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libeart

OF THE

U. S. Department of Agriculture.

Glass l . Z.

At 5

THE BIOLOGY OF FERNS BY THE
COLLODION METHOD

The Study of

The Biology of Ferns

By the

Collodion Method

FOR ADVANCED AND COLLEGIATE STUDENTS

GEORGE F. ATKINSON, Ph.B.

Associate Professor of Cryptogamic Botany in Cornell University

Nefa Hotfe

MACMILLAN AND CO.

AND LONDON

1894

By MACMILLAN & CO.

Norfoooh 3|r?0g :

J. S. Cushing & Co. — Berwick & Smith.
Boston, Mass., U.S.A.

49606

PREFACE.

The author was led to the preparation of this little work by the
success which attended his efforts in applying in his classes the “ col-
lodion method ” to the preparation of the very delicate tissues of
ferns, and especially to the infiltration of prothallia, without shrinkage.
A class of nine students sectioned prothallia with ease and accuracy,
making permanent microscopic preparations showing various stages of

development of the sexual organs and the embryo, besides good

aperies showing the development of the sporangia and spores. The
^rst suggestion was the preparation of a simple laboratory guide
giving directions for preparing the various tissues, accompanying this
QCwith a few illustrations, so far as possible made from preparations put
^p by the students in their regular work, and some descriptive matter
which would be helpful to the student in mastering the detail of
structure and development.

It seemed desirable to the author that some features in the devel-
opment not represented by specimens selected from the work of the
students should be included. Accordingly, he was led to a protracted
study of various phases of development, since it was desirable that
all illustrations should be original, and that those of sections should
be from preparations put up by this method. The work thus grew,
since several questions arose which it seemed important to enquire
into quite closely. Especially the question of the structure of the
annulus in the various orders of ferns, and the function of the different
parts of the sporangium in the dispersion of the spores, called for
study.

PREFACE.

The author does not wish to insist on the merits of the collodion
method in comparison with the paraffin method of infiltrating plant
tissues, although perhaps the very delicate tissues will suffer less from
treatment by the former method. Those who have been accustomed
to the paraffin method can doubtless use it to good purpose in con-
nection with the practical part. Therefore the methods described in
Part II. for the preparation of the tissues for infiltration are not insep-
arable from the collodion method, but will, perhaps, serve as well to
prepare the tissues for paraffin infiltration.

The fact that all the illustrations are original and drawn from
preparations put up according to a method in plant histology within
the reach of all students of botany, it is hoped, will give a stimulus
to many to enquire into the mysteries of fern development, and the
encouragement that like results will certainly attend them.

Where the illustrations are made from preparations put up by the
students, credit is given to the preparator. All the other illustrations
are from preparations made by the author.

Ferns, from their intermediate position in the plant kingdom, as
well as from their varied beauty of graceful form, are objects of
great interest to the student of nature. The differential characters
found in their well-developed tissues and in the specialization of their
leaves and fruit structures, offer a wide field for observation and dis-
crimination to those interested in questions of taxonomy. But the
subject appeals especially to the student of biology, since the great
phylogenetic problem of the line of succession reaching from the
lower Thallophyta, as they are sometimes called, to the Spermaphyta,
is being traced through this group and its near relatives.

The study of the biology of ferns is, therefore, of double impor-
tance. Not only does it offer to the student of plant biology a field
in which the phenomena of plant development and plant structure
come in touch, on the one hand, with groups of extremely simple
manifestations of life and form, and, on the other hand, with those of
great complexity ; but it also offers inducements in the way of return
for research. For great as is the work which has been accomplished

PREFACE.

vii

in studies of development and in tracings of phylogeny, the life
histories of but few individuals have been accurately traced, while
the line of descent needs to be more clearly unveiled by farther
careful studies of life histories.

The present work relates chiefly to the homosporous Leptosporan-
giate Filicinese, and seven chapters of descriptive matter are devoted
to them. One chapter is added on the Ophioglosseae, not so much
because it is held that they stand next the former in the natural
series, but because it is quite easy to obtain fresh material for study ;
its members present excellent subjects for comparative study, and
they are popularly known as ferns.

Cornell University, Ithaca, N.Y.,

December, 1893.

CONTENTS

PART I. DESCRIPTIVE.

Chapter I. Gametophyte . . 3

Life cycle of ferns .......... 3

Spores ............ 3

Germination of spores ......... 5

Prothallium ........... 6

Archegonia 12

Antheridia . . . 15

Spermatozoids . . . 17

Fertilization ........... 20

Chapter II. Sporophyte 23

Embryo . . 23

Chapter III. Sporophyte, continued 33

Stem 33

Morphology .......... 33

Anatomy ........... 34

Root .... 41

Morphology .......... 41

Anatomy . 43

Chapter IV. Sporophyte, continued 45

Leaves ............ 45

Morphology .......... 45

Anatomy 46

Sterile and fertile leaves ........ 48

Dimorphism .......... 48

Fructification .......... 50

CONTENTS.

PAGE

Chapter V. Sporophyte, continued . . . . . 53

Sporangia 53

Development of the sporangia 53

Structure of the sporangia, Polypodiaceae . . . .58

Cyatheaceae ......... 60

Hymenophyllaceae ........ 62

Gleicheniaceae ......... 63

Schizaeaceae ......... 64

Osmundaceae 66

Chapter VI. Sporophyte, concluded 68

Dehiscence of sporangia and dispersion of spores .... 68

Polypodiaceae .......... 69

Cyatheaceae . 72

Hymenophyllaceae . . . . . . . . 72

Gleicheniaceae . -73

Schizaeaceae .......... 74

Osmundaceae . 74

Comparison . . . . . . . . . . .7 4

Mechanism of the annulus . . . . . . . -75

Chapter VII. Substitutionary Growths 77

Sporophytic budding 78

Gametophytic budding . 83

Apogamy 84

Apospory 84

Chapter VIII. Ophioglosse^e 87

Stem 87

Leaf ............ 89

Sporangia . . . . 91

Roots 92

PART II. METHODS.

Chapter I. Notes on Technique 101

Preparation of collodion . . . . . . . . .101

Materials ........... 101

CONTENTS.

PAGE

Two per cent collodion ioi

Five per cent collodion . . . . . . . . .102

Dehydrating apparatus . . .102

Tubes 102

Dehydrating-jar . . . . . . . . .102

Dehydrating and orienting the firmer and older tissues . . -103

Chapter II. Gametophytic Phase 106

Development of the prothallia 106

Sowing the spores . . . . . . . . .106

Structure of the spores . . . . . . . .108

Germination of the spores 108

Prothallia .......... 109

Abnormal prothallia . . . . . . . .109

Development of the sexual organs . . . . . . .109

Selection of prothallia for sectioning 109

Dehydrating . . . . . . . . . .110

Infiltrating with collodion . . . . . . .111

Imbedding the prothallia in collodion . . . . .111

Orienting the prothallia . . . . . . . .112

Sectioning prothallia . . . . . . . 113

Fixing the sections to the glass slip. . . . . .114

Archegonia and antheridia . . . . . . . 1 1 5

Development of the embryo . . . . . . . .116

Chapter III. Sporophytic Phase . . . . . . .118

Macroscopic study 118

Stem 1 19

Root . . . . * 1 19

Leaf . . . . 1 19

Parts of the leaf .119

Stalk 1 19

Lamina . . . . . . . . . .119

Reproductive bodies 119

Microscopic study . . . . . . . . . .120

Stem . . . . . 120

Cutting the sections . . . . . „ . .121

Apical cell ......... 121

xii CONTENTS.

Structure of the stem, transection .
Sclerenchyma ....
Vascular bundles
Parenchyma ....
Leaf traces and origin of roots .
Structure of stem, longisection.
Vascular bundles
Scalariform tracheides
Spiral tracheides
Scalariform vessels .

Xylem parenchyma .

Sieve tubes ....

Bast ...

Phloem parenchyma .

Phloem sheath and bundle sheath
Root ......

Selection of material
Apical cell ....

Structure of root, transection .

Leaves, structure ....

Epidermis

Development of stomates .
Development of sporangia and spores
Spores ......

Dehiscence of sporangia .

Bibliography ......

Index to Part I.

PAGE

122

123

I23

123

I23

123

124

125

126

I29

133

Part I.

DESCRIPTIVE.

THE BIOLOGY OF FERNS.

GAMETOPHYTE.

Life Cycle of Ferns. — The normal life cycle of ferns con-
sists of two successional or complemental phases : the game-
tophyte (prothalline stage, oophyte) and sporophyte (fern
plant). The gametophyte is the earliest form to appear m
the life cycle, and probably also was the first in time to appear
on the earth. It is usually a flat expanded plate of tissue,
or it may be filamentous and alga-like. It is termed the pro-
thallium. It proceeds from the germinating spore, and bears
the sexual organs of reproduction. As a result of fertilization
the egg cell develops into the fern plant with which we are
all so familiar, the sporophyte. This in turn bears the spores,
and is usually perennial. The elimination of one or the other
of these phases from the normal life cycle, or the production
of new gametophytes or sporophytes as buds, frequently hap-
pens, and will be referred to in detail hereafter.

With this preliminary general statement we will proceed to
discuss more in detail the various phenomena of development
and the special conformation of the different phases.

Since the prothallium is a result of growth from the ger-
minating spore, we may look at the characters of the spores
in general, while their development will be reserved for study

in connection with the sporophyte.

Spores. — The spores of ferns in form are of two different
types, resulting from two ways of development. In most of

4 THE BIOLOGY OF FERNS. [part i.

the Polypodiaceae, Gleicheniaceae, and Schizaeaceae the form
approaches that of a quadrant of a sphere, and they are said
to be bilateral or radial. The spore usually consists of two
coats, an inner coat, the endospore, which
surrounds the protoplasm, and is quite
thin compared with the outer coat, the
exospore. The exospore is usually cutic-
ularized and coloured, being also variously
marked with warts, papillae, or ridges.
In a pretty green-house fern, Niphobolus
crispum corymbiferum , a native of Japan,
the spores are bright yellow, and marked
with stout, irregular warts. In various
species of Aspidium , the shield ferns, the
exospore is produced into prominent wings which anastomose
irregularly. In Polypodium vulgare the elevations of the sur-
face of the exosporium are in the form of short stout papillae,

Fig. i. Spore of Pteris
serrulata, showing the
roughened exospore
and the three-rayed
fissure. Magnified 30
times more than the
scale ; scale = 1 mm.

Fig. 2. Spore of Aspidium acrostichoides with winged exospore. — Fig. 3. Same crushed
to remove exospore, and showing the endospore. — Figs. 4 and 5. Spores of Asple-
nium filix-foemina, showing same conditions. All magnified 30 times more than the
scale ; scale = 1 mm.

while in Cystopteris bulbifera they are nearly cylindrical and
quite long. In Sckizcea pusilla the surface of the exospore
is beautifully marked, reminding one of the tessellated mark-
ing on the frustum of some diatom.

In some cases in the above-named families, and generally
in the Cyatheaceae, Hymenophyllaceae, and Osmundaceae, the
spores are rounded or tetrahedral in shape.

I.]

GAMETOPHYTE.

Germination of Spores. — With the exception of the Hymeno-
phyllacese and Osmundaceae, the spores are long-lived, and
require a period of rest before they will germinate, several
species having been known to germinate after storage in the
herbarium for several years. Having passed this period, usually
a few months, they will germinate in a few days’ time if placed
under favourable conditions. If placed on moist soil, or some
porous substratum which will retain a moist surface when
protected from above, the coats of the spore absorb water so
that it comes in contact with the protoplasm within. Some
substance in the protoplasm possesses a strong avidity for water,
which is then drawn in with great force. The protoplasmic
lining of tfye cell will not permit water to filter out, and thus
the strong endosmotic pressure exerted causes the bulk of
the protoplasm to increase. This produces a powerful tension
upon the two coats of the spore. The exospore cannot stretch
to accommodate the increasing bulk of the protoplasm, and
therefore it bursts. In a number of cases the endospore bursts
also, and an entirely new wall of cellulose is deposited about
the protoplasm.

Campbell found this to be the case in Onoclea. According
to Rauwenhoff it occurs in the Gleicheniaceae. If the stout
exospore did not cling so tenaciously in many other ferns,
this might be observed in quite a large number of cases
probably. In most cases in the Polypodiaceae after the exo-
spore has burst, the cell elongates, producing a short pro-
tonemal thread containing chlorophyll and starch grains in
the protoplasm. It thus issues from the fissure in the exospore,
and soon divides by a cross wall into two cells, the proximal
cell containing less chlorophyll and giving rise to the first
rhizoid. The rhizoid is an elongated, unsegmented, slender
cell, usually destitute of chlorophyll. It may be entirely
colourless, or in some cases assumes a brown colour. It en-
ters the soil or other nutritive substratum on which the spore
is, and functions as an absorbing organ to supply the young

THE BIOLOGY OF FERNS.

[PART I.

prothallium with food. It describes a sinuous course, and the
free end is often somewhat flattened and irregular in outline,
which thus forms a suitable hold for adherent particles, from

Fig. 6. Spore of Niphobolus crispum corymbiferum. — Fig. 7. Same in early stage of
germination, showing first cell of protonemal thread. — Figs. 8 and 9. Farther
development, showing young rhizoid and protonemal thread of two and three cells.
— Fig. 10. Still older prothallium, showing the beginning of the expanded plate of
cells, with the wedge-shaped apical cell at the growing end. A portion of the exo-
spore still clings to the first cell of the prothallium. All the figures magnified 30 times
more than the scale ; scale = 1 mm.

which moisture and nutritive substances are drawn up much
as in the root hairs of higher plants.

Prothallium. — The terminal cell of this young protonemal
thread continues to elongate and divide by transverse walls, until
a thread of several cells’ length is developed, when under normal
conditions growth takes place laterally as well as in a direct

I-]

GAMETOPHYTE.

line. An expanded plate of cells is thus formed. This is usu-
ally introduced by an oblique wall across the terminal cell of
the protonemal thread, fol-
lowed by another oblique
wall forming an angle with
the first. This starts a
wedge-shaped apical cell.

For some time successive
oblique walls are formed
across this growing apical
cell, and transverse walls
in the lateral cells produce
the plate of a single layer
of cells. The beginning of
the plate of cells is not,
however, always introduced
by oblique division result-
ing in an apical cell, but
sometimes by a perpen-
dicular wall, thus forming
quadrangular apical cells.

For sometime this apical
cell is in advance of the
lateral growth, but soon
the tissue on either side extends in advance of the apical cell,
so that the young prothallium is heart-shaped.

Before long, growth takes place in a direction perpendicular
to the surface of the prothallium at the sinus, so that a cushion
of tissue several cells in depth is formed at this point. Thus a
merismatic tissue, composed of small cells richly filled with
protoplasm, takes the place of the apical cell. Meanwhile other
rhizoids are developed from the under side of the prothallium
at the posterior end, which give it a firm hold upon the
substratum.

In the development of the meristematic cushion, in place of

Figs, ii and 12. Germinating spores of Pteris
serrulata. In Fig. 12 the spores were still
within the sporangium, the sporangium hav-
ing been sown at the time of the sowing of
the spores. Magnified 6 times more than
the scale; scale = 1 mm.

THE BIOLOGY OF FERNS

[PART I

Tig* 13. Ripe prothallium of Adiantum cuneatum ; archegonia in a cluster near the
sinus, antheridia scattered over a large part of the surface and among the rhizoids.

I-]

GAMETOPHYTE.

the apical cell, several quadrangular cells in a crescentic row
participate. The breadth of the prothallium is increased by
dividing walls perpendicular to the surface of the prothallium,
but parallel with its axis ; while depth is produced by walls also
perpendicular to the surface, but transverse to the axis, cutting
off basal cells, each of which then divides by a wall whose plane
is parallel with the surface of the prothallium. The lower of
these cells is usually the larger. By a perpendicular wall it is
divided into two cells, one of which may become the mother

Figs. 14, 15, and 16. Various forms of male prothallia of Niphobolus crispum corymbi-
ferum. In Fig. 16 are two trichomes, at the dystal end sometimes developed on the
margin of various prothallia. Magnified 6 times more than the scale ; scale = 1 mm.

cell of an archegonium. By the more rapid increase of these
lower cells the cushion projects below the surface of the pro-
thallium.

