
cavity, which was now considerably enlarged, was
found to be filled with a thin and transparent fluid.
This fluid was the amnios, but the embryo was not
yet perceptible.

On the 13th, when a legume was opened which
has acquired nearly its full length, and of which
the nucleus measured one fifth of an inch in diame-
ter, the embryo was perceptible floating in the upper
region of the amnios, and measuring ^V of an inch in
length ; the two lobes being expanded somewhat in
the shape of a horseshoe, but without any apparent
attachment to the sides of the cavity. The radi-
cle was not yet distinguishable, nor the plume-
^et ; but there was a protuberance in the cleft of the
lobes.

On the 1 5th, when the nucleus measured one-fourth
of an inch in diameter, the embryome&sured one-eighth.
It was still floating in the fluid, and still apparently
without any point of attachment to the exterior
portion of the nucleus. The lobes were much ex-
panded at the top, resembling individually the seg-
ments of an egg or pear bisected longitudinally, and
united by the small end. The additional cavity
observed on the eighth proves to be the section of

5

<884 CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII.

a perforation, which originating at the sear, and run-
ning a considerable way along the back of the seed,
seems to be the passage through which the nutri-
tious fluid is conveyed from the umbilicus into the
interior of the seed. If the radicle is not attached
to the testa at the extremity of this perforation, it
, is at least turned towards it.

On the 20th, when the nucleus was' still about one
fourth of an inch in diameter, and nearly globular, the
embryo occupied about one half the cavity. The
lobes were now approaching, and the radicle, with
its integument, was seen projecting in the form of a
conical protuberance from their point of union. The
plumelet was not yet visible.

On the 22d, when the nucleus measured about
one third of an inch, the cotyledons occupied al-
most the whole of the cavity. The lobes were nearly
united; and the radicle, with its integument which
projected about ^V of an inch in the form of a conical
protuberance, was curved in the line of the cir-
cumference of the lobes. The plumelet was now
also discernible, split into several divisions at the
top and lodged between the lobes, but forming a
sort of cavity in one of them of about ~ of an inch in
length.

On the 25th, when the seed had attained to its
full size, the lobes were completely united ; and the
embryo occupied the whole of the cavity of the
envelope ; the radicle measuring one eighth of an
inch, and the plumelet Tv»

SECT. III. SPECIFIC EXAMPLES. 385

SUBSECTION III.

Wheat.— On the 10th of June, 1808, when the
spike was yet wholly invested with the sheathing
part of the leaf, the anthers, which were closely in-
vested with a corolla, were yet green and pulpy, and
measured about ^ of an inch in length ; the filaments
were not quite so long. The nectaries measured
about T'T of an inch in length. The styles, which were
not yet expanded, formed by their union a sort of
cone upon the top of the ovary, and measured about
•jV °f an inch in length. The ovary, which was besides
crowned with a fine down, measured about -^ of an
inch in length. It had assumed something of its tur-
ban-shaped figure, and the convex and furrowed sides
were readily distinguishable. When cut open with
the knife it presented the appearance of a white and
pulpy mass, seemingly homogeneous ; but when in-
spected more minutely it was found to contain a
central globule of a looser texture and darker colour,
measuring about the -^ part of an inch in diame-
ter. This globule was the chorion of Malpighi.

On the 15th, when the spike was half extricated,
the anthers exhibited nearly the same appearance as
before ; but the filaments were now equal to them in
length. The nectaries were -jV of an inch in length,
plump and bulging at the base, and finely fringed
with down. The styles were somewhat expanded.
The ovary, which now measured about TV of an i

VOL. ii. 2 q

386 CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII,

was a white and fleshy mass, but slightly tinged
with green where it invests the contained globule,
which is now more viscid.

On the 2Oth, when the spike was completely ex-
tricated, the anthers were beginning to change to
yellow. They were now about one sixth of an inch in
length and the filaments twice as long. Some of
them had shed their pollen, of which thousands of
particles were found adhering to the expanding
styles. The nectaries were somewhat shrunk at the
base. The ovary exhibited more of green on the
inner surface. ' The enclosed globule or chorion was
as before.

On the 2Qth, when the pollen was shed and the
styles beginning to fade, the nectary scales were
much shrunk. The ovary, now ^ of an inch in
length, was thick and less fleshy in its contexture.
The green substance is a film lining its interior sur-
face. The enclosed globule somewhat enlarged.

On the 6th of July, when the ovary measured one
eighth of an inch and had assumed an oblong figure,
the green film was detachable from its inner surface,
seeming to be formed of an expansion of the umbi-
lical cord. The enclosed globule measured -^ of an
inch, and was now separable into an envelope and a
thin and colourless fluid, into which the jelly-like
substances of the former stages had been converted.
Perhaps this should now be called the amnios.

On the 10th, when the nectaries were now shrunk
into thin scales fringed with hairs, the ovary

SECT. III. SPECIFIC EXAMPLES. :387

measued about one fifth of an inch, and was also much
shrunk ; being now instead of a thick and fleshy
.mass only a thin and fibrous envelope. The green
film that formerly adhered to the inner surface of
the ovary, and was detached from it with difficulty,
is now perceptible even through the ovary, and
begins to adhere to the nucleus which is still a clear
fluid enclosed in its proper envelope, and not so
much globular in its figure as oval, tapering to a
small point at the base.

On the 14th, when the ovary measured about
one fourth of an inch, the fluid of the nucleus was be-
ginning to be converted into albumen, within its
proper envelope, to which the green film adheres,
but from which, as well as from the ovary, it may
readily be detached though not always entire, being
of a very slender texture. Its colour is less de-
cidedly green, except at the furrow, where it origi-
nates in the umbilical cord. The embryo is not yet
perceptible.

On the 20th, when the ovary had augmented
considerably in width, the length being as before,
end the nucleus had been converted almost entirely
into a soft albumen, the embryo was at last dis-
coverable in the base of the nucleus, but scarcely dis-
tinguishable into its several parts ; the whole mea-
suring only TV °f an inch by T^ at the broadest part.

On the 24th, when the seed was swollen to
nearly its full size, the three envelopes were still
very distinct. The outer envelope is what was the

2 c 2

388 CHANGES SUCCEEDING IMPREGNATION. CHAP, VIII.

ovary ; the middle envelope is the green film, now
changing to brown ; the inner envelope is the pro-
per integument of the albumen. The albumen is
now pretty firm ; the embryo plainly distinguish-
able into its radicle, plumelet, and scale-like appen-
dages, whether vitellus or cotyledon ; the scale
being TV °f an ^ncn *n length, the plantlet TV-

On the 28th, when the seed was now at its full
size, being more than one fourth of an inch in length,
the nectary scales were still adherent to the base of
the ovary ; but shrunk to a thin membrane, though
retaining their fringed borders. The green film was
now more closely united to the inner envelope.
The embryo was also very distinctly seen by means
of removing the envelopes, and easily extricated
from the albumen9 on the surface of which it is ae-
cumbent. It measured together with its scale-like
vitellus -yV of an inch in length by -^ in breadth. The
vitellus does not seem to be very correctly discribed
by calling it a scale, or at least, not completely de-
scribed ; for at the base of the scale and continuous
with its substance, there may now be seen project-
ing a sort of little bag or pocket with an upright
flap in front, in which the radicle of the embryo is
lodged, and out of which the plumelet protrudes
itself accumbent on the upper part of the scale.

On the 1st of August, when the seed seemed
nearly ripe, and the scale measured -^ of an inch in
length byT'-s in breadth, the plumelet had increased
Considerably in size, filling up almost the whole of

SECT. III. SPECIFIC EXAMPLES. 38$

the area of the upper portion of the scale. The
upright flap of the pocket is distinctly visible,
from which the true radicle may now be disengaged
with a little dexterity of manipulation, though only
by means of tearing the plantlet from the scale at
the collar.

On the 4th, when the seed seemed to be quite
ripe, the green film after changing to a pale brown
had disappeared by insinuating itself into the inner
envelope, or adhering to it so closely as to be
separable from it only by scraping it off in small
fragments. The plumelet filled up the area of the
upper portion of the scale entirely. The rudiments
of the lateral fibres were now visible in the form of
small protuberances issuing from the collar, one on
each side the flap. And when the plantlet was cut
open at the collar, several small globules were dis-
coverable, which are perhaps destined to become
future stalks. The embryo and albumen were firm
and compact; and in the course of a day or two
the Wheat was cut down.

SUBSECTION IV.

The Hazel-nut.— On the 30th of June, 1808, the
most advanced nuts were about one third of an inch
in length. When the nut was cut in two, theputamen,
which was of a greenish colour, but somewhat firm
at the apex, was found to contain the chorion, a
white and succulent mass, resembling the pith of

SQO CHANCES SUCCEEDING IMPREGNATION. CHAP. VIII.

the Elder ; through which the umbilical cord was
seen passing in the direction of its axis, and having
attached to it, near the apex, a small gelatinous
globule on each side of about TV °f an lnc^ m
diameter. There were two incipient nuclei 'similar to
the two small bags found in the young Cherry.

On the 14th of July appearances were much as
before, with the exception of that of a small cavity ge-
nerated in the centre of the gelatinous globules ; and
a sort of net-work of fibres overspreading their sur-
face. In some cases three nuclei were visible.

On the 25th, the nut seemed nearly at its full
size. The chorion was now more firm ; but the
umbilical cord was less distinctly visible. It was
visible, however, on the horizontal section, as a
small speck in the centre ; and also on the longitu-
dinal section near the apex where the nuclei were
attached to it ; of which, one only was in a thriving
state, the other being somewhat shrunk. The
healthy one, which was somewhat egg-shaped, mea-
sured TV of an inch in length, and was white and full
of veins on the surface. When cut asunder, it was
found to consist of a pretty thick coat enclosing a
watery fluid. This fluid Was no doubt the amnios>
but the embryo was not yet visible*

On the 2d of August the progress of develope-
ment was as follows : — In a nucleus or kernel
measuring -?- of an inch, the embryo was just visi-
ble together with its two lobes, occupying the upper
part of the cavity, and measuring about the

SECT-HI. SPECIFIC EXAMPLES.

part of an inch. It was surrounded with a clear
and transparent fluid— -the amnios. In a nucleus
measuring one sixth of an inch, the embryo mea-
sured -—. In a nucleus measuring one fifth, the
embryo measured -^. The surrounding substance
was now gelatinous. In some cases both the nuclei
seemed to be impregnated and were continuing to
thrive ; and it is known they do sometimes both
ripen, as may be seen in the course of cracking a
good many nuts. In the larger specimens the veins
were very conspicuous.

On the 15th, many nuts had attained to nearly
their full size. In one specimen in which the
nucleus measured one fourth of an inch in length,
the outer envelope now full of veins was not easily
separated from the under envelope, though both
were easily separated from the cotyledons, which
measured about one fifth of an inch, having the re-
mainder of the amnios lodged between them at the
top, but still gelatinous and attached to the coats.
The plantlet measured about TV of an inch.

In another specimen in which the nucleus mea-
sured about one third of an inch, the remainder of the
amnios^ which was still gelatinous, was now wholly
within the cleft of the lobes, and lodged in a sort of
hollow near the apex.

In a third specimen in which the kernel seemed
nearly ripe, the amnios had totally disappeared, ex-
cept a thin and membranaceous film, which was
still separable from the cotyledons. The umbilical

CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII

cord was now also very distinct, as well as the mark
which it had occasioned on the surface of the kernel.

SUBSECTION V.

General Remarks. — In the above examples the
process of the developement of the vegetable em-
bryo will be found to be analogous to that of the
developement of the animal embryo, according to
the observation of Malpighi and Gaertner. In
tracing the progress by means of the repeated in-
spection of the ovary, the chorion is found to be
first developed ; then the umbilicus pervading the
centre of the chorion, and expanding at the ex-
tremity into the sacculus colliquamcnti; then the
amnios, which after being elaborated in the chorion,
is conveyed by the umbilicus to the sacculus ; and
lastly the embryo, occupying the upper region of
the amnios — at first a mere point incapable of being
distinguished into its several parts, but by and by
exhibiting the rudiments of root, stem, and leaf,
together with its cotyledons or seed-lobes, between
which the amnios penetrates, and hence reaches the
embryo.

Malpighi is of opinion, however, that the amnios
is augmented and the embryo nourished, not merely
by means of the nutriment that passes through the
umbilicus ; but also by means of the juice of the
chorion which penetrates through the sacculus col-
liquamenti and so reaches the embryo ; because in

8

*ECT. III. SPECIFIC EXAMPLES.

some plants there . is no visible umbilicus passing
through the chorion and forming a sacculus for the
amnios, an example of which we have seen in
Wheat, and which Malpighi exemplifies in the
Laurel ;* though in this example I think there must
have been some mistake.

On the 30th of June, 1808, the appearances of the
ovary of the common Laurel of the gardens, Laurus
nobilis, were as follows: — The amnios had just made
its appearance in the upper region of the chorion which
now resembled a mass of transparent jelly. There
was no umbilicus visible upon the mere inspection
of the chorion even with all its transparency. But
when the chorion was laid open by means of care-
ful dissection, in the direction of its longitudinal
axis, the umbilicus was now discernible adhering to
the lower extremity of the amnios. On a transverse
section the chorion was also evidently perforated in
the direction of its axis. This seemed at first to
have been the perforation of its umbilicus, but was
found at last to be merely the canal through which
it passed. It seemed impractibable to extricate it
entire ; it was so very tender.

On the 6th of July, I succeeded at last in ex-
tricating it entire, together with the amriws, when
the external umbilical cord was also equally visible
passing from the ovary into the nucleus. As I ef-
fected this extrication in many specimens, I can

* In lauro iiciem occurrunt humores concreti nullo taraen iu-
t«rcedente umbilico. Anat. Plant, p. 58.

3Q4 PROPAGATION OF THE SPECIES. CHAP. IX.

have no doubt of the existence of an umbilicus in
the chorion of the Laurel.

CHAPTER IX.

THE PROPAGATION OF THE SPECIES.

As the life of the vegetable, like that of the animal,
is limited to a definite period, and as a continued
supply of vegetables is always wanted for the sup-
port both of man and beast, nature has taken care
to institute such means as shall secure the multiply-
ing and perpetuating of the species in all possible
cases ; art has invented others for the use and ac-
commodation of man, and fancy has imagined more.

SECTION I.

Equivocal Generation.

IT was long a vulgar error, countenanced even by
the philosophy of the times, that vegetables do often
spring up from the accidental mixture of putrid
water and earth, or other putrid substances, in the
manner of what was called the equivocal generation
of animals ; or at the very least, that the earth con-
tains the principle of vegetable life in itself, which
in order to develope it is only necessary to expose
to the action of the air. The former alternative of

SECT. I. feaUIVOCAL GENERATION. 3Q5

the error has been long ago refuted, and as I believe
eradicated, no one now contending for the doctrine
of vegetable generation from putrefaction : but the
latter, though it has been also refuted, has not yet
lost its hold of the minds of the unlearned. The A vulgar
farmer still believes, and will still tell you, that theprejuc
earth throughout its whole mass teems with the
rudiments of vegetables, or at least of all such as he
is not under the necessity of cultivating, which it
will develope without any seed if only exposed to
the action of the air ; alleging in support of his
opinion that earth dug up from any depth and
thrown in heaps on the surface, will immediately
begin to send up young plants, though no seed has
been sown upon it. But the fallacy of this argu-
ment is easily exposed, for in the first place the
roots of such plants as are near to it will extend
themselves around its edges, and make encroach-
ments upon the lower part of it ; and in the next
place the seeds of plants, whether near or at a dis-
tance, will be conveyed to it by the winds, by cattle,
or by birds, and so furnish the upper part of it, so
that the argument is good for nothing. Let the
experiment be made where the earth shall be per-
fectly insulated, except from light, air, and water,
and let the result be marked. This was done long Refuted
ago by Malpighi, who having procured some earth pfghi.a "
that had been dug up from a great depth, enclosed
it in a glass vessel over the mouth of which he
spread several folds of silk, so as to admit air and

3Q0 PROPAGATION OF THE SPECIES. CHAP. IX*

water ; but to exclude all such small seeds as might
be wafted on the winds : the result was that no
plant came up.*

In the summer of 1811, I had an opportunity of
making some similar experiments on earth obtained
from a considerable depth by the digging of a well
at Purleigh, near Maldon, in the county of Essex.
On the 15th of April I exposed a lump of this
earth, being chiefly a black clay taken from the
depth of 100 feet, to the action of the air and
weather, and to the operation of such other contin-
gencies as might occur : it was placed upon a slate
in one of the quarters of my garden. On the lOth
of May I placed another lump taken from the depth
of 150 feet upon a slate also, but under a hand-glass,
which was removed only to give it an occasional
watering. No symptoms of vegetation appeared in
either the one or the other till the 3d of September
following, when several plants were found in a state
of protruding their seed leaves from the surface of the
exposed clay, and one also from the surface of the in-
sulated clay; the former proved afterwards to be plants
of Senecio vulgar is, or Common Groundsel, which
was now coming up from seed all over the garden, and
hence easily accounted for : the latter proved to be
a plant of Ranunculus sceleratus, the seed of which
was undoubtedly brought to the clay along with
the water it was watered with, which came from a
pond at no great distance, round the edges of which
* Anat. Plant. Pars Altera, p. 92.

SECT. II. SEEDS.

the plant was springing up in great plenty from
seeds previously dispersed, which, as they float
long on the surface of the water, could not but have
mixed more or less with the portion conveyed to
the clay. This presumption is grounded upon the
fact that a number of other plants of the same
species were coming up in other parts of the garden
that were watered from the same pond ; while in
the exposed clay which never was watered except
by rains or dews, no such plant was found : hence
it follows equally as from the experiment of Malpi-
ghi, that the earth produces no plant without the
intervention of a seed, or of some other species of
vegetable germe deposited in it by nature or by art.

SECTION II.

Seeds.

WHEN the seed has reached maturity in the due Their
and regular course of the developement of its several profusion,
parts, it detaches itself sooner or later from the
parent plant, either singly or along with its pericarp,
and drops into the soil, where it again germinates
and takes root, and springs up into a new individual.
Such is the grand means instituted by nature for
the replenishing and perpetuating of the vegetable
kingdom ; the wisdom and efficacy of which will
equally appear whether we regard the great fertility
of vegetables in general, and incalculable fertility of

PROPAGATION OF THE SPECIES. CHAP. IX.

some species in particular, as has been already
stated ;* or the care with which nature has provided
for the dispersion of the ripened seed.

And dis- If seeds were to fall into the soil merely by dropping
down from the plant, then the great mass of them
instead of germinating and springing up into distinct
plants, would tend only to putrefaction and decay ;
to prevent which consequence nature has adopted a
variety of the most efficacious contrivances, all tend-
ing to the dispersion of the seed.

By the The first means I shall mention is that of the
of the peri- elasticity of the pericarp of many fruits, by which it
opens when ripe with a sort of sudden spring, eject-
ing the seed with violence, and throwing it to some
considerable distance from the plant. This may be
exemplified in a variety of cases ; the seeds of oats
when ripe are projected from the calyx with such
violence, that in a fine and dry day you may even
hear them thrown out with a slight and sudden snap
in passing through a field that is ripe. The pericarp
of the Dorsiferous Ferus is furnished with a sort of
peculiar elastic ring, intended as it would appear
for the very purpose of projecting the seeds. The
capsules of the Cucumber, Geranium, Geum, and
Fraxinelta, discharge their seeds also when ripe
with an elastic jerk. But the pericarp of Impatiens,
which consists of one cell with five valves, exhibits
perhaps one of the best examples of this mode of
dispersion. If it is accidentally touched when ripe
* Book i. chap iii.

SECT. II. SEEDS.

it will immediately burst open, while the valves,
coiling themselves up in a spiral form and springing
from the stem, discharge the contained seeds and
scatter them all around.

The bursting of the pericarp of some species of
Pines is also worthy of notice. The pericarp,
which is a cone, remains on the tree till the sum-
mer succeeding that on which it was produced, the
scales being still closed. But when the hot weather
has commenced and continued for some time, so as
to dry the cone thoroughly, the scales open of their
own accord with a sudden jerk, ejecting the con-
tained seeds : and if a number of them happens to
burst together, which is often the case, the noise is
such as to be heard at some considerable distance.
This crackling noise was observed and traced to a
fir-tree, namely Pinus Pinea, at tiendlesham Par-
sonage, on July 14th, 1808, by two young gentle-
men, my pupils, who thought the tree was bewitched
till the cause of the noise was pointed out to them.

The twisted awn of Avena jatua, or Wild Oat, By the
as well as that particularly of Geranium cicutarium,
and some others, seems to have been intended for
the purpose of aiding the further dispersion of the
seed, after being discharged from the plant or peri-
carp. This spiral awn or spring, which is beset with
a multitude of fine and minute hairs, possesses the
property of contracting by means of drought, and of
expanding by means of moisture. Hence it remains
of necessity in a perpetual state of contraction or
2

PROPAGATION OF THE SPECIES. CHAP. IX.

dilatation, dependant upon change of weather ; from
which, as well as from the additional aid of the fine
hairs, which act as so many fulcra, and cling to what-
ever object they meet, the seed to which it is attached
is kept in continual motion till it either germinates
or is destroyed.*

The awn of Barley, which is beset with a multi-
tude of little teeth all pointing to its upper ex-
tremity, presents also similar phenomena. For when
the seed with its awn falls from the ear and lies flat
upon the ground, it is necessarily extended in its
dimensions by the moisture of the night, and con-
tracted by the drought of the day. But as the teeth
prevent it from receding in the direction of the
point, it is consequently made to advance in the
direction of the base of the seed, which is thus often
carried to the distance of many feet from the stalk
on which it grew. If any one is yet sceptical with
regard to the travelling capacity of the awn, let him
only introduce an awn of Barley with the seed upper-
most between his coat and shirt sleeve at the wrist,
when he walks out in the morning, and by the time
he returns to breakfast, if he has walked to any
great distance he will find it up at his arm-pit. This
journey has been effected by means of the continued
motion of the arm, and consequently of the teeth of
the awn acting as feet to carry it forward.

It is obvious, however, that the modes of dis-
persion now stated can never carry the seed to any

* Withering Arrang. vol. ii. p. 6lO.

SECT. II. SEEDS. , 401

great distance ; but where distance of dispersion is
required, nature is also furnished with a resource.
One of the most common modes by which seeds are
conveyed to a distance from their place of growth
is that of the instrumentality of animals.

Many seeds are thus carried to a distance from By the in-
the place of growth merely by their attaching them- aih^of1'"
selves to the bodies of such animals as may happen animals>
accidentally to come in contact with the plant in
their search after food ; the hooks or hairs with
which one part or other of the fructification is often
furnished serving as the medium of attachment, and
the seed being thus carried about with the animal
till it is again detached by some accidental cause,
and at last committed to the soil. This may be
exemplified in the case of the Bidens and Myosotis,
in which the hooks or prickles are attached to the
seed itself; or in the case of Galium aparine and
others, in which they are attached to the pericarp ;
or in the case of the Thistle and Burdock, in which
they are attached to the general calyx.

Many seeds are dispersed by animals in conser
quence of their pericarps being used as an animal
food. This is often the case with the seeds of the
Drupe, as Cherries, Sloes, and Haws, which birds
often carry away till they meet with some con-
venient place for devouring the pulpy pericarp
and then drop the stone into the soil. And so also
fruit is dispersed that has been hoarded up for the
winter, though even with the view of feeding on the

VOL. II. 2 D

4O2 PROPAGATION OF THE SPECIES. CHAP. IX.

v

seed itself, as in the case of nuts hoarded up by
Squirrels, which are often dispossessed by some other
animal, that not caring for the hoard scatters and
disperses it. Sometimes the hoard is deposited in
the ground itself, in which case part of it is generally
found to take root and spring up into plants. But
it has been observed that the Ground Squirrel often
deprives the kernel of its germe before it deposits
the fruit it collects ; which it has been supposed to
do from some peculiar instinct as the means of pre-
venting the germination of the seed. It has been
suggested, however, that the preference thus given
to the embryo arises perhaps from its possessing
some specific flavour peculiarly agreeable to the
animal's taste ; and this is perhaps the true solution
of the question.* Crows have been also observed
to lay up acorns and other seeds in the holes of
fence-posts, which being either forgot or acci-
dentally thrust out, fall ultimately into the earth
and germinate.