Even full-grown prothallia are quite small, perhaps averaging
from 4 mm. -6 mm. Sometimes they are much larger, quite fre-
quently twice this size. Goebel records one of Oswinudci , which
had grown several years, to be 4 cm. long. In colour they vary
from light yellowish green to dark green.

THE BIOLOGY OF FERNS.

[part I.

The sexual organs may be produced both on the same pro-
thallium, when the latter is said to be monoecious. This is
probably the more common. They are, however, produced on
separate prothallia, which are then dioecious. Sometimes a
prothallium bears antheridia for a period, and then archegonia
appear, i.e. it is proterandrous. Very commonly a few anther-
idia appear before the archegonia. In some species male pro-
thallia are quite small, while the hermaphrodites are large.
This dimorphism of the prothallium has been long known, and
is probably largely due to conditions of nutrition.

The form and size of the prothallia are greatly influenced by
the amount of nutriment, as well as by the more or less crowded

condition. When the spores are sown
thickly and under such conditions that
many prothallia obtain but little nutri-
ment, they may be very rudimentary
and consist of nothing but simple or
variously branched protonemal threads.
The normal prothallium in the Polypo-
diaceae, when not crowded, is flat and
quite regularly cordate, or the wings
may be somewhat rectangular, while the
margins are more or less wavy or fluted.
When they are crowded there is a greater
or less tendency, according to the prox-
imity of the individuals, to grow erect
and to be ‘curved and distorted.

In Adiantum cuneatum the writer
has observed some curious forms of
starved prothallia. In one case, first
noted by a student, the protonemal
thread forked a short distance from the
spore, and the branches extended at
right angles to the primary thread like the arms of the letter
T, each arm bearing a prothallium. In another case observed

Fig. 17. Very rudimentary
male prothallium of Ni-
phobolus crispum corym-
biferum. a , very young
antheridia ; b y somewhat
older one, showing the
annular cells; c , mature
antheridium. Magnified
30 times more than the
scale; scale = 1 mm.

I-]

GAMETOPHYTE.

I L

the young prothallium produced nearly colourless protonemal
threads from marginal cells. Each of these threads bore a
prothallium, and in turn produced marginal threads bearing
other prothallia. Sometimes even in
the Poly.podiaceae there is no primary
protonemal thread, but the expanded
plate of cells arises directly from the
spore. The writer has noted several
cases in studying the germination of
spores of Niphobolus crispum , and in
one case two such prothallia were devel-
oped from a single spore. In another
example the ruptured exospore showed
a group of four cells, one of which was
producing a rhizoid.

Occasionally also in the Polypodiaceae
as well as in the Cyatheaceae, according
to Bauke, and in the Gleicheniaceae,
according to Rauwenhoff, a cell mass
is developed directly from the spore.

In the Osmundaceae the prothallium
is usually ribbon-like, with a midrib of several layers of cells,
along the edge of which the archegonia are developed. As a
rule it arises directly from the spore without the intervention
of the protonemal thread. This more simple condition of the
prothallium in Osmunda frequently closely resembles the thallus
of the Hepaticeae. Campbell has found that the prothallium of
O. claytoniana is frequently more expanded and resembles
that of the Polypodiaceae.

The growing point of the prothallium is sometimes lateral
in the Polypodiaceae, in which case the prothallium is not
cordate. This is very common in the Schizaeaceae.

Goebel found that the prothallium of Gymnogramme lepto-
phylla is very irregularly lobed, there being several growing
points on the margin. A peculiar outgrowth from the pro-

Fig. 18. Spore of Niphobolus
crispum corymbiferum di-
vided into four cells before
issuing from the exospore ;
a rhizoid is developing from
one cell. Magnified 30
times more than the scale;
scale = 1 mm.

THE BIOLOGY OF FERNS.

[PART I.

thallium forces its way into the soil, where it develops into
a tuber-like organ rich in reserve material, and called the
fertile shoot. The antheridia and archegonia are borne on
its upper side. If fertilization does not occur, two new pro-
thallia grow out from the tuber. As the prothallia die away,
adventitious shoots usually grow from the margin or surface.
Many of these are tuber-like, but differ from those of the
primary fertile shoot in bearing only antheridia. This stage
of Gymnogramme leptophylla is therefore perennial, the tubers,
after a period of rest, during which they resist drying and
other changes, developing new prothallia. Its sporophyte is
annual. Marginal shoots also occur on the prothallia of other
ferns.

In the Hymenophyllaceae the prothallium is very variable.
Frequently it consists entirely of a long, much-branched, pro-
tonemal growth, bearing antheridia laterally and archegonia
terminally. In Trichomanes pyxidiferum the archegonia are
borne on stalked multicellular bodies, which are lateral out-
growths of the protonema, and are termed archegoniophores.
In other species expanded plates of cells occur along with
the protonemal threads.

Archegonia. — The archegonia are flask-shaped organs, pos-
sessing a broad venter, which is sunk in the tissue of the
prothallium. The neck projects beyond the surface and con-
sists of four rows of cells surrounding a canal. Each arche-
gonium contains an egg cell (oosphere), a ventral canal cell,
and one or more canal cells. They arise from superficial cells
of the cushion of tissue at the anterior end of the prothallium.
This cushion of tissue is more richly supplied with protoplasm
than the part of the prothallium on which the antheridia are
borne. This is in accordance with a general law which obtains
in relation to the orientation of the sexual organs as governed
by the supply of nutriment to different prothallia or to different
parts of the same prothallium. The office of the archegonium
being the development and protection of the egg cell, the

GAMETOPHYTE.

I-]

provision of a canal for the direct approach of the spermato-
zoids, and a substance to entangle them at the mouth of the
canal, together with the necessity for a supply of nutriment
to the embryo from the prothallium until it shall have gained
a foot-hold in the soil, necessitates a better provision of
nutriment for the archegonia than for the short-lived antheridia.

Usually the archegonia are developed only on the under side
of the prothallium. In two cases the writer found them on
both surfaces on prothallia of Pteris sernilata. The prothallia
were crowded so that they stood nearly perpendicular and the
light reached both surfaces. Campbell notes archegonia on
both surfaces of an undetermined fern prothallium. Heinricher
and others have found that lighting prothallia from below
causes the development of archegonia on the upper surface.

The superficial cell, which is the mother cell of the archego-
nium, first divides by periclinal walls into three cells, the basal
cell, central cell, and neck cell. The central cell is very rich in
granular protoplasm, and has a larger, more distinct nucleus
than the other cells. The basal cell, with other cells of the
prothallium bounding the central cell, develop into the venter
of the archegonium, which consists of smaller cells than those
of the surrounding tissue of the prothallium. The neck cell
is the mother cell of the neck of the archegonium. It divides
by two successive anticlinal walls into four cells, which, by
growth nearly perpendicular to the surface of the prothallium,
produce four rows of cells forming the neck of the archego-
nium. The two rows of cells on the anterior side of the neck
grow faster than those on the posterior side, and are larger,
sometimes also being greater in number, from four to five on
the posterior side, and five to six on the anterior. This causes
the neck of the archegonium to be curved toward the posterior
end of the prothallium. The central cell, meanwhile, is growing.
It becomes strongly convex on the outer side, and a protrusion
extends between the four neck cells. It now divides by a
periclinal wall into two unequal cells. The smaller one in the

Figs. 19 to 28. Various stages in the development of the archegonium : 21, from Pteris
serrulata; 26, from Adiantum concinnum ; the remainder from Adiantum cuneatum.
Figs. 19, 20, and 21 : successive stages of the development of the superficial cell of
the prothallium into the three cells : a, neck cell ; b, central cell; c , basal cell. In Fig.
26, e, the egg ; f the ventral canal cell ; g, the neck canal cell, shows the nuclear
spindle preparatory to the division into two cells. Fig. 27 shows the complete
division of the neck canal cell into two cells. In 28, the canal cells are deliquescing
into the slimy substance. Magnified 30 times more than the scale; scale = 1 mm.
Fig. 24 from preparation by S. G. Harris.

!•]

GAMETOPHYTE.

canal elongates by growth, and sometimes at least divides,
forming two neck canal cells. The larger cell divides again,
and a second small cell is cut off from it, forming the ventral
canal cell. The larger cell of these two is the egg cell. At
maturity, the ventral and neck canal cells swell, and deliquesce
into a slimy substance. The four stigmatic cells at the end of
the neck spread wide apart, and permit the slimy substance to
protrude part way out of the neck, where it serves to entangle
the passing spermatozoids.

The neck canal cells begin so soon after maturity to change
to the slimy substance, it is difficult to demonstrate the division
into two cells, though it is quite easy to demonstrate two nuclei
in the protoplasm of the neck canal cells. In several cases, I
have observed an undoubted division into two cells. In another
case, the preparation presented a beautiful case of the karyoki-
netic condition of the nucleus of the canal cell (Fig. 26).

Antheridia. — The antheridia are papillate outgrowths of the
prothallium. Each consists of a single layer of chlorophyll-
bearing cells forming the 'wall. This wall encloses at first a
single cell rich in protoplasm, which eventually develops into
the spermatozoids.^ On well-developed prothallia, the usual
position for the antheridia is among the rhizoids near the
posterior end, and extending from this point over a surface
outward on each side of the cushion of tissue which bears the
archegonia. Especially on old prothallia are the antheridia
very numerous on the under surface of the wings each side of
the group of archegonia, but usually some distance from the
margin of the prothallium. In two cases, where prothallia of
Pteris serrulata were so crowded that they stood erect, per-
mitting light to reach both sides, antheridia were found on both
surfaces. In quite young prothallia, they are frequently borne
on the margin. Many male prothallia are very simple, consist-
ing only of a protonemal thread with well-developed antheridia
extending as branches in various directions. In some cases,
they are very rudimentary, the protonemal threads of one or a

Figs. 29 to 37. Various stages in the development of the antheridia : 32 and 37 from
Pteris serrulata; the remainder from Adiantum cuneatum. Various stages in the
development of the central cell to form the mother cells of the spermatozoids are also
shown. In Fig. 36, the spermatozoids are mature. In Fig. 37, the antheridium
possesses a stalk cell. Magnified 30 times more than the scale ; scale = 1 mm.
Figs. 34 and 35 from preparation by K. M. Wiegand.

1 6 THE BIOLOGY OF FERNS. * [part i.

very few cells maturing, with several antheridia clustered at the
end. The protonemal thread may branch several times irregu-
larly, bearing antheridia on all the branches. All stages, from
very simple rudimentary male prothallia, which recall the male

prothallia of the Salviniaceae, through various conditions of
protonemal development, to the more or less expanded plates
of cells, are found.

GAMETOPHYTE.

1 7

i-i;

The antheridium begins as a small protuberance of a super-
ficial cell of the prothallium, so that it is difficult at first to tell
whether an antheridium or a rhizoid is to result. But very
soon the young antheridium shows a richer and more granular
content of protoplasm. Growth of the protuberance continues,
and finally it is delimited from the cell of the prothallium by a
periclinal wall. The next wall is shaped like a funnel, or watch-
glass, more rarely straight, the point, or convexity, usually
reaching -the first, or basal, wall. The third wall is nearly like
that of a half-sphere, its convexity lying parallel with the outer
convex wall of the antheridium, its rim meeting the preceding
wall, thus forming a central cell. This central cell is very rich
in protoplasm, and possesses a very distinct nucleus about
which granular protoplasm is arranged in an irregularly stellate
fashion. A fourth wall now arises similar to the second, cut-
ting off from the end of the antheridium the cap cell. The
central cell is the mother cell of the spermatozoids. Some-
times a short stalk cell is developed before the antheridium
begins to differentiate.

The superficial cells contain chlorophyll, and they constitute
the wall of the antheridium. Two of them are annular, i.e.
in the form of complete rings, surrounding the central cell.
Because of the thinness of their walls near the point of the
transverse diameter of the central cell, in optical section it not
infrequently appears as if each annular cell were composed of
several cells.

The central cell by division develops into the mother cells of
the spermatozoids. It first divides by a longitudinal wall into
two cells. The second wall is also longitudinal and perpen-
dicular to the first, thus forming four cells arranged as quadrants
when seen from the end of the antheridium. Division proceeds
until quite a large and variable number of mother cells results.

Spermatozoids. — The mature spermatozoids are spirally coiled
bodies in the form of a screw, with numerous cilia attached to
the anterior smaller end. The spermatozoid is developed prin-

THE BIOLOGY OF FERNS.

[PART I.

cipally from the nucleus of the mother cell. The granules of
the nucleus finally become arranged in the form of a spiral.
The anterior end, according to Strasburger, is developed from
the cytoplasm, and the cilia are outgrowths of this part. The
spiral is smaller at the anterior end, and before motion begins

Figs. 38 to 41. Niphobolus crispum corymbilerum. Fig. 38, distal portion of male pro-
thallium, showing different views of the antheridia, some open; 39 and 40, showing
the change in the form of the superficial cells at time of the expulsion of the sper-
matozoids, both figures being drawn from the same specimen. Fig. 41, two dehiscent
antheridia, each containing a spermatozoid rotating in the base. Magnified 30 times
more than the scale ; scale = 1 mm.

the cilia are coiled about it. The body of the screw is some-
what flattened, being usually broader at the posterior end.

When the spermatozoids are mature, a portion of the cyto-
plasm changes to a mucilaginous substance, so that they are
partly freed. At this stage also the superficial cells of the
antheridium possess a strong avidity for water. Thus, when

!•]

GAMETOPHYTE.

water comes in contact with them, during rain, or when watered

artificially, these superficial cells absorb quantities of it, which
produces such a pressure upon the contents of the antheridiurn
that it becomes ruptured. The rift is irregular, and usually
takes place in the cap cell. By this means the spermatozoids
are forcibly and usually completely expelled from the anther-
idium. For a few moments after expulsion they remain nearly
motionless. Slight voluntary movements sometimes occur
before the rupture of the antheridiurn. After a few moments
of comparative quiet they frequently seem to awake to life
suddenly. For usually from a state in which only a slight
movement of the cilia is perceptible, suddenly a violent whirling

Figs. 42 to 44. Different views
of spermatozoids in a quiet
condition ; Fig. 44, in mo-
tion ; from Adiantum con-
cinnum.

of the lashes begins, and the spermato-
zoid darts away, dragging behind it for
a time a hyaline sphere, a remnant of
the mother cell. When no mature
archegonia are near, the spermatozoid
continues in an irregular course, darting
hither and thither for fifteen to thirty
minutes or more. Finally the move-
ment becomes slower and slower, until
with slow and feeble lashes the cilia are
not able to move the body for any considerable distance, and
eventually all voluntary movement ceases. When mature
archegonia are near, the spermatozoids in passing are caught
in the slimy substance which is expelled at the mouth and held
there in great numbers. Movement continues, but the activity
is impeded by the slime, and the spermatozoids plough their
way down the funnel-shaped mouth toward the neck. In
dehydrating prothallia and infiltrating them with some sub-
stance preparatory to sectioning, great numbers of spermato-
zoids are sometimes retained in the slime at the mouth of the

archegonium in section.

The action of the superficial cells of the antheridiurn in the
expulsion of the spermatozoids probably assures the escape of

THE BIOLOGY OF FERNS.

[part I.

more spermatozoids than would take place were they left to
escape of their own movement after rupture of the lid cell
takes place. In two cases which I observed a spermatozoid
was left in an antheridium. In each case the anterior end
happened to be directed toward the base of the antheridium.
When movement began, the spermatozoid madly ploughed for
more than half an hour against the base of the antheridium,
and did not make its escape.

In Osmunda , according to Campbell, the mother cell of the
antheridium is divided by a wall in such a way that a trian-
gular apical cell is produced, from which several successive
tabular cells are cut off. Eventually a convex wall parallel
with the convex outer surface of the apical cell arises, which
cuts off a central cell, the primary mother cell of the spermato-
zoids.

Fertilization. — If a prothallium with mature antheridia and
archegonia be inverted on a glass slip and mounted in water
for microscopic observation of the under surface, after a few
moments, five to twenty minutes, it will be noticed that the
spermatozoids are being expelled from the antheridium. In
a few moments more they commence to swarm by whirling
rapidly about. By chance a great many of them pass into the
region of the archegonia, and if the attention be now fixed
on this spot, hundreds of spermatozoids will be seen swarming
in and out among the projecting necks of the archegonia.
It will also be noted that the necks of certain archegonia have
opened by the wide spreading apart of their four stigmatic
cells, and that a slimy, granular, stringy mass, the disorganized
canal cells, is protruding. In this many of the spermatozoids
become entangled. Some free themselves and swim away, but
many of them do not escape. The slimy substance of the
canal cells appears to be arranged in numbers of strings which
lie parallel with its walls, and at the mouth radiate therefrom.
In this the spermatozoids can be seen, the smaller end of the
coil directed toward the canal. Some can be seen quite far

I.]

GAMETOPHYTE.

down in the canal, but at the open end they are sometimes
crowded very close together. Most prothallia are unsuitable
for observing the entrance of the spermatozoid into the egg.
After numerous sections Strasburger succeeded in observing
it in Pteris serrulata. However, the prothallia of Cei'atopteris
thalictroides were found to be excellent objects to employ for
this purpose. Because of their thinness and their translucency

Fig. 45. Dehiscent archegonium of Adiantum cuneatum, var. princeps, showing sper-
matozoids making their way down through the slime in the neck of the archegonium.
Magnified 30 times more than the scale ; scale == 1 mm.

as well as the position of many of the archegonia near the
margin, he was able to see the egg and the entire canal in
optical section. According to him several spermatozoids may
enter the cavity at the ventral surface of the central cell. In
passing through the slime in the canal the spermatozoids lose
the vesicle. They rotate more slowly on their axis, and the
coil becomes longer and more open. Upon reaching the cavity

THE BIOLOGY OF FERNS.

[part I.

at the ventral surface of the egg, the coil partly closes up again
and the rotation becomes more active. After a time one is so
situated that its anterior end comes in contact with the recep-
tive spot of the egg, a light spot in the protoplasm at the
ventral surface. It becomes fixed unless soon crowded away
by the jostling of the other spermatozoids. It continues to
rotate on its axis and slowly sinks within the egg, and in a few
minutes becomes invisible. Campbell was able to see the
entrance of the spermatozoids into the cavity of the central
cell in living specimens of Osmunda , the position of some of
the archegonia favouring the observation. The spermatozoid
fuses with the nucleus of the egg and fertilization is accom-
plished.

Without the influence which the addition of this new sub-
stance, the body of the spermatozoid, exerts upon the egg, it
could not develop into a new plant. Probably the majority
of cases where fertilization does take place, the fertilized egg
fails to develop into the embryo, for it is a common thing for
several eggs to be fertilized on a single prothallium, but the
large majority of prothallia perish without the development
of a new plant.

SPOROPHYTE.

II.

EMBRYO.

After fertilization the egg increases in size and completely
fills the space in the base of the archegonium. Sometimes it

Fig. 46. Two-celled embryo of Pteris serrulata, surrounded by the venter of the arche-
gonium and prothalline tissue. A remnant of the neck of the archegonium is still
attached. The basal wall has divided the embryo into two unequal segments, the
anterior or stem segment being smaller than the posterior or root segment. Magnified
30 times more than the scale ; scale = 1 mm.

THE BIOLOGY OF FERNS.

[PART I.

also arches out with a stronger convexity at the junction of the
canal. In experiencing this change the embryo becomes oval,
the form being determined by that of the cavity. The longer
axis is perpendicular to the surface of the prothallium. The
embryo next experiences growth the influence of which, so far

as cell multiplication is con-
cerned, is in a direction parallel
with the axis of the prothal-
lium. The first division wall
of the young embryo is nearly
or quite parallel with the axis
of the archegonium, conse-
quently nearly perpendicular
to the surface of the prothal-
lium, and it is also perpen-
dicular to the antero-posterior
axis of the prothallium. It
divides the embryo into two
parts, an anterior part and a
posterior part. This first wall
is termed the basal wall. It
separates the stem segment
(anterior segment) from the
root segment (posterior seg-

also smaller than the root segment. ment). Two Other walls follow,
Magnified 30 times more than the scale ; , . , . ...

scale = 1 mm. though the order of their suc-

cession is not definitely known.
One, the transversal wall, is perpendicular to the basal wall
and parallel with the surface of the prothallium, while the
other, the median wall, is perpendicular both to the basal wall
and to the surface of the prothallium. The eight parts into
which these three walls divide the embryo are termed the
octants, and the four parts formed by the intersection of the
basal and transversal walls are termed the quadrants.

The upper anterior quadrant is the stem quadrant ; the lower

Fig. 47. Two-celled embryo of Adiantum
cuneatum. The stem segment here is

II.]

SPOROPHYTE.

anterior quadrant, the leaf quadrant ; the lower posterior quad-
rant, the root quadrant; while the upper posterior quadrant
develops an organ of attachment to the prothallium termed,
inappropriately, the foot. The stem, root, and leaf quadrants
are so named because those parts of the plant are developed
respectively from those quadrants or parts of the embryo. Of
the two anterior upper octants only one develops the stem, the
other undergoes little or no farther differentiation. So of the
two lower posterior quadrants only one takes part in the devel-
opment of the root. The stem and root octants lie on the same
side of the median wall, but diagonally opposite as regards the
basal wall. One of the lower anterior octants is concerned in
the development of the first leaf, or cotyledon. Both of the
upper posterior octants are concerned in the development of
the foot.

Following the completion of these three walls are two others.
They extend nearly parallel with the basal wall : one, the hypo-
basal wall, across the posterior part ; the other, the epibasal
wall, across the anterior part. These walls are slightly convex
on their inner faces, i.e ., on the side toward the basal wall.
The stem and root octants serve as tetrahedral apical cells, and
by successive walls nearly parallel with the basal, transversal,
and median walls, the form of the apical cell is preserved. Ac-
cording to Goebel, in the leaf quadrant no walls arise parallel
with the transversal wall. In Osmunda Campbell found the
leaf octant to serve as the three-sided apical cell, and it is quite
probable that the same thing occurs in other ferns whose leaf
possesses a three-sided apical cell. Very early in the develop-
ment of the root segment, walls arise parallel also to the outer
surface of the apical cell, the first cell so cut off being the
beginning of the root cap.

In Fig. 48, a longitudinal section of a young embryo of
Adiantum concinnum y it can be seen that in the tetrahedral root
segment, besides the hypobasal wall nearly parallel with the
basal wall, one wall has formed nearly parallel with the trans-

THE BIOLOGY OF FERNS.

[PART I.

versal wall, and the nucleus of the apical cell shows the nuclear
spindle in process of segmentation prior to the formation of

Fig. 48. Young embryo of Adiantum concinnum. A remnant of the neck of the arche-
gonium is attached to the calyptra. The basal wall is in a plane continuous with the
canal of the archegonium. The direction in which the neck of the archegonium
points indicates the root, or posterior segment ; on the anterior side is the epibasal
wall and on the posterior side is the hypobasal wall, the transversal wall crossing these
neaily in the middle. A, leal quadrant; S, stem quadrant; F, foot quadrant ; R t root
quadrant. Magnified 30 times more than the scale ; scale = 1 mm.

the wall cutting off the root cap. In the leaf segment, which
appears always to grow more rapidly at first than the root s eg-

II.]

SPOROPHYTE.

2 7

ment, the apical cell has been formed and several cells have
already been separated from it. The stem segment is always
belated in growth, and shows little development in the figure.
The foot segment, on the other hand, shows greater growth in
extent than any of the others. It can also be seen that there
is a definite variation in the richness and granular condition of
the protoplasm in the different segments. The foot segment
is poor in protoplasmic content, while the cells of the pro-
thallium with which it is connected are very rich in protoplasm,
and continue to be so throughout the dependence of the embryo
upon it. The root segment shows richer and more granular
protoplasm, while the stem and leaf segments possess very rich
granular protoplasm, that in the leaf segment exceeding that in
the stem segment.

This variation in the richness of the protoplasm bears a defi-
nite relation to the functions .of the four segments. The func-
tion of the foot is to convey nutriment from the prothallium
to the essential parts of the embryo. It has need, therefore, of
a comparatively small amount and relatively poor quality. Its
growth is soon limited, since its function is to be performed for
a short time only. Although the function of the root is ulti-
mately to collect and transfer nutrient solutions, it requires a
long period of growth in order that it may reach the soil, fix
the plant, and then extend for a considerable distance through
the soil in search of food. The young root segment therefore
shows a richer content of protoplasm than the foot. The stem
and leaf segments have higher functions to perform, the leaves
ultimately bearing reproductive bodies. While the first leaves
never attain this end, it is very important that they should be
developed early, since they act as assimilatory organs, and elabo-
rate starch from the carbon dioxide of the air. The stem is
concerned chiefly in the production of new leaves, and while in
its growing point we would look for a richer content of proto-
plasm than in the root, it is not of such immediate importance
as in the leaf.

THE BIOLOGY OF FERNS.

[PART I.

Turning now to Fig. 49, we see this law of the distribution
of the quality of the protoplasm more highly exemplified in an
older embryo. It is also to be noted that the older cells of the

stem, leaf, and root now are becoming poor in protoplasm.
They are losing the power of growth and cell multiplication,
are becoming carriers of nutriment, and are taking on the form
of cells of the vascular bundles. At a are cells taking on the

II.]

SPOROPHYTE.

character of the cortex. The growing ends of the stem, leaf,
and root, however, contain rich, granular protoplasm.

If we now examine still older embryos, we will observe steps
in the continuation of this process of change in cell content
and cell form accompanying progressive change in function.
Fig. 50 represents an older embryo of Adiantum cuneatum.
Those cells which in Fig. 49 were seen to be losing the richness
of their protoplasm and to be elongating in form, have become
here changed to scalariform vessels, characteristic of the vas-
cular bundles, while the growing points are still more remote
from each other.

In noting these various steps in the development of the
embryo it will be seen that as the embryo enlarges, that part of
the prothallium which surrounds it grows and bulges downward,
producing a prominent convexity at this point on the under side,
termed the calyptra. Eventually the embryo breaks through
the calyptra, the root fastens it to the soil, and taking on the
function of collecting nutriment for the plant, the foot ceases
its function, and the prothallium disappears.

Fig. 50. Embryo of Adiantum cuneatum free from the calyptra, but still attached to the
prothallium, a , leaf (or cotyledon) ; b , stem ; c, root ; d, prothallium. Magnified 5
times more than the scale ; scale = 1 mm.

The young fern plant, the sporophyte, having now gained an
independent existence by taking firm hold on the substratum,

THE BIOLOGY OF FERNS.

[part I,

rapidly develops into the fern plant with which we are familiar.
The rudiments of the stem, root, and leaf, so nearly alike in the
early segmentation, have already diverged quite widely from one
another in form, structure, and development, and they are
destined to become in the mature plant more widely different.

The young root pierces the soil
or substratum on which the plant is
growing, or crowds its way into the
crevices of rocks, or in the interstices
of the bark of trees. Its general
course is first of all downwards after
having once become well differenti-
ated and developed in the embryo.

On the other hand, the course of
the cotyledon and leaves is upward.
The tip of the cotyledon soon
becomes curved inward toward the
prothallium. The general direction
of growth is at first forward, i.e.
towards the anterior end of the pro-
thallium. By the larger size and
the more rapid segmentation of the
cells on the under side of the young
cotyledon, it curves over toward the
prothallium. As it approaches the
sinus at the anterior end of the pro-
thallium, it ascends and passes up
between the open lobes ; or if the
lobes overlap, as sometimes happens,
it passes out beyond them. This
curling inward of the cotyledon, and
the more pronounced curling of the
older leaves, is characteristic of ferns, and they are said to be
circinate in vernation.

It was once asserted that gravitation controlled the position

Fig. 51. Young plant of Pteris ser-
rulata, with prothallium still at-
tached.

II.]

SPOROPHYTE.

of the root and other parts of the plant in the young embryo,
so that if the prothallium were inclined at various angles, the
root and other parts would take the same position relative to
the direction of the force of gravitation that they did when the
prothallium was perpendicular to the direction of this force.
But Leitgeb showed, by growing prothallia in various positions,
and by lighting some from below so that the archegonia were
produced upon the upper surface, that the parts of the young
embryo always had the same position relative to the archegonia
that they had when the prothallia were grown horizontally, and
lighted from above.

Hein richer, by growing prothallia of Ceratopteris thalictroides
in such a way as to throw light upon them both from below and
above, succeeded in producing archegonia on both surfaces.
On two such prothallia, two eggs, one each in an archegonium
above and below, became fertilized, and developed into embryos.
The parts of the embryo in the archegonia upon the upper
surface were in the same position relative to the archegonia
that they were below, or in opposite position with reference to
the direction of the force of gravitation, or to the upper and
lower surfaces of the prothallium.

Several archegonia on a single prothallium may possess eggs
which become fertilized, but rarely more than one develops into
a perfect plant capable of an independent existence. The cases
just cited from Heinricher show that two embryos are some-
times developed, but we have no assurance that both could have
gained an independent existence. Rauwenhoff records several
cases of two embryos being developed on single prothallia of
the Gleicheniaceae. It is not stated that each can become
independent plants. Campbell found two embryos on a single
prothallium of Osimmda , but he states that one was far in
advance of the other, and would probably have starved it out.

In my studies of the Polypodiaceae, I observed a prothallium
of Adiantmn cuneatum which showed two well-developed coty-
ledons of apparently about the same age, and growing parallel

THE BIOLOGY OF FERNS.

[part I.

to each other. Examining the specimen carefully, it was found
that both cotyledons were attached to the under surface of the
prothallium side by side, and by the base of each was a very
young leaf, the tip of which was rolled up in circinate fashion.

Two well-developed roots also is-
sued side by side a little to the
rear of the cotyledons. They gave
every appearance of being two
well-developed plants fixed to the
soil, and capable of an independent
existence. A sketch was made of
the prothallium with its two plants,
and is shown in Fig. 52.

It occurred to me that possibly
this apparent development of two
perfect plants from a single pro-
thallium might be some abnormal
condition of a single embryo in
which the stem and root, or possibly
the stem and root segments, had
forked at a very young period in
its existence. To be certain what
the real condition of things was,
the bulk of the cotyledons and
roots was cut away, and the pro-
thallium and attached parts were
dehydrated, infiltrated with collo-
dion, and cut longitudinally into
sections. From the point of start-
ing into one embryo to the passing
out of the other, all the sections
were preserved and mounted serially. A study showed two
perfect plants.

It will now be in order to take up the farther study of the
plant parts separately.

Fig. 52. Adiantum cuneatum; two
independent plants from a single
prothallium.

SPOROPHYTE.

ill.

MORPHOLOGY AND ANATOMY.

STEM.

Morphology. — In the Polypodiaceae the stem is usually
creeping or ascending, and is termed the rhizome. In Poly-
pocLium vulgare it creeps upon the surface of the ground. In
Adiantum pedatum it lies usually in the surface soil, or is
covered by leaf mould. In Pteris aquilina the rhizome is

Fig. 53. Stem (rhizome) of Onoclea sensibilis.

several inches, sometimes six to twelve, below the surface, and
describes quite a sinuous course. It is somewhat flattened,
and two lateral ridges give it a bilateral symmetry. In some
species the rhizome creeps over rocks or trees, and in many

THE BIOLOGY OF FERNS.

[PART I.

others it rises obliquely in the soil. The largest stems are
found in the Cyatheaceae, where are found the erect, often
columnar, trunks of the tree ferns. Contrasted with these are
the delicate filmy plants of many of the Hymenophyllaceae.