But sometimes the seed is even taken into the
stomach of the animal, and afterwards deposited
in the soil, having passed through it unhurt. This
is often the case with the seed of many species of
berry, such as the Miseltoe, which the thrush
swallows and afterwards deposits upon the boughs
of such trees as it may happen to alight upon. The
seeds of the Loranthus americanus, another parasiti-
cal plant, arc said to be deposited in like manner on
* Barton's Elem, of Bot. p. 233.

SECT. II. . SEEDS. 403

the branches of the Cocoloba grandiflora, and other
lofty trees ;* as also the seeds of Phytolacca de-
candria, the berries of which are eaten by the
robin, thrush, and wild pigeon. And so also the
seeds of Currants or Roans are sometimes deposited
after having been swallowed by blackbirds or other
birds, as may be seen by observing a Currant-
bush or young Roan-tree growing out of the cleft of
another tree, where the seed has been left, and where
there may happen to have been a little dust collected
by way of soil ; or where a natural graft may have
been effected by the insinuation of the radicle into
some chink or cleft. It seems indeed surprising
that any seeds should be able to resist the heat and
digestive action of the stomach of animals ; but it is
undoubtedly the fact. Some seeds seem even to re-
quire it. The seeds of Magnolia glauca which have
been brought to this country are said to have generally
refused to vegetate till after undergoing this process,
and it is known that some seeds will bear a still
greater degree of heat without any injury. Spallan-
zani mentions some seeds that germinated after
having been boiled in water : and Du Hamel gives
an account of some others that germinated even
after having been exposed to a degree of heat
measuring 235° of Fahrenheit.

In addition to the instrumentality of brute ani-
mals in the dispersion of the seed I might add also
that of man, who for purposes of utility or oforna-
* Barton's Elera. of Bot. p. 232. f Ibid, p. 234»
2 D 2

104 PROPAGATION OF THE SPECIES, CHAP. IX.

ment, not only transfers to his native soil seeds in-
digenous to the most distant regions, but sows and
cultivates them with care. But this view of the
subject I will leave to the reader's own reflections,
and hasten to the other modes of dispersion insti-
tuted by nature ; one of the most effective of which
is that of the agency of winds.

By the Some seeds are fitted for this mode of dispersion

° from their extreme minuteness, such as those of the
Mosses, Lichens, and Fungi, which float invisibly
on the air and vegetate wherever they happen to
meet with a suitable soil. Others are fitted for it by
means of an attached wing, as in the case of the
Fir-tree and Liriodendron tulipifera, so that the
seed in falling from the cone or capsule is imme-
diately caught by the wind and carried to a distance.

Others are peculiarly fitted for it by means of
their being furnished with an aigrette or down, as
in the case of the Dandelion, Goat's-beard, and
Thistle, as well as most plants of the class Synge-
nesia ; the down of which is so large and light in
proportion to the seed it supports, that it is wafted
on the most gentle breeze, and often seen floating
through the atmosphere in great abundance at the
time the seed is ripe.

Others are fitted for this mode of dispersion by
means of the structure of their pericarp, which is
also wafted along with them, as in the case of Sta~
phylea trifolia, the inflated capsule of which seems
as if obviously intended thus to aid the dispersion of

SECT. II. SEEDS. 405

the contained seed by its exposing to the wind a
large and distended surface with but little weight.
And so also in the case of the Maple, Elm, and
Ash, the capsules of which are furnished, like some
seeds, with a membranous wing, which when they
separate from the plant the wind immediately lays
hold of and drives before it.

Finally, a further means adopted by nature for Rivers and
the dispersion of the seeds of vegetables is that of
the instrumentality of streams, rivers, and currents
of the ocean. The mountain-stream or torrent
washes down to the valley the seeds which may
accidentally fall into it, or which it may happen to
sweep from its banks when it suddenly overflows
them. The broad and majestic river, winding
along the extensive plain, and traversing the conti-
nents of the world, conveys to the distance of many
hundreds of miles the seeds that may have vegetated
at its source. Thus the southern shores of the Baltic
are visited by seeds which grew in the interior
of Germany, and the western shores of the Atlantic
by seeds that have been generated in the interior
of America. But fruits indigenous to America and
the West Indies have sometimes been found to be
swept along bv the currents of the ocean to the
western shores of Europe. The fruit of Mimosa
scandens, Dolichos pruriens, Guilindina bonduc,
and Anacardium occidentale, or Cashew-nut, have
been thus known to be driven across the Atlantic
to a distance of upwards of 200O miles: and

406 PROPAGATION OF THE SPECIES. CHAP. IX.

although the fruits now adduced as examples are
not such as could vegetate on the coast on which
they were thrown, owing to soil or climate ; yet it is
to be believed that fruits may have been often thus
transported to climates or countries favourable to
their vegetation.

SECTION III.
Gents.

Gems dis- THOUGH plants are for the most part propagated
frornseeds. by means of seeds, yet many of them are propa-
gated also by means of gems ; which have been
already defined, in as far as their definition could be
given without a direct reference to the mode of
their generation, as being distinct from that of the
seed, but which, till after the discussion of the sub-
ject of vegetable sexuality, it was pehaps premature
to introduce. What then are the essential marks
by which gems are to be distinguished from seeds ?
The following are the discriminations of Gaertner :*—
First The first and most essential marks by which the

A/T L-

gem .is to be distinguished from the seed is that of
its being formed without the intervention of a sexual
apparatus ; and merely by the agency of the vital
and organizing principle of the plant. Gsertner
describes it as originating in what he calls the flesh
of the plant, which he does not, however, accurately
* Ititrod. de Seminibus.

SECT. III. GEMS. 407

define, calling it the pith, loosely speaking ; though
in the case of woody plants it is plain that he means
by it the alburnum, as he says all buds are rooted
in that substance which is under the inner bark,
and form with it one body.

Secondly, the gem is distinguished from the seed Second
as consisting chiefly of a pith, and having no divi-
sions internally into distinct parts, similar to the
albumen vitellus and cotyledons of the seed ; nor
any proper integuments externally, similar to the
Testa and Subtesta of the seed ; but merely a bark
modifying the medullary substance, and giving it
its external and proper form : which bark consists
either of the indurated substance of the granule
itself; or of divisions of the cellular tissue adhering
to it, as in the Propago ; or of the bark of the
parent plant by which the granule has been en-
veloped, as in the Gongylus ; or of the inner bark
forming a permanent part, or outer bark forming
only a temporary appendage, as in the case of the
bud and bulb.

Thirdly, the gem is also often distinguished from Third
the seed by means of its appendages, the theca and in
involucrum, or sheath and involucre ; which origi-
nate in the bark of the parent plant. The sheath is
peculiar to some species of Propago, and is a vessel
containing a number of individuals, which it retains
for a certain time, and then disperses ; as may be
exemplified in the genus Marchantia. The invo-
lucre is peculiar to compound gems, it consists of

408 PROPAGATION OF THE SPECIES. CHAP. IX.

one or more cortical scales, which defend the tender
gem and are attached to it only by the base. In
buds it is deciduous, in bulbs it is permanent : but
it does not form a complete envelope, being always
open at that part where the gem is to burst out ; or if
shut, it is shut only by the over-lapping of its parts.
Fourth Lastly, the gem is distinguished from the seed in

BftJUTICfl

its mode of developement. The integuments of the
seed perish after germination, but the covering or
appendages of the gem do not. They are incor-
porated into the substance of the new plant, as in
the Propago and Gongylus ; or at least they con-
tinue to vegetate along with it, as in the case of the
i scales of the bulb. The gem sends out a number of
small roots formed from the bark, and but seldom
one ; while the seed sends out one main root only
from the pre-existing radicle, and but seldom more
than one. In the gem, the interior part is first
formed and then the appendages or covering ; in
the seed the integuments are first formed, and then
the embryo appears.

Definition If the scope of the above distinctions is taken into
"' the account the definition of the gem will then be
as follows : — The gem is an organized substance
bursting from the surface of the plant without the
aid of sexual apparatus, or previous fecundation ;
and developing its parts either by forming a con-
tinued extension of the parent plant, or by detaching
itself from the parent plant altogether, and forming
a new individual.

SECT. III. GEMS. 409

This definition is obviously applicable, in one The bulb,
alternative or other, both to the bud and bulb ; by
which last it is well known that the species is often
propagated, as in the very common case of bulbous
rooted plants. If the bulb of a Snow-drop or Lily
is taken up when the season of flowering is past and
deprived of its external coats or scales, the rudiments
of young bulbs will be discovered lurking at the
base of the scales in the form of small buds, though
some may perhaps be found farther advanced and
ready to burst their integuments ; which after they
have ultimately done, they then detach themselves
from the parent bulb altogether and form new indi-
viduals. Such is the mode of the propagation of the
radical bulb.

But the species is also often propagated by means
of the caulinary bulb. This bulb generally appears
in the axil of the leaves, as in Dentaria bulbifera
(PL III. Vol. I.), and Lilium bulbiferum. At first
it seems a sort of knob or tubercle ; but by and by
it is a bulb, often separating spontaneously from the
parent plant and taking root in the soil. In some of
the alliaceous plants the caulinary bulb is very com-:
mon, and is produced at the origin and between the
spokes of their umbels. Among gardeners they are
known by the name of Cloves.

Some plants produce a sort of bulb even in the
midst of their spike of flowers, which detaching
itself from the parent plant strikes root and forms
also a new individual. Such are Potygonum vivi-

41O PROPAGATION OF THE SPECIES. CHAP. IX.

parum and Poa alpina; and as plants of this kind
are mostly alpine, it has been thought to be an in-
stitution or resource of nature to secure the propa-
gation of the species in situations where the seed
may fail to ripen.

The bud. The bud though it does not spontaneously de-
tach itself from the plant and form a new individual,
will yet sometimes strike root and develope its
parts if carefully separated by art and planted in
the earth : but this is to be understood of the leaf-
bud only, for the flower-bud if so treated always
perishes.*

But the species may sometimes be propagated
even by means of the leaves ; as is, I believe, the
case with the leaves of the Orange3 Aloe, Sea-onion,
and some species of Arum, which if carefully de-
posited in the soil will grow up into new plants, — by
virtue, no doubt, of some latent gem contained in
them ; in which case, as well as in all of the preced-
ing cases, the propagation of the species is obviously
effected by means of a principle different from the
seed, which botanists generally designate by the ap-
pellation of the gem.

The pro- But this is not so obviously true in the case of
gongylus. the Propago and Gongylus — the simple gems of
Gaertner ; because it has been contended that they
are still but seeds. Gaertner, however> excludes
them entirely from the rank of seeds upon the fore-
going grounds, and maintains, in opposition to the
* Mirbel Phys. Veg. vol. i. p. 220.

SECT. III. GEMS. 411

opinions Hedwig and others, that several tribes of
what are usually denominated cryptogamous plants
are propagated solely by gems.

The Lichens, according to Gaertner, are of this
description ; that which is usually regarded as their
seed being merely a powdery propago bursting from
the surface of the plant, and vegetating without
changing its form. Hedwig, after Adanson, con-
tends indeed that the granules immersed in the
scut dice of the Lichens are true seeds. But it is to
be recollected that all Lichens are not furnished with
scutellce, nor all scutellce with granules ; and much
less, consequently, with a sexual apparatus.

The Fungi also, according to Gaertner, are alt
gemmiferous, having no sexual organs, and no pollen
impregnating a germe. In the genus Ly coper don
the gelatinous substance that pervades the cellular
tissue is converted into a proliferous powder; in
Clavaria the fluid contained in the cavities of the
plant is converted into a proliferous powder also :
and in the Agarics, Hydnum, and Boletus, vesicles
containing soboliferous granules are found within
the lamina, pores, or tubes. Hedwig, on the con-
trary, ascribes to the Fungi a sexual apparatus,
and maintains that the pollen is lodged in the volva.
But here it is to be recollected as in the cases of the
scutellae of the Lichens, that all Fungi are not fur-
nished with a volva, and consequently not furnished
with pollen.

The Conferva and Ulva, together with the ge-

412 PROPAGATION OF THE SPECIES. CHAP. IX.

nera Blasia and Riccia, are also, according to
Gaertner, propagated only by gems ; while Mar~
chantia, Anthoceros, Jungermannia, and Lycoper-
don are said to be propagated both by gems and
seeds.
Challenge such js the sum of the theory of Gaertner, who

of Gaert-
ner. adds — If it be said that these granules are not gems

but seeds, let it be proved that they have the usual
integuments of seeds : and if it be said that they are
exceptions to the general rule, and are seeds though
destitute of the usual integuments, let it be proved
that the plants producing them are furnished with
sexual organs.

Accepted The challenge thus held out to the Cryptogamist
a has been accepted by M. Corrca de Serra,* at least
with regard to the proscribed genera of submersed
Alga ; which he has endeavoured to restore to the
rank of seed-bearing plants. The true Fuel were
admitted by Gaertner to produce perfect seed,
though only upon the Adansonian notion of vege-
table Aphroditism ; but the Ceramiums, together
with the Ulva and Conferva were regarded as
producing gems merely, and on the following
grounds : —

1. Because in the Ceramiums and Ulv& the
grains are solitary, are not contained in a proper
uterus, and are consequently without a placentation,

'2. Because in germinating they leave no coat
behind.

* Phil. Trans. 1796.

SECT. III. GEMS. 413

3. Because in the Confervtf two or more of
them often coalesce, and yet form but one indi-
vidual.

In reply to the first argument, Mr. Correa main-
tains that the grains of the Ceramiums and Ulvce
are precisely similar to those of the true Fuci9 en-
closed in a uterus enveloped with a soft and juicy
substance, affixed no doubt by some placentation,
furnished with a proper skin, and disengaging them-
selves from the parent plant at the period of their
maturity, though Gaertner says only by the plant's
decay.

In reply to the second argument Mr. Correa does
not pretend directly to controvert the fact which he
seems to think no observation can accurately ascer-
tain, but merely the principle by which it has been
supposed that no substance can possibly be a seed
unless it has a coat to leave behind it in germinating,
and that no substance can be a gem if it has one; —
a principle arising, as he thinks, out of the supposed
analogy between the seed of vegetables and eggs of
animals, or between the gem and the living foetus :
but gems, as he asserts, do sometimes leave a coat
behind them, as in the scales of the bud ; and eggs
have sometimes no coat to leave, as in the spawn of
Frogs.

In reply to the third argument he contends that
its scope is precisely the reverse of that alleged by
Gaertner, because it is known that in the case of the
coherence of other acknowledged gems, the one

414 PROPAGATION OF THE SPECIES. CHAP. IX,

always proves abortive and falls, tending only to
nourish the other ; but in the case of the ad-
herence of other acknowledged seeds, as in that of
Daleciy Lagtfcia, Hasselquestia, and others, the abor-
tive seed does not fall, but still continues adherent.

Having thus pulled to pieces the hypothesis of
Gaertner, the next object of Mr. Correa is to es-
tablish his own — namely, that the mucous substance
surrounding the grains of the plants in question
is a true pollen. If this, he adds, is found to be
contrary to the character of the pollen of terrestrial
plants, so, it should be remembered, is the medium
through which it has to pass; and if it should be
said that the pollen of some aquatics, such as Po-
tamogeton and Vallimeria is still powdery, it is to
be recollected that their flowers emerge above water
at the season of fecundation ; or if there are any
aquatics which do not emerge and have yet a powdery
pollen, it should be recollected that the process takes
place wholly under cover, as in the case of Zostera, in
which the flower is situated in the cavity of the stem,
and does not open till fecundation is over : and even
in plants vegetating in the open air, nature em-
ploys various expedients to preserve the pollen
from wet.

But it is not absolutely necessary that the pollen
should be farinaceous even in terrestrial plants, or
rather it is known and acknowledged that this is not
always so. In the Orchidea it consists of a mass of
solid particles, assuming in the aggregate a sort of

SECT. III. GEMS. 415

waxy appearance; in some of the Contorts it is
viscid ; and in most of the Apocynece it is almost
altogether a fluid. But if this is the case even with
some terrestrial plants, much more with aquatics
vegetating in a medium so ill adapted to the trans-
mission of a farinaceous pollen. It follows, there-
fore, that the mucilaginous vesicles of the submersed
Alga surrounding the uterus are anthers furnished
with pollen, and that the grains by which they are
propagated are perfect seed, the flowers being thus
Hermaphrodites : which conclusion is further coun-
tenanced by the fact that the parts here alluded to
are merely temporary, the grains after fecundation
increasing and finally disengaging themselves, and
the mucous substance totally disappearing, as in
plants with conspicuous flowers.

Such is the view of the subject offered by Mr. Its issue,
Correa, extremely perspicuous indeed, and almost
convincing. But it must at the same time be ob-
served that in his reply to the first of Gaertner's
arguments he adduces no examples in proof of his
assertions ; and does not even pretend to have dis-
covered the placentation of the grains; but merely
concludes that they must be so affixed. In his
reply to the second argument of Gaertner I am not
at all satisfied that the case is correctly stated.
Because although the scales of the bud are indeed
left behind, yet they do not at all come under the
notion of proper integuments as understood by
Gaertner ; but merely of an exterior covering or

3

41 6 PROPAGATION OF THE SPECIES. CHAP. IX.

appendage not necessarily included in the notion
of the gem. And if the account of zoologists is
true, the eggs of frogs are covered with a proper
integument independant of what Mr. Correa calls
their mucous albumen, which they unquestionably
leave behind. In consequence of which I cannot
think that Mr. Correa has established the point
for which he contends.

SECTION IV.

Runners.

RUNNERS are young shoots issuing from the
collar or summit of the root, and creeping along
the surface of the soil ; but producing a new root
and leaves at the extremity, and forming a new
individual, by the decay of the connecting link.
Exempli- This takes place in a great variety of herbs, but
Straw- particularly the Strawberry which is a good ex-
ample,, and from the root of which a number of
creeping shoots are protruded in the course of the
summer, extending like the radii of a circle to the
distance of eight, ten, or twelve inches or more ;
and then striking root towards the extremity and
producing a new individual which in the following
year becomes wholly separated from the parent, by
the decay of the connecting link, and sends out
also new runners in its turn.

SECT. V. SLIPS. 417

SECTION V.
Slips,

As the process of raising perennials from seed is
very slow, gardeners have discovered or invented
several ways of expediting the propagation of the
species by means of artificial aid. For it has been
found that if a young shoot or branch is cut off
with the knife, and then planted in the soil, it will
in many cases still continue to vegetate, sending out
roots below and branches above, and forming a new
individual. But this mode of propagation should An exten-
perhaps be regarded after all as an extension of the ™ l

old plant, rather than as the generation of a new PIant'
one ; though it serves the purpose of the cultivator
equally well as a plant raised from seed, with the
additional advantage of bearing fruit much sooner.
It will not succeed, however, in all plants indiscri-
minately ; but it succeeds extremely well in the
case of Currants, Gooseberries, and Vines ; as also
in that of the Willow and Poplar, of which you
can scarcely knock a stake into the ground that
will not strike root. The shoot thus detached from
the plant, and placed in the soil is denominated a
slip.

But how is the root generated which the slip The root
thus produces ? If the trunk of a tree is lopped, °sei
and all its existing buds destroyed, then there will

VOL. ii. 1 E

418 PROPAGATION OF THE SPECIES. CHAP. IX.

be protruded from between the wood and bark a
sort of protuberant lip or ring formed from the
proper juice, and from which there will spring a
number of young shoots. And if a root is taken
and lopped it will in like manner send out new
roots. But the formation of the root in the case of
the slip is effected in the same manner, the mois-
ture of the soil encouraging the protrusion of buds
at and near the section ; the bud that would have
been converted into a branch above ground being
converted into a root below.

SECTION VI,
Layers.

Artificial. INSTEAD of cutting off a portion from the parent
plant altogether, in the manner of a slip, gardeners
frequently select a branch and bend it down to the
ground, till a part of it can be laid in the soil ; the
summit being still exposed to the air, and the whole
being yet connected to the stem by the inferior part
of the branch. When the branch is thus treated,
the portion that is laid in the soil strikes root and
elevates a new stem from the original summit of
the branch, which is now denominated a layer, and
converted into a new individual by detaching the
branch wholly from the original stem. This mode
of propagation is practised upon trees that are de-
licate and which cannot readily be propagated by

SECT. VII. SUCKERS.

means of slips ; in which case the root is generated
nearly as in the former, the soil stimulating the pro-
trusion of buds which are converted into roots,
But in many plants, such as the Currant and Natural.
Laurel, this is altogether a natural process effected
by the spontaneous bending down of a branch to
the surface of the soil.

SECTION VII.
Suckers.

MANY plants protrude annually from the collar
a number of young shoots, encircling the principal
stem and depriving it of a portion of its nourish-
ment, as in the case of most fruit-trees. Others Exempli-
send out a horizontal root, from which there at last|^'"n^h
issues a bud that ascends above the soil and is con- syrinsa*
verted into a little stem, as in the case of the Elm-
tree and Syringa. Others send out a horizontal
shoot from the collar or its neighbourhood; or a
shoot that ultimately bends down by its own weight
till it reaches the ground, in which it strikes root
and again sends up a stem, as in the abovemen-
tioned case of the Currant Bush and Laurel. The
two former are called suckers or offsets, though the
term offset should perhaps be restricted to the
young bulbs that issue and detach themselves an-
nually from bulbous roots. The latter is not desig-
nated by any particular name, but may be regarded

2 E 2

PROPAGATION Or THE SPECIES. CHAP. IX.

as a sort of natural layer, resembling also, in some
respect, the runner ; from which, however, it is dis-
tinguished in that it never detaches itself sponta-
neously from the parent plant, as is the case also
with the two former. But if either of them is
artificially detached together with a portion of root,
or a slice of the collar adhering to it, it will now
bear transplanting, and will constitute a distinct
plant.

SECTION VIII.
Grafts.

Artificial. THE species is also often propagated, or at least
the variety is multiplied, by means of grafting,
which has been already shown to be an artificial
application of a portion of the shoot of one tree to
the stem or branch of another, so as that the two
shall coalesce together and form but one plant.
The shoot which is to form the summit of the new
individual is called the graft; and the stem to
which it is affixed is called the stock.

As the graft is merely an extension of the parent
plant from which it came, and not properly speak-
ing a new individual, so it is found to be the best
method of propagating approved varieties of fruit-
trees without any danger of altering the quality of
the fruit, which is always apt to be incurred in
propagating from seed, but never in propagating

SECT. VIII. GRAFTS. 431

from the graft. Some gardeners will indeed tell
you that a Rose grafted on a black Currrant will
produce black Roses ; but this is a vulgar error.
The graft will also bear fruit much sooner than the
tree that is raised from seed ; and, if effected on a
proper stock, will be much more hardy and vigo-
rous than if left on the parent plant. And hence
the great utility of grafting in the practice of gar-
dening.

CHAPTER X.

CAUSES LIMITING THE PROPAGATION OF THE SPECIES.

FROM the various sources of vegetable reproduc-
tion, but particularly from the fertility and dis-
persion of the seed, the earth would soon be over-
run with plants of the most prolific species, and
converted again into a desert, if it were not that
nature has set bounds to their propagation by sub-
jecting them to the control of man, and to the
depredations of the great mass of animals ; as well
as in confining the germination of their seeds to
certain and peculiar habitats. The operation of the
two former causes it is not necessary for me to il-
lustrate at present. My remarks shall therefore be
directed merely to the illustration of the latter;
namely, that of the circumscription of the habi-
tats and propagation of plants as dependant on soil,
climate, and altitude.

422 CAUSES LIMITING PROPAGATION. CHAP. X.

SECTION I.
Soils.