The stem is usually perennial, and the branching is dichot-
omous. The growing end is usually protected by a profuse
development of scales, which converge over the apex. In some

species, especially those which
rise above the ground, these
scales frequently persist over
considerable lengths of the
stem, and in age are brown
in color. The apex is free in
Pteris aquilina , Polypodium
vulgar e, and others, while it
is concealed beneath the leaf-
bud in many.

The growth of the stem
proceeds from an apical cell,
which is either wedge-shaped,
and probably accompanies
creeping stems with a bi-
lateral structure, or it is three-
sided, and usually accompa-
nies erect or ascending stems
with crowded leaves arising
on all sides. The successive
oblique divisions of the apical
cell give a stratified appear-
ance to the resultant tissue,
which soon disappears by the apparent merging of the ele-
ments from repeated cell divisions, and pressure exerted by the
development of the leaves.

Anatomy. The fundamental tissue of many species does
not undergo any subsequent change, but remains in the form

Fig* 54* Stem (rhizome) of Aspidium acros-
tichoides, traced from a photograph.

III.]

SPOROPHYTE.

of thin-walled parenchyma. In Ptens aqinlina portions of
the fundamental tissue change to sclerenchyma. In a tran-
section of the stem of this species near the centre are seen
two groups of sclerenchymatous tissue in the form of bars,
which form longitudinal ribbon-like strips that run parallel
through the stem. The cell walls are dark brown and traversed
by numerous lacunae connecting the cells. In age, groups of
cells here and there through the parenchyma change to scleren-

Fig. 55. Transection of vascular bundle in stem of Pteris aquilina. c, bundle sheath ;
b, phloem sheath ; a, phloem portion of bundle ; d, xylem portion ot bundle. The
thick-walled cells are tracheides; intermingled with them are thin-walled cells, the
xylem parenchyma. Magnified 10 times more than the scale ; scale = 1 mm.

chyma and are seen as dark points in the transection. An
external layer several cells deep also changes to somewhat
thinner walled sclerenchyma, forming what is termed a shell.
A similar shell is also found in the tree ferns and others.
In Lygodium palmatum the entire parenchyma outside the
single central vascular bundle becomes transformed into thick-
walled sclerenchyma, which accounts for the stiffness of old
stems.

3 6 THE BIOLOGY OF FERNS. [part I.

Sheaths of sclerenchyma are also said to be formed about
the several vascular bundles in the stems of tree ferns and
in Poly podium vaccinifolium. In Adiantum pe datum nearly
the entire fundamental parenchyma becomes transformed into
brown sclerenchyma ; only a thin layer each side the single

Fig. 56. Transection of vascular bundle in the stem of Polypodium vulgare. a , bundle
sheath ; b , phloem sheath. Magnified 30 times more than the scale ; scale ==■ 1 mm.

nearly tubular bundle remains unchanged. The medullary
sclerenchyma possesses much thicker walls than that in the
foliar gaps of the bundle or outside.

The vascular bundles of the stem of most ferns are concen-
tric, the xylem or woody portion being surrounded by the
phloem, and the whole encased in a bundle sheath, the endo-
dermis. They are thus closed, growth taking place while the
tissues are being differentiated in the procambium about the
apical cell. Lying next the bundle sheath inside is a single
layer of parenchyma cells, sometimes termed the phloem sheath.
The bundle sheath and phloem sheath have a common origin
from a single layer of parenchyma cells. The cells of the
bundle sheath are narrower in their radial diameter than those

III.]

SPOROPHYTE.

of the phloem sheath, somewhat elongated in a peripheral
line, more early lose their protoplasmic content, and are quite

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THE BIOLOGY OF FERNS.

[PART I,

easily differentiated from the larger parenchyma cells on either
side. The radial walls of the bundle sheath are usually weaker
than those of the other cells, and in shrinkage, which occurs
in drying, frequently they are broken, and the bundle thus
partly separated from the surrounding parenchyma.

The xylem portion of the bundle is made up of several kinds
of tissue. Fundamental tissue in the form of rather small,
thin-walled cells is intermingled with the various tracheides,
which possess rather thick walls, variously sculptured. Scalari-
form, reticulate, and spiral tracheides occur frequently in the
same bundle, and in addition in Pteris aquilina are true scalari-

Figs. 58 and 59. From Pteris aquilina; 58, longitudinal section of scalariform vessel;
59, longitudinal section of scalariform tracheid. Magnified 30 times more than the
scale ; scale = 1 mm.

form vessels, shown by the perforation of their cross-walls.
The cells of the phloem vary greatly in size, and are inter-
mingled with sieve tubes and parenchyma.

The bundles vary in number, arrangement^ and position in
different species, fundamental tissue occupying the intervening
spaces, except, as stated above, where portions become changed
to sclerenchyma. In Pteris aquilina the bundles are in two
groups. -In cross-section of the stem one group, composed
of small oval or irregular bundles, is arranged in the form of
a ring enclosing the bars of sclerenchyma; the other group

SPOROPHYTE.

in j

is composed of two bundles usually, nearly as broad as the
bars of sclerenchyma, parallel with, and inside of, them. In
Polypodhim vulgare several bundles are arranged in a single
ring, the medullary parenchyma connecting by radial strips
between the bundles with the cortical parenchyma. The same
type occurs in Onoclea sensibilis , Asplenium filix-f oemina , and

Fig. 60. Transection of the stem of Lygodium palmatum. The radial walls of the
bundle sheath are ruptured, thus separating the single central bundle from the
sclerosed tissue outside. All of the cortical parenchyma has changed to scleren-
chyma. Magnified 6 times more than the scale ; scale = i mm.

•many others, these being cited as examples only, and having
been examined by the writer.

In Adiantum pe datum a single bundle in the form of a tube
with perforations, or gaps, associated with the leaf traces, runs
through the stem. At the intersection with the leaf stalk the
bundle in transection has the form of a horseshoe, while the
bundle of the leaf trace is C-shaped, the open part being next

THE BIOLOGY OF FERNS.

[part I.

that of the open part of the stem bundle. As the sections pass
either side of the centre of the foliar gap, the ends of the
horseshoe-shaped bundle approach each other until the margin

of the leaf trace is
reached, when the bun-
dle in transection forms
a complete ring with an
oval outline. At the
same time the sections
about two-fifths the way
around show a narrow-
ing of the width of the
bundle ring, which pro-
ceeds in the series of
sections until another
foliar gap is reached,
when the bundle ring
is again open.

In those ferns which
possess several bundles
in the stem, the bundles
fork and anastomose,
forming a cylindrical net-
work. With some of the
gaps formed by this net-
work the leaf traces are
associated. These gaps
usually have a spiral
arrangement, frequently
showing a definite re-
lation to the phyllotaxy.
In Lygodium palmatum and other species of the Schizaeaceae,
various species of the Hymenophyllaceae, and Gleichenia of the
Gleicheniaceae, there is but a single central bundle.

In the Osmundaceae the bundles of the stem are collateral ;

Fig. 61. Portion of vascular bundle of Lygodium
palmatum. a , bundle sheath ; b t phloem por-
tion ; c t xylem portion ; d, xylem parenchyma.
Magnified 30 times more than the scale; scale
— 1 mm.

III.]

SPOROPHYTE.

i.e. the xylem occupies one side, and the phloem the other.
The bundles are arranged in a circle, the xylem occupying
the axial side, and the phloem the peripheral side, where it
forms a complete ring outside the circle of xylem groups.
In Osmunda the entire cortical parenchyma becomes trans-

Fig 62 Diagrammatic section of the stem of Pteris aquilina. x, xylem portion of
bundle- ph phloem portion; sc., thick-walled sclerenchyma ; a, thin-walled
sclerenchyma ; par., parenchyma. — Fig. 63. Diagrammatic section of the stem
of Lygodium palmatum. x, xylem portion ; ph., phloem portion ; sc., sclerenchyma.

Pig. 64. Diagrammatic section of the stem of Polypodium vulgare. x , xylem

portion of bundle ; ph., phloem portion ; par., parenchyma.

formed into hard, dark sclerenchyma, through which the
vascular bundles of the leaves course upward and outward,
several being seen in one transection of the stem. The
medullary parenchyma remains unchanged.

ROOT.

Morphology. — The roots arise in succession in the growing
end of the stem. They originate in the procambium before
the differentiation of the vascular bundles. As the xylem of
the bundle is formed, the cells of the radial side of the stem
bundle pass obliquely into the bundle of the root, and no gap
occurs as in the case of the origin of the leaves.

THE BIOLOGY OF FERNS.

[PART I.

The growing point of the root is a tetrahedral apical cell,
with its faces sometimes slightly curved, especially the side
toward the root cap. Triangular tabular cells are cut off usually
successively on the four sides. The segments cut off in front
develop into the root cap. The lateral triangular tabular seg-
ments divide in such a way that the cells formed from the point
where they meet in the centre of the root differentiate into the

Fig* 65. Section of central portion of the root of Pteris aquilina, showing the single
radial bundle and the sclerenchyma immediately surrounding it. b.s ., bundle sheath ;
x, one of the two xylem groups; ph., one of the two phloem groups; sc., scleren-
chyma. Magnified 30 times more than the scale ; scale = 1 mm.

vascular bundles, while the peripheral ones produce the cortex.
The young roots grow through the cortex of the stem to the
outside. Transections or longisections of the growing end of
the stem frequently show the young root with its apical cell
and root cap still within the cortex. Roots also arise in some
species from the base of the leaf stalk, especially if these are
covered with soil. The young roots are covered with root hairs,

hi.] SPOROPHYTE.

which are simple non-septate cells. Similar hairs are also found
in some cases on the stems and bases of the leaf stalks.

In tree ferns numerous roots are developed from the aerial
part of the stem. In some cases where the trunk is slender
at the base it really appears stouter from the thick mat of roots
which extend downward over it.

The roots branch in a monopodial fashion. Lateral roots are
also produced. They are not connected with the bundle of the
root, but arise outside the pericambium from an innermost cell
of the cortex (one of the cells of the bundle sheath), which
forms a mother cell. Three obliquely anticlinal walls in this
mother cell form the tetrahedral apical cell, and a periclinal
wall then forms the primary cell of the root cap.

Figs. 66 and 67. Tetrahedral apical cell of root of Onoclea sensibilis, with surrounding
tissue, a.c., apical cell ; r.c., root cap. Both sections are taken from very young
roots still within the tissue of the stem. Magnified 30 times more than the scale ;
scale = 1 mm.

Anatomy. — A single central vascular bundle is present, and
is surrounded by cortical parenchyma, the innermost layers of
which are sometimes sclerosed. The formation of xylem usually
begins at two diametrically opposite points near the outside, the
first tracheides formed being narrow and fibrously thickened,
and lying side by side. The transformation then proceeds inward,
one or more rows of large scalariform tracheides being formed.
According to Russow, true vessels are only found in the root
of Athyrium ( Asplenium ) filix-foemina. This arrangement of
the xylem in the root bundle De Bary calls a “ diarch” bundle.
According to the same authority triarch and tetrarch bundles
are sometimes found in thick roots of some species. Accord-

THE BIOLOGY OF FERNS.

[part I.

in g to Mettenius and Russow, tetrarch and octarch bundles are
the rule in species of Trichomanes , diarch bundles being rare,
while diarch bundles are usual in Hyjnenophyllum.

In Adiantum pedatum , which is usually diametrically diarch,
I observed one root, the consolidated xylem plates of which
formed a crescent, the points of origin of the xylem being
nearer on one side, and at the point of consolidation on the
other side was an extra large tracheid.

The xylem groups are usually united in the middle by two
large tracheides crossing the consolidated plate at right angles.
In Osmunda and Todea of the Osmundaceae a transection of
the root shows the consolidated xylem plates to present an
elliptical outline.

The phloem groups alternate with the xylem, giving the
appearance of a radial bundle.

SPOROPHYTE.

IV.

MORPHOLOGY AND ANATOMY ( continued ).

LEAVES.

Morphology. — The origin of the first leaf in the embryo we
have already traced, where it is cut off as a segment from the
primary stem segment of the embryo. The other leaves arise
by the arching out of a superficial cell, at the side of the
growing end of the stem, which becomes the apical cell. In
the mature stem at this point of origin of the leaf occurs what
is known as the leaf trace, marked by the leaf bundle in the
cortex of the stem. In connection with the study of the first
leaf, it has already been noted that the leaf grows rapidly in
advance of the stem. This is a character of all leaves of ferns,
though in many cases the leaves develop very slowly, requiring
in the case of Ptems aquilina two years. The development is
basifugal ; i.e. the base is developed first.

The leaves are the most conspicuous part of the plant, and
are usually quite well differentiated into two parts, the lamina,
and the stipe, as it is called. The function of the stipe is in
the main that of support for the lamina, and to continue the
channel for the interchange of nutrient matters between dif-
ferent parts of the plant. It is quite stout and hard in Pteris
aquilina; hard, black, and rather slender in Adiantum. In
such ferns as Asplemum and Aspidium it is usually shorter,
compared with the extent of the lamina, and in many cases
bears numerous brown scales, termed chaff.

46 THE BIOLOGY OF FERNS. [part i.

The function of the lamina in general is twofold : a physio-
logical one, which includes the phenomena of transpiration,
the reduction of the elements of carbon dioxide, and the pro-
duction of starch ; and a reproductive one, the development of
spores. The simplest form occurs in such ferns as Scolopen-
drium vulgare and Camptosorus rhizophyllus , the lamina being
normally simple, while in some cases the end forks. In Poly-
podium vulgare it becomes pinnate; in Pteris aquilina , once

ternate and twice pin-
nate. In Adiantum pe-
datum it is forked into
two recurved divisions,
which bear several sec-
ondary pinnate divisions
on one side. In various
species of Asplenium
and Aspidium it is
once, twice, or thrice
pinnate. The large,
handsome lamina of the
ostrich fern, Onoclea
struthiopteris , is once pinnate, the pinnae being pinnately
divided. These examples will serve as characteristic illustra-
tions of some of the various forms of the lamina.

Anatomy. — The vascular bundles are usually concentric, and
vary in number and form in various genera. In Adiantum
pedatum there is a single bundle which is strongly crescent
shaped or semilunar in transection near the base of the stipe,
while near the junction of the lamina it is much broader in
proportion to its length in the section and comparatively little
curved. In Cystopteris btilbifera there are two bundles, while
in Pteris aquilina , in one specimen observed there were ten in
transection, which varied greatly in form and size. True ves-
sels occur in the stipe of Pteris aquilina as well as in the stem.

The vascular bundles which branch from those in the stipe

Fig. 68. Diagrammatic section of the stipe of Os-
munda regalis, showing position and form of the
single concentric vascular bundle.

IV.]

SPOROPHYTE.

or rachis, and course into the divisions of the lamina, form the
framework. They are termed veins, and either terminate in
free ends or in some cases anastomose. The soft parts, or
mesophyll, of the leaf is composed of loosely arranged paren-
chymatous cells richly filled with chlorophyll, and possessing
very large interspaces. Both surfaces of the lamina are cov-
ered with an epidermis, the cells of which are well supplied
with chlorophyll, usually in much greater abundance than
occurs in the higher plants, and is one of the distinguishing
features of ferns as com-
pared with the higher forms.

The epidermis' is variously
clothed with hairs. Sto-
mates of the usual form and
with the guard cells charac-
teristic of higher plants
occur in abundance on the
under side of the leaf. They
are situated usually in the
margin of an epidermal cell.

In Aneimia and Poly podium
lingua , Goebel says they are
in The middle of an epider-
mal cell.

The development of the Fig. 69. Portion of the epidermis of the leaf
.-.of Adiantum pedatum, showing irregular
StomateS can be very easily epidermal cells and the stomates in the side

traced by making horizontal of the cells - Magnified 30 times more than

J 0 the scale; scale = i mm.

sections in the plane of the

under side of very young leaves. The epidermal cells are still
quite small, and do not present such lobed, interlacing margins
as are seen in the fully developed epidermal cells. Their
margins are plane or only slightly irregular. The cells are
also very rich in protoplasm, with prominent nuclei, and various
stages of cell and nuclear division can be seen. A semicircular
wall in the margin of an epidermal cell cuts out an oval cell,

48 THE BIOLOGY OF FERNS. [part i.

which sometimes becomes directly the mother cell of the guard
cells. These are formed by longitudinal division of the oval

cell. Sometimes a second semi-
lunar wall cuts out a cell from
this one, which becomes the
mother cell of the guard cells.