ALL plants will not vegetate in all soils, many
of them even affect a peculiar soil ; and where that
soil is not to be found, they will not grow. It
should be observed, however, that in this view of
the subject the term soil is used in a very extensive
acceptation, as signifying not only the various sorts
of mould which copstitute the surface of the earth,
but every substance whatever on which plants are
found to vegetate, or from which they derive their
nourishment. The most general division of soils
in this acceptation of the term is that of aquatic,
terrestrial, and vegetable soils ; corresponding to the
division of aquatic, terrestrial, and parasitical plants,

SUBSECTION I.

Aquatic Soils. — Aquatic soils are such as are

either wholly or partially inundated with water,

and are fitted to produce such plants only as are

denominated aquatics. Of aquatics there are several

subdivisions according to the particular situations

they affect, or the degree of immersion they require.

Producing One of the principal subdivisions of aquatics is

plants? tnat °f marme plants such as the Fuci and many of

the Ulvce, which are very plentiful in the seas that

SECT. I. SOILS. 423

wash the coasts of Great Britain, and are generally
attached to stones and rocks near the shore. Some
of them are always immersed ; and others which
are situated above low water mark are immersed
and exposed to the action of the atmosphere alter-
nately. But none of them can be made to ve-
getate except in the waters of the sea.

Another subdivision of aquatics is that of river River
plants, such as Chara, Potamogeton, and Nym- p a
phtea, which occupy the bed of fresh water rivers,
and vegetate in the midst of the running stream ;
being for the most part wholly immersed, as well
as found only in such situations.

A third subdivision of aquatics is that of paludal Marsh
or fen plants, being such as are peculiar to lakes, p ants
marshes, and stagnant or nearly stagnant waters,
but of which the bottom is often tolerably clear.
In such situations you find the Isoetis lacustris,
Flowering Rush, Water Ranunculus, Water Lily,
and a variety of others which uniformly affect such
situations, some of them being wholly immersed
and others immersed only in part.

SUBSECTION II.

'Earthy Soils. — Earthy soils are such as emerge
above the water and constitute the surface of the
habitable, globe that is every where covered with
vegetable productions. Plants affecting such soils,

424 CAUSES LIMITING PROPAGATION. CHAP. x.

which comprise by far the greater part of the ve-
getable kingdom, are denominated terrestrial, being
such as vegetate upon the surface of the earth
without having any portion immersed in water or
requiring any further moisture for their support
beyond that which they derive from the earth and
atmosphere. This division is, like the aquatics,
distributed into several subdivisions according to the
peculiar situations which different tribes affect.
Producing Some of them are maritime, that is, growing only

maritime, , *. . r

sylvatic, °w the sea-coast, or at no great distance trom it,
othe7cle"d suc^ as ^tatice^ Glciux9 Samolus, Samphire, Sea

othecle

nomina- Pea. Some are fluviatic, that is, affecting the banks

tions of

plants. of rivers, such as Ly thrum, Lycopus, Eupatonum.
Some are champaign, that is, affecting chiefly the
plains, meadows, and cultivated fields, such as Car-
damine, Tragopogon, Agrostemma. Some are
dumose, that is, growing in the hedges, such as the
Bramble. Some are ruderate, that is, growing on
rubbish, such as Senecio viscosus. Some are syl-
vatic, that is, growing in woods or forests, such as
Stachys sylvatica, Angelica sylvestris. And finally,
some are alpine, that is, growing on the summits
of mountains, such as Poa alpina, Epilobium al-
pinum, and many of the Mosses and Lichens.

SUBSECTION III.

Vegetable Soils. — Vegetable soils are such as are

SECT. I. SOILS. 425

formed of vegetating or decayed plants themselves,
to some of which the seeds of certain other plants
are found to adhere, as being the only soil fitted
to their germination and developement. The plants
springing from them are denominated Parasitical, as
being plants that will vegetate neither in the water
nor earth, but on certain other plants, to which they
attach themselves by means of roots that penetrate
the bark, and from the juices of which they do
often, though not always derive their support. This
last circumstance constitutes the ground of a sub-
division of parasitical plants, into such as merely
adhere to other plants but do not feed on them,
and such as do not merely adhere to other plants
but do also feed on them.

In the first subdivision we may place parasitical Producing
Mosses, Lichens, and Fungi, which are found as plants,
often and in as great perfection on the stumps of
rotten trees, and on rotten pales and stakes, as on
trees that are yet vegetating ; whence it is also plain
that they do not derive their nourishment from the
plants on which they grow, but from the atmos-
phere by which they are surrounded ; the plant
to which they cling serving merely as a basis of
support.

In the second subdivision we may place all such
plants as are strictly parasitical, that is, all such as
do actually abstract from the juices of the plant to
which they cling the nourishment necessary to the
developement of their parts ; and of which the

426 CAUSES LIMITING PROPAGATION. CHAP. X.

most common, at least as being indigenous to Bri-
tain, are the Missletoe, Dodder, Broom-rape, and
a sort of tuber that grows on the root of Saffron,
and destroys it if allowed to spread.

Missletoe. The Missletoe, Viscum album, is found for the
most part on the Apple-tree ; but sometimes also
on the Oak. The fruit of it when ripe is a soft,
white, and shining berry, filled with a glutinous
and sweetish juice, and about as large as a Pea. If
this berry, whether by accident or design, is made
to adhere to the trunk or branch of either of the
foregoing trees, which from its glutinous nature it
may readily be made to do, it germinates by send-
ing out a small globular body attached to a pedicle,
which after it acquires a certain length bends to-
wards the bark, whether above it or below it, into
which it insinuates itself by means of a number of
small fibres which it now protrudes, and by which
it abstracts from the plant the nourishment neces-
sary to its future developement. When the root
has thus fixed itself in the bark of the supporting
tree, the stem of the parasite begins to ascend, at
first smooth and tapering, and of a pale green colour,
but finally protruding a multiplicity of branches
by continually dividing into jointed forks. The
leaves are of the colour of the stem, tongue-shaped
entire, smooth. The plant is an evergreen ; not
readily distinguished in the summer, when the
leaves of the tree on which it grows are fully ex-
panded ; but becoming very conspicuous in the

SECT. I. SOILS. 427

winter, from the green and bushy appearance of
its leaves, or from the white appearance of its
ripened berries.

It seems to have been thought by some botanists
that the roots of the Missletoe penetrate even into
the wood, as well as through the bark.* But the
observations of Du Hamel show that this opinion
is not well founded. The roots are indeed often
found within the wood, which they thus seem to
have penetrated by their own vegetating power.
But the fact is, that they are merely covered by the
additional layers of wood that have been formed
since the fibres first insinuated themselves into the
bark.-}-

Among the Druids, the Missletoe of the Oak-tree
was revered as sacred ; and its medical virtues were
held in the highest estimation. But it forms no
prominent article in the Materia Medica of present
times ; except that it is still regarded by farmers
and cow doctors as being of peculiar efficacy in
some diseases incident to cattle; and by the lower
orders of people in general as possessing some pe-
culiar medical properties, in which they seem to
think it operates as a sort of charm, but particu-
larly in its capacity of affording a preventative to
sterility ; which accounts for the institution of the
ancient and still prevailing custom with the inha-
bitants of the cottage of gathering boughs of it

* With. Arrang. vol. ii. p. 203.
f Phys. des Arb. liv. v. chap. i.

423 CAUSES LIMITING PROPAGATION. CHAP. X,

and suspending them from the ceiling of their
apartments, about the season of Christmas when
the fijuit is ripe.

Dodder. Cuscuta europcza, or Dodder, though it is to be
accounted a truly parasitical plant in the issue, is
not yet originally so. For the seed of this plant
when it has fallen to the ground takes root ori-
ginally by sending down its radicle into the soil and
elevating its stem into the air. It is not yet, there-
fore, a parasitical plant. But the stem which is
now elevated above the surface lays hold of the first
plant it meets with, though it is particularly partial
to Hops and Nettles, and twines itself around it,
attaching itself by means of little parasitical roots
at the points of contact, and finally detaching itself
from the soil altogether by the decay of the ori-
ginal root, and becoming a truly parasitical plant.
Withering describes the plant in his arrangements
as being originally parasitical ; but this is certainly
not the fact.

The Orobanchc, or Broom-rape, which attaches
itself by the root to the roots of other plants, is also
to be regarded as being truly parasitical, though it
sometimes sends out fibres which seem to draw
nourishment from the earth. It is found most fre-
quently on the roots of common Broom ; but I
have found it also on the roots of Scabiosa arvensis;
and even upon the root of Samolus Valerandi.
This last case I met with in the garden of the Rev.
Dr. Dawson, of Burgh, in Suffolk, in the month
8

SECT. II. CLIMATE. 42$

of September, 1808. I think the Samolus Vakrandl
was raised from seed by the Doctor, who cultivated
British plants with as much industry as others often
cultivate exotics.

The Epidendron flos aeris, a native of India Epiden-
beyond the Ganges, is regarded also by botanists ^nt.
as a parasitical plant, because it is generally found
growing on other trees.* But there is a circum-
stance related concerning it which seems to excite a
suspicion that it cannot be truly a parasitical plant.
Mr. Loureiro says it will continue to vegetate for
years even when suspended from the ceiling of a
room, producing blossoms that exhale the richest
fragrance; from which I think it may be inferred that
it derives its nourishment wholly from the atmos-
phere, and not from the plant to which it adheres.

SECTION II,
Climate.

MOST plants are affected by climate, and many
are confined to a particular hemisphere or latitude
which they are seldom found to pass. Such is the
case with the Proteacece of Jussieu, which are con-
fined almost entirely to the southern hemisphere,
and abound chiefly in the latitude of the Cape of
Good Hope.-)- Hence it is that habitats and cli-

* Willdenow, Princ. Bot. p. 263.
f Lin. Trans, vol. x. p. 20.

4-30 CAUSES LIMITING PROPAGATION. CHAP. X.

mates are often the same ; and hence also plants
Equate- that are natives of the equatorial regions cannot be
made to vegetate in high latitudes, except by
putting them into a hot-house and keeping up an
artificial heat This is known to every body who
is the least conversant in gardening, and forms one
of the most difficult branches of the art. Hence
it is impossible to naturalize the equatorial plants
in this climate such as the Palms, Pine-apple, and
others ; because the degree of cold naturally sub-
Tropical sisting in it would infallibly kill them. In like

and polar . *

plants, manner plants that are indigenous to the more tem-
perate regions, cannot be made to vegetate in the
equatorial regions, because the excessive heat of
such regions would destroy them. The Wheat and
Barley of Europe will not grow within the tropics ;
the same remark applies to plants of still higher
latitudes, such as those within the polar circles
which cannot be made to vegetate in more southern,
latitudes, nor can the plants of more southern lati-
tudes be made to vegetate there.

Such is the case with plants in general, and such
are the boundaries which they cannot pass, con-
fining them to the peculiar habitat destined by
Inured by nature. But some plants may be inured to cli-
to opposite rciates of which they are not indigenous; and this
climates, seems ^o be most easily done in going from a hot
to a cold climate, particularly with herbaceous
plants. Because it often happens that the frosts of
winter are accompanied with snow which shelters

SECT. II. CLIMATE. 431

the plant from the inclemency of the atmosphere
till the return of spring. Trees and shrubs, on the
contrary, are naturalized with more difficulty, be-
cause they cannot be so easily sheltered from the
colds, owing to the greater length of their stem and
branches. But nature, always provident for the pre- Or adapt-
servation of all her works, and always fertile in sehrs'by"
resources for the accomplishment of her object, has nature'
also furnished some plants with the capacity of
vegetating in almost all climates, or of naturalizing
themselves in almost any. This is particularly the
case with greens and eatable roots, such as Cabbages,
Carrots, Potatoes, that is, the common culinary
plants most useful to man. And hence they have
followed man into all climates and quarters of the
globe. Some aquatic plants are found capable of
vegetating also in almost all climates, perhaps be-
cause the water modifies in some measure the tem-
perature. Lemna minor has been found through-
out almost the whole of Europe, North America,
and even Asia;* and Fucus natans, both under the
equator and within the polar circles. Plants which
grow in the depths of the ocean are not at all af-
fected by climate, because they are beyond the
reach of the influence of the sun's rays, and air ;
go that habitats in this case must be fixed by the
greater or less degree of salts held in solution by
the water. As the habitats dependant on climate
are, like the climates themselves, bounded by certain
* Willdenow, p. 395.

CAUSES LIMITING PROPAGATION. CHAP. X.

parallels of latitude as they recede from or approach
to the equator; they are consequently the same in
all longitudes, and nearly so in corresponding lati-
tudes, on either side of the equator. But the
warmer climates are more favourable upon the
whole to vegetation than the colder, and that nearly
in proportion to their distance from the equator.
In Spitzbergen botanists have hitherto found only
3O indigenous plants, in Lapland 534, in Iceland
553, in Sweden 1299, in Brandenburg 2OOO, in
Piemont 28,00, in Jamaica, Madagascar, and the
coast of Coromandel, from 4OOO to 5000.* The
same plants, however, will grow in the same degree
of latitude, throughout all degrees of longitude, and
also in correspondent latitudes on different sides of
the equator ; the same species of plants, as some
of the Palms and others, being found in Japan,
India, Arabia, the West Indies, and part of South
America, which are all in nearly the same latitudes;
and the same species being also found in Kams-
chatka, Germany, Great Britain, and the coast of
Labrador, which are all also in nearly the same la*
titudes.

* Willdenow, p. 374.

SECT. III. ALTITUDE. 433

SECTION III.
Altitude.

ALTHOUGH the above rule with regard to cli-
mates is of pretty general application, yet it is at
the same time liable to a good many exceptions,
owing chiefly to the difference of altitude that may
and often does occur in countries of the same lati-
tude ; as well as to a variety of other causes af-
fecting the vegetable. This must be obvious from
the consideration that the temperature of any place
is affected as much from its altitude as from its lati-
tude. The summit of the mountains of the Andes, AS effect*
even where situated almost directly under the pe^ui™"
equator, are yet covered with eternal snow.

Hence it follows that all variety of climates may And con-
exist even in the same latitude merely by means of vegetable
the altitude of the place, and consequently all va- ha°ltat'
rieties of vegetable habitat. And this was found
by Tournefort to be literally the case during his
travels in Asia. At the foot of mount Ararat he
met with plants peculiar to Armenia ; above these
he met with plants which are found also in France ;
at a still greater height he found himself surrounded
with such as grow in Sweden, and at the summit
with such as vegetate in the polar regions.

This accounts for the great variety of plants And natu-
which are often found in a Flora of no great ex- ra

VOL. ii. 2 F

434 CAUSES LIMITING PROPAGATION. CHAP. X.

tent: and it may be laid down as a botanical
axiom, that the more diversified the surface of the
country the richer will its Flora be, at least in the
same latitudes. It accounts also for the want of
correspondence between plants of different coun-
tries though placed in the same latitudes ; because
the mountains or ridges of mountains, which may
be found in the one and not in the other, will pro-
duce the greatest possible difference in the character
of their Floras. And to this cause we may ascribe
the diversity that often actually exists between
plants growing in the same latitudes, as between
those of the north-west and north-east coast of
North America, as also of the south-west and south-
east coast ; the former being more mountainous, the
other more flat. Sometimes the same sort of dif-
ference takes place between the plants of an island
and those of the neighbouring continent; that is,
if the one is mountainous and the other flat ; but
if they are alike in their geographical delimation,
then they are generally alike in their vegetable pro-
ductions.

Cold and lofty situations are the favourite habitat
of most cryptogamic plants of the terrestrial cfass^
especially the Fungi, Alga, and Mosses ; as also of
plants of theclass Tetr adynamia, and of the Umbellate
and Syngencsial tribes. Whereas trees and shrubs,
Ferns, Parasitic plants, Lilies, and Aromatic plants,
are most abundant in warm climates ; only this is not
to be understood merely of geographical climates,

SECT. III. ALTITUDE. 435

because, as we have seen, the physical climate de-
pends upon altitude. In consequence of which,
combined with the ridges and direction of the
mountains, America and Asia are much colder in
the same degrees of northern latitude than Europe.
American plants vegetating at 42° of northern lati-
tude will vegetate very well at 52° in Europe. The
same, or nearly so, may be said of Asia, which in
the former case is perhaps owing to the immense
tracts of woods and marshes covering the surface,
and in the latter to the more elevated and moun-
tainous situation of the country affecting the degree
of temperature. So also Africa is much hotter
under the tropics than America; because in the
latter the temperature is lowered by immense
chains of mountains traversing the equatorial re-
gions, while in the former it is increased by means
of the hot and burning sands that cover the greater
part of its surface.

The effects of altitude are observable also even
in the case of aquatics, as modifying the habitats ;
thus some acquatics float always on the surface of
the water, as Lemna, while others are either par-
tially or wholly immersed. Such as grow in the
depths of the sea are not influenced by climate ;
but such as are near the surface are influenced by
climate, and have their habitats affected by it.

2 F

436 CAUSES LIMITING PROPAGATION. CHAP. X.

SECTION IV.

General Remarks.

Habitatin- THE habit of vegetables is sometimes affected by
habiT"5 *e habitat, so as to give to plants of different coun-
tries, though of the same genus, a sort of charac-
teristic feature by which their country may often
be discovered, in the same manner as the national
distinctions which are observable in the looks and
colour of mankind, and which are effected chiefly
by climate. On this subject botanists have made
Ascxcm- the following remarks : — Asiatic plants are remark-
5!iSric|n able for their suPerior beauty ; African plants for
European, their thick and succulent leaves, as in the case of
and Ame- the Cacti ; and American plants for the length
plants. a"d smoothness of their leaves, and for a sort of
singularity in the shape of the flower and fruit.
The flowers of European plants are but rarely beau-
tiful, a great proportion of them being amenta-
ceous. Plants indigenous to polar and mountainous
regions are generally low, with small compressed
leaves ; but with flowers large in proportion. Plants
indigenous to New Holland are distinguishable for
small and dry leaves that have often a shrivelled
appearance. In Arabia they are low and dwarfish ;
in the Archipelago they are generally shrubby and
furnished with prickles; while in the Canary Islands
many plants, which in other countries are merely
herbs, assume the port of shrubs and trees.

£CT. IV. GENERAL REMARKS. 43?

The shrubby plants of the Cape of Good Hope
and New Holland exhibit a striking similarity, as
also the shrubs and trees of the northern parts of
Asia and America, which may be exemplified in
the Platanus orientalis of the former, and in Pla-
tanus occidentalis of the latter, as well as in Fagtis
sylvatica and Fagus latifolia, or Acer cappadoci-
cum, and Acer saccharinum ; and yet the herbs and
undershrubs of the two countries do not in the
least correspond.*

A change of habitat will often alter the habit of
a plant so much that the species can scarcely be
recognized ; particularly if you remove it from its
natural and uncultivated state into a state of culti-
vation. Hence the colour of the flower is some- influenc-
times changed and frequently the figure of the ^ figure'
leaves, as in common Colewort, and Celery : and
hence the Crab-tree and others divest themselves
of their thorns, and flowers are often rendered
double.

But plants will often thrive very well though Though
transported from their native habitats by the art helioTof
and industry of man even into countries where they thePlant>
would not naturally have disseminated themselves.
Most of the culinary plants of Europe have been
brought from the east, through the Greeks and
Romans. And several useful vegetables, but par-
ticularly the Potatoe, have been brought from Ame-

* Willdenow, Prin. Bot. p. 390,

438 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

rica.* Phaseolus vulgaris, and Impatiens Bal-
samina where brought originally from India ; and
Datura Stramonium) which is now naturalized in
Europe was brought originally from India or Abys-
sinia. Buckwheat and most species of Corn and
Peas came also from the east, and along with them
several plants found among Corn only, such as
Centaurea Cyanus, Agrostemma Githago, Ra-
phanus Raphanistrum, and Myagrum sativum.

CHAPTER XI.

EVIDENCE AND CHARACTER OF VEGETABLE VITALITY.

Criterion THE best and most satisfactory evidence of the
principle, presence and agency of a vital principle as inherent
in any subject is perhaps that of its rendering the
subject in which it inheres capable of counteract-
ing the laws of chemical affinity. This rule, which
seems to have been first instituted by Humboldt, is
obviously applicable to the case of animals, as is
proved by the process of the digestion of the food,
and its conversion into chyle and blood ; as well as
from the various secretions and excretions effected
by the several organs, and effecting the growth and
developement of the individual, in direct opposition

* This most useful plant was first brought into Europe by Sir
W. Ralegh, in 1623.

SECT. I. EXCITABILITY. 439

to the acknowledged laws of chemical affinity,
which, as soon as the vital principle is extinct,
begin immediately to give indication of their action
in the incipient symptoms of the putrefaction of
the dead body.

But the rule is also applicable to the case of ve- Applied to
getables, as is proved by the intro-suseeption, di- V
gestion, and assimilation of the food necessary to
their developernent ; all indicating the agency of a
principle capable of counteracting the laws of che-
mical affinity ; which, at the period of what is
usually called the death of the plant, begin also
immediately to act, and to give evidence of their
action in the incipient symptoms of the putrefac-
tion of the vegetable. Vegetables are therefore
obviously endowed with a species of vitality. But
admitting the presence and agency of a vital prin-
ciple inherent in the vegetable subject, what are
the peculiar properties by which this principle is
characterized?

SECTION I.
Excitability.

ONE of the most distinguishable properties of
the vital principle of vegetables is that of its ex-
citability, or capacity of being acted upon by the
application of natural stimuli) impelling it to the
exertion of its vegetative powers; the natural
stimuli thus impelling it being light and heat.

*V\

OF THE

(i UNIVERSITY )

44O CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

SUBSECTION I.

Action of Light. — The stimulating influence of
light upon the vital principle of the plant is dis-
coverable, whether in the stem, leaf, or flower.
The direction of the stem is influenced by the
action of light.

Jnfluenc- If a plant is placed in a room or cave in which
rection of" there is only one small aperture for the admission
ttoiten, Qf ijgj^ the gtem wiH gradualiy bend towards that

aperture. Bonnet sowed some French Beans in a
dark cave, with a view to ascertain the effect of the
small portion of light transmitted to them through
the entrance : the stem was a little inclined to-
wards the entrance during the day, but it re-
gained its erect position partially at least during
the night.

The vl- The vigour and colour of the stem are also af-
cobur"of fected by the presence or absence of light. If a
the plant, cu^ting of Potatoe is left to vegetate in a cellar,
where there is but little access to light and air, the
stem will shoot out to a great length in the direc-
tion of the light ; but pale, and limber, and trailing
on the floor, Bonnet planted three Beans for the
purpose of comparative experiment, one in the
open air, another in a tube of glass covered at the
top ; and a third in a tube of wood covered at the
top also. The first plant was strong and luxuriant ;
the second was also strong, and inclined towards the

SECT. I. EXCITABILITY. 441

sun ; but the third, though tall, was pale and sickly.
Hence it is upon the principle of the exclusion of
light that plants are blanched, as in the case of the
blanching of Celery, which is sometimes termed also
etiolation.

The direction and luxuriance of the branches The direc
depend also on the presence and action of light, as branches,
is particularly observable in the case of hot-house
plants, the branches of which are not so conspicu-
ously directed, either to the flue in quest of heat,
or to the door or open sash in quest of air, as to
the sun in quest of light. Hence also the branches of
plants are often more luxuriant on the south than on
the north side ; or at least on the side that is best
exposed to light.

The position of the leaf is also strongly affected The posi-
by the action of light to which it uniformly turns f^0
its upper surface. This may be readily perceived
in the case of trees trained to a wall, from which
the upper surface of the leaf is by consequence
always turned ; being on a south wall turned to the
south, and on a north wall turned to the north.
And if the upper surface of the leaf is forcibly
turned towards the wall and confined in that po-
sition for a length of time, it will soon resume its
primitive position upon regaining its liberty, but
particularly if the atmosphere is clear. Bonnet
tried to retain a leaf in its inverted position by
means of twisting the leaf-stalk ; but it was always
found to untwist itself again in the course of a

442 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

short time, and again to present its upper surface
to the sun or light. This it was sometimes found
to do even in the night ; but always the most ex^
peditiously in young subjects. If the experiment
is often repeated, the leaf resumes its original posi-
tion with more difficulty, and exhibits evident
marks of being injured by the exertion, in the
appearance of several black spots about the veins
of the under surface, and in the scaling off of the
cuticle.