Sterile and Fertile Leaves. —
The first leaves of young ferns
are always sterile. Of mature
plants, if more than one leaf is
developed each year, some of the
leaves are usually sterile while
others are fertile. Sterility and
fertility depend largely upon
external conditions, season, soil,
habitat, etc. In some cases,
there is no great difference
between the sterile and fertile
leaves, except that the latter
bear spores. This is quite com-
monly noted in such ferns as
Polypodium vulgare , various spe-
cies of Asplenium and Aspidium .

Dimorphism. — Still in Asplenium angustifolium , fertile leaves
possess somewhat narrower pinnae than the sterile ones, and the
latter are coarser in general aspect. In Aspidium acrostichoides ,
the terminal portion of some of the leaves is fertile, while the
lower portion is sterile. Here the fertile pinnae are much
narrower and shorter, presenting a dwarfed appearance. Yet

there are leaves which are entirely sterile. In a single tuft of

leaves from the same plant, it is common to note all gradations
of fertility of the various leaves, some bearing only a few fertile
pinnae at the tip. The fertile leaves of Pellcea atropurpurea are
simply pinnate at the tip, and usually twice pinnate at the base,
and the pinnules are narrowly elongate, while those of the
sterile leaf are simple and oval.

Fig. 70. Portion of very young epider-
mis of the leaf of Pteris aquilina. e ,
mother cell of a stomate cut off from
an epidermal cell by a semicircular
wall ; d, a similar mother cell of a
stomate cut off from a cell, whjch was
cut off in like manner from the epi-
dermal cell and prior to it. Magnified
30 times more than the scale ; scale
= 1 mm.

IV.]

SPOROPHYTE.

In Onoclea , the leaves are usually completely differentiated
into a sterile leaf and a fertile leaf, presenting a definite case of
dimorphism. In the fertile leaf, the pinnae and pinnules are
much dwarfed, and form together a somewhat crowded one-
sided spike-like fructification, while the sterile leaves are broadly
expanded. Various modifications of this differentiation in Ono-
clea sensibilis occur. For example, leaves are found, many of
the pinnae of which are sterile, while from this condition, vari-
ous grades of dwarfed fertile pinnae exist. Underwood calls
attention to the fact that probably this latter form of the fertile
leaf follows an injury to the plant which destroys the sterile
leaf. This would throw the responsibility for the vegetive
function solely upon the fertile leaf. In accordance with the
law of correlation, then, the increase of the vegetive structure
and function in the fertile leaf would lessen the reproductive
function, and the partially expanded pinnae would bear a few
sori.

Schizcea pusilla of the Schizaeaceae possesses very slender
linear tortuous sterile leaves, the fertile leaves possessing pinnae
arranged in a crowded one-sided arched spike-like fructification.

In Lygodinm , the leaf resembles a dimbing leafy stem. The
fertile portions of the leaf are much contracted.

Osmunda presents an interesting variation in the different
species. The terminal portion of the leaf is fertile in O. regalis ,
the middle portion in O. claytoniana , while in O. cinnamomea
the leaves are differentiated into a fertile and sterile one.
Various modifications of this differentiation occur in the differ-
ent species. In the fertile portions of the leaf of O. regalis ,
various dwarfed stages of the sterile pinnules occur, in some
cases nearly all of the pinnae being sterile and expanded, a few
of them being dwarfed and fertile on the margin, or on both
surfaces.

In certain epiphytic ferns, according to Goebel, one kind of
leaf is differentiated in species of Polypodium to catch and hold
humus, and thus serves a function in the supply of nutriment.

THE BIOLOGY OF FERNS.

[PART I.

Similar leaves were also found in Bolbophyllum. In Platy cerium
alcicorne , the staghorn fern of our conservatories, the fertile
leaves are narrow and forked. There are also specialized
sterile leaves, very broad and oval in outline, which hug very
closely around the roots, and serve to catch humus, and con-
serve the moisture. They are at first green in colour, but in age
become brown. They are sometimes called mantle leaves. In
New South Wales there are specimens growing around the
trunks of standing trees which form massive growths two to
three feet in diameter, completely encircling the trunk of the
tree.

Fructification. — The fructification of ferns consists of spo-
rangia, containing the spores, usually grouped at definite places
on the under side of the leaf, or on the leaf margin. These
groups, or fruit dots, technically sori, are oval, circular, linear,
or very much elongated and sinuous. They are either naked,
or covered by a plate of thin cells of epidermal origin called the
indusium. The sorus is usually upon one side of a vein, or at
its apex. The indusium varies greatly in form in different
ferns. This, together with the form of the sorus, and its
position on the leaf, including the variation of the same, form
excellent differential characters in the classification of the gen-
era and species. To illustrate this, several examples may be
taken from the Polypodiacem.

In Polypodium the sori are naked and situated on or at the
termination of the veins, in a row near each margin of the
pinnae. Perhaps to partly replace the indusium in Polyp odium
vulgare there are numerous multiseptate hairs among the spo-
rangia, the enlarged free end projecting beyond the sporangia.
In Adiantum and Pteris the sori are at the ends of the veins at
the margin of the leaf, where they are covered by the incurved
margin, which forms what is called the false indusium. In
Pteris there is in addition a true indusium on the opposite side
of the sorus in the form of a flap. In Adiantum the main rib,
when present, of the pinnules is marginal, while in Pteris it is

IV.]

SPOROPHYTE.

central. In a number of genera the sori are oblong or linear,
and extend along one side of fertile veins with the indusium
attached by one edge. Thus in Woodwardia they are in a
chain-like row each side of the midvein of the pinnae and

Fig. 71. Section through sorus of Polypodium vulgare, showing different stages of the
development of the sporangia, and a single multicellular capitate hair. Magnified 6
times more than the scale ; scale = 1 mm.

pinnules. In Asplenium they are separate and extend obliquely
on the leaf. In Campto sorus they are scattered and extend in
various directions, while those nearest the midrib tend to con-
verge in pairs at their outer extremities, forming V-shaped
figures. In Scolopendrium they are closely approximated in
pairs which stand nearly perpendicular to the midrib, appearing
to have a double indusium opening along the middle.

Fig. 72. Section through sorus and shield-shaped indusium of Aspidium acrostichoides.

Aspidium has a shield-shaped indusium, thus opening all
around. Cystopteris has an ovate one attached by its broad base

THE BIOLOGY OF FERNS.

[PART X.

somewhat under the roundish sorus. In Ouoclctx there is a
hood-shaped indusium fixed by one side and arching over the
sorus, and then the closely inrolled pinnule covers both indusium
and sorus. In Woodsia the indusium is inferior and is attached
all around the placenta. It is either open at first, or it covers
the sorus, and later opens by irregular, radiating slits. Dicksonia
possesses an elevated placenta surrounded by a hood-shaped
indusium which opens toward the margin on the leaf.

Year by year the old leaves die down, while new ones arise' at
the growing end of the stem. Frequently in a single season
leaves of two or more years may be seen in a single cluster, the
old ones dead and in various stages of disorganization.

SPOROPHYTE.

SPORANGIA.

Development of the Sporangia. — The sporangia are capsules
which contain the reproductive bodies known as spores. They
vary in form and structure in the different families. Their de-
velopment as known in the Polypodiacese will be described and
followed by a comparison of their structure and function in the
different families. In the Polypodiaceae they are said to be
trichomic in their origin ; i.e. they originate from a single super-
ficial cell.

The cell surface from which they arise is termed the placenta.
The cells of the placenta are richer in protoplasm than those of
the other epidermal surfaces at this time. The mesophyll
beneath is also rich in protoplasm. The placenta is in close
communication with a vascular bundle of the leaf, and is thus
in direct communication with the channels for the conveyance
of nutriment.

A transection through a placenta at the time of the early
development of the sporangia will show various degrees of pro-
longation of individual cells of the surface. The cell, first of
all elongates perpendicularly, so that its outer surface is raised
above that of its fellows. This elongation continues, and as
the growing end of the cell passes the line of the surface it
broadens out, because it is relieved from the pressure of adja-
cent cells and is strongly turgescent. The more granular
protoplasm collects in the outer end of this elongated cell and
surrounds the prominent nucleus. From the granular proto-

THE BIOLOGY OF FERNS.

[part I.

plasm immediately surrounding the nucleus granular strands
radiate in all directions to the periphery of the cell lumen,

Figs. 73 to 80. Development of the sporangia of Asplenium bulbiferum. Fig. 73, section
through the placental region, showing vascular bundle, epidermal cells rich in chloro-
phyll, one of them elongating to form a sporangium. Figs. 74, 75, 76, and 77, progres-
sive stages in the farther development. In Fig. 77 the central tetrahedral cell sur-
rounded by the mother cells of the sporangial wall. Figs. 78 and 79, progressive stages
in the development of the tapetal cells, which are cut off as tabular cells from the
four sides of the central cell. Fig. 80, farther division of the tapetal cells. In Fig. 79
the tetrahedral cell is the primordial mother cell of the spores. Magnified 30 times
more than the scale; scale = 1 mm. Figs. 75 and 76 from preparation by O. D.
Humphry; Fig. 77, by H. D. Watson.

v.]

SPOROPHYTE.

where the protoplasm is less granular. Between these radia-
ting granular strands are clear spaces in the protoplasm, com-
paratively small in the outer end of the cell, but in the base
of the cell very large. Fig. 73, from a section through the
placental region of Asplenium bulbiferum , shows in detail
some of the various phenomena described. By a transverse
wall near the surface of the placenta this cell now divides into
two cells. The basal cell develops into the stalk, while the
terminal one is the mother cell of the sporangium, is richly
filled with protoplasm, and contains a large nucleus. The next
line of division in the terminal cell is an oblique one. This is
followed by another oblique wall in the apical cell which joins
the former one at an angle of about sixty degrees. A third
oblique wall now joins these two, forming an end cell shaped
like an inverted, three-sided pyramid. This is followed by a
transverse wall in the tetrahedral cell, which abuts all three of
the others and forms a central tetrahedral cell, very rich in
protoplasm and possessing a large nucleus in comparison with
those of the superficial cells.

By successive oblique walls a tabular cell is cut off from each
side of this central cell, leaving a tetrahedral cell in the centre
which is the primordial mother cell of the spores, or arche-
sporium. The tabular cells surrounding it divide farther, form-
ing one or two rows of cells between the archesporium and the
layer of cells forming the wall of the sporangium. These are
termed the tapetal cells, collectively the tapetum. Meanwhile
the cells of the sporangial wall undergo division by perpendicu-
lar walls, thus increasing the superficial extent to accommodate
the increasing size of the contents, but they remain in a single
layer. Over one edge a straight row of cells is differentiated
to form the annulus, while the pedicel develops usually into
three rows of cells.

The tetrahedral archesporium now divides by successive bi-
partitions into sixteen spore mother cells, with large and
prominent nuclei. Meanwhile the tapetal cells are being

THE BIOLOGY OF FERNS.

[PART I.

dissolved into a mucilaginous substance in which the spore
mother cells float free within the sporangium. The nuclei of
the tapetal cells seem to resist the change to a mucilaginous
substance much longer than does the cytoplasm, since they
may frequently be seen entangled in a disorganized substance
collapsed about the spore mother cells.

The steps by which these spore mother cells develop into the
spores vary even in the Polypodiaceae. It will be more conven-
ient to first describe the more common method, not only because
it is of more frequent occurrence, but also because it is the
method which the writer has observed.

The finely granular content of the nucleus becomes coarser,
the granules apparently becoming denser and fewer in number.
These increase in size, showing distinct intermediate places of
a more homogeneous nature. The granules also coalesce into
groups, at first of very irregular, elongated shapes and of various
sizes.

The coalescence of these groups continues ; the groups
become more and more elongated, and tend also to become
arranged nearly parallel, until finally the nucleus has become
elongated, elliptical in outline, and the granular part arranged
into nearly parallel fibrillae which converge at the poles of the
nuclear spindle. Now, the granular fibrillae begin to disinte-
grate in a transverse plane across the centre of the spindle.
This disintegration proceeds each way, the disappearing fibrillae
becoming irregular in form, and the entire figure becoming
somewhat dumb-bell-shaped, until finally the nucleus is com-
pletely divided, and the two smaller nuclei stand off at opposite
sides in the cytoplasm of the mother cell, the position being
near that of the poles of the former nuclear spindle. No cell
wall has appeared separating the cytoplasm.

Each of these nuclei now undergo division in like manner, so
that the cytoplasm of each mother cell contains four nuclei.
The nuclei now increase in size, granular protoplasm accumu-
lates about them, walls are formed about each quadrant, and

V.]

SPOROPHYTE.

eventually the spores are mature. Figs. 84 to 90 show various
details of this process. A few cases which I observed seemed

Figs. 81 to 96. Farther development of the tapetum, its dissolution, and the develop-
ment of the spores. Figs. 81 and 82 from Pteris albo-lineata, 91 to 94 from Polypodium
vulgare, the remainder from Asplenium bulbiferum. See text for details. Figs. 83 to
90, and 95 and 96, from preparations by E. G. Merritt. Figs. 85 to 90 magnified 30
times more than the scale ; scale = .5 mm. The remaining figures magnified 30 times
more than the scale ; scale = 1 mm.

to show that, in Polypodium vulgare , the four nuclei came quite
close together in the centre of the cytoplasm. As they increase

THE BIOLOGY OF FERNS.

[PART I.

in size, and the granular protoplasm accumulates about them,
the close pressure of the four causes them to form flat surfaces
at their planes of junction. The two inner faces of each form-
ing spore meet at the inner angle perpendicularly, forming a
rectangle, while the outer face of each forming spore is convex.
Two spores in every group were always so arranged that their
longitudinal axes were parallel. Sometimes all four were thus
arranged. In the majority of cases, each two pairs lay obliquely
or perpendicularly across each other. Figs. 91 to 94 show
some of the details of these forming spores. The spores are
thus arranged radially, and are said to be radial or bilateral.

According to the other plan of development of the spores
from the mother cells, each mother cell by successive biparti-
tions becomes divided into four cells. The protoplasm in each
of these now forms a new wall which is the wall of the spore.
The original walls forming the divisions of the mother cells dis-
solve, and set the spores free. These spores are of a rounded
or tetrahedral form. This mode of spore formation is said to
occur invariably in the Cyatheaceae, Hymenophyllaceae, and the
Osmundaceae, while the former occurs for the most part in
the other families. In the Schizaeaceae and Osmundaceae, the
sporangia arise from superficial cells on the margin of the leaf
before the differentiation of the epidermis.

Structure of the Sporangia. Polypodiaceae. — In the Poly-
podiaceae, the mature sporangium is a somewhat flattened obo-
void capsule supported by a long pedicel. It consists of a single
layer of cells. The lateral walls are very thin, and present a
convexity of surface approaching that of the faces of a biconvex
lens. Their margins are separated for about two-thirds the
distance by a single row of thicker, nearly cuboid, cells, which
form an incomplete ring termed the annulus, prominent upon
the back and vertex of the sporangium, its proximal end
attached to the pedicel. The front of the sporangium consists
of thin cells extending from the distal end of the annulus to the
front attachment of the pedicel, and continuous with the lateral

V.]