But all leaves are not equally susceptible to the
action of the stimulus of light. The leaves of the
Mallow are said to exhibit but slight indications of
this susceptibility, as also sword shaped leaves ; the
leaves of the Missletoe, which have never been
known to resume a former position in consequence
of any change in the position of the branch, be-
cause perhaps they are equally susceptible on both
sides.* But succulent leaves are said to be parti-
cularly susceptible, notwithstanding their thick and
firm texture ; and if the leaf of a Vine is even se-
parated from the branch and suspended by a fine
thread, so as that the upper surface shall be turned
from the light, it will yet gradually alter its position
till it comes round again to it.-f- This experiment
requires to be made with great care and delicacy
lest the leaf should be made to turn by means of
the effect of the atmosphere upon the thread ;
though in this case it may perhaps be said that the

* Smith's Introduction, p. 208. t Ibid.

SECT. I. EXCITABILITY. 443

change is not effected by the stimulus of the light
acting on the vital principle, but rather on the
fibres of the leaf. But the reply is that the leaf is
not yet entirely deprived of the vital principle ; as
it is not to be supposed that the experiment would
succeed upon a leaf that is withered and decayed.

Such are the effects produced. Is light the sole Light the
agent? It had been conjectured that the effect is"0
partly attributable to the agency of heat ; and to
try the value of the conjecture Bonnet placed some
plants of the Atriplex in a stove heated to 25° of
Reaumur. Yet the stems were not inclined to the
side from which the greatest degree of heat came ;
but to a small opening in the stove. Heat then
does not seem to exert any perceptible influence in
the production of the above effects. Does mois-
ture? Bonnet found that the leaves of the Vine
exhibited the same phenomenon when immersed in
water as when left in the open air. Whence it
seems probable that light is the sole agent in the
production of the effects in question.

But as light produces such effects upon the leaves. Counter
so darkness or the absence of light produces an effect
quite the contrary ; for it is known that the leaves
of many plants assume a very different position in
the night from what they have in the day. This is
particularly the case with winged leaves, which,
though fully expanded during the day, begin to
droop and bend down about sun-set and during the
fall of the evening dew, till they meet together on the

44/1 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

inferior side of the leaf-stalk, the terminal lobe, if
the leaf is furnished with one, folding itself back till
it reaches the first pair ; or the two side lobes, if the
leaf is trifoliate, as in the case of common Clover,
which seems to have been first observed by the
daughter of Linnaeus. So also the leaflets of the
False Acacia and Liquorice hang down during the
night, on each side of the mid-rib, but do not meet
beneath it. The leaves of Mimosa pudica fold
themselves up along the common foot-stalk so as to
overlap one another. But, perhaps, this effect is
produced partly by the agency of moisture as it is ac-
celerated by dews and rains, and may even be oc-
casioned by artificial watering : or perhaps such
leaves as fold themselves up in the above man-
ner may require an interval of rest, which they thus
obtain, after having been exposed throughout the
day to the stimulus of light. And if so, then Linnaeus
has not without propriety designated the above
phenomenon by the appellation of The Sleep of
Plants.
Influence The expansion of the flower is also effected by the

Sower". acti°n °f ]i£ht- Many PlantS d° n0t fulty exPan(i
their petals except when the sun shines ; and hence

alternately open them during the day and shut
them up during the night. This may be exemplified
in the case of papilionaceous flowers in general,
which spread out their wings in fine weather to ad-
mit the rays of the sun, and again fold them up as
the night approaches. It may be exemplified also

6

SECT. I. EXCITABILITY. 445

in the case of compound flowers, as in that of the
Dandelion and Havvkweed. But the most singular
case of this kind is perhaps that of the Lotus of the
Euphrates as described by Theophrastus, which he
represents as rearing and expanding its blossom by
day, closing and sinking down beneath the surface
of the water by night, so as be beyond the grasp of
the hand, and again rising up in the morning to
present its expanded blossom to the sun.* The
same phenomenon is related also by Pliny.-f~

But although many plants open their flowers in
the morning and shut them again in the evening,
yet all flowers do not open and shut at the same
time. Plants of the same species are, however,
pretty regular to an hour, other circumstances being
the same ; and hence the daily opening and shutting
of the flower has been denominated by botanists
The Horologium Flora. Flowers requiring but a Horolo-
slight application of stimulus open early in the florae,
morning, while others requiring more open some-
what later. Some do not open till noon, and some,
whose extreme delicacy cannot bear the action of
light at all, open only at night, such as the Cactus
grandiflora, or Night-blowing Cereus.

But it seems somewhat doubtful whether or not Islightthe

f, . , sole agent?

light is the sole agent in the present case ; tor it has
been observed that equatorial flowers open always
at the same hour, and that tropical flowers change
their hour of opening according to the length of

, re. A. •]• Lib. xiii. 18.

44() CHARACTER OF VEGETABLE VITALITY. CHAP. XT.

. the day. It has been observed also, that the flowers
of plants that are removed from a warmer to a
colder climate expand at a later hour in the latter.
A flower that opens at six o'clock in the morning at
Senegal, will not open in France or England till
eight or nine ; nor in Sweden till ten. A flower
that opens at ten o'clock at Senegal will not open
in France or England till noon or later, and in
Sweden it will not open at all. And a flower that
does not open till noon or later at Senegal, will not
open at all in France or England. This seems as if
heat or its absence were also an agent in the open-
ing and shutting of flowers ; though the opening of
such as blow only in the night cannot be attributed
either to light or heat.
Vegetable But the opening or shutting of some flowers

weather-
glass, depends not so much on the action or the

stimulus of light as on the existing state of the at-
mosphere, and hence their opening or shutting
betokens change. If the Siberian Sowthistle shuts
at night, the ensuing day will be fine; and if it opens,
it will be cloudy and rainy. If the African Mari-
gold contines shut after seven o'clock in the morn-
ing, rain is near at hand. And if the Convolvulus
arvensis, Calendula jluvialis, or Anagallis arvemis,
are even already open, they will shut upon the ap-
proach of rain, the last of which from its peculiar
susceptibility has obtained the name of the Poor
Man's Weather-glass.
Nutation. But some flowers not only expand during the

SECT. I. EXCITABILITY. 447

light of day ; they incline also towards the sun, and
follow his course, looking towards the east in the
morning, towards the south at noon, and towards
the west in the evening ; and again returning in the
night to their former position in the morning. Such
flowers are designated by the appellation of Hello-
tropes, on account of their following the course of
the sun ; and the movement they thus exhibit is
denominated their nutation. This phenomenon
had been observed by the ancients long before they
had made any considerable progress in botany, and
hadevenbeenintervoven into their mythology,having
originated, according to the records of fabulous his-
tory, in one of the metamorphoses of early times.
Clytie, inconsolable for the loss of the affections of
Sol, by whom she had been formerly beloved, and
of whom she was still enamoured, is represented as
brooding over her griefs in silence and solitude ;
where refusing all sustenance, and seated upon the
cold ground, with her eyes invariably fixed on the
sun during the day, and watching for his return
during the night, she is at length transformed into
a flower, retaining, as much as a flower can retain
it, the same unaltered attachment to the sun. This
is the flower which is denominated He Hot r opium Exempli-
by the ancients, and described by Ovid as Flos qui

adsolemvertitur.* But it is to be observed that plura>
the flower alluded to by Ovid cannot be the Helio-
tropium of the moderns, because Ovid describes it

* Metamorph. lib. iv, 1. 2,50.
4

448 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

as resembling the Violet : much less can it be the
Sun-flower of the moderns, which is a native of
America, and could not consequently have been
known to Ovid ; so that the true Hdiotropium of
the ancients is perhaps not yet ascertained.

Bonnet has further remarked that the ripe ears
of Corn, which bend down with weight of grain,
scarcely ever incline to the north, but always less or
more to the south ; of the accuracy of which re-
mark anyone may easily satisfy himself by looking
at a field of Wheat ready for the sickle ; he will
find the whole mass of ears nodding, as if with one
consent, to the south.

And in The cause of the phenomenon has been supposed
co^Td to be a contraction of the fibres of the stem or
flower-stalk on the side exposed to the sun ; and
this contraction has been thought by M. De La Hire
and Dr. Hales to be occasioned by an excess of
transpiration on the sunny side ; which is probably
the fact, though there seems upon this principle to
be some difficulty in accounting for its returning at
night ; because if you say that the contracted side
expands and relaxes by moisture, what is it that
contracts the side that was relaxed in the day ? The
moisture, of which it is no doubt still full, would
counteract the contraction of its fibres, and pre-
vent it from resuming its former position in the
morning.

SECT. I. EXCITABILITY, 44 Q

SUBSECTION II.

Action of Heat. — Heat as well as light acts also
as a powerful stimulus to the exertion of the vital
principle. This has been already shown in treating
of the process of germination, in which it was found
that seeds will not germinate at a very low tem-
perature, even though placed in a proper soil, so that
such as sow themselves do not generally come up
till the spring when the temperature has been raised
to some considerable height by the rays of the re-
turning sun. But the same thing is observable As influ-
with regard to the developement and maturation of protrusion

the leaves, flower, and fruit ; for although all plants
produce their leaves, flower, and fruit, annually, yet and frulU
they do not all produce them at the same period
or season. This forms the foundation of what Lin-
naeus has called the Calendarium Flora, including
a view of the several periods of the Frondescence
and Efflorescence of Plants, together with that of the
Maturation of the Fruit.

ART. 1. Frondescence. — It must be plain to every Seasons
observer that all plants do not protrude their leaves different °
at the same season, and that even of such as doPlants
protrude them in the same season, some are earlier
and some later. The Honeysuckle protrudes them
in the month of January ; the Gooseberry, Currant,
and Elder, in the end of February or beginning of
March ; the Willow, Elm, and Lime-tree, in April;

VOL. II. 2 G

4.5O CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

and the Oak and Ash, which are always the latest
among trees, in the beginning or towards the middle
of May. Many annuals do not come up till after
the summer solstice ; and many Mosses not till
after commencement of winter. This gradual and
successive unfolding of the leaves of different plants
seems to arise from the peculiar susceptibility of the
species to the action of heat, as requiring a greater
or less degree of it to give the proper stimulus to the
vital principle. But a great many circumstances
will always concur to render the time of the unfold-
ing of the leaves somewhat irregular ; because the
mildness of the season is by no means uniform at
the same period of advancement ; and because the
leafing of the plant depends upon the peculiar de-
gree of temperature, and not upon the return of a
particular day of the year. Hence it has been
thought that no rule could be so good for directing
the husbandman in the sowing of his several sorts
of grain as the leafing of such species of trees as
might be found by observation to correspond best
to each sort of grain respectively, in the degree of
temperature required.

A signal to Linnaeus, who instituted some observations on
bandmaii. the subject about the year 1750, with a view chiefly
to ascertain the time proper for the sowing of Barley
in Sweden, regarded the leafing of the Birch-tree as
being the best indication for that grain, and recom-
mended the institution of similar observations with
regard to other sorts of grain, upon the ground of

2

*ECT. I. EXCITABILITY. 451

its great importance to the husbandman. But
however plausible the rule thus suggested may be
in appearance, and however pleasing it may be in
contemplation, it is not likely that it will ever be
much attended to by the husbandman ; because
nature has furnished him with indications that are
still more obvious in the very evidence of his own
feelings, as well as perhaps more correct ; as all trees
of the same species do not come into leaf precisely
at the same time, and as the weather may yet alter
even after the most promising indications.

ART. 1. Efflorescence. — The flowering of the Seasons
plant, like the leafing, seems to depend upon the different
degree of temperature induced by the returning flowers*
spring, as the flowers are also protruded pretty re-
gularly at the same successive periods of the season.
The Mezereon and Snow-drop protrude their flowers
in February ; the Primrose in the month of March ;
the Cowslip in April ; the great mass of plants in
May and June ; many in July, August, and Septem-
ber ; some not till the month of October, as the
Meadow Saffron ; and some not till the approach or
middle of winter, as the Laurustinus and Arbutus.
Such at least is the period of their flowering in this
country ; but in warmer climates they are earlier,
and in colder climates they are later.

Between the tropics, where the degree of heat is

always high, it often happens that plants will flower

more than once in the year ; because they do not

there require to wait till the temperature is raised to

2 G 2

452 CHARACTER OF VEGETABLE VITALITY. CHAP. XI,

a certain height, but merely till the developement
of their parts can be effected in the regular opera-
tion of nature, under a temperature already suffi-
cient. For the greater part, however, they flower
during our summer, though plants in opposite
hemispheres flower in opposite seasons. But in
all climates the time of flowering depends also
much on the altitude of the place as well as on
other causes affecting the degree of heat. Hence
plants occupying the polar regions, and plants oc-
cupying the tops of the high mountains of southern
latitudes are in flower at the same season ; and
hence the same flowers are later in opening in North
America than in the same latitudes in Europe, be-
cause the surface of the earth is higher, or the win-
ters more severe.

Notde- ART. 3. Maturation of the Fruit. — Plants ex-
hibit as much of diversity in the warmth and length
of time necessary to mature their fruit as in their
frondescence and flowering ; but the plant that
flowers the soonest does not always ripen its fruit
the soonest. The Hazle-tree, which blows in
February, does not ripen its fruit till autumn ;
while the Cherry, that does not blow till May.
ripens its fruit in June. It may be regarded, how-
ever, as the general rule that if a plant blows in
spring it ripens its fruit in summer, as in the case
of the Currant and Gooseberry ; if it blows in
summer it ripens its fruit in autumn, as in the case
of the Vine ; and if it blows in autumn it ripens its

SECT. I. EXCITABILITY. 453

fruit in the winter. But the Meadow Saffron,
which blows in the autumn, does not ripen its fruit
till the succeeding spring.

Such are the primary facts on which a Calenda- Calenda-
rium Florae should be founded. They have not
hitherto been very minutely attended to by bota-
nists ; and perhaps their importance is not quite
so much as has been generally supposed : but they
are at any rate sufficiently striking to have at-
tracted the notice even of savages. Some tribes of
American Indians act upon the very principle sug-
gested by Linnaeus, and plant their corn when the
wild Plum blooms, or when the leaves of the Oak
are about as large as a squirrel's ears. The names of
some of their months are also designated from the
state of vegetation. One is called the budding
month, and another the flowering month ; one the
Strawberry month, and another the Mulberry
month : and the autumn is designated by a term
signifying the fall of the leaf* So that the French
revolutionists were anticipated even by the Indians,
in their new names for months and seasons.

But there are several other ways in which the Miscellan-
agency of heat may be observed as exciting the
energies of the vital power. The leafits of some
of the leguminous plants, when exposed to the
action of an ardent sun, are often erected into a
vertical position on each side the leaf-stalk, which
they sometimes even pass so as to close together.
* Barton's Elem. p. 248.
3

454 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

Under similar circumstances the leaves of the
Indian Mallow become concave ; and it seems as if
the effect were produced merely, or at least, chiefly
hy means of heat ; because the same effect may be
produced even by means of the application of a hot
iron ; and yet the leafits of many such plants fold
themselves back at night so as to meet under the
leaf-stalk, a phenomenon equally wonderful with
that of nutation, and not attributable to heat.
But several species of Mimosa exhibit a singular
phenomenon even in the common foot-stalk, which is
found to have a sort of natural movement dependant
upon temperature also, so that it is elevated in the
course of the day, and depressed in the course of the
night, according to the observation of Du Hamel. At
nine o'clock in the morning of a day in the month of
September, the weather being moderately fine, the
foot-stalk of a leaf of the Mimosa pudica formed
by its position an angle of 100° with the lower part
of the stem : at noon it formed an angle of 112°:
at three o'clock in the afternoon it had fallen to an
angle of 100* : and during the night it fell to an
angle of QO° ;* thus indicating an evident suscepti-
bility to the stimulus of the action of heat.
Jfce vital As the elevation of temperature induced by the
exertsPits heat of summer is essential to the full exertion of
evengiT tne energies °f tne vital principle, so the depression
winter. of temperature consequent upon the colds of winter
has been thought to suspend the exertion of the

* Phys, des Arb. liv. iv. chap, vi.

SECT. I. EXCITABILITY. 455

vital energies altogether. But this opinion is evi-
dently founded on a mistake, as is proved by the
example of such plants as protrude their leaves and
flowers in the winter season only, such as many of
the Mosses ; as well as by the dissection of the yet
unfolded buds at different periods of the winter,
even in the case of such plants as protrude their
leaves and blossoms in the spring and summer, and
in which it has been already shown there is a regu-
lar, and gradual, and incipient developement of
parts, from the time of the bud's first appearance
till its ultimate opening in the spring. The sap, it
is true, flows much less freely, but is not wholly
stopped. Hales lopped off some branches from
plants of the Hazle, Vine, and Jessamine respect-
ively, in the course of the winter, and covered the
section of the separated branches with mastic, which
in a few days were found to have lost considerably
in weight ; whence he inferred the motion of the
sap, because it seems but reasonable to suppose that
the dissipation of sap thus lost would have been re-
paired if the branches had not been cut off. Du
Hamel planted some young trees in the autumn,
cutting off all the smaller fibres of the root, with a
view to watch the progress of the formation of new
ones. At the end of every fortnight he had the
plants taken up and examined with all possible care
to prevent injuring them, and found that, when it
did not actually freeze, new roots were always uni-
formly developed.

45(3 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

Though it Hence it follows that even during the period of

is roused ... ,, ,

into in- winter, when vegetation seems totally at a stand,

" the tree being stripped of its foliage, and the herb
the spring. apparent]v withering in the frozen blast, still the
energies of vegetable life are exerted ; and still the
vital principle is at work, carrying on in the interior
of the plant, concealed from human view, and shel-
tered from the piercing frosts, operations necessary
to the preservation of vegetable life, or protrusion
of future parts ; though it requires the returning
warmth of spring to give that degree of velocity to
the juices which shall render their motion cognizable
to man, as well as that expression to the whole
plant which is the most evident token of life : in the
same manner as the processes of respiration, diges-
tion, and the circulation of the blood are carried on
in the animal subject even while asleep ; though the
most obvious indications of animal life are those of
the motions of the animal when awake.
Bythesti- Heat then acts as a powerful stimulus to the
heat. operations of the vital principle, accelerating the
motion of the sap, and consequent developement
of parts ; as is evident from the sap's beginning to
flow much more copiously as the warmth of spring
advances, as well as from the possibility of antici-
pating the natural period of their developement by
forcing them in a hot-house. But it is known that
excessive heat impedes the progress of vegetation as
well as excessive cold ; both extremes being equally
prejudicial. Arid hence the sap flows more copiously

SECT, I. EXCITABILITY.

in the spring and autumn, than in either the sum-
mer or winter ; as may readily be seen by watching
the progress of the growth of the annual shoot,
which after having been rapidly protruded in the
spring, remains for a while stationary during the
great heat of summer, but is again elongated during
the more moderate temperature of autumn.

There are also several substances which have been
found to operate as stimulants to the agency of the
vital principle when artificially, dissolved in water
and applied to the root or branch. The germination
of Peas is accelerated by means of moistening them
in water impregnated with oxygenated muriatic
acid, as was first ascertained by Humboldt: and
the vegetation of the bulbs of the Hyacinth and
Narcissus is accelerated by means of the application
of a solution of nitre. * Dr. Barton, of Philadelphia,
found that a decaying branch of Liriodendron tu-
lipifera and a faded flower of the yellow Iris re-
covered and continued long fresh when put into
water impregnated with camphor ; though flowers
and branches, in all respects similar, did not recover
when put into common water.

* Willdenow, p. 295.

458 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

SECTION II.

Irritability.

PLANTS are not only susceptible to the action of
the natural stimuli of light and heat, exciting them
gradually to the exercise of the functions of their
different organs in the regular progress of vegeta-
tion ; they are susceptible also to the action of a
variety of accidental or artificial stimuli, from the
application of which they are found to give indica-
tions of being endowed also with a property similar to
what we call irritability in the animal system.
This property is well exemplified in the genus Mi*
mosa ; but particularly in that species known by the
name of the Sensitive Plant.
Exempli- If a leafit of this plant is but touched, however

fiedinthe

Sensitive slightly, by any extraneous body, it immediately
ant> shrinks into itself, and communicates the impulse,
if strong, perhaps to the whole wing, each leafit
shrinking, or each pair of leafits collapsing in suc-
cession, and the leaf-stalk itself sinking downwards
as if by a joint, at its point of union with the stem.
The following experiments were made by Duhamel
with a view to ascertain the extent of its susceptibi-
lity :* — At eight o'clock in the morning of a day in
September a leaf-stalk of a Sensitive Plant formed
with the lower part of the stem an angle of 135°,
which upon being touched fell to an angle of 80°;
* Phys. des Arb. liv, iv. chap, vi,

SECT. II. IRRITABILITY. 45Q

an hour afterwards it rose again to 135°, and upon
being touched a second time fell again also to 80°;
an hour and a half afterwards it rose to 145°, and
upon being touched fell to 135°, where it remained
till five o'clock in the evening, when upon being
touched it fell to 1 10°. Hence it follows that the
susceptibility is greatest in the morning, or during
the heat of the day ; but the leaf recovers itself
sooner or later according to the vigour of the plant,
the season of the year, and temperature of the at-
mosphere, as well as the hour of the day at which
the experiment is made ; though it does not always
recover itself in the same way: for sometimes the
common foot-stalk recovers first, sometimes the
lateral foot-stalk, and sometimes the leafits them-
selves.

The leaves of Diontea Muscipula, or Venus1 nionaea
Fly-trap, are also extremely susceptible to the action ia>usclpl1"
of accidental stimuli. They are all radical and ap-
proaching to battledore-shaped, with a sort of cir-
cular process at the apex, which is bisected by a
midrib and ciliated with fine hairs like an eye-lash :
this circular process is the seat of irritability,, which,
if it is touched with any sharp-pointed instrument,
or if an insect but alights upon it, the segments im-
mediately collapse and adhere so closely, that the
insect is generally squeezed to death in its grasp ; or
at the least detained a prisoner.

A similar susceptibility to the action of accidental Drosera,
stimuli has been observed in the leaves of the seve-

40O CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

ral British species of Drosera, or Sun-dew, of which
a very full and satisfactory account is given in the
second volume of Withering's Arrangements, under
the head of this genus.
Berberis But sometimes the irritability resides in the

commu- ji- • i •

nis, flower, and has its seat either in the stamens or style.
The former case is exemplied in the flower of the
Berberry, the stamens of which when undisturbed
lie reclined upon the petals, and shelter the anthers
under their concave tips. But if the inner side of
the filament is accidentally or intentionally touched
with any fine instrument or other pointed substance,
the stamen immediately bends itself inwards till its
anther strikes against the stigma. This fact had
been long known to botanists, but it remained to
be ascertained whether the susceptibility in question
was confined to the inner side of the filament merely,,
or whether it pervaded the whole stamen. With this
object in view, Sir J. E. Smith, having procured some
flowers fully blown, on the 25th of May, JJ86, ex-
amined them with great care, and after applying
the point of a quill or fine bristle with all possible
delicacy to every part of the surface of the stamen,
he found that it no where exhibited any indications
of susceptibility except on the inner side of the fila-
ment and towards the base. It had been thought
that the stamens possessed this property only at the
time of shedding the pollen; but Sir J. E. Smith
found that they possess it at all ages, and even when
the petal with its annexed filament has fallen to the

SECT. II. IRRITABILITY.

461

ground, gradually recovering their original situation,
and capable of being again stimulated as before.*

The stamens of Cactus Tuna, a sort of Indian Cactus
Fig, are said to be endowed with a similar irritabi-
lity. If a quill or feather is drawn across its long
and slender filaments, which surround the germen
in great numbers, they will immediately begin to
bend to the one side, and will by and by sink down
to the bottom of the flower.^

The latter case, or that in which the seat of irri- ^nd Stli-
tability is confined to the style, is exemplified in
Stylidium glandulosum, a native of New Holland.
The style of this flower, which is about an inch in
length, is bent backwards a little above the base, in
the manner of the piece of iron that is fixed to the
end of a shepherd's crook, or to the end of the pole
of a chaise ; so that the style forms a sort of hook
with the flower-stalk, the stigma being reflected so
as in many cases to touch it. But if the stigma is
itself touched with the point of the finger, -n other
suitable instrument, the style is immediately put
into motion, and flies back till it bends itself as
much in a contrary direction, and on the other side
of the flower, as it did in its first direction. This
experiment I had an opportunity of making on a
plant in Kew Gardens, on the 31st of May, ]810.

* Smith's Tracts. i Ibid.

462 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

SECTION HI.

Sensation.

FROM the facts adduced in the preceding sections
it is evident that plants are endowed with a capacity
of being acted upon by the application of stimuli,
whether natural or artificial, indicating the existence
of a vital principle, and forming one of the most
prominent features of it scharacter. But besides this
obvious and acknowledged property, it has been
thought by some phytologists that plants are en-
dowed also with a species of sensation.

As ascrib- The detail of the arguments adduced in support
plants by of this opinion is to be met with in a paper written
*al and Sir by Dr. Percival, and published, as I believe, in the
Smith second volume of the Manchester Transactions,
though I have never had an opportunity of consult-
ing it ; but as the opinion has been also adopted by
Sir J. E. Smith and advocated with some degree of
zeal, it is to be presumed he has selected and exhi-
bited the most substantial arguments which the case
affords, either in his Lectures or Introduction. And
yet it cannot be said that he advances his arguments
with any great degree of confidence, as he seems
rather to hope that the doctrine may be true, than
to think he has proved it to be so. But he regards
On the the irritability of the Sensitive Plant and others,
phenome- tne phenomenon of the fecundation of the Valis-
ncr'ia> together with that of the sleep of plants, as

SECT, III. SENSATION. 463

observed in the Papilionacece, Water-lily, and Plant and
others, as affording at least a strong presumption that
plants are endowed with the faculty of sensation : be-
cause he thinks it difficult to account for the phe-
nomena on any other supposition ; and because the
supposition is besides the most consonant to our
notions of the Divine goodness, as there are but
few plants in comparison that suffer from the attacks
of men or animals.*

The opposers of this doctrine argue thus : — If the
mere communication of a sentient principle were
sufficient to secure the happiness of the sentient
being, however situated and in whatever degree con-
ferred, then it might be consonant to our notions of
the Divine Goodness to suppose its existence in
plants. But as plants have no means whatever of
self-preservation or defence, and are exposed indis-
criminately to the perpetual attacks both of men
and animals, sensation could hardly be regarded as
a blessing if it were even conferred on them. We
detract nothing therefore from the Divine Goodness
by supposing them devoid of sensation ; we rather
add to it.

And perhaps it is less difficult to account for the That may
phenomena in question than has been imagined. Is Counted
not the susceptibility of the Mimosa, Stylidium, f<

wise

and others to the action of irritating stimuli, some-
thing similar to that of the muscular fibre of ani-
mals when exposed to the action of the Galvanic

* Introduction, chap. i.

464 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

fluid, after the sentient principle is gone ? Is not the
submersion of the Water Lily during the night, if
such is the fact, the result merely of the shrinking
of the stem, in the absence of light and warmth ? or
of an alteration in the specific gravity of the flower,
in consequence of the folding in of the petals ? Is
not the emerging of the male flowers of the Valis-
neria at the period of impregnation, as well as the
subsequent sinking down of the female flower, to be
attributed to the same cause ? And is not the ex-
pansion of the petals during the day, and their shut-
ting up during the night, as well as also the muta-
tion of the plant, to be attributed merely to the
chemical action of light and heat operating upon
the fibres, or vital principle of the plant, as was
supposed by Hales ? If these causes are sufficient
to account for the effects in question, then it would
be altogether unphilosophical to allege the agency
of a higher cause.

Hedysa- But one of the strongest indications of the ex-
istence of a species of sensitive principle in the plant
is perhaps that which is exhibited in the case of
Hedysarum gyrans. This plant is a native of
India, and grows on the banks of the Ganges, its
leaves are ternate, the middle leafit being larger,
and the lateral leafits smaller. All of them are in
perpetual motion up and down, sometimes equably
and sometimes by jerks, but without any unison be-
tween each other; the motion being always the
most distinct and most rapid in the lateral leafits.

SECT. IV. INSTINCT.

If their motion is temporarily suspended by grasping
them in the hand, they quicken it when the hand
is removed, as if to make up for lost time, and by
and by resume their original velocity. This move-
ment does not depend upon the application of any'
external stimulus, because it takes place alike by
night and by day, in the dark and in the light, and
requires only a very warm and fine day to be effected
in the best style ; the leaves exhibiting then a sort
of tremulous motion in addition to that already de-
scribed. Such is a phenomenon that puzzles and
astonishes every beholder, and still remains inexpli-
cable ; but which participates more of the character
of animal spontaneity than any other movement
hitherto observed in vegetables.

SECTION IV.
Instinct.

THERE is also a variety of phenomena exhibited Difficulty
throughout the extent of the vegetable kingdom, goodTJl-3
some of which are common to plants in general, niuon-
and some peculiar to certain species, that have been
thought by several botanical writers to exhibit indi-
cations, not merely of sensation, but of instinct.
The tendency of plants to incline their stem and to
turn the upper surface of the leaves to the light, tire
direction which the extreme fibres of the root will
often take to reach the best nourishment, the fold-

VOL. II. 2 H

466 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

ing up of the flower on the approach of rain, the
rising and falling of the Water Lily, and the pe-
culiar and invariable direction assumed by the twin-
ing stem in ascending its prop, are among the phe-
nomena that have been attributed to instinct.* I
have myself endeavoured to establish the doctrine of
the existence and agency of an instinctive principle
in the plant, upon the ground of the direction in-
variably assumed by the radicle and plumelet respect-
ively in the germination of the seed ; and to my
paper on this subject I must for the present be
content to refer my reader.-}*

SECTION V.

Definition of the Plant.

BUT if vegetables are living beings endowed with
sensation and instinct, or any thing approach-
ing to it, so as to give them a resemblance to ani-
mals, how are we certainly to distinguish the plant
from the animal ? At the extremes of the two king-
doms the distinction is easy ; the more perfect
animals can never be mistaken for plants, nor the
more perfect plants for animals, but at the mean,
where the two kingdoms may be supposed to unite,
the shades of discrimination are so very faint or
evanescent that of some individual productions it is
almost impossible to say to which of the kingdoms

* Tapper's Probability of Sensation in Vegetables,
t Lin. Trans, vol. xi. part ii.

SECT. V. DEFINITION OF THE PLANT. 467

\

they belong. Hence it is that substances which
have at one time been classed among plants, have at
another time been classed among animals; and
there are substances to be met with whose place
has not yet been satisfactorily determined. Of
these I may exemplify the genus Corollina, which
Linnaeus placed among animals, but which Gaertner
places among plants ; and between authorities so
great who shall attempt to decide ? To the unex-
perienced naturalist perhaps the undertaking may
appear easy ; but the great diversity of rules which
have been devised for the purpose of fixing the
limits of the two kingdoms shows but too plainly the
difficulty of the task.

The definitions of the earlier botanists were very Defini-
inaccurate. One of the ancients defined a plant to Se^bo-
be an animal fixed by means of a root. But this tamsts-
definition is good for nothing, for it requires the as-
sistance of at least two others to make it intelligible
— one for the term animal, and another for the term
root ; and if when you come to the term animal you
proceed upon the same principle, you must then say
that it is a wandering plant that has no root to fix it :
so that thus you define your terms in a circle, and
explain nothing.

Jungius,, a botanist who flourished about the Of Jim-
beginning of the 17th century, defined a plant to beglus'
a body possessing vitality, but without sensation,
and fixed to a certain spot from which it derives the
nourishment necessary to the developement of its

2 H 2

468 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

parts, and reproduction of the species. This defini-
tion is no doubt a great improvement upon the
former, but it cannot be said to be by any means
correct ; for as it has not yet been proved that plants
are endowed with sensation, so neither has it been
proved that they are totally devoid of it. And it is
very well known that all vegetables are not confined
to a particular spot, and that such as are so con-
fined do not always derive their nourishment from
that spot ; many of the aquatics even in their vege-
tating state are wafted on the surface of the water
by means of the winds, or impelled by the action
of the waves, and many of the Lichens and Algae
are attached even to the solid rock.

Of Lin- Linnaeus, the great reformer of natural history
and chief of all botanists, undertook, as well be-
came him, to fix and define the boundaries of the
mineral, vegetable, and animal kingdom ; his defi-
tion is as follows : — " Stones grow ; plants grow
and live ; animals grow, live, and feel." This defi-
nition is extremely plausible, and bears upon the
face of it the genuine stamp of the bold and mas-
terly manner of Linnseus. But with all due defe-
rence to that great and illustrious naturalist, still
his definition must be regarded as defective, at
least as relative to the distinction between the
animal and the plant. For in the first place, as it
is not quite certain that some plants do not also feel
as well as live, it is liable to the same objection with
the definition of Jungius, on which indeed it seems

SECT. V. DEFINITION OF THE PLANT.

to be founded ; and in the next place, as we are
possessed of no criterion by which we may infallibly
judge of the existence of the faculty of sensation,
the difficulty of decision remains the same as before.
For if I should happen to meet with an animal which
does not exhibit what I might be inclined to regard
as a satisfactory evidence of sensation, I must of
necessity arrange it in the class of vegetables, while
at the same time it still remains an animal.

M. Bonnet, of Geneva, defined the plant to be an Of Bon-
organized body nourished by means of roots placed net"
externally ; the animal being just the converse —
that is, an organized body nourished by means of
roots placed internally, namely, the lacteals of the
animal system. This definition is sufficiently ap-
plicable to the generality of cases, but it fails just
where the foregoing definitions have been found to
fail — that is, in cases which are really doubtful. And
if this criterion is the only true test of distinction
between the animal and vegetable, then all animals"
whatever before they are protruded from the egg or
womb are to be regarded as plants ; because they
are then nourished by means of an umbilicus, which
we cannot but regard as an external root.

Dissatisfied with all previous distinctions, and Of Hed-
qualified from the depth of his knowledge and ex- Wlg"
tent of his views to mark and select the most de-
cisive characters of discrimination, the acute and in-
defatigable Hedwig suggested the following rule,
founded as he thought on a universaj law of vege-

470 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

table nature, and affording the only incontrovertible
test by which the plant is to be discriminated from
the animal ; namely, that the reproductive organs
after having discharged their peculiar functions,
uniformly decay and drop off before the fruit has
reached maturity, while those of the animal remain
permanent, and perish only with the individual
itself.* But if it is true, as Gaertner maintains,
that some genera, perhaps even some tribes of
plants are destitute of sexual organs altogether, and
propagated not by seeds but by gems ; or if there
are either plants or animals whose sexual organs
have not yet been detected, as in the case of the
Polypi, what after all is the value of the rule ?
OfMirbel. Finally, M. Mirbel, a botanist of some consider-
able celebrity on the continent, has introduced a
criterion founded on the character of the substances
on which plants and animals respectively feed.
Plants feed upon unorganized substances, that is,
upon earths, salts, water, or gases : animals feed
upon substances already organized, that is either
upon vegetables, or animals, or their products ; but
never wholly upon substances in an unorganized
state. Such is obviously the fact, at least in the
case of the more perfect animals and vegetables,
which M. Mirbel was accordingly not the first to
remark ; for the remark had been made, essentially
at least, by Lord Bacon, though the division of ma-
terial substances into organized and unorganized
* Tracts relative to Bot. London, 1805,

SECT. V. DEFINITION OF THE PLANT. 471

was not yet introduced : * but it was made in the very
terms of the division by M. Bonnet, in his Consi-
derations sur les Corps Organises; and by Fourcroy,
in his Systeme des Conaissances Chimiques,-}- who
regards it as affording the best criterion for dis-
tinguishing the mineral from the plant. But M.
Mirbel seems to have been the first who has adopted
it as affording a universal criterion for distinguish-
ing the plant from the animal, and it seems to have
already obtained a preference even with some of the
best judges, though it does not yet appear to have been
very scrupulously put to the test.^ Is it true that the
Lumbricus terrestris feeds only on earthy as has been
generally supposed, or does it feed also on roots ?
What is the food of leeches and minnows, which have
been known to live for years merely in pure water ?
And what is the food of zoophytes in general?
Till these questions are satisfactorily answered the
criterion cannot be deemed infallible. Regarding
it, however, as the best ground of distinction that
has hitherto been suggested, I deduce from it the
following definition of the vegetable and animal : —
A vegetable is an organized and living substance
springing from a seed or gem, which it again pro-
duces ; and effecting the developement of its parts
by means of the intro-susception and assimilation of

* Videmus enim herbas et plantas, ex terra et aqua nutriri;
animalia vero, ex herbis et fructibus. De Aug. Scien. 1. iv.
+ Smith's Introduction, chap. i.
I Tome vii. p. 34.

472 CHARACTER OF VEGETABLE VITALITY. CHAP. XI.

unorganized substances, which it derives from the
atmosphere or the soil in which it grows. The defi-
nition of the animal is the counter-part : an animal
is an organized and living being proceeding from an
egg or embryo, which it again produces ; and effect-
ing the developement of its parts by means of the
intro-susception of organized substances, or their
products.

If no one of the foregoing rules or definitions is
altogether without exception, neither is there any
one of them without its utility. They are all founded
on some leading feature observable in at least the
greater part of the subjects meant to be characterized :
and if the naturalist does not succeed in the attain-
ment of his object by means of the adoption of any
one rule, he will probably succeed by means of the
aid of another ; for if all of them should even prove to
be defective, they will not all be defective in the same
respect; and at the most it is only in a few cases
jthat difficulties are likely to occur, and in which it is
to be feared that difficulties will always remain.
For if nature has not assigned to the animal and
vegetable kingdoms respectively any definite and
specific limits, but has blended them as it were both
together, it is in vain for man to institute his dis-
tinctions. It is extremely desirable, however, that
some criterion should be established, as general in
its extent and as easy in its application as possible :
and for all practical purposes, perhaps plants may
J3<3 distinguished from animals with sufficient ac-

SECT. I. WOUNDS. 473

curacy by means of the trial of burning ; as animal
substances in a state of ignition exhale a strong
and phosphoric odour, which vegetable substances
do not.

CHAPTER XII.

CASUALTIES AFFECTING THE LIFE OF VEGETABLES.

As plants are, like animals, organized and living
beings, they are, like animals also, liable to such acci-
dental injuries and disorders as may affect the
health and vigour, or occasion the death of the indi-
vidual ; which is at any rate eventually effected by
means of the natural decay and final extinction of
the vital principle. Hence the subject of vegetable
casualties divides itself into the three following
heads — Wounds, Diseases, Natural Decay.

SECTION I.

Wounds.

A WOUND is a forcible separation of the solid parts intention
of the plant effected by means of some external ci
cause. It maybe intentional, as in the case of incision,
boring, girdling, grafting, pruning, felling, and such
like operations ; or it may be accidental, as in the
case of injuries sustained by the rubbing or browsing
of cattle ; by the bite and depredation of insects,

474 CASUALTIES OF VEGETABLES. CHAP. XII.

hares, rabbits ; by lightning ; by weight of fruit ;
or by violent storms of wind, hail, snow.

SUBSECTION I.

Some- Incision. — Incisions are sometimes necessary to

^e health of the tree, in the same manner perhaps
as Bleeding is necessary to the health of the animal.

plant. The trunk of the Plum and Cherry-tree seldom ex-
pand freely till a longitudinal incision has been
made in the bark ; and hence this operation is often
practised by gardeners. If the incision affects the
epidermis only it heals up without leaving any scar ;
if it penetrates into the interior of the bark it heals
up only by means of leaving a scar ; but if it pene-
trates into the wood, the wound in the wood itself
never heals up completely ; but new wood and bark
are formed above it as before.

SUBSECTION II.

Employed Boring. — Boring is an operation by which trees
are °ften wounded for the purpose of making them
part with their sap in the season of their bleeding,
particularly the Birch-tree and American Maple. A
horizontal or rather slanting hole is bored in them
with a wimble, so as to penetrate an inch or two into
the wood, from this the sap flows copiously; and
though a number of holes is often bored in the same
trunk, the health of the tree is not materially if at
1

SECT. I. WOUNDS. 475

all affected. For trees will continue to thrive though
subjected to this operation for many successive years ;
and the hole, if not very large, will close up again
like the deep incision, not by the union of the
broken fibres of the wood, but by the formation of
new bark and wood projecting beyond the edge of
the orifice, and finally shutting it up altogether.

SUBSECTION III.

Girdling. — Girdling is an operation to which Employed
trees in North America are often subjected when the piant.
farmer wishes to clear his land of timber. It con-
sists in making parallel and horizontal incisions
with an axe into the trunk of a tree, and carrying
them quite round the stem so as to penetrate through
the alburnum, and then to scoop out the intervening
portion. If this operation is performed early in the
spring and before the commencement of the bleed-
ing season, the tree rarely survives it; though some
trees that are peculiarly tenacious of life, such as
Acer saccharinum and Nyssa infegrifolia, have
been known to survive it a considerable length of
time.*

SUBSECTION IV.

Fractures. — If a tree is bent so as to break part
only of the cortical and woody fibres, and the stem
or branch but small, the parts will again unite by

* Barton's Elem. of Rot. Part ii.

470 CASUALTIES OF VEGETABLES. CHAP. XII.

being put back into their natural position, and well
propped up. Especially the cure may be expected
to succeed if the fracture happens in the spring ;
but it will not succeed if the fracture is accompanied
with contusion, or if the stem or branch is large ;
and even where it succeeds the woody fibres do not
contribute to the union, but the granular and herba-
ceous substance only which exudes from between
the wood and liber, insinuating itself into all inter-
stices and finally becoming indurated into wood.

SUBSECTION V.

Pruning. — Wounds are necessarily inflicted by
the gardener or forester in the pruning or lopping off
of superfluous branches, but this is seldom attended
with any bad effects to the health of the tree, if done
by a skilful practitioner ; indeed no further art is
required merely for the protection of the tree be-
yond that of cutting the branch through in a sloping
direction so as to prevent the rain from lodging,
In this case the wound soon closes up by the
induration of the exposed surface of the section, and
by the protrusion of a granular substance, forming a
sort of circular lip between the wood and bark ; and
hence the branch is never elongated by the growth
of the same vessels that have been cut, but by the
protrusion of new bu,ds near the point of section,

SECT. I. WOUNDS. 477

SUBSECTION VI.

Grafting. — In this operation there is a wound
both of the stock and graft ; which are united, as has
been shown in a former chapter, not by the imme-
diate adhesion of the surfaces of the two sections, but
by means of a granular and herbaceous substance
exuding from between the wood and bark, and in-
sinuating itself as a sort of cement into all open
spaces : new wood is finally formed within it, and
the union is complete.

SUBSECTION VII. /

Felling. — Felling is the operation of cutting down
trees close to the ground which many of them wijl
yet survive, if the stump is protected from the in-
juries of animals, and the root fresh and vigorous.
In this case the fibres of the wood are never again
regenerated, but a lip is formed as in the case of
pruning ; and buds, that spring up into new shoots,
are protruded near the section : so that from the old
shoot, ten, twelve, or even twenty new stems may
issue according to its size and vigour. The stools of
the Oak and Ash-tree will furnish good examples ;
but there are some trees, such as the Fir, that never
send out any shoots after the operation of felling.

478 CASUALTIES OF VEGETABLES. CHAP. XII.

SUBSECTION VIII.

Destruction of Ends. — It has been already
shown that the buds which expand in the spring are
generated in the preceding summer, and augmented
and prepared for developement in the intervening
winter. But if the buds are destroyed in the course
of the winter, or in the early part of the spring,
many plants will again generate new buds that will
develope their parts as the others would have done,
except that they never contain blossom or fruit. By
what means are the buds regenerated ?

Du Hamel thought they sprang from pre-or-
ganized germes which he conceived to be dispersed
throughout the whole of the plant. His proofs arc
founded on the following experiments : — Having
taken some cuttings of the Willow,, he stuck them
in the earth, and made them at the same time pass
through a barrel filled with earth, so as to have a
portion exposed to the air between the earth and
the barrel, and another portion projecting above the
barrel. The part inserted in the ground produced
roots, and the part passing through the earth con-
tained in the barrel produced also roots, but the other
two portions produced branches. It was of little con-
sequence whether they were inserted in the earth
by the upper or under extremity; and they vege-
tated even when made to pass through the barrel
horizontally. But a cutting which was stuck into

SECT. I. WOUNDS. 47Q

the under surface of the earth contained in the bar-
rel, with the top pointing downwards, did not
vegetate. Hence he concluded that germes both
of the root and branch are dispersed throughout the
whole of the plant, and are developed as the exi-
gency of the case requires.*

Others less prodigal of germes think that the
buds are regenerated only from the plexus of the
vessels of the inner bark ; perhaps, because it is
from the inner bark that the union of the graft and
stock is effected. But Mr. Knight thinks he has dis-
covered the true source of the regeneration of buds
in the proper juice that is lodged in the alburnum.
This conjecture is supported by the following facts :

If the stalk of Crambe maritima is cut off near
the ground in the spring, the pith within that part
of the stalk which remains still attached to the root
rots, and a cup is formed that collects water in the
succeeding winter. The sides of the cup consist of
a woody substance which resembles the alburnum
of trees, and new buds are often seen in the follow-
ing spring to be protruded from within the cup.

Buds were also observed to be generated on the »
sections formed by the knife in separating Potatoes
into cuttings, and were in many instances elongated
into runners, which gave origin to other tubers.
Now the Potatoe, says Mr. Knight, consists of four
distinct parts ; the epidermis, true skin, bark, and in-
ternal mass, which he denominates an alburnum,
* Phys. des Arbres, liv. iv. chap. v.

480 CASUALTIES OF VEGETABLES. CHAP. XII.

though it may well be doubted whether this deno-
mination is correct.

Mr. Knight's experiments were now extended to
woody plants, a number of which he raised in the
spring of 1802, from seeds of the Apple, Pear, and
Plum-tree, and cut down in the autumn to the col-
lar, exposing at the same time part of the root. In
the beginning of the following spring, a number of
small protuberances were observed on the bark of
the exposed roots, which were found to be occa-
sioned by small processes issuing from the albur-
num. They were incipient buds, and were deve-
loped as the spring advanced, forming shoots similar
in every respect to those which might have been
expected from the stem that was cut down. Ex-
periments that were made upon the stem and root
of aged trees gave the same result, establishing, as
Mr. Knight thinks, the position that the alburnum
possesses the power of organizing and regenerating
buds.

But this after all is not much different from the
doctrine of the pre-organized germes of Du Hamel ;
and certainly not quite so convenient. For the
germes of Du Hamel are always ready against the
occurrence of any accident ; whereas those of Mr.
Knight are manufactured out of the alburnum only
after the accident has occurred.

But is it not singular that buds thus regenerated
never contain or produce either flower or fruit ? Per-
haps it is because the fruit bud requires more time

SECT. I. WOUNDS. 481

to develope its parts, or a peculiar and higher degree
of elaboration ; and that this hasty production is
only the effect of a great effort of the vital principle
for the preservation of the individual, and one of
those wonderful resources to which nature always
knows how to resort when the vital principle is in
danger.

SUBSECTION IX.