SPOROPHYTE.

faces. The more central of these frontal cells extend quite far
back, forming a considerable portion of the lateral walls. Two
of these immediately in the centre of the front are so modified
in form as to guide the cleavage of the sporangium at the
moment of dehiscence. These extend farther back over the
lateral aspect of the sporangium than the other frontal cells ;
they meet in a straight line, thus offering a direct path for the
cleavage ; while the line of their union with the cells directly

Figs. 97 to 99 . Three different views of the sporangium of Aspidium acrostichoides.
a, lip cells ; c f connectives ; d to e, annulus. Magnified 10 times more than the scale ,
scale = 1 mm.

above and below is a sinuous one, the upper lip cell arching-
upward at its middle, and the lower one arching downward.
The opening between these two lip cells is termed the stomium,
and a front view of the sporangium presents a semblance to
that of the lips and mouth of some animal.

The thirteen or more cells, arranged in a linear series, and
comprising the annulus, possess a peculiar structure. Their
inner and transverse walls are much thickened, while the lateral

60 THE BIOLOGY OF FERNS. [part i.

and dorsal walls are very thin and flexible. The inner walls
form a continuous band with undulations formed by a slight

margins of this band are
crenate, the crenations cor-
responding in number to
the number of the cells of
the annulus. Figs. 9 7 to
99 show the details.

Cyatheaceae. — The cla-
vate or obovate sporangia
are short or long stalked.
They are collected in sori
frequently upon a more or
less prominent columnar
placenta at the end of
veins. Some are naked,
but more frequently they
are surrounded by an open,
circular, cup-shaped indu-
sium, or enclosed in an
ovate indusium which
cleaves by a vertical slit
and exposes the sporangia.

Goebel says the sporangia possess a complete annulus. It
is oblique, running vertically around the asymmetric flattened
sporangium.

In Cibotium chamissoi H. & B., which I have examined from
the Horace Mann Herbarium of Cornell University (from
Hawaii, distributed in 1867 from the Kew Herbarium), the
annulus is nearly complete, but not entirely so. It varies in
width and strength, the broader and stouter portions extending
over the base, dorsal, and vertical surfaces. On the front it is
composed of much smaller cells with thinner lignified walls,
and is interrupted in two places, one at the anterior basal angle,
and another above the middle of the front. These cells pos-

arching inward of each cell. The

Figs. 100 and 101. Right and left view of sporangium
of Cyathea brunonis. b, annulus; a , frontal
series of cells (lip cells) ; c f connectives. Mag-
nified 10 times more than the scale ; scale =
1 mm.

V.]

SPOROPHYTE.

6 1

sess thin walls, are in all respects like those of
of the sporangium, in age sometimes possess
and are frequently collapsed. They form a
connective between the ends of the true
annulus and the frontal series of cells. The
line of cleavage proceeds between two cells
of the frontal series. Two lateral views of
the sporangium of Cibotimn chamissoi are
shown in Figs. 103 and 104.

In Cyathea brunonis there is a nearly com-
plete annulus which runs also vertically at a
small, oblique angle around the flattened, cla-
vate, asymmetrical, short-stalked sporangium.
The annulus is interrupted in two places, at
the anterior basal angle, and just above the
middle of the front, these portions forming
the connectives. Sometimes the cells of the
connective possess stouter walls on one side,
but they are very much thinner than those of
and also thinner than those of the short

the lateral walls
brown contents,

Fig. 102. Sporangium
of Hemitelia spe-
ciosa. a , frontal
series of cells ; c,
connectives ; b, an-
nulus. Magnified 6
times more than the
scale; scale = i
mm.

the true annulus,
frontal segment

Figs. 103 and 104. Right and left view of sporangium of Cibotium chamissoi. a , frontal
series of cells ; c, connectives. Magnified 10 times more than the scale ; scale = 1 mm.

62 THE BIOLOGY OF FERNS. [part i.

between the individuals of which the cleavage takes place. In
some cases observed, two different walls in this frontal segment
showed the line of cleavage marked out, but it probably would
have taken place only in one. The number of cells in this
segment varies also as in Cibotium chamissoi. The right and

Fig. 105. Sporangium of Hymenophyllum demissum. — Figs. 106 to 108. Sporangia
of Hymenophyllum ciliatum. a , cleavage cells (lip cells) ; c, connectives. Magnified
6 times more than the scale ; scale = 1 mm.

left faces of the sporangium are shown in Figs, ioo and ioi ;
the annulus is seen to pass close by the side of the base at
the point of attachment of the pedicel, which is at one- side.

Hymenophyllaceae. — The sporangia are collected into sori
at the ends of fertile leaves or lobes, protected by an indusium
in the form of a flap. A more or less elongated columnar or
pointed placenta projects as a continuation of the vein of the
pinnule bearing the sporangia in short rows. The indusium
with the terminal portion of the pinna present the appearance
of two slightly broadened laminae, entirely or only partly enclos-
ing the sorus. The sporangia are sessile, or short-stalked, de-
pressed, asymmetrical, and possess a horizontal, nearly complete

V.]

SPOROPHYTE.

annulus. The short pedicel is at one side of the depressed
sporangium, the ends of the annulus approaching just above
the pedicel. At this point on the upper
angle of the sporangium are the elongated,
narrow cells with lignified walls which mark
the line of cleavage. A few thin, irregular
cells with thin walls like those of the other
parts of the sporangium form the con-
nectives, so that the annulus is almost
complete.

Gleicheniaceae. — The sporangia are ses-
sile, naked, three or four in a sorus on the Fls * I09 ‘ ^°™ s of ^ y "

’ ’ menophyllum de-

under side of the leaves. They are some- missum.
what depressed, obovate, and asymmetric. The broad annulus,
usually said to be complete, extends around the sporangium
obliquely or transversely. In Gleichenia emarginata the annulus
extends obliquely around the sporangium, which usually arises

Figs, no to 1 12. Three different views of sporangia of Gleichenia emarginata. a , cleavage
cells; c, connectives. Magnified 6 times more than the scale; scale = 1 mm.

at an oblique angle from the leaf. It presents a broad series of
cells with stout, perpendicular walls. It passes underneath the
sporangium near the point of attachment with the leaf, and
extends up the sides to near the vertex, where it is interrupted
on each side by a group of cells forming the connectives. At

6 4

THE BIOLOGY OF FERNS.

[PART I.

maturity they sometimes collapse, tend to harden, and are like
those of the other parts of the sporangium. They are shorter
than those of the annulus, overlap at their ends, lie in several
rows, and extend outward to form an attachment to the edges of

the series of elongated
cells where cleavage takes
place. The cleavage cells
extend across the vertex
and down the front of
the sporangium. All the
cells of the true annulus
arch outward, since the
course of the sporangium
over which they extend is
strongly convex.

Schizaeaceae. — The spo-
rangia are oval and sessile.

Fig. 113. Section of the annulus of Gleichenia .

emarginata. a , cleavage cells; c, connectives. I hey are naked in

Magnified 10 times more than the scale; scale, and Aneimid and en-

= i mm.

closed in a pocket-shaped
indusium in Lygodium. They are arranged in two rows on the
under side of narrow pinnae. The pinnae in Schizcea have the
appearance of a crowded crescent-shaped panicle, while in Anei-
mia the panicle is loose and spreading, and in Lygodium the
fertile pinnae are contracted and forked and form a loose
panicle. The sporangia are asymmetric, bulging out on one side.
The annulus is horizontal, and extends around the conical apex.
On the bellied side of the sporangium it consists of narrow and
very long cells which extend down to the base in several rows,
marking the line of cleavage, which is thus seen to be vertical.
The true annulus consists of narrow V-shaped cells, their apices
joining the very small plate of thin cells which form the vertex
of the sporangium. From this point the V-shaped cells of the
true annulus radiate down over the sides of the cone. The wall
closing the large part of the V-shaped cells is also thickened,

V.]

SPOROPHYTE.

and sometimes the wall of overlapping cells below is thickened
for a short distance,
cells of the annulus
stand in one or two
rows, thus extending
farther down the sides
of the sporangium,
and uniting with the
narrow connectives for
some distance. A sim-
ilar structure of the
annulus was observed
in Lygodium palmatum
and Aneimia demis-
sum. The annulus is
thus situated at the
opposite end of the
sporangium from the
point of attachment of the sporangium to the leaf, and is per-
pendicular to the vertical line of attachment. The middle

part of the annulus is also on
the same side of the sporangium
as its point of attachment, the
front of the sporangium belly-
ing out on the other side. A
transection of the annulus of
Schizcea pusilla is shown in
Fig. 1 1 5. Since the annulus
represents, when viewed from
the side, a section of a cone,
the inner walls of its cells in
transection would appear very
broad, since it would be impos-
sible to make, with a straight
cut across the annulus, a section

Figs. 1 16 and 117. Lateral and vertical
views of the sporangium of Aneimia
phyllitidis. a , cleavage cells ; c, con-
nectives. Magnified 10 times more

tVian +Vw=» cr>alp • cr>a1p» r— T mm

Toward the front on either side a few

Fig. 114. Sporangium of Schizaea pusilla. Magnified 6
times more than the scale; scale = 1 mm. — Fig.
115. Section of annulus of Schizaea pusilla. The
annulus being in the form of a segment of a cone,
the transection runs obliquely through the inner wall.
Magnified 30 times more than the scale ; scale in
both figures = 1 mm.

66 THE BIOLOGY OF FERNS. [part i.

perpendicular to its inner wall which would at the same time
be transverse to the annulus. The figure, therefore, shows
an oblique section through the wall. Fig. 117 is from a section
of the annulus of Aneimia phyllitidis. The section is perpen-
dicular to the inner wall, but not to the entire extent of the
annulus.

Osmundaceae. — The sporangia are rounded, obovate, short-
stalked, or sessile. They are asymmetric, possessing a very sim-
ple annulus on the dorsal surface of the broad vertex. The

narrow, elongated cells with lignified
walls, which mark the line of cleavage
of the sporangium, extend perpendicu-
lar to the annulus, several in parallel
rows, down on the front of the sporan-
gium, which bellies out from the short
pedicel or point of attachment. The
cells of the annulus form about two
rows transversely across the dorsal
side of the vertex, their longer diam-
eters radiating from the vertical side
transversely to the annulus, and thus
vertically on the sporangium. The
annulus is connected with the cleavage
cells at the vertex by rather small cells
with lignified walls, farther down by cells similar to those of
the lateral walls of the sporangium. The cells bordering the
annulus below and overlapping its cells have their walls lignified
for a short distance at the point of union with the annulus.

The internal walls of the annulus are very thick and form
a stout plate upon which the bases of the fulcra of the annulus
are fixed. The fulcra, the longer or transverse walls of the
annulus, are shown in transection of the sporangium (longisec-
tion of the annulus) to be quite broad at the base, tapering out-
ward to a rather thin edge at their union with the superficial
wall, appearing in the section narrowly triangular. The entire

Fig. 118. Dorsal view of the
sporangium of Todea rivu-
laris, showing annulus and
cleavage cells. Magnified 6
times more than the scale ;
scale = i mm.

V.]

SPOROPHYTE.

longisection of the annulus presents a crescent figure, the con-
vexity of which is more strongly curved than the concavity,
while the intervening perpendicular fulcra become shorter from
the middle toward each end.

The transection of the annulus
(longisection of the sporangium)
presents a somewhat different
figure. It is shorter and has
the outline of a small segment
of a circle, the inner wall being
straight. The section being
parallel with the long diameter
of the cells of the annulus might
be several cells deep, when it
would present quite a number
of fulcra, the oblique perpendicu-
lar walls of the annulus. They
do not all stand perpendicular
to the inner plate, but lean at
various angles, reminding one
of an arch bridge span. The
external wall of the annulus ap-
pears to be slightly lignified, but
very much thinner than the
other walls. The annulus here
is also transverse to the line of
the short pedicel, its middle part
being on the same side of the sporangium as in the Gleicheni-
aceae and Schizaeaceae. The short annulus is, however, from
the shape of the sporangium, situated more nearly across the
middle.

Figs. X19 and 120. Transverse and lon-
gitudinal sections through the annu-
lus of the sporangium of Osmunda
regalis. Magnified 6 times more than
the scale ; scale = 1 mm.

SPOROPHYTE.

VI.

DEHISCENCE OF SPORANGIA AND DISPERSION
OF SPORES.

Polypodiaceae. — In the Polypodiaceae dehiscence of the spo-
rangium is brought about by the everting of the annulus, which
is permitted by the unequal flexibility of its unequally thick-
ened cell walls. While the opening of the stomium between
the lip cells is aided by their peculiar form, it seems possible
that at maturity the line of union is less firm than between the
other cells. The fissure once started proceeds across the lateral
walls of the sporangium usually in a straight line, thus splitting
in half the cells of the middle row, their frailty favouring this.
The drying of the annulus brings about the unequal tension
on its cell walls. During this process it slowly straightens,
carrying between the distal portion of the lateral walls of the
sporangium which remain attached to the free extremity, the
greater number of the spores. When straight it continues to
evert, and thus usually proceeds until the two ends of the
annulus nearly or quite meet, when with a sudden snap it
throws the spores violently away and returns nearly to its
normal position, with the sporangium nearly closed again.
Where the annulus completely everts before a return thrust is
made, the drying has proceeded evenly throughout its length.
It frequently happens that the annulus dries unevenly ; a short
segment having dried will snap, while the remaining portion
continues to straighten or evert. Several sections of the

V,.] SPOROPHYTE. 69

annulus may thus act, as it were, independently, there being
several distinct snaps or “jerks” in succession.

After this mechanical function of the annulus has been once
performed, and the annulus is dry, it will not take place again
until after the absorption of moisture it dries again, when the

performance is repeated. This is quite a wonderful and effec-
tive provision for the mechanical dispersion of the spores.
With successive periods of wet and dry weather, or humid and
dry air, the annulus repeats this eversion, followed by the vio-

7 °

THE BIOLOGY OF FERNS.

[part I.

lent snapping, so that the spores which are not at first cast away
will be at a later period. This process goes on in nature until
the annulus is literally “ worn out ” by everting, so that the
flexible cell walls become stiffened by age and the accumula-
tion of foreign substances. The annulus will even then respond
to changes in moisture content, but it does not snap suddenly.

The dehiscence of the sporangia and dispersion of the spores
can be accelerated by artificial drying, and beautiful demon-
strations of the mechanism be made. After observing that

Figs. 126 and 127. Aspidium acrostichoides. Fig. 126, complete eversion of the
annulus before the springing occurs. Magnified 10 times more than the scale ;
scale = 1 mm.

material dried for several weeks could be moistened and used
for demonstrations of the mechanical function of the annulus,
the writer examined quite a number of species of ferns in the
herbarium of Cornell University, and found that the following
species responded promptly to the test of moisture followed by
drying with artificial heat. The dry sporangia were scraped
from the sori with a scalpel to a glass slip, moistened with a
drop of water, and dried over an alcohol flame. Just as the
moisture disappeared from the glass slip, the annuli could be

VI.]

SPOROPHYTE.

7 *

seen to evert slowly, and then snap into position again with
such violence as in many cases to throw them from the field
of view. The following species, collected in the vicinity of
Ithaca, N.Y., fourteen to twenty years ago, showed great
activity of the annulus : Asplenium filix-foemina , angustifolhtm ,
and thelypteroides , eighteen years old ; Asplenium trichomanes
and ebeneum , twenty years old ; Aspidium marginale and acros-
tic hoides, eighteen years ; Aspidium thelypteris and spinulosum ,
fourteen years ; Pellcca atropurpurea , eighteen years ; Pteris
aquilina , fifteen years. The following showed little activity :

Figs. 128 to 131. Aspidium acrostichoides ; different stages in the opening and
springing of a free sporangium. Magnified 10 times more than the scale; scale
= 1 mm.

Aspidium goldianum , nineteen years old ; Aspidium novebo-
racense , eighteen years. In the following, after moistening,
many of the annuli would straighten and partially evert, but
on drying would slowly return : Aspidiitm cristatum , collected
Sept. 9, 1880; several different specimens of A. cristatum ,
collected in 1879. They appeared as if collected after they
were badly weathered, while sporangia of Aspidium bootii , col-
lected in September, 1879, would not open, probably never
having ripened. Specimens of Polypodium vulgare , matured

THE BIOLOGY OF FERNS.

[fart I.

in 1892 and examined in 1893, after weathering in the meantime,
showed slow movements of the annuli, but no sudden return.