Destruction of Leaves. — Sometimes the leaves
of a tree are destroyed partially or totally as soon
as they are protruded from the bud, whether by the
depredations of caterpillars or other insects, or by
the browsing of cattle. But if the injury is done
early in the spring, new leaves will be again pro-
truded with subsequent shoots. This I observed in
the case of a small Roan-tree that had been totally
stripped of its leaves by the browsing of a cow ; but
new leaves were soon afterwards produced, as well
as new shoots, though the tree had been transplanted
both early in that spring, and in the spring preced-
ing. The shoots were but short, and the leaves
were protruded from buds not so forward as those
that were first developed, and which would, per-
haps, not have been developed that season except
for this accidental defoliation. Some trees will bear
to be stripped even more than once in a season, as
is the case with the Mulberry-tree which they cul-
tivate in the south of France and Italy for the pur-
pose of feeding the silk-worm. But if it is stripped
VOL. ii. 2 i

482 CASUALTIES OF VEGETABLES. CHAP. XII =

more than once in the season it requires now
and then a year's rest.

SUBSECTION X.

Destruction of Bark. — The decortication of a
tree, or the stripping it of its bark, may be either
intentional or accidental, partial or total. If it is
partial and affects the epidermis only, then it is again
regenerated, as in the case of slight incision, with-
out leaving any scar. But if the epidermis of the
petal, leaf, or fruit, is destroyed, it is not again re-
generated, nor is the wound healed up except by
means of a scar. Such is the case also with all
decortications that penetrate deeper than the epider-
mis, particularly if the wound is not protected from
the action of the air. And if the decorticaticn
reaches to the wood, then the wound will not heal
up in the foregoing manner at all. This Du Hamel
proved by means of experiment.* Having stripped
a trunk in the spring of a portion of its bark to the
extent of a few square inches, he left the decorticated
part exposed to the air. In the course of a few days
after there appeared issuing from the lip of the
wound, as if from between the wood and bark, a ring
of new bark, which became broader and more solid
during the summer, lessening the area of the origi-
nal wound. At the end of the summer it was
found that a new layer of wood was formed under

* Phys. eks Arb. Jiv. iv. chap. iii.

SECT. I. WOUNDS. 483

this bark ; and in the following year a new ring of
bark was generated concentric to the former, and
also a new layer of wood beneath it ; and so on suc-
cessively, approaching the centre of the wound, till
at last the whole area was covered, but without any
actual union of the old and new wood. Such then
is the process of nature in healing up wounds of
this kind when left exposed to the air.

But the result is not the same when the wound is
covered from the air. In the season of the flowing
of the sap Du Hamel detached a ring of bark, of
three or four inches in breadth, from the trunks of
several young Elm- trees, taking care to defend the
decorticated part from the action of the air, by
surrounding it with a tube of glass cemented above
and below to the trunk. After a few days the tubes
became cloudy within, particularly when it was hot ;
but when the air became cool, the cloud condensed
and fell in drops to the bottom. At last there be-
gan to appear as if exuding from between the bark
and wood of the upper part of the wound, a sort of
rough scurfy substance ; and on the surface of the
wood, as if exuding from between the longitudinal
fibres of the alburnum, a number of gelatinous
drops. They were not connected with the scurfy sub-
stance at the top, but seemed to arise from small
slips of the liber that had not been completely de-
tached. Their first appearance was that of small
reddish spots changing by degrees into white, and
finally into a sort of grey, and extending in size till

2 i 2

484 CASUALTIES OF VEGETABLES. CHAP. XII.

they at last united and formed a cicatrice, which was
a new bark, not indeed covering the whole wound
uniformly, for some parts of it still remained un-
covered, and not altogether like the other bark.

Hence, says Du Hamel, it is proved that the
, wood can produce bark. But the legitimacy of this
conclusion is, I think, somewhat questionable. For
in the first place the liber was not wholly stripped off
and in the second place the cicatrice was not com-
plete; and in the third place the bark was not
perfect.

If the decortication is total, the tree dies. Of
sixty trees which Du Hamel barked in the spring,
no one survived the experiments above three or
four years, though many of them generated a por-
tion both of wood and bark, originating at the sum-
mit, and descending sometimes to the extent of a
foot.*

SECTION II.

Diseases.

DISEASES are corrupt affections of the vegetable
body, arising^from a vitiated state of its juices, and
tending to injure the habitual health either of the
whole or part. The diseases that occur the most
frequently among vegetables are the following: —
Blight, smut, mildew, honey-dew, dropsy, flux of

* Phys, des Arb. liv. v. chap. ii.

SECT. II. DISEASES. 485

juices, gangrene, etiolation, suffocation, contor-
tion, consumption.

SUBSECTION I.

Blight. — Much has been written on the nature of
blight ; and in proportion as words have been multi-
plied on the subject, the difficulties attending its
elucidation have increased. This disease was well
known to the ancient Greeks, who, were however
totally ignorant of its cause, regarding it merely as
a blast from heaven, indicating the wrath of their
offended deities, and utterly incapable of prevention
or cure. It was known also to the Romans under the
denomination of rubigo, who regarded' is in the
same light as the Greeks, and even believed it to be
under the direction of a particular detiy, Rubigus,
whom they solemnly invoked that blight might be
kept from corn and trees. It is still well known
from its effects to every one having the least know-
ledge of husbandry or gardening ; but it has been
very differently accounted for. And, perhaps, there
is no one cause that will account for all the different
cases of blight, or disease going by the name of
blight; though they have been supposed to have
all the same origin. If we take the term in its
most general acceptation I think it will include at
least three distinct species — blight originating in Divisible
cold and frosty winds, blight originating in a sort of species,
sultry and pestilential vapour, and blight originat-

486 CASUALTIES OF VEGETABLES. CHAP. XII.

ing in the immoderate propagation of a sort of small
and parasitical fungus.
First The first species is often occasioned by the cold

SDccics

and easterly winds of spring, which nip and destroy
the tender shoots of the plant, by stopping the cur-
rent of the juices. The leaves which are thus
deprived of their due nourishment wither and fall,
and the juices that are now stopped in their passage
swell and burst the vessels, and become the food of
innumerable little insects that soon after make their
appearance. Hence they are often mistaken for the
cause of the disease itself; the farmer supposing
they are wafted to him on the east wind, while they
are only generated in the extravasated juices as
forming a proper nidus for their eggs. Their mul-
tiplication will no doubt contribute to the spreading
of the disorder, as they always breed fast where
they find plenty of food.

But a similar disease is often occasioned by the
early frost of spring. If the weather is prematurely
mild, the blossom is prematurely protruded, which
though it is viewed by the unexperienced with de-
light, yet it is viewed by the judicious with fear.
For it very often happens that this premature blos-
som is totally destroyed by subsequent frosts, as
well as both the leaves and shoots, which conse-
quently wither and fall, and injure if they do not
actually kill the plant. This evil is also often aug-
mented by the unskilful gardener even in attempt-
ing to prevent it — that is, by matting up his trees

SECT. II, DISEASES.

too closely, or by keeping them covered in the
course of the day, and thus rendering the shoots so
tender that they can scarcely fail to be destroyed by
the next frost.

The second species generally happens in the sum- Second
mer when the grain has attained to its full growth, spec
and when there are no cold winds or frosts to oc-
casion it. Such was the blight that used to damage
the vineyards of ancient Italy, and which is yet
found to damage our Hop plantations and Wheat
crops. The Romans had observed that it generally
happened after short but heavy showers occurring
about noon, and followed by clear sunshine, about
the season of the ripening of the Grapes, and that
the middle of the vineyard suffered the most. This
corresponds pretty nearly to what is in this country
called the fire-blast among Hops, which has been
observed to take place most commonly about the
end of July, when there has been rain with a hot
gleam of sunshine immediately after ; the middle of
the Hop-ground is also the most affected whether
the blight is general or partial, and is almost always
the point in which it originates. In a particular case
that was minutely observed, the damage happened
a little before noon, and the blight ran in a line
forming a right angle with the sunbeams at that
time of the day. There was but little wind, which
was however in the line of the blight.*

Wheat is also affected with a similar sort of blight,
* Kale's Body of Husbandry.

4S8 CASUALTIES OF VEGETABLES. CHAP. *XIT.

and about the same season of the year, which
totally destroys the crop. In the summer of 180Q,
I had watched the progress of the growth of a field
of wheat on rather a light and sandy soil, merely
from having had occasion to pass through it every
Sunday in going to serve a church. It came up
with every appearance of health, and also into ear,
with a fair prospect of ripening well. I had taken
particular notice of it on a Sunday about the be-
ginning of July, as exceeding any thing I should
have expected on such a soil. But on the following
Sunday I was surprised to find a portion of the
crop, on the east side of the field, to the extent of
several acres totally destroyed ; being shrunk and
shrivelled up to less than one-half the size of what
it had formerly been, with an appearance so wither-
ed and blasted that I for some time imagined I had
got into the wrong field. The rest of the field
produced a fair crop.

Third The third species attack the leaves or stem both

of herbaceous and woody plants, such as Eu-
phorbia CyparissiaS) Berberis vulgar is, and Rham-
nus catharticus, but more generally Grasses ; and
particularly our most useful grains, Wheat, Barley,
and Oats. It generally assumes the appearance of
a rusty-looking powder that soils the finger when
touched. On the 25th of March, 1807, I ex-
amined some blades of Wheat that were attacked
with this species of blight ; the appearance was that
ot a number of rusty-looking spots or patches dis-

SECT. II. DISEASES.

persed over the surface of the leaf, exactly like that
of the seeds of Dorsiferous Ferns bursting their indu-
slum. Upon morq minute inspection these patches
were found to consist of thousands of small globules
collected into groups beneath the epidermis, which
they raised up in a sort of blister and at last burst.
Some of the globules seemed as if imbedded even
in the longitudinal vessels of the blade. They were
of a yellowish or rusty brown, and somewhat trans-
parent. But these groups of globules have been
ascertained by Sir J. Banks to be patches of a
minute Fungus, the seeds of which, as they float in
the air, enter the pores of the epidermis of the leaf,
particularly if the plant is sickly ; or they exist in
the manure or soil, and enter by the pores of the
root.* This Fungus has been figured by Mr.
Sowerby and by Mr. F. Bauer and Grew. It is
known among farmers by the name of Red Rust,
and as it affects the stalk and leaves only it does not
materially injure the crop.

But there is another species of Fungus, known
to the farmer by the name of Red Gum, which at-
tacks the ear only, and is extremely prejudicial. In
the aggregate it consists of groups of minute globules
interspersed with transparent fibres. The globules are
filled with a fine powder which explodes when they
are put into water. It is very generally accom-
panied with a maggot of a yellow colour, that preys

* Sir J. Banks on Blight, 1805.

4gO CASUALTIES OF VEGETABLES. CHAP. XII.

also upon the grain, and increases the amount of
injury. It has been well figured by Mr. Bauer.

SUBSECTION II.

.— Smut is a disease incidental to cultivated
Corn by which the farina of the grain, together
with its proper integuments and even part of the
husk, is converted into a black soot-like powder. If
the injured ear is struck with the finger, the powder
will be dispersed like a cloud of black smoke ; and
if a portion of the powder is wetted by a drop of
water and put under the microscope, it will be found
to consist of millions of minute and transparent
globules, which seem to be composed of a clear and
glary fluid encompassed by a thin and skinny mem-
brane.

This disease does not affect the whole body of the
crop, but the smutted ears are sometimes very nu-
merously dispersed throughout it. Some have at-
tributed it to the soil in which the grain is sown,
and others have attributed it to the seed itself,
Alleging that smutted seed will produce a smutted
crop. But in all this there seems to be a great deal
of doubt. Willdenow regards it as originating in a
small Fungus, which multiplies and extends till it
occupies the whole ear.* But Mr. F. Bauer, of
Kew, seems to have ascertained it to be merely a

* Princip, of Bot. p. 356.
5

SECT. II. DISEASES.

morbid swelling of the ear, and not at all connected
\vith the growth of a Fungus*

It is said to be effectually prevented by steeping
the grain before sowing in a weak solution of arsenic.

But besides the disease called smut there is also
a disease analogous to it, or a different stage of the
same disease, known to the farmer by the name of
Bags or Smut-balls, in which the nucleus of the seed
only is converted into a black powder, whilst the
ovary, as well as the husk, remains sound. The ear
is not much altered in its external appearance, and
the diseased grain contained in it will even bear the
operation of threshing, and consequently mingle
with the bulk. But it is always readily detected by
the experienced buyer, and fatal to the character of
the sample. It is prevented as in the case of smut.

SUBSECTION in.

Mildew.— Mildew is a thin and whitish coating
with which the leaves of vegetables are sometimes
covered, occasioning their decay and death, and in-
juring the health of the plant. It is frequently
found on the leaves of Tussilago Farfara, Humulus
Lupulus, Corylus Avellana, and the white and yel-
low Dead-nettle. It is found also on Wheat in the
shape of a glutinous exudation, particularly when
the days are hot and the nights without dew.

Willdenow says it is occasioned by the growth of
* Smith's Introd. p. 34$.

CASUALTIES OF VEGETABLES. CHAP. XII.

a Fungus of great minuteness, the Mucor ErisypJic
of Linnaeus ; or by a sort of whitish slime which
some species of aphides deposit upon the leaves.*
In cultivated crops it is said to be prevented by
manuring with soot*

SUBSECTION IV.

Honey-dew. — Honey-dew is a sweet and clammy
substance which coagulates on the surface of the
leaves during hot weather, particularly on the leaves
of the Oak-tree and Beech, and is regarded by Mr.
Curtis, who wrote a paper on the subject, as being
merely the dung of some species of aphides.^ This
seems to be the opinion of Willdenow also, % and it
is no doubt possible that it may be the case in
some instances or species of the disease. But Sir
J. E. Smith contends that it is not always so, or
that there are more species of honey-dew than one,
regarding it particularly as being an exudation, at
least in the case of the Beech, whose leaves are, in
consequence of an unfavourable wind, apt to become
covered with a sweet sort of glutinous coating,
similar in flavour to the fluid obtained from the
trunk.^

It is certain, however, that saccharine exudations
are found on the leaves of many plants, though not

* Piincip. of Bot. p. 343. f Lin. Trans, vol. vi.

J Princip. of Bot. p. 343. § Introd. p. 1S9-

4

SECT. II. DISEASES.

always distinguished by the name of honey-dew ;
which should not perhaps be applied except when
the exudation occasions disease. But if it is to be
applied to all saccharine exudations whatever, then
we must include under the appellation of honey-
dew the saccharine exudation observed on the
Orange-tree by M. De la Hire,^ together with that
of the Lime-tree which is more glutinous, and of
the Poplar which is more resinous ; as also that of
the Cistus creticus, from which the resin called
Labdanum is collected, by means of beating the
shrub with leathern thongs, and of the manna
which exudes from the Ash-tree of Italy and Larch
of France. It is also possible that the exudation
of excrement constituting honey-dew may occa-
sionally occur without producing disease ; for if it
should happen to be washed off soon after by rains
or heavy dews, then the leaves will not suffer.

SUBSECTION V.

Dropsy. — Plants are also liable to a disease Occasion-
which affects them in a manner similar to that of much"*
the dropsy in animals, arising from long continued moisture-
rain or too abundant watering. Willdenow de-
scribes it as occasioning a preternatural swelling of
particular parts, and inducing putrefaction. It is
said to take place chiefly in bulbous and tuberous

* Phys. des Arb. torn. i. p. 150.

CASUALTIES OF VEGETABLES. CHAP. XII.

roots, which are often found much swelled after
rain. It affects fruits also which it renders watery and
insipid. It prevents the ripening of seeds, and oc-
casions an immoderate production of roots from
the stem. Succulent plants in particular are apt
to suffer from too profuse waterings, and the
Incurable, disease thus occasioned is generally incurable.*
The leaves drop, even though plump and green ; and
the fruit rots before reaching maturity. In this
case the absorption seems to be too great in propor-
tion to the transpiration ; but the soil when too
much manured produces similar effects. Du Hamel
planted some Elms in a soil that was particularly
well manured, and accordingly they pushed with
great vigour for some time ; but at the end of five
or six years they all died suddenly. The bark was
found to be detached from the wood, and the cavity
filled up with a reddish-coloured water.

SUBSECTION VI.

Notal- Flux of Juices. — Some trees, but particularly
\KHciafe" tile ^ak and Birch, are liable to a great loss of sap,
either bursting out spontaneously, owing to a super-
abundance of sap, or issuing from accidental wounds.
Sometimes it is injurious to the health of the plant,
and sometimes not. There is a spontaneous ex-
travasation of the sap of the Vine, known by the
name of the Tears of the Vine, which is not injuri-
* Princip. of Bot. p.

SECT.%1. DISEASES.

ous. As it often happens that the root imbibes sap,
which the leaves are not yet prepared to throw off
because not yet sufficiently expanded, owing to an
inclement season, the sap which is first carried up,
being propelled by that which follows, ultimately
forces its way through all obstructions, and exude*
from the bud. But this is observed only in cold
climates ; for in hot climates, where the develope-
ment of the leaves is not obstructed by cold, tbef
are ready to elaborate the sap as soon as it reaches
them. There is also a spontaneous extravasation of
proper juice in some trees, which does not seem in
general to be injurious to the individual. Thus
the gum which exudes from Chery, Plum, Peach,
and Almond trees, is seldom detrimental to their
health, except when it insinuates itself into the
other vessels of the plant and occasions obstructions.

But when the sap ascends more copiously than it In what
can be carried off, it sometimes occasions a fissure of judieal.
the solid parts, inducing disease or deformity by en-
couraging the extravasation and corruption of the
ascending or descending juices. Sometimes the
fisssure is occasioned by means of frost, forming
what is called a double alburnum ; that is, first a
layer that has been injured by the frost, and then a
layer that passes into wood. Sometimes a layer is par-
tially affected, and that is generally owing to a
sudden and partial thaw on the south side of the
trunk, which may be followed again by a sudden
frost. In this case the alburnum is split into clefts,

406 CASUALTIES OF VEGETABLES. CHAP. XII*

or chinks, by means of the expansion of the frozen
sap. But a cleft thus occasioned often degenerates
into a chilblain that discharges a blackish and acrid
fluid to the great detriment of the plant, par-
ticularly if the sore is so situated that rain or snow
will readily lodge in it, and become putrid. The
same injury may be occasioned by the bite or
puncture of insects while the shoot is yet tender ;
and as no vegetable ulcer heals up of its own ac-
cord, the sooner a remedy is applied to it the better,
as it will, if left to itself, ultimately corrode and
destroy the whole plant, bark, wood, and pith. The
only remedy is the excision of the part affected, and
the application of a coat of grafting wax.*

*

SUBSECTION VII.

Dry gan- Gangrene. — Of this disorder there are two varie-
ties, the dry and the wet. The former is occasioned
by means of excessive heat or excessive cold. If by
means of cold, it attacks the leaves or young shoots,
and causes them to shrink up, converting them from
green to black; as also the inner bark, which it
blackens in the same manner, so that it is impos-
sible to save the plant except by cutting it to the
ground. If by means of heat, the effects are nearly
similar, as may oftentimes be seen in gardens, or
even in forests, where the foresters are allowed to clear
away the Moss and withered leaves from the roots.-}-

* Willdeaow, p. 354. | Ibid. p. 355.

SECT. II. DISEASES. 49?

Sometimes the disease is occasioned by the too
rapid growth of a particular branch, depriving the
one that is next it of its due nourishment, and
hence inducing its decay. Sometimes it is occa-
sioned by means of parasitical plants, as in the case
of the bulbs of the Saffron, which a species of
Lycoperdon often attaches itself to and totally cor-
rupts. The harmattan winds of the coast of Africa
kill many plants, by means of inducing a sort of
gangrene that withers and blackens the leaves, and
finally destroys the whole plant. The Nopal of
Mexico is also subject to a sort of gangrene that
begins with a black spot, and extends till the whole
leaf or branch rots off or the plant dies.

But plants are sometimes affected with a gan- Wet gan-
grene by which a part becomes first soft and moist,
and then dissolves into foul ichor. This is confined
chiefly to the leaves, flowers, and fruit. Sometimes
it attacks the roots also, but rarely the stem. It
seems to be owing in many cases to too wet or too
rich a soil ; but it may originate in contusion, and
may be caught by infection.

But the Nopal is subject also to a disease called Dissolu-
by Thiery la dissolution, and considered by Sir J. E.
Smith as distinct from gangrene. I cannot however
perceive the difference ; I think it is Willdenow's
dry gangrene. A joint of the Nopal, or a whole
branch, and sometimes an entire plant, changes in
the space of a single hour from a state of apparent
health to a state of putrefaction or dissolution.

VOL. II. 2 K

CASUALTIES OF VEGETABLES. CHAP. XfL

Now its surface is verdant and shining, and in an
itstant it changes to a yellow, and its brillancy is
gone. If the substance is cut into, the parts are
found to have lost all cohesion, and are quite rotten;
the only remedy is speedy amputation below the
diseased part. Sometimes the vital principle col-
lecting and exerting all its energies, makes a stand
as it were against the encroaching disease, and
throws off the infected part.*

SUBSECTION VIII.

Occasion- Etiolation. — Plants are sometimes affected by a
«f light?"1 disease which entirely destroys their verdure, and
renders them pale and sickly. This is called etiola-
tion) and may arise merely from want of the agency
of light, by which the extrication of oxygene is ef»
Rationale, fected, and the leaf rendered green. And hence it is
that plants placed in dark rooms, or between great
masses of stone, or in the clefts of rocks, or under
the shade of other trees, look always peculiarly
pale. But if they are removed from such situations
and exposed to the action of light, they will again
recover their green colour.

Etiolation may also ensue from the depredation
of insects, nestling in the radicle, and consuming
the food of the plant, and thus debilitating the
vessels of the leaf so as to render them insuscepti-
ble to the action of light. This is said to be often
* Smith's Introxluction, p. 340.

SECT. II. DISEASES. 4Q9

the case with the radicles of Secale cereale, and the
same result may also arise from poverty of soil.

SUBSECTION Dt.

Suffocation. — Sometimes it happens that the
pores of the epidermis are closed up and transpira-
tion consequently obstructed, by means of some ex-*
traneous substance that attaches itself to and covers
the bark. This obstruction induces disease, and
the disease is called suffocation. Sometimes it is
occasioned by the immoderate growth of Lichens
upon the bark covering the whole of the plant, as
may be often seen in fruit trees, which it is ne-
cessary to keep clean by means of scraping off the
Lichens, at least from the smaller branches. For if
the young branches are thus coated, so as that the
bark can not perform its proper functions, the tree
will soon begin to languish, and will finally become
covered with Fungi inducing or resulting from
decay, till it is at last wholly choaked up.

But a similar effect is also occasionally produced
by insects, in feeding upon the sap or shoot. This
may be exemplified in the case of the aphides
which sometimes breed or settle upon the tender
shoot in such multitudes as to cover it from the
action of the external air altogether. It may be ex-
emplified also in the case of Coccus Hesperidum and
Acarus tdlarius, insects that infest hot-house plants,
the latter by spinning a fine and delicate web over
2 K 2

SOD CASUALTIES OF VEGETABLES. CHAP.

the leaf, and thus preventing the access of atmos*
pheric air.*

Examples. Sometimes the disease is occasioned by an extra-
vasation of juices which coagulate on the surface of
the stalk so as to form a sort of crust, investing it as
a sheath, and preventing its further expansion. On
the 7th of July, 1 8 1 6, 1 observed some stalks of a Grass
partly enveloped with a crust, not unlike a piece of
dried orange-peel, particularly when viewed through
the microscope ; the part thus enveloped proved to
be that in which the spike was yet contained within its
sheathing leaves. The crust which thus totally locked
up and suffocated the spike extended from about If
to two inches in length, surmounted by the terminat-
ing leaf whose base it also invested, and thus
giving to the Grass the appearance of a Typha in
miniature.

On examining the crust more minutely it seemed
to consist of thousands of yellowish globules imbed-
ded in a sort of ground resembling mortar. But in
some species the crust was much paler, and not
unlike the Boletus Medullapanis in a recent state. It
not only invested the outer leaf, but also the inner
leaf though sheathed by the outer, and the spike
though sheathed by the inner leaf. The ear was so
totally consumed or so imperfectly formed that
I could not yet ascertain what Grass it was. But
it had the habit of Holcus lanatus, which, by

* Willdenow, p. 350.

SECT. II. DISEASES. £01

finding in one specimen a part of the ear uninjured,
I afterwards ascertained it to be.

If this crust is not originally occasioned by the
puncture of insects, it is at least selected as afford-
ing a fit nidus for depositing their eggs. For in look-
ing at some specimens about a week after, I found
several in which the surface of the crust was dis-
figured with a sort of protuberant blister, which
when opened up was found to contain a maggot.
And even in unsheathing an ear which was thus
locked up and apparently inaccessible to insects, I
yet found a small black fly rummaging about in it.

Sometimes the disease is occasioned from want
of an adequate supply of nourishment as derived
from the soil, in which the lower part of the plant
is the best supplied, while the upper part of it is
starved. Hence the top shoots decrease in size
every succeeding year, because a sufficient supply
of sap cannot be obtained to give them their pro-
per developement This is analogous to the pheno-
mena of animal life when the action of the heart
is too feeble to propel the blood through the whole
of the system. For then the extremities are always
the first to suffer. And perhaps it may account
also for the factr that in bad soils and unfavourable
seasons, when the ear of Barley is not wholly per-
fected, yet a few of the lower grains are always
completely developed ;* which not only shows the

* Smith's Introduction, p. 344.

502 CASUALTIES OF VEGETABLES. CHAP. XII.

great care of Providence for the preservation of the
species, but points out also the efficient cause.

SUBSECTION X.

Caused Contortion. — The leaves of plants are often in-

puncture jured by means of the puncture of insects, so as to

of insects, jR(juce a sort of disease that discovers itself in the

contortion or convolution of the margin, or wrinkled

appearance of the surface.

As occur- The leaves of the Apricot, Peach, and Nectarine,
16 .are extremely liable to be thus affected in the months

°^ ^une an^ J^Y' The leaf that has been punc-
tured soon begins to assume a rough and
wrinkled figure, and a reddish and scrophulous ap-
pearance, particularly on the upper surface. The
margins roll inwards on the under side, and en-
close the eggs which are scattered irregularly on the
surface, giving it a blackish and granular ap-
pearance, but without materially injuring its
health.

Of the In the Vine the substance deposited on the leaf is
ne> whitish, giving the under surface a sort of a frosted
appearance, but not occasioning the red and scro-
phulous aspect of the upper surface of the leaf of
the Nectarine.

Poplar, In the Poplar the eggs when first deposited re-
semble a number of small and hoary vescicles con-
taining a sort of clear and cojourjess fluid, The

SBCT. II. DISEASES. 503

leaf then becomes reflected and conduplicate, en-
closing the eggs with a few reddish protuberances
on the upper surface. The embryo is nourished by
this fluid ; and the hoariness is converted into a fine
cottony down, which for some time envelopes the
young fly.

The leaf of the Lime-tree in particular is liable And

Lime-tree.
to attacks from insects when fully expanded ; and

hence the gnawed appearance it so often exhibits.
The injury seems to be occasioned by some species
of puceron depositing its eggs in the parenchyma,
generally about the angles that branch off from the
midrib. A sort of down is produced, at first green,
and afterwards hoary ; sometimes in patches, and
sometimes pervading the whole leaf, as in the case
of the Vine. Under this covering the egg is
hatched ; and then the young insect gnaws and in-
jures the leaf, leaving a hole, or scar of a burnt or
singed appearance.

Sometimes the upper surface of the leaf is covered
with clusters of wart-like substances somewhat
subulate and acute. They seem to be occasioned
by means of a puncture made on the under sur-
face, on which a number of openings are discover-
able, penetrating into the warts which are hollow an4
villous within,

SUBSECTION XI.

Consumption. — From barren or improper soil, Cause? of.
unfavourable climate, careless planting, or too fre-

504 CASUALTIES OF VEGETABLES. CHAP. XII.

quent flowering exhausting the strength of the
plant, it often happens that disease is induced which
terminates in a gradual decline and wasting away of
the plant till at length it is wholly dried up. Some-
times it is also occasioned by excessive drought, or by
dust lodging on the leaves, or by fumes issuing
from manufactories which may happen to be si-
tuated in the neighbourhood ; or by the attacks of
insects.

There is a consumptive affection that frequently
Teredo attacks the Pine-tree called Teredo Pinorum,*
morum. ^jch aflrects the alburnum and inner bark chiefly,
and seems to proceed from long continued drought,
or from frost suddenly succeeding mild or warm-
weather or heavy winds. The leaves assume a tinge
of yellow bordering upon red. A great number of
small drops of resin exude from the middle of the
boughs of a putrid odour. The bark exfoliates, and
the alburnum presents a livid appearance. The tree
swarms with insects, and the disease is incurable,
inducing inevitably the total decay and death of
the individual.

* Willdcnow, Princ, Hot. p. 351.

SECT. II. DISEASES, 505

SECTION III.

Natural Decay.

IN the preceding section I have stated the chief Inducing
of the diseases to which plants are liable, whether
from external injuries, or from internal derange-
ment. But although a plant should not suffer from
the influence of accidental injury, or from disease,
still there will come a time when its several organs
will begin to experience the approaches of a na-
tural decline insensibly stealing upon it, and at last
inducing death. For in the vegetable as well as
in the animal kingdom there is a term or limit set,
beyond which the individual cannot pass, though
the duration of vegetable existence is very different
in different species.

Some plants are annuals and last for one season Whether

, . i i i r i . . in the case

only, springing up suddenly from seed, attaining Of annuals,
rapidly to maturity, producing and again sowing
their seeds, and afterwards immediately perishing.
Such is the character of the various species of
Corn, as exemplified in Oats, Wheat, and Barley.
Some plants continue to live for a period of two
years, and are therefore called biennials, springing
up the first year from seed, and producing root and
leaves, but no fruit ; and in the second year pro-
ducing both flower and fruit, as exemplified in the
Carrot, Parsnip* and Caraway. Other plants are
perennials, that is, lasting for many years ; of

506 CASUALTIES OF VEGETABLES. CHAP. XII.

which some are called under-shrubs, and die down
to the root every year; others arc called shrubs,
and are permanent both by the root and stem, but
do not attain to a great height or great age ; others
are called trees, and are not only permanent by
both root and stem, but attain to a great size and
live to a great age. The Oak-tree in particular is
remarkable both for its longevity and size, being
at least 100 years before it attains to its utmost per-
fection, continuing vigorous for perhaps 100 years
more; and then beginning to decay. The inir
mense Oak at Colethorpe, near Wetherby, is said
to have exhibited symptoms of decay even in the
reign of Queen Elizabeth,

But even of plants that are woody and perennial,
there are parts which perish annually, or which are,
at least annually separated from the individual ;
namely, the leaves, flowers, and fruit, leaving no-
thing behind but the bare caudex which submits
in its turn to the ravages of time, and ultimately
to death. Hence the ground of a division of the
subject exhibiting, first, the phenomena of the
decay of the temporary organs, and secondly, the
phenomena of the decay of the permanent prgans^
and consequent death of the plant,

SUBSECTION I,

Decay of the temporary Organs.— The decay
of the temporary organs which takes place annually

SECT. Ill, NATURAL DECAY. 50?

is a phenomenon familiar to every body, and com-
prehends the fall of the leaf, the fall of the flower,
and the fall of the fruit.

ARTICLE 1. The Fall of the Leaf.— The fall of
the leaf, or annual defoliation of the plant, com-
mences for the most part with the colds of autumn,
and is accelerated by the frosts of winter, that strip
the forest of its foliage, and the landscape of its
verdure. But there are some trees that retain their
leaves throughout the whole of the winter, though
changed to a dull and dusky brown, as those of the
Beech-tree ; and there are others that retain them
even in verdure till the succeeding spring, wrhen
they ultimately fall. Such plants are denominated
Evergreens.

It was at one time indeed a vulgar error, and
perhaps it continues to be so still, that Evergreens
never shed their leaves at all. This error may be
traced back even to the period of the fabulous his-
tory of the Greeks, with whose mythology it was
closely interwoven, at least in one particular ex-*
ample as related by Theophrastus ; who says that in
the country of Cortynia, in Crete, it was reported
there was a Plane-tree growing by a fountain which
never shed its leaves, being the tree under the
shade of which Jupiter was said to have had his
interview with Europa.*

* Ev Kpyirri Je, teyeTai, wXaravov -nva wou £v irt yopTWoux. Trpo;

o Zsy$. Heft <pyj«v. TO. A.

CASUALTIES OF VEGETABLES. CHAP. Xlf.

But Theophrastus was himself acquainted with
the fact of the fall of the leaves of Evergreens, as
every accurate observer of nature must be, though
they do not actually fall till the young leaves have
begun to appear, so that trees of this sort are never
left wholly without leaves, which it was hence sup-
posed they never shed. In warm climates it is said
that many plants retain their leaves for several
years ; but in temperate and polar climates there
are no such plants to be found.

Such is the fact of the annual fall of the leaves.
What is the cause of their fall ? The solution of
this question seems to have totally baffled the at*
tempts of phytologists, and to have been a puzzle
that no one could make out. Du Hamel, one of the
most sagacious and industrious of all phytologists,
laboured hard to explicate the phenomenon, but
without success. He observed that leaves which
fall the soonest transpire the most, and are conse-
quently the soonest exhausted and rendered unfit
for the discharge of their functions ; so that the
period of the fall of the leaves of different species
is probably in proportion to their capacity for trans-
piration. Their fall is accelerated by frost, or by
excessive heat, followed by rain. It is also acce-
lerated, if not actually induced, by the structure of
the pedicle which is very different from that of the
branch, having no prolongation of pith, and nothing
analogous in its mode of insertion, nor in its ex-
ternal figure, which is divisible into an upper and

SECT. III. NATURAL DECAY.

under surface resembling the figure of the leaf.
He compares the union of the leaf and stem to that
of the joints of the Vine-twig, which at a certain
period of its growth are stronger than the inter-
nodia, but which readily give way after a frost.
The comparison, however, throws but little light
on the subject, as, the illustration is itself to the
full as dark as the thing to be illustrated. But he
offers an additional conjecture which is considerably
more luminous ; when the sap begins to flow less
plentifully, the leaves, to whose vigour a great sup»
ply is necessary, soon become dry and consequently
less fit to convey it. But it is known that the
branches grow in thickness after they have ceased
to grow in length, which must necessarily occasion,
in some degree, a disruption of the fibres of the
footstalk and stem, or branch, at the point of arti-
culation ; and hence the leaf loses its hold, and
falls. * This is certainly a very plausible conjec-
ture ; though it may be doubted whether the ex-
plication will apply to the case of Evergreens, or of
plants in warm climates, that retain their leaves for
several years. It is not therefore, altogether satis-
factory ; and hence other explications have accord-
ingly been offered.

The first of these explications of which I shall
now take any notice is that of Willdenow; it is
as follows : — As the sap is conveyed to the leaves
in greater abundance during the summer, the vessels

* Phys. des Arbres, liv. ii. chap. ii.
4

CASUALTIES OF VEGETABLES. CHAP. Xlf.

of the petiole become gradually more woody, as
well as the whole of the leaf. The sap by conse-
quence stagnates, and at last the bond of union
between the leaf and stem is dried up, and cracks.
The wound that the stem thus receives cicatrizes
before the petiole separates ; and the petiole sepa-
rates at last in consequence of the interrupted con-
nexion between the leaf and stem which the crack
has occasioned.*

This, it must be confessed, does not make up for
the deficiencies of the hypothesis of Du Hamel;
for in the first place there is no proof that the bond
of union between the leaf and stem cracks in the
manner here supposed. And even upon the sup-
position of its being the fact, it is, in the second
place, extremely improbable that the petiole should
after the cracking of this bond of union still con-
tinue attached to the stem, till the wound thus oc-
casioned has cicatrized ; because when the original
bond of union cracks there remains no other bond
of union by which the petiole is to retain its hold.

Another explication is that of Vorlick, as quoted
by Willdenow ; the leaf which possesses a peculiar
vitality within itself, though dependant upon the
vitality of the plant, and generally of shorter du-
ration, dies when it reaches maturity ; and the
plant, being able to exist for a time without leaves,
throws off the dead leaf as the animal throws off
the dead part from the sound part.
* Princip. of Bot. p. 305.

SECT. III. NATURAL DECAY. 5ll

But the peculiar vitality which the leaf is here
supposed to possess seems to me to be altogether a
groundless assumption, and an unphilosophical
multiplication of causes without any apparent ne-
cessity. Is it not rather the individual vitality of
the plant extended to a perishable organ, and again
withdrawn when that organ has discharged its des-
tined functions, or become by disease or decay
unfit for the purposes of vegetation ? This, I pre-
sume, is a better founded supposition than the fore-
going ; though the reference to the phenomenon of
the throwing off of the dead part from the sound
part in the animal subject is sufficiently well
adapted to the purposes of illustration; and the
analogy sufficiently striking, at least under soms
of its aspects, to warrant its introduction. For
which, or for similar reasons, our learned president
Sir J. E. Smith gives his sanction to the opinion of
Vorlick, which he had himself indeed been pre-
viously led to adopt, though he was anticipated in
the publication. The notion was first suggested to
him by some remarks of Mr. Fairbairn, of Chelsea,
who had observed that in the transplanting of trees,
if the injury extends suddenly beyond the leaf,
then the leaf remains firmly attached to the twig
even though dead ; but when the leaves alone are
affected, and the vital energy acting with full force
in the branch, the leaves are thrown off or fall upon
the slightest touch. Hence Sir J. E. Smith con-
cludes that leaves are thrown off by a process si-

512 CASUALTIES OF VEGETABLES. CHAP. Xtl.

ttiilar to that of the sloughing of diseased parts in
the animal economy.

It does not, however, seem quite evident to me
that the idea of sloughing is comprehended in the
opinion of Vorlick, at least as represented by Will-
denow ; but if so, I do not think that the analogy
is very well made out. Sloughing, in the animal
economy, is that power or the exertion of that
power by which the vital principle is capable of
throwing off a part that has accidentally become
diseased and unfit for discharging the functions to
which it was originally destined ; but not that power
by which it is capable of throwing off a distinct
organ intended by nature to be finally separated
from the individual. Now in the case of the defo-
liation of the plant, there is, for the most part no
disease, but merely a gradual and natural decay
which reduces the leaf to a state, indeed, no
longer fit for the purposes of vegetation, but to
which it was intended by nature to be reduced for
the purpose of facilitating its separation from the
plant : and hence it always separates in a determi-
nate manner, and at a determinate point, namely, at
the base of the foot-stalk, which forms as it were a
sort of natural joint or articulation, to which there
is nothing analogous in the case of sloughing. If
this were not the fact, it might be expected that a
part of a leaf, or even the whole of it, should occasion-
ally become permanent, as well as the branches,
though no such thing has ever yet happened.

SECT. III. NATURAL DECAY. 5 13

And in the sloughing of the diseased part there is
yet another circumstance clashing with the analogy
that is here instituted. The part supplying the
place of the slough, or throwing it off, is formed or
exists already formed immediately beneath it, and
is precisely of the same character with what the
slough originally was ; which slough it pushes off as
it comes itself to maturity, or acquires strength suffi-
cient for the effort. But the leaves fall off when they
have reached maturity of their own accord, without
being at all pushed off by the new ones, which are
yet merely in embryo, and do not even occupy the
place of the old leaves, but are only formed conti-
guous to them, except in the case of the Plane-tree,
the new leaf of which is formed precisely under the
base of the foot-stalk of the old leaf: and yet I would
not call the fall of that leaf sloughing, because the
new leaf does not after all push off the old one ; and
because there is here, as in other cases, the same na-
tural articulation uniting the leaf to the branch or
stem, and rendering it a distinct organ that is ulti-
mately and spontaneously to detach itself from the
plant. Not that there exists no example whatever
of vegetable sloughing, which the same tree will also
furnish in the annual or rather continual exfoliation
of its bark, but that the fall of the leaf does not seem
to me to afford that example.

I can foresee an objection that may be urged
against the above argument from the fact of the
sloughing of the entire skin of the snake, and other

VOL. n. 2 L

534 CASUALTIES OF VEGETABLES. CHAP. XII.

species of serpents, which may be regarded as a
distinct organ. But although the skin of the snake
or of any other animal may be regarded as a distinct
organ, yet it must be in a light very different from
that of an organ attached to the body of a plant or
animal by a natural joint or articulation that comes
asunder of its own accord; for the skin of the animal
in question is forced off in the manner of a slough
merely by means of the formation of a new skin be-
neath it, which has already taken the place of the
old skin in the living system, and to which it has
just been shown that there exists nothing whatever
analogous in the fall of the leaf. So that, after all, the
best reason we can give is, perhaps, that the leaves
fall in consequence of their being worn out, and no
longer necessary to the immediate process of vege-
tation ; which is evidently divisible into animal
stages commencing with the approach of spring,
and terminating with the return of winter, which
is to the vital principle, apparently, a period of rest.
If it is necessary, however, to attempt an explica-
tion of the process by which the leaf is made ulti-
mately to detach itself from the plant, it may be
observed that it consists wholly in the change that
is effected in the articulation uniting the foot-stalk
to the branch, as is evident from the remarks of Mr.
Fairburn ; for in the case in which the injury ex-
tends suddenly beyond the leaf, the leaf may wither
and decay, but will not fall off, because the articula-
tion has not been duly prepared, and because the

6

«.^T. III. NATURAL DECAY. 515

vital principle can now no longer act upon it from
the intervention of the dead or diseased portion of
the plant beyond which it has withdrawn itself.
But in the natural process of vegetation the neces-
sary change is effected by the leaf on the one hand,
in its yielding to the influence of physical or chemi-
cal agencies, and withering and shrinking into nar-
rower compass, when the usual supply of sap is no
longer transmitted to it ; and by the vital principle on
the other, in its controlling and directing of chemical
agencies so as to facilitate the final detachment of
the foot-stalk, and form the scar necessary to its own
protection. And this effect is operated by the con-
verting of the substance that cements the respective
fibres of the leaf-stalk and branch together from a
soft and glutinous to a dry and brittle consistence,
analogous to the change that takes place in the
seams of the valves of ripening capsules or pericarps,
so that the leaf falls at last merely by force of its
own weight, or of the slightest breath of wind, but
without the intervention of any previous chink o*
crack.

And if it is necessary to illustrate the fall of the
leaf by any analogous process in the animal economy,
it may be compared to that of the shedding of th4
antlers of the stag, or of the hair or feathers of other
beasts or birds, which being like the leaves of
plants, distinct and peculiar organs, fall off and are
regenerated annually, but do not slough.

ART. a. The Fall of the Flower.— The flowers,
2 L 2

516 CASUALTIES OF VEGETABLES. CHAP. XII.

which, like the leaves, are only temporary organs, are
for the most part very short-lived ; for as the object
of their production is merely that of effecting the
impregnation of the germe, that object is no sooner
obtained than they begin again to give indications of
decay, and speedily fall from the plant ; so that the
most beautiful part of the vegetable is also the most
transient. The flower of the Night-blowing Cereus,
the most 'magnificent of all flowers, no sooner ex-
pands than it begins to decay, and before the sun has
risen upon it its beauty is gone. The flowers of the
Poppy and Tulip, though very gaudy, are very short-
lived ; and the beautiful blossom of our fruit-trees
soon begins to fade. The scene often continues
blooming indeed, both in the landscape of nature
and of art, but that is more owing to the succession
of blossoms on the same or on different plants, than
to the permanency of individual blossoms. And so
also of the flowers that adorn the field or meadow ;
they spring up in perpetual succession, but are in-
dividually of very short duration.

ART. 3. The Fall of the Fruit.— The fruit, which
begins to appear conspicuous when the flower falls,
expands and increases in volume, and, assuming a
peculiar hue as it ripens, ultimately detaches itself
from the parent plant and drops into the soil. But
it does not in all cases detach itself in the same
manner : thus in the Bean and Pea the seed-vessel
opens and lets the seeds fall out ; while in the Apple,
Pear, and Cherry, the fruit falls entire, enclosing the

5

SECT. III. NATURAL DECAY. 517

seed, which escapes when the pericarp decays.
Most fruits fall soon after ripening, as the Cherry
and Apricot, if not gathered ; but some remain long
attached to the parent plant after being fully ripe,
as in the case of the fruit of Crattfgm and Evony-
mus, which may be seen in the hedges in the midst
of winter, and of Mespilus, which continues till the
succeeding spring. But these, though tenacious of
their hold, detach themselves at last, as well as all
others, and bury themselves in the soil, about to
give birth to a new individual in the germination of
the seed.

The fall of the flower and fruit is accounted for in
the same manner as that of the leaf.

SUBSECTION II.

Decay of the Permanent Organs. — Such then is
the process and presumptive rationale of the decay
and detachment of the temporary organs of the
plant. But there is also a period beyond which
even the permanent organs themselves can no longer
carry on the process of vegetation. Plants are af-
fected by the infirmities of old age as well as ani-
mals, and are found to exhibit also similar symp-
toms of approaching dissolution. The root refuses
to imbibe the nourishment afforded by the soil, or if
it does imbibe a portion, it is but feebly propelled,
and partially distributed, through the tubes of the
alburnum ; the elaboration of the sap is now effected

518 CASUALTIES OF VEGETABLES. CHAP. XII.

with difficulty, as well as the assimilation of the
proper juice, the descent of which is almost totally
obstructed ; the bark becomes thick and woody, and
covered with Moss or Lichens ; the shoot becomes
stunted and diminutive; and the fruits palpably dege-
nerate, both in quantity and quality. The smaller or
terminal branches fade and decay the first, and then
the larger branches also, together with the trunk
and root; the vital principle gradually declines
without any chance of recovery, and is at last to-
tally extinguished ; while the solid mass of the
plant exposed to the chemical action of surrounding
substances, to which it now yields, withers and dies
away, presenting to the eye a decayed and rotten
appearance, and crumbling into dust from which it
originally sprang. Such is the transient duration of
the vegetable, and counter-part of animal life.

END OF VOL. II.

INDEX.

Vol. Page Vol. Page

Absorption ii. 90 Aquatic ii, 44S

Acer Saccharinum i. 390 Aril i. 189

Acids, vegetable i. 415 Aristotle, his botanical works i. 10

oxalic i. 416 ascribes sex to plants ii. 299

acetic i. 416 Armature i. 76

citric i. 417 Arrangements, origin of bo-
malic i. 418 tanical i. 16

gallic i. 418 Arteries of the leaf ii. 184

tartaric i. 419 Ascent of the sap ii. 101

benzoic i. 420 of the plumelet ii. 22

prussic i. 420 Ashes i. 464

Acini i. 161 Assafretida i. 443

Acotytedonous seeds or Axillary leaf i. 56

plants i. 264 flower i. 65

Adansonia digitata i. 48 Auxiliary pistils i. 221

Adherent calyx i. 89

jEscuIapius i. 5 Babylonian Palm ii. 298

Affinity by which oxygene is Bacon i. 19

retained ii. 101 Bag i. 159

Agave vivipara ii. 4 Balsams i. 443

Albumen i. 254,397 ofTolu i. 445

Alburnum i. 296 ofPeru i. 445

induration of ii. 256 Bark i. 294

Alcinovis, garden of i. 6 Barren flowers i. 110

Aldrovanda vesiculosa i. 83 of Mosses .. i. 219

Alga3 i. 232 of Hepatic* i. 229

Alkalies i. 466 Beard i. 184

Alston, Dr. his experiments ii. 331 Beak i. 192

Altitude, limiting propaga- Beauvois on Fructification

lion ii. 433 of Messes ii. 345

Amaryllis formosissima .... ii. 217 Beet-root ii. 272

Ammoniac i. 441 Benzoin i. 444

Amnios, its developement . . ii. 375 Berberis communis ii. 460

Anaxagoras i. 9 Berry i. 160

Animalculist ii. 361 Bitten-root i. 35

Antme i. 437 Bitter principle i. 412

Anomalies of vegetable de- Bleeding of plants ii. 102

velopement.. ii. 268 Blight ii. 485

conservative ap- Border i. 88, 96

pendages.... i. 82 Botany, origin of i. 1

Animal, definition of ii. 472 decline i. 12, 19

Apertures i. 364 revival i. 14

Aphrodites ii. 372 Botanical Travels i. 18

Apophysis i. 224 Botanic gardens i. 18

Appendages, conservative .. i. 61 Botany Bay resin i. 437

reproductive., i. 172 Bracte i. 177

elementary ... i. 371 Branch of perfect plants ... i. 48

Apple, its organization .... ii. 264 Branch of Ferns i. 19S

£20

INDEX.