Cyatheaceae. — In the Cyatheaceae the dehiscence is very
similar to that in the Polypodiaceae. Specimens of Cyatkea
brunonis in the Horace Mann Herbarium of Cornell University,
collected in the Malayan Peninsula, and distributed from the
Kew Herbarium in 1867, on treatment of the sporangia, showed
active annuli, which completely everted and returned with a
sudden thrust. The sporangium normally divides across the’
middle line, guided at one place or another through the frontal
series of cells.

Hymenophyllaceae. — In the specimens of the Hymenophylla-
ceae examined very few of the sporangia had dehisced, and in
those which had opened, the large majority of spores still
remained in the sporangium. Attempts to induce the mechan-
ical action of the annulus were almost complete failures. In
many cases the sporangia would partially open, but in only one
case was it observed that the annulus sprung, and this case was
very feeble. In all the other cases the return was very slow.
Nearly all the spores were retained in the sporangium. It is
well known that the natural habitat of the Hymenophyllaceae
is in damp situations and humid atmosphere. This may account
for the fact that nearly all the sporangia contained their spores,
since in a moist or humid atmosphere the sporangia and annu-
lus would have little opportunity to dry out thoroughly. The
long time to which the annulus might be subject to moisture
might reduce the flexibility of its cell walls so that it would not
respond readily to treatment. Bower also calls attention to the
fact that very frequently the spores germinate while still within
the sporangium. This also goes to show that the spores in the
Hymenophyllaceae are not very effectively dispersed.

The short pedicel being attached near one end of the annulus
at one side of the edge of the sporangium, the line of dehiscence
passes by the side of the pedicel, guided by the cleavage cells,
and divides the sporangium into halves.

VI.]

SPOROPHYTE.

Gleicheniaceae. — In Gleichenia emarginata specimens at least
thirty years old showed a very active condition of the annulus.
Only those cells which above are described as constituting the
true annulus showed any of the characteristic changes, or flexi-
bility of the walls, which is the property of the annulus. The
opening was different, however, from that in either the Poly-

Figs. 132 to 135. Different stages in the dehiscence of the sporangia of Osmunda regalis.
Magnified 6 times more than the scale ; scale = 1 mm.

podiacese or Cyatheaceae, since the latter possess a vertical or
nearly vertical annulus, extending in nearly the same plane as
the pedicel. In those two orders the pedicel holds the lower
part of the sporangium fixed, unless it becomes separated, and
the upper half opens out on the end of the everting annulus.

7 4

THE BIOLOGY OF FERNS.

[part I.

In Gleichenia emarginata the annulus is transverse to the line
of attachment, the middle part of the annulus being near this
point. The two halves of the sporangium then open out equally
on each side, and when the annulus is sprung the two halves
move nearly together again. The opening is much the same
in the Polypodiaceae and Cyatheaceae, if the sporangia are free
from the pedicel.

In the Schizaeaceae and Osmundaceae, the annulus being situ-
ated transversely to the line of attachment of the sporangium
with the leaf, both halves of the sporangium open out and
spring much as in the Gleicheniaceae, and the spores are thrown
in two directions, as shown in P'ig. 135.

Comparison. — From this study of the structure and dehis-
cence of the sporangia, it will be seen that there is a remark-
able adaptation of various parts to special functions in the
dispersion of the spores. The true annulus in all consists of an
incomplete ring. By the true annulus is meant that portion
which functions as the spring. It consists of a series of cells
possessing stout and firm inner and perpendicular walls, and
thin, flexible outer walls enclosing a considerable space which
can alternately be occupied by water and air under changing
conditions of moisture and dryness, and which under these
varying conditions yields to the tension in such a manner that
it may be partially or completely everted, the relief from this
tension producing a sudden return of the annulus to nearly its
former position. The lip cells, or cells of the frontal series, are
two in number in the Polypodiaceae; several rectangular ones in
a series in the Cyatheaceae, and perpendicular to the line of
cleavage ; a few very narrow and long ones, in a series parallel
with the line of cleavage, in the Hymenophyllaceae, Gleicheni-
aceae, Schizaeaceae, and Osmundaceae. The lip cells approach
more nearly the form and structure of those of the true annulus
in the Cyatheaceae, less so in the Polypodiaceae, and far less so
in the four other orders. In the Polypodiaceae, Cyatheaceae,
Hymenophyllaceae, and Gleicheniaceae there are two series of

VI.]

SPOROPHYTE.

cells similar to those of the lateral faces of the sporangium,
which serve as connectives between the ends of the true annu-
lus and the lip cells. These are smaller and fewer in number
in the Hymenophyllaceae, and greater in extent in the Polypodi-
aceae. In the Osmundaceae the connective consists of a very
few small cells with lignified walls at the vertex of the sporan-
gium, bordered by larger cells similar to those of the lateral walls.

The function of the lip cells is to start the line of cleavage
for the dehiscence so that the sporangium shall open by two
nearly equal parts. The function of the connective is not only
to serve as the pull on the lip cells, and to form an attachment
to the lateral walls of the sporangium, but also to hold the
lateral walls of the sporangium from going to pieces, in order
that this part of the sporangium may retain so far as possible
its normal form and position, and hold the spores in place until
the annulus springs, when they are violently hurled away.

A complete annulus in these orders would defeat such an
effective dispersion of the spores, since the entire length of the
line of cells around the sporangium would then evert, and in
doing so would tear the lateral walls apart, or completely evert
them, and the spores would fall away before the annulus would
spring. In the Schizaeaceae, it is also doubtful if the entire
series of cells functions as the spring ; but if it should, being
situated on a small tapering apex of the oval sporangium, it
could not completely evert the walls of the sporangium, and so
would not operate against the effective dispersion of the spores.

Mechanism of the Annulus. — Prantl, in 1879, described the
mechanical function of the annulus, having observed it in the
Polypodiaceae, Cyatheaceae, Hymenophyllaceae, Gleicheniaceae,
and Osmunda. In the layers of protoplasm lining the internal
surface of the cells of the annulus, he states there is some
substance which possesses a strong avidity for water. On
placing dehiscent sporangia in water, he observed that the
strong endosmotic pressure resulting from the absorption of
water in the cells caused the air in their cavities to be quickly

THE BIOLOGY OF FERNS.

[PART I.

absorbed. Upon drying, or by treating with glycerine, alcohol,
strong solutions of potash or chloriodide of zinc, or any sub-
stance which would withdraw the water, the cell walls not being
permeable to air, the pressure from the outside caused the thin
dorsal and lateral membranes to infold, and in doing so pulled
on the radial walls of the annulus. These acting as fulcra,
their outer ends were pulled near together, causing the annulus
to be looped in the opposite direction. Finally, when nearly all
the water was abstracted, the air held in solution is suddenly
set free. The outside pressure thus being overcome, the
annulus suddenly returns nearly to its former position. Since
plasmolysis does not occur, the substance in the cells which
possesses a strong avidity for water does not escape, and the
process can be repeated successively.

Where the process goes on evenly in all the cells, the annulus
is completely everted before it springs ; but when it goes on
unequally in different cells, several sections of the annulus may
evert and spring independently.

Schinz, in 1883, made the statement that the straightening of
the annulus and dehiscence of the sporangium were due to the
unequal contraction in drying of the unequally thickened cell
walls of the annulus.

In 1885 Leclerc du Sablon gave an explanation similar to
that of Prantl. In the same year Schrodt said the opening of
the sporangium was due to atmospheric pressure on the thin
dorsal and lateral membranes during the abstraction of water ;
that the sudden return was caused by the sudden entrance of
air through the membrane, which moist was not permeable by
air of the pressure of one atmosphere. According to his
theory, the membrane, reaching a certain degree of dryness,
becomes permeable to air of the pressure of one atmosphere.
The air which then enters is rarefied, and the annulus does not
entirely close. Prantl showed that this theory was untenable ;
for example, when glycerine was used to withdraw the water
from the cells, there was no air surrounding the annulus which
could suddenly pass into the cells.

VII.

SUBSTITUTIONARY GROWTHS.

The normal life cycle, as illustrated by the succession of the
gametophyte and sporophyte phases of the fern plant, is fre-
quently interrupted by various substitutionary growths. While
the perennial character of
nearly all ferns renders it a
very common thing for the
individual sporophyte to
exist for years independent
of the gametophyte phase
and produce successively
crops of spores, this does
not necessarily interfere
with the normal sequence
of the two phases. For,
omitting exceptional cases
to be described hereafter,
the spores produced each
year from these perennial in-
dividuals are capable, under Fi s- ^ Sporophytic bud from leaf of Aspie-
x _ mum bulbiferum.

normal conditions, of intro-
ducing the normal life cycle again, and originating new
plants. We might then consider the normal life cycle to be
the production of new plants by a succession of these two
phases.

It is now known, however, that new plants in many cases
may be introduced either by substitutionary growths or by the

THE BIOLOGY OF FERNS.

[PART I.

direct omission or arrest of a part or the whole of one of the
two normal phases.

Sporophytic Budding. — What is called sporophytic budding
has long been known to occur in various species of Asplenium ,
Cystopteris , etc., where bulbs are formed which are indeed young
plants, and are capable of developing into perfect plants. In
this case superficial tissues of the sporophyte, usually near a
vascular bundle on the leaves, grow out directly into a new
sporophyte. Various species of Asplenium grown in conserva-
tories afford beautiful examples of this phenomenon. Asple-

Figs. 137 and 138. Asplenium bulbiferum. Fig. 137, section of normal pinnule, showing
epidermis, mesophyll cells, and part of vascular bundle. Fig. 138, section through
pinnule at very young sporophytic bud, showing mesophyll cells, small and rich in
protoplasmic content, and the apical cell of the bud. Magnified 30 times more than
the scale ; scale = 1 mm.

nium bulbiferum , for example, presents frequently numerous
young plants in various stages of growth, and of various sizes.
A single leaf may bear more than a dozen, and frequently
several may be found upon one pinna, one each on several of
the pinnules near the extremity of the pinna. By examining a
growing leaf, it will be observed that near the tip some of the
very young pinnules are abruptly curved, forming a greater or
less angle near their attachment to the pinna. If this angle of
such a young pinna be examined with a pocket lens, the surface

VII.]

SUBSTITUTIONARY GROWTHS.

Figs. 139 and 140. Sections through young sporophytic buds of Asplenium bulbiferum.
Magnified 30 times more than the scale ; scale = 1 mm.

THE BIOLOGY OF FERNS.

[PART I.

of the vein in the angle will usually appear somewhat broader,
and a greater or less convexity of the surface is present, accord-
ing to the age of the growth. Sectioning such a pinnule shows,
at this point, a tissue on that side of the vein composed of
mesophyll and epidermal cells, very rich in protoplasm and with
somewhat smaller mesophyll cells than those of the opposite
side of the section, or in other parts of the pinnule. The

Fig. 141. Section of young bulb of Asplenium bulbiferum, magnified 6 times more than
the scale. — Fig. 142. Apex of leaf with apical cell from section adjacent to 141. —
Fig. 143. Detail of vascular bundle from 141, showing the origin of the tracheides
of the bud. Figs. 142 and 143 magnified 30 times more than the scale ; scale = 1 mm.

smaller size of the mesophyll cells, and their rich content of
protoplasm, indicates at once a very different function from the
ordinary mesophyll cells. The tissue has become a growing
point, or bud, in which are to be found the primary elements of
stem, and later of leaf also. This changed function of the cells
in this area of the pinnules, carrying with it, according to the

VII.]

SUBSTITUTIONARY GROWTHS.

law of correlation, change in the form and size of the cells,
accounts for the angle in the pinnule at the point of origin of
the bud. The other mesophyll cells have grown to their accus-
tomed size, thus producing unequal tension on the two opposite
sides of the pinnule.

Sections at a very early age show what appears to be an
apical cell, perhaps of the stem (see Fig. 138), though it is not
always well apparent. It would be incorrect, however, to say
that the bud is derived from a single epidermal cell, or indeed
from the epidermis. The mesophyll cells between the epidermis
and the vascular bundle partake also in the growth and cell
divisions. Later its cells are the first to elongate, lose their
rich protoplasm, and take on the character of scalariform
tracheides, which are in immediate communication with those
of the bundle of the pinnule. It may be that the bud is derived
from a single superficial cell of the young leaf before the dif-
ferentiation of the epidermis.

As the bud grows, numerous elongated brown scales are
developed, which cover or protect it, and later young leaves
arise from different places, unrolling in circinate fashion, the
earliest ones soon expanding, and the form of the young fern
plant is then apparent. These buds on Asplenium bulbiferum
usually arise from the upper surface of the pinnule, near its
base. Occasionally they arise from the under side. Fre-
quently a sorus occurs along the side of the vein by a bulb
containing well-developed sporangia and spores, so that no
sporal arrest occurs in connection with the sporophytic budding
in this fern. Other species of Asplenium produce similar
sporophytic buds, which have been studied by Heinricher, as
A. c e It i difolium, bellangerii , viviparum , decussatum , etc.

In Cystopteris bulbifera , a very common fern in cool, damp
rocky glens, the bud while still attached to the leaf does not
resemble a young plant at all. It presents more the appearance
of a fleshy bulb. Large specimens present an oval form, the
larger part of which is composed of two opposite thick rudi-

THE BIOLOGY OF FERNS.

[PART I.

mentary leaves, elliptical in outline, convex on the outer face
and plane on the inner. Their outer ends are separated by the
younger rudimentary leaves, two of which can usually be seen
in well-matured buds, and the stem axis. The basal half of the
bud appears as a consolidated mass of tissue. All these rudi-
mentary leaves are different in size, since they arise succes-
sively. The buds easily break away and fall to the ground,
where they grow into new plants by an elongation of the stem

tion of leaf. Magnified 6 times more than the scale ; scale = i mm.

axis and the production of roots and new leaves. The first
leaves so produced are usually rudimentary, and their stipes
possess very large bases. The tissue of these rudimentary
leaves in the bud is chiefly composed of large parenchymatous
cells with intercellular spaces and packed with starch grains,
which form reserve material to supply the young plant with
food until it shall gain a foothold in the soil or in the crevices
of rocks.

VII.]

SUBSTITUTIONARY GROWTHS.

Longitudinal sections of even quite young bulbs show the
vascular bundle of the stem in connection with that of the
rachis of the leaf, while leaf bundles branch off from this into
the rudimentary leaves. Fig. 147 is from a section of a bud
only about one-third grown,
showing two rudimentary leaves,
the growing end of the stem,
and a young root which has not
yet emerged from the tissue of
the stem. The buds are situ-
ated on the under side of the
leaves in the axils of the
pinnae.

Bulbs in the axils of the
leaves of Asplenium ( Athyrium )
filix-foemina , var. clarissima , and
in connection with the sorus in
var. plumosum , are reported by
Drury. Bower records sporo-
phytic buds on the leaves of
Aspidium erythrosorum , var. pro-
liferum , and Trichomanes pyxi-
difemm. They also occur on
the base of the stipe in Pteris
aquilina ; in Aspidium jilix-mas ,
farther up on the lateral edge of the stipe. Blechnum hastatum
and Onoclea struthiopteris produce stolons or adventitious buds.
Other cases are such as occur when a leaf is “'layered,”' and
which habitually takes place in the walking fern, Camptosorus
rhizophyllus.

Gametophytic Budding. — This is the development of new
prothallia as direct outgrowths from other prothallia. It occurs,
as we have seen above, according to Goebel, in Gymnogramme
leptophylla. According to Rauwenhoff it occurs in Gleichenia ,
and, as the writer has observed, in Adiantum cuneatum. Bower

Figs. 145 and 146. Cystopteris bulbifera.
Fig. 145, bulb in the axil of the leaf;
146, young plant developing from a
bulb.

THE BIOLOGY OF FERNS.

[PART I.

first termed this “ oophytic budding,” and he cites a case in a
fern prothallium observed by Cramer.