Vol. Page

Branch of Mosses — - — i. 210
deveiopement of .... ii. 255

Bryum argenteum ii. 345

Bud, its description and va-
rieties i. 65

origin and deveiopement ii. 256

anomalies ii. 279

regeneration ii. 479

Bulb, its description and va-
rieties i. 62

origin and deveiopement ii. 260

Bulbous root i. 37

Bunches or tumors ii. 278

Butter of Cacao i. 430

of Coco i. 430

of Nutmeg i. 430

Cactus Tuna ii. 461

Caducous corolla i. 97

calyx , i. 89

Caesalpinus, his botanical ar-
rangements . i. 17
notion of vegeta-
ble sexuality ii. 302

Calandrium Florae ii. 449

Calyptra or veil i. 222

Calyx, its description and

species i. 86

howxlistinguished from

the corolla i. 98

anatomy of the i. 270

of Mosses i. 222

Cambium ii. 182

Camerarius, his experiments ii. 305

Camphor i. 446

Caoutchouc i. 448

Cap or Pileus i. 241

Caprification ii. 313

Capsule i. 157

of Mosses i. 222

Carbon, solution of ii. 86

augmentation of . . ii. 49
in plants growing in

water ii. 47

Carbonic acid a vegetable

food ii. 53

elaboration of ii. 144

oxide ii. 64

Cassava ii. 394

Casualties affecting vegetable

life i. 473

Catkin i. 145

Caudex of Linnaeus i. 42

its anatomy i. 284

Caul inary bulb i. 64

flower i. 85

Causes of the sap's ascent .. ii. 125
as assigned by Gjrew ... ii. 125

Vol, Page
Causes of the sap's asceut as

assigned by Malpighi ii. 126
De la Hire ii. 127
Borelli ... ii. 126
Du Hatnel ii. 128
Saussure.. ii. 131
Knight. .. ii. 132
Causes of the sap's descent . ii. 191
as assigned by the ear-
lier phy-
tologists . ii. 191
Knight ... ii. 192
Causes limiting propagation if. 421

Cavities, nectarous i. 183

Cellular tissue i. 316

Cells of the pericarp i. 155

Central tubes of Knight .... ii. 117
their function , ii. 185

Chalaza i. 254

Changes consequent upon

impregnation.,., ii. 371

external ii. 371

internal ii. 373

Channel of the sap's ascent . ii. 106
according to Malpighi ii. 106

Grew ii. 108

DelaBaisse ii. 112
Du Hamel . ii. 114
Knight .... ii. 115

Mirbel ii. 118

Channel of the sap's descent ii. 184

according to Du Hamel ii. 187

Hales ... ii. 188

Knight... ii. 189

Character of veg. vitality .. ii. 438

Charcoal i. 454

Chemical processes i. 380

phenomena of vege-
tation ii. 27

Cherry, deveiopement of. ... ii. 37$
Chiron, his skill in herbs . . i. 5
Chorion, its character and

deveiopement ii. 375

Circulation of veg. juices . . ii. 236
according to the ear-
lier botanists ii. 236

Hedwig ii. 240

Willdenow... ii. 240

Knight ii. 240

Cistus creticus ii. 142

Claw i. 96

Climate limiting propagation ii. 429

Climbing stem i. 45

Cloves ii. 409

Cluster i. 141

Clutiatenella ii. 327

Coccus i. 159

Coffee Bean, its germination ii. 5

INDEX.

521

Vol. Page

Collar i. 34

Coloured infusions ii. 112

Colouring matter i. 403

Column i. 225

Common receptacle i. 134

tubes of Knight ... ii. 116

Composite Organs, what ... i. 301

formation of ii. 208

Compound flower i. 93

products i. 383

Concentric layers of wood . . i. 329

formation of ii. 216

Conditions of germination .. ii. 3
Conservative Organs of per-

feet Plants i. 32

Ferns i. 196

Mosses.... i. 208

Hepatica? i. 196

Algae i, 232

Fungi i. 240

Appendages .. i. 61

Consumption ii. 503

Contortion ii. 502

Copaiva i. 436

Copal i. 437

Cork i. 451

Corolla, its description .... i. 93

its anatomy i. 270

how distinguished

from the calyx . i. 98

Cornus mascula ii. 140

Corollet i. 184

Cortical layers i. 325

Corymb :...., i. 142

Cotyledon i. 258

Cowslip, multiplicate ii. 288

bordered with purple ii. 291

Cratejas i. 10

Cruciform flower i. 96

Cryptogamous plants i. 194

Cucumber, cultivation of . . ii. 322

Culm i. 45

Cup or calyx i. 86

Cups or saucers i. 2.86

Curtain or veil i. 242

Cuscuta europea ii. 428

Cyamus nelumbo i. 187

Cyme i. 144

Date Palm i. 290

Datisca cannabina ii. 324

Death of the plant ii. 518

Decay, natural ii. 505

of temporary organs ii. 506

of permanent organs ii. 517

Decomposite organs, what . . i. 250

their formation ii. 245

appendages . . i. 299

Vol. Page
Decomposition of carbonic

acid .. ii. 149
water .. ii. 176

Decortication ii. 482

Definition of the plant ii. 486

Democritus i. 9

Descent of the Radicle . . . . ii. 22

accounted for ii. 24

of proper juice .... ii. 182

Descending root ii. 271

Destruction of leaves ii. 481

buds ii. 478

Detached calyx i. 89

Developement of elementary

organs... ii. 200
composite or-
gans ii. 20S

decomposite or-
gans ii. 245

Dicotyledonous seeds or

plants i. 259

Dictamnus Fraxinella i. 142

Dioecious plants i. 116,225

DionaeaMuscipuIa i. 82

Dioscorides i. 13

Diseases of plants ii. 484

Dispermous pericarp i. 155

Dissection of the seed i. 250

Distichous flowers i. 85

Divisions of vegetables .... i. 29
perfect plants .. i. 31
imperfect plants i. 195

Divergent layers, what i. 332

formation of ii. 288

Dodder.. ii. 42S

Double flowers ii. 288

Down i. 191

Dragon's blood i. 436

Dropsy ii. 498

Druids i. 14

Drupe, its description i. 163

anatomy i. 269

Duration of plants ii. 505

anomalies of ii. 296

Earths absorbed by plants . . ii. 74
Earths found in vegetable

ashes . i. 469

Efflorescence ii. 451

Elaboration of sap ii. 135

carbonic acid ii. 144

oxygene .... ii. 153

Elementary organs i. 341

develope-

ment of ii. 200

principles .... i. 375

Elemi i. 434

Embracing leaf i. 5fr

522

INDEX.

Vol. Page

Embryo, its description .... i. 257
developement .. ii. 375

Empedocles i. 9

Epidermis of the seed i. 251

plant . . i. 287, 295

its structure i. 302

how generated . . ii. 200

Epidendron Flos agris ii. 429

Epigenisist ii. 364

Epygyuous insertion i. 106

Epipetalous insertion i. 106

Equivocal generation ii. 394

Equatorial plants ii. 430

Etiolation ii. 498

Eupliurbium i. 442

Evidence of veg. vitality. . . ii. 438

Evolution of the cotyledon ii. 15

radicle. . ii. 15

plumelet, ii. 16

Excitability ii. 439

Exclusion of light ii. 440

External tubes of Knight ii. 117, 185
External structure of plants i. 29

Extract i. 400

of Catechu i. 402

of Senna i. 402

of Quinquina i. 402

of Saffron i. 403

Exudation of sap ii. 141

Fall of the leaf ii. 507

flower ii. 515

fruit ii. 516

Fascicle i. 143

Felling of trees ii. 477

Fecundation, spurious ii. 377

incomplete . . . ii. 377

Fence i. 221

in germination i. 28

Ferns i. 195

Fertility of vegetables i. 171

Fertile plants i. 116

flowers i. 116

of Mosses . . i. 220

of Hepaticae i. 229

Fibres, longitudinal . .. . i. 338, 342

Fibrina i. 399

Fibrous root i. 36

Fig, impregnation of ii. 311

Figures, introduction of

wooden., i. 15
copper-plate i. 18

Filament i. 108

Flattened stem ii. 275

Flower of perfect plants . . i. 84
developement of .. ii. 261

anomalies of ii. 287

origin of ii. 264

Vol. Page
Flower, whence nourished .. ii. 265

Flower-stalk i. 85

Floral leaves i. 173

Flux of juices . . ii. 494

Foliated fruit ii. 294

Food of plants ii. 41

Foramen of seeds i. 171

Force of ascending sap ii. 105

Fox-tail root ii. 269

Fringe or peristonium i. 224

Fractures ii. 478

Frond of Palms i. 60

Ferns i. 199

Hepaticae i. 227

Alg« i. 233

Fungi i. 241

Frondescence ii. 449

Fructification i. 31

Fruit, origin of ii. 264

whence nourished .. ii. 265
developement of ii. 263,371

mai tuition of ii. 452

anomalies of ii. 293

Full flowers ii. 289

Fungi i. 239

models of i. 246

Gaertner De Fruct. et Sem.

Plant i. 148, 250

Galbanum i. 440

Galls ii. 279

Gamboge or gumgutt i. 442

Gangrene « ii. 496

Gaps i. 370

Gases, a vegetable food . . .. ii. 50

Gems, description of i. 61

anatomy of j. 276

propagation by ii. 406

Geoffroy, his experiments .. ii. 307

Germen ii. 263

Germes, preorganized ii. 478

Germination ii. 2

condition of in

the earth .... if. 3
physical pheno-
mena of .... ii. 14
chemical phe-
nomena of... ii. 27
in mediums con-
taining oxy-

gene ii. 30

in mediums de-
prived of oxy-

gene ii. 35

in vacuo ii. 10

Gesner i. 16

Gills i. 242

Girdling of trees ii. 475

INDEX.

523

Vol. Page

Habit ii. 295

Half adherent calyx i. 89

Hazle-nut, its developement ii. 389

Headofflowers i. 136

Hedwig, his definition of the

plant ii. 469

Hedysarum gyrans ii. 464

Herodotus, his notion of ve-
getable sexuality ii. 298

Heliotropiom ii. 447

Hepaticae i. 226

Hermaphrodites i. 116

Hilnm i. riO

Hippocrates i. 9

Homosestrophous flowers. . . i. 85

Honey i. 391

Honey-dew ii. 143

Horologium Florae ii. 445

Hybrids ii. 367

Hydrogene, whether a vege-
table food ii. 63

Hypogynous insertion i. 105

Imperfect Plants i. 194

Impregnation of the Seed. .. ii. 251

Indigo 5. 405

Indusium ii. 205

Inferior calyx ii. 89

Inflorescence ii. 135

Inhalation ii. 90

Incisions ii. 474

Insects ; their agency in fe-
cundation ii. 352

Instinct ii. 465

Internal structure i. 247

Integuments of the Seed .... i. 251

Intro-susception ii. 89

Inversion of the Plant ii. 273

Involucre i. 173

Irritability ii. 458

Jnngius, his definition of the
plant ii. 467

Keel i. 97

Knots or bunches ii. 278

Knight, Andrew, on the de-
scent of the radicle ii. 26
ascent of the sap. . ii. 115
cause of its ascent . ii. 132
elaboration in the

leaf. ii 135, 223

descent of proper

juice ii. 182

course of descent., ii. 191
formation of annual

layers ii. 222

induration of wood ii. 232

Vol. Page
Knight on the presumed regt.

circulation ii. 240

structure of the Ap-
ple and Pear. ... ii. 264
mode of theirgrowth ii. 266
generation of vege-

tablehsbrids ii. 366

regeneration of buds ii. 479

Labdanum

Labiate calyx

corolla

Lac

Layers, concentric

divergent ,

cortical

ligneous

whence formed

propagation by

Lateral communication

Leaves of Perfect Plants.. . .

Ferns. . ,

absorb moisture. . . .
inhale and evolve

gases

developement of. . . .

anomalies of.

Leaf-stalk

structure of.

Legume

Lid or operculum

Liber

Linnaeus introduces his me-
thod

demonstrates vege-
table sexuality. .
defines the plant .

Leipsic Palm

Luxuriant flowers. .

i. 455

i. 88

i. 96

i. 438

i. 329

i. 332

i. 325

i. 328

ii. 214

ii. 418

ii. 122

i. 51

i. 198

i. 211

ii. 91

ii. 97

ii. 282

ii. 282

i. 52

i. 272

i. 166

i. 224

i. 327

i. 22

ii. 308

ii. 468

ii. 325

ii. 28?

Mace... i. 190

Maculae iudicantes^ ii. 353

Malpighi i. 20

Maple-tree i. 390

Manures ii. 79

Marchantia polymorpha. ... i. 334

Mastic i. 434

Medea i. 4

Mechanical Processes i. 378

Medullary rays i. 333

sheath i. 324

Metallic oxides i. 473

Methods, botanical i. 22

of veget. analysis , i. 377

Midrib i. 51

Mildew ii. 491

524

INDEX.

Vol. Page

Millington, Sir Thomas ii. 303

Migratory root ii. 272

Mirbel defines the plant ii. 470

Misseltoe ii. 426

Molasses i. 389

Moisture, access of ii. 8

transmitted by the

cotyledons ii. 20

Monoecious plants i. 1 16

Monocotyledonous seeds or

plants i. 258

Monogynous flowers i. 117

Monospermous pericarp. ... i. 155

Monophyllous calyx i. 87

Monopetalous corolla. ..... i. 94

Morland his account of the

pollen ii. 362

Mosses, description of. ... . i. 206
whether hermaphro-
dites ii. 345

Mouth i. 94

Mucilage i. 387

Multiplicate flowers ii. 288

Mutilated flowers ii. 291

Myrrh i. 442

Naked pericarp i. 150

seed K 156

Narcotic principle i. 414

Natural decay ii. 505

Nectary.... i. 180

Nepenthes distillatoria. i. 83. ii. 286

Nerves of the leaf. ii. 53

Nitrogene, its influence on

vegetables ii. CO

Nodding flower i. 85

Nucleus of the seed i. 254

Nutation ii. 447

Nut-shell, its description.... i. 162

anatomy i. 269

Nyrapbaea Lotus ii. 315

alba ii. 314

Oak Apples ii. 280

Olibanum i. 442

Oils, fixed i. 421

volatile i. 425

Operculum or lid i. 224

Opobalsamum i. 435

Opoponax i. 441

Orobanche ii. 428

Ovary, its description i. 118

origin ii. 263

Oxygene, its agency in ger-
mination ii. 29

a vegetable food. . ii. 57
elaboration of. ... ii. 153
influence on soil. . ii. 173

Vol. Page

Palms, the structure of i. 289

growth of ii. 253

Panicle i. 140

Papilionaceous flowers i. 97

Parasitical plants ii. 425

Parenchyma i. 320

Partitions of the pericarp. . . i. 154

Pea, developement of ii. 382

germination of. ii. 18

Pedicle i. 52

Peduncle i. 85

Pellicle i. 251

Petiole i. 52

Perfect Plants i. 31

Perianth i. 87

Pericarp i. 152

Perigynandra i. 102

Perigonium i. 102

Perigynous insertion i. 129

Perichsetium i. 221

Peristonium, or fringe i. 224

Periods of germination ii. 14

Perspiration imperceptible. . ii. 137

perceptible.... ii. 140

Phenomena of vegetable life ii. 1

of germination ii. 14, 27

Phleum pratense ii. 270

Physical virtues of plants.. . ii. 296

Pbytology, origin of i. 7

decline of. i. 12

revival of. i. 19

Pileus, or cap i. 241

Pith, its description i. 322

formation ii. 209

function ii. ib.

Pine Apple ii. 310

Pistachio-tree ii. 326

Pistils i. 116, 221

Pliny i. 13

his notion of vegetable

sexuality ii. 301

Plant, definition of. ii. 466

Plantlet i. 165

Plumelet i. 267

Pneumatic chemistry i, 26

Pollen, description of i. 112

discharge of. ii. 315

transmission of ii. 331

access of. . . ii. 351

agency of. . . ." ii. 858

Polygamous plants i. 1 17

Polypetalous corolla i. 96

Polyspermous pericarp i. 155

Pome i. 160

Pontedera denies a vegt. sex. ii. 329

Pores i. 365

Priestley, his exp. on leave* ii. 153
Prickles i. 77

INDEX.

525

Vol. Page Vol. Page

Primary principles i. 37fc Sagapenum i. 442

Proper receptacle i. 128 Sago i. 393

Propago i. 283 Salop i. 394

Proper juice, its analysis ... i. 460 Salts ii. 69

descent.... ii. 182

Process of nutrition ii. 89

veget. develope

ment ii. 199

Samara i. 150

Sandarack i. 434

Sap, its analysis i. 457

ascent and cause... ii. 101

Propagation of the species. . ii. 394 Sarracenia purpurea i. 83

by seeds ii. 397 adunca ii. 285

by gems ii. 406 Saucers, or cups i. 236

by slips H..417 Scale i. 91

by layers ii. 418 Scape , . . . i. 125

by suckers ii. 419 Scammony i. 441

by graft* ii. 420 Secundinae internae i. 254

limited ii. 421 Seed, its description i. 16*

Proliferous flowers ii. 290 anatomy i. 250

Pteris aquilina i. 289 developement ii. 373

Pulp i. 314 germination ii. 2

Pubescence, external i. 79 dispersion of ii. 398

internal i. 372 Sensation ii. 462

Pythagoras i. 8 Sensitive Plant .. .« ii. 462

Pyrena i. 168 Sexuality of vegetables ii. 297

anticipations of . . ii. 297

discovery of ii. 302

Radicle ................... i. 266

Radical, bulb.

i. 62

leaf. i. 56

flower i. 85

Ramenta i. 74

Raraeal flower i. 85

Raw Sugar i. 389

proofs of. ii. 309

objections to ii. 328

Sheath of Mosses i. 222

gems ii. 407

medullary i. 324

i

Sheathing leaf. i. 59

Rays, medullary i. 333 Silique i. 165

Receptacle of the flower. . . i. 128 Simple flower i. 93

seed i. 155 Simple products i. 476

Regeneration of buds ii. 479 Simple tubes i. 352

Reproductive Organs of per- Sinking stem i. 209

feet Plants i. 84 Sleep of Plants ii. 444

Ferns i. 200 Slipper i. 184

Mosses .... i. 214 Slips, propagation by ii. 417

Hepaticae.. i. 228 Smellie, his objections to

Algae i. 235 vegetable sexuality ii. 338

Fungi i. 243 Smith, Sir J. E i. 24

Appendages i. 172 his Essay on Dorsif.

Ferns , . i. 226

Resins ..................... i. 432

Ringent corolla ........... i. 96

Roots of imperfect Plants. . i. 33 Soils, their varieties

Ferns ............ i. 196 composition ........ i. 41

Mosses ........... i. 208 analysis ........... i. 81

Hepaticae ......... i. 227 fertility and ameliora-

Smut .................... ii. 490

i. 82

Algae ............ i. 232

Fung*.; ......... i. 240

tion ............. .

Solomon, his Treatise on

82

developement of ii. 246 Vegetables i.

anomalies of ii. 269 Solution of Carbon ii.

7
86

consumes and inhales So wans i. 394

oxygene ii. 165 Spalanzani, his experiments ii. 334

Rye, germination of ii. 17 Spiral tubes, their descrip-
tion u 353

Sacculus coliquamenti ii. 375 function ii. 119

Sacks i. 230 Spathe i. 176

526

INDEX.

Vol. Page

Spadix i. 146

Spike |. 138

Spindle-shaped root i. 35

Spur i. 184

Stamens of Perfect Plants. . . i. 104
Mosses ... i. 220

inserted in the calyx i. 132

Standard i. 97

Starch i. 392

Stem of Perfect Plants .... i. 43
its d«velopement ii. 251

anomalies ii. 274

Stipeof Palms i. 46

Fungi i. 241

Stipules i. 72

Stigma i. 123

Stings i. 76

Strobile i. 167

Style of Perfect Plants i. 121

Mosses i. 225

Storax i. 445

Styrax i. 445

Stylidium glaudulosum ii. 461

Sabtesta i. 253

itsdevelopement. . .. ii. 374

Sugar i. 388

Suffocation ii. 499

Succulent threads i. 219

Superfetation ii. 368

Superior Calyx i. 89

Suckers, propagation by... ii. 419

Tacambac i. 435

Tail i. 192

Tan^ekolli ii. 4

Tannin i. 409

Tendrils i. 70

Terminal leuf. i. 56

flower i. 85

Terrestrial Plants ii. 424

Testa, its description i. 251

developernent ii. 374

Theophrastus, his Treatise

on Plants .. i. 11
notion of vegt.

sexuality... ii. 299

Thorns i. 77

Threads.... i. 270

Thyrse i. 141

Tipula pennicornis ii. 354

Tournefort, his method i. 22

Trachea i. 384

Transpiration of Sap ii. 140

Trunks of Perfect Plants. . . ii 42

Ferns ii. 197

Tube of the calyx i. 88

corolla i. 94

nectary i. 183

Vol. Page

Tubes large i. 351

small i. 363

simple i. 352

porous. i. 353

spiral i. 353

false spiral i. 362

mixed i. 363

their function. . ii. 119, 191

formation ii. 201

Tubercles, or warts i. 235

Tuberous root i. 38

Tuft i. 192

Tumours or bunches ii. 278

Vaillant, his Dissertation on

Vegetable Sexuality

Vali&neria spiralis

Valves of the pericarp

sap vessels. . .

Vascular organs

Vault

Vegetable extract

fibre

Veil or curtain

calyptra

Veins of the leaf. . .

Vessels -conducting sap

Vitality, vegetable....

Vitellus

Umbel

Umbilicus, or umbilical cord
its developement.

Unilateral flowers

Union of Botany and Phy-

tology

Volva, or wrapper

Urn, or capsule of Mosses . .

Utricle

Utricles

Utricularia vulgaris

minor . .

ii. 307

ii. 320
i. 152

ii. 126
i. 341
i. 184
i. 401
i. 338
i. 242
i. 222
i. 184
i. 118

ii. 438
i. 256
i. 143
i. 170

ii. 373
i. 85

i. 25
i. 243
i. 222
i. 158
i. 348
i. 83
ii. 271

Water, a vegetable food. ... ii. 43
its decomposition. , . ii. 176

Wax i. 427

Warts, or tubercles i. 235

Weather-glass, vegetable. . . ii. 446
Wheat, developement of. . . . ii. 385
Willow of Van Helmot . . . . ii. 44

Wing i. 97. 192

Whirl i. 137

Winged leaf i. 54

Woody fibre i. 453

Witches-knots ii. 278

Wounds ii. 473

Wrapper or volva i. 243

Zeluzianski . . ... ii. 302

UNIVEESITY OF CALIFORNIA LIBEAEY,
BEEKELEY

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

Books not returned on time are subject to a fine of
50c per volume after the third day overdue, increasing
to $1.00 per volume after the sixth day. Books not in
demand may be renewed if application is made before
expiration of loan period.

1941

OCT

J94Jt

2319!
MAY 1 5 1951

50m-7,'29

^-.BERKELEY LIBRARIES

PIOLOGY

LIBRARY

G

UNIVERSITY OF CALIFORNIA UBRARY