There are other departures from the normal life cycle of ferns
which consist in the partial or complete arrest of the usual
reproductive bodies, and the appearance in
their stead of the complementary phase of
the life cycle. Such phenomena are known
as apogamy and apospory.

Apogamy. — This was first described by
Farlow as occurring in Pteris cretica , and
is the development of the sporophyte from
the gametophyte without the intervention
of the sexual organs. The meristematic
tissue, instead of developing archegonia,
showed scalariform tracheides, and later a
development of young fern plants directly
from the prothalline tissue. De Bary re-
corded it in Aspidium filix mas, var. cris-
tatum , A. falcatum , and Todea africana.
According to these investigators, prothallia
of all these species bear antheridia. Arche-
gonia are entirely absent in such prothallia of Aspidium filtx-
mas , var. cristatum ; never reach maturity in Pteris cretica;
while they may reach maturity in Aspidium falcatum and
Todea africana. Bower has described cases of apogamy in
Trichomanes alatum , and Berggren on the prothallia of Noto-
chlcena distans.

Apospory. — Apospory is the development of the gameto-
phyte from the sporophyte without the intervention of the
spores, and occurs in several different ways. This was first
reported by Drury in the case of Asplenium \Athyrium) filix-
fcemina, var. claris sima, Jones, and Polystichum angular e , var.
pidcherrimum, Padley, and was later carefully studied by Bower.
In A. f-f, var. clarissima, no mature sporangia or spores are
developed. Accompanying this complete sporal arrest, the

Fig. 147. Diagrammatic
section of a bulb of
Cystopteris bulbifera
made up from sev-
eral longitudinal se-
rial sections. a, point
of attachment of the
bulb with the rachis
of the leaf.

VII.]

SUBSTITUTIONARY GROWTHS.

sporangia have taken on the function of producing prothallia
directly. This occurs in two ways. Prothallia may be devel-
oped from the cells of the wall of the sporangium or from the
stalk. In no case does the archesporium partake in this apo-
sporus growth. In certain arrested sporangia some of the cells
show a rich content of protoplasm, and later, by growth and
division of these cells, the prothallia are developed. The forms
of these growths are various, and many of them depart widely
from the normal form of prothallia, but their gametophytic
nature is assured by the pro-
duction of antheridia, and in
some cases by archegonia.

In Polystichum angular e,
var. pulcherrimitm , prothallia
are produced from four differ-
ent places on the sporophyte :
from the apex of pinnules
not connected with a vein ;
from the surface of pinnules
near a vein ; from arrested
sporangia ; and from the base
of the sorus.

Farlow has described apospory in Pteris aquilina . The
prothalline growths arise from arrested sporangia on fertile
pinnules which are much dwarfed and curled, and on which
sporangia much in advance of those on normal pinnae occurred.

Bower has farther given a very interesting account of apospory
in two species of Trichomanes. In T. pyxidiferum prothallia
are produced from the leaf with partial sporal arrest. In T.
alatum the prothallium is either protonemal-like, or an expanded
plate of cells. Protonemal threads may arise from cells of the
apex of the leaf, from its margin, or from the surface of the
leaf in connection with a vein, or from the sporangia. Later
flattened expansions may be produced on these protonemal
threads. In other cases, the prothallia as flattened expansions

Fig. 148. Young fern plant, an apogamous
growth from the prothallium of Pteris
cretica.

THE BIOLOGY OF FERNS.

[PART I.

may arise directly from the leaf without the intervention of the
threads. Frequently these bear at their apex gemmae, which
are several-celled bodies ovoid or elliptical in form and sup-
ported by sterigma. They have been seen to germinate.

VIII.

OPHIOGLOSSE^E.

The prothallia of the Ophioglosseae are not well known. In
the species examined a tuberous body has been found, desti-
tute of chlorophyll, and bearing both antherida and archegonia.
Goebel suggests the probability that a green prothallium is at
first developed, much as in the case of Gymnogramme lepto-
phylla in the Polypodiaceae.

In Botrychium the antheridia are sunk in cavities in the tis-
sue, while in Ophioglossum they only project slightly above the

surface. In Ophioglossum , accord-
ing to Goebel, the mother cells of
the spermatozoids are developed
from one or two cells of the inner
tissue of the antheridium. The
archegonium is similar in devel-
opment to that of the homospo-
rous leptosporangiate Filicinae.
The venter is sunk in the tissue
of the prothallium, and the short
neck projects above.

Sporophyte. Stem. — The stem
of the Ophioglosseae is very
short, sometimes with a bulbous base, and fleshy. It is usually
erect and ascending, but in Helminthostachys the underground
stem is creeping. It rarely branches. The fundamental tissue
consists of large, usually cylindrical cells, with prominent inter-
cellular spaces and richly filled with starch. It is separated by

Fig. 149. Diagrammatic transection of
the stem of Botrychium virginianum.
x, xylem; ph., phloem ; m.p., medul-
lary parenchyma ; c.p ., cortical. paren-
chym ; c, cortex.

THE BIOLOGY OF FERNS.

[PART I.

the annular bundle into cortical and medullary portions. In
age the cortical tissue sometimes develops a deep layer of cork
cells. There is no sclerenchyma.

The annular bundle consists of a hollow cylindrical network,
with foliar gaps associated with the leaf traces. Sometimes

Fig. 150. Section of the annular bundle of Botrychium virginianum, showing the radial
bands of parenchyma connecting the medullary parenchyma with the phloem. Mag-
nified 6 times more than the scale ; scale — 1 mm.

the tissue of the foliar gaps changes to scalariform tracheides,
and a continuous hollow cylinder of xylem results. The xylem
of the bundle is on the axial side, the phloem on the peripheral
side, and the bundle is thus collateral. In Botrychium rutce-
folium , according to De Bary, parenchyma is present in the
annular bundle in the form of radial bands which resemble

VIII.]

OPHIOGLOSSE^E.

medullary rays, while in several
specimens of B. lunaria which he
examined it was not found.

In Botrychium virginianum ,

which I have examined, paren-
chyma is present in the annular
bundle. It appears as radiating
bands of one or two rows of cells
connecting the medullary with the
cortical parenchyma. The radial
diameter of these cells is two to
three times their tangential diam-
eter. In radial longisection, the
band is seen to consist of four to
eight rows of cells, or more. The
cells are rectangular in outline.
Their narrow tangential diameter
shows that they have been flat-
tened by the pressure of the xylem.

A rudimentary bundle sheath is
present in the stem of Botrychium.
It can be distinguished by the
transverse folding of the middle of
the longitudinal radial side walls
of its cells.

Leaf. — In the leaf stalk of
Ophioglossum , the bundles are col-
lateral, the xylem consisting of
narrow reticulate tracheides with
no intercellular spaces. In Botry-
chium, the bundles of the leaf stalk
are concentric, the xylem consist-
ing of scalariform or reticulate
tracheides. In Botrychium there
are four bundles, while in Ophio-

THE BIOLOGY OF FERNS.

[PART I.

glossum there may be eight. They are arranged in a circle
separated by parenchyma.

The leaves require several years for development ; for Botry-
chium lunaria , it is said, over four years. In some species only
one leaf is developed each year, while in any case the number

is few. Usually the leaf,
in its embryonic devel-
opment, divides into a
fertile and sterile por-
tion, but some species of
one section of Ophio-
glospum possess both
fertile and sterile leaves.
The fertile portion of
the leaf may be simple
and entire, as in Ophio-
glossum ; simple, or
once, twice, or thrice
pinnate or ternate in
Botrychium. There is a
long petiole with sheath-
ing margins at the base,
which, equitant fashion,
ride upon and enclose
the end of the stem and
younger leaves. The
leaves are not circinate
in vernation, but when
young may be straight,
partly inclined, or wholly
inclined, according to

Fig. 152. Portion of transection of bundle in the stem
of Botrychium virginianum : xylem portion, con-
sisting of tracheides, separated by radial bands of
parenchyma; phloem, bundle sheath, and a por-
tion of the cortical parenchyma. Magnified 30
times more than the scale ; scale = 1 mm.

the species. The epi-
dermis of both surfaces
possesses stomates, and
the mesophyll is pro-

VIII.]

OPHIOGLOSSE^.

vided with intercellular spaces. The bundles of the leaf are
weak, are said to branch dichotomously in Botrychium and
Helminthostachys , while they anastomose in Ophioglossum.

In a number of species the fertile branch is destitute of
chlorophyll. In a specimen of Botrychium lunarioides from
Concord, Mass., two divisions of the usually sterile lamina were
changed to fertile ones.

Sporangia. — The sporangia are an entire year in completing
their development. They originate in what is called the sporog-

Figs. 153 and 154. Botrychium virginianum. Fig. 153, tangential section of portion of
xylem showing a transection of one of the radial bands of parenchyma ; 154, radial
section of bundle, b.s., bundle sheath; p.s., phloem sheath; s.t, sieve tubes; x,
xylem ; m.p ., medullary parenchyma ; r.b. t radial band of parenchyma. Magnified
30 times more than the scale ; scale = 1 mm.

enous tissue of the fertile part of the leaf. The wall is devel-
oped from the epidermis, while a terminal cell of an axial row
beneath forms the archesporium, according to Goebel ; while
Holzman thinks a large superficial cell, in Botrychium , present
in the early development, may be considered the mother cell of
the sporangium, though it does not project above the surface
before division. A tapetum surrounding the spore mother cells

THE BIOLOGY OF FERNS.

[PART I.

is developed from tabular cells cut off from the archesporium.
Numerous spores are developed in a single sporangium. The
sporangia are modified pinnules of the fertile part of the leaf.
In some species, where the leaf is more simple, the sporangia
appear on the inner side of the fertile leaf. In Oph ioglossum
the sporangia closely cohere, and the form of the fertile part of

Fig- 155* Longitudinal section of the end of the stem of Botrychium virginianum, show-
ing apical cell. The dotted lines represent the borders of cells of a leaf closely
crowding upon the end of the stem. Magnified 30 times more than the scale;
scale - - 1 mm.

the leaf is a two-ranked spike. In Botrychium they are more
separated, and once to thrice pinnate.

Roots. — The roots are quite fleshy, usually somewhat brittle,
and when dry, spongy, so that they swell to nearly their normal
size when soaked in water. They arise one at the base of each
leaf trace in the stem. In Ophioglossum , the roots do not
branch, while in Botrychium , a few lateral roots arise in a
monopodial fashion. In Ophioglossum , many of the roots pro-
duce adventitious buds which develop into new plants. The
epidermis of the roots consists of cells with hard brown walls.
The various tissues are differentiated from a tetrahedral apical

VIII.]

OPHIOGLOSSE^E.

cell, the cells of the root cap, in some species, soon losing the
stratified character so persistent in the roots of ferns. In

Fig. 156. Diagrammatic section of the stipe of Botrychium virginianum, showing the
arrangement of the bundles. — Fig. 157. Diagrammatic section of the end of the
stem and equitant bases of the leaves, with leaf traces and open portion of the stem
bundle (B. virginianum).

Botrychium virginianum the stratification is quite well marked.
Very few root hairs are developed. The bundle sheath is feebly
developed ; it can be differentiated by the folding of the middle
of the longitudinal radial side walls of its cells.

In Ophioglossum the small bundle is collateral. The xylem,
the cells of which are similar in transection to those of the
stem, in the form of a crescent occupies one side, its convexity
separated by a layer of one or two
rows of delicate cells from the bun-
dle sheath. The phloem, in several
layers, borders directly on the bundle
sheath on the opposite side of the
bundle. According to Van Tieghem,
two of the outermost cells of the
xylem sometimes border directly on
the bundle sheath.

In Botrychium the bundle is con-
centric, or perhaps, more correctly
speaking, radial. In primary roots it
usually consists of three, sometimes

Figs. 158 and 159. Mature and de-
hiscent sporangia of Botrychi-
um virginianum.

THE BIOLOGY OF FERNS.

[PART I.

four, radial narrowly oval groups of xylem alternating with as
many groups of phloem. The triarch bundle is the more
common, the tetrarch bundle occurring sometimes in stout
roots. I have observed the triarch in B. matricaricefolium and
B. virginianum , and the tetrarch in B. virginianum and B. ter-
natum. In the lateral roots the bundle is usually diametrically
diarch ; occasionally it is triarch in B. virginianum.

The structure of the elements of the xylem is the same as
that in the stem, except that no rays corresponding to those in
the stem bundle of B. virginianum and B. rutcefolium are
present. The xylem begins by the appearance of a few small
tracheides at two, three, or four points, a few cell layers inside
the bundle sheath, according as the bundle is to be di-, tri-, or
tetrarch. The transformation of the cells to xylem then pro-
ceeds inward from these points toward the centre, the number
of rows of xylem cells as well as their size usually increasing
on the axial side. In old roots the intermediate parenchyma
cells in the centre sometimes become completely obliterated by
their transformation to xylem. In one old root of B. ternatum
of the tetrarch type, the four groups of xylem appeared to
have coalesced. Only here and there was a single cell
compressed between the xylem, and indicating the earlier four
radiating lines of separation. In this case the xylem pre-
sented four concave, external faces, the concavities occupied
by the phloem.

The development of the phloem proceeds from similarly
situated, alternating points with that of the xylem. From each
point the transformation of the procambium then proceeds in
three directions as seen in cross-section, one toward the centre,
and two tangentially. According to the age of the root, more
or less of the tissue intervening between the lateral faces of the
xylem is thus transformed to phloem. It consists of thick-
walled cells which, untreated, possess a bright gleam viewed by
transmitted light, and by treatment take a deep stain. Sieve
tubes occur.

OPHIOGLOSSE^E.

vim]

Figs. 160 and 161. Longitudinal section of root tips of Botrychium virginianum, with
apical cell and root cap. Fig. 160, from mature root, magnified 20 times more than
the scale; 161, from young root still within the stem, magnified 30 times more than
the scale. Scale = 1 mm.

9<5

THE BIOLOGY OF FERNS.

[part I.

The xylem is separated from the bundle sheath by one or two
layers of large, thin-walled cells, and even in old roots there
appears at least one layer of such cells between the phloem
and bundle sheath.

Fig. 162. Transection of the bundle of the root of Ophioglossum vulgatum. x, xylem ;
ph., phloem ; b.s., bundle sheath. Magnified 6 times more than the scale ; scale =
1 mm.

The fundamental tissue is made up of deep layers of cortical
parenchyma, richly filled with starch, and possessing large inter-
cellular spaces.

As the writer has shown, symbiosis occurs in connection with
the roots of the Ophioglosseae. A filamentous fungus occupies
areas of varying extent, at a definite distance from the surface

VIII.]

OPHIOGLOSSEHl.

of the root. From this localized centre of metabolic activity
threads of the fungus extend to the outside of the root. The
presence of this microsymbiont probably bears a close relation
to the almost complete absence of root hairs in the order. The

Fig. 163. Transection of the bundle of the root of Botrychium virginianum, a tetrarch
bundle in a stout root, showing four groups of xylem alternating with four groups of
phloem, and separated by parenchyma. The bundle sheath is the external series of
cells shown in the figure. Magnified 30 times more than the scale ; scale = 1 mm.

following species have been examined by the author, and in all
of them the fungus was present : —

Botrychium matricaricefolium , ternatzim , and virginianum , from New York
State.

B. lanceolatum, Massachusetts and Vermont.

B. suhbifoliatum , Hawaiian Islands.

B. lunaria, Cloon Mountains.

Botrychium (No. 484, Drummond’s collection, Boston Soc. Nat. Hist.),
Louisiana.

THE BIOLOGY OF FERNS.

[part I.

Ophioglossum vulgatum , New York State and suburbs of Paris.

O. lusitanicum , Sardinia and Island of Madeira.

O. palmatum, Eastern Cuba.

O. pendulum, Oahu, Hawaiian Islands. The latter was collected on trees,
which is quite strong evidence of the probable necessity for the presence
of the microsymbiont .

Part II.

METHODS.

NOTES ON TECHNIQUE.

Preparation of Collodion. — The description of methods given
here is offered mainly in the way of suggestions upon the
technique, such as the writer has found useful, especially in
the handling of the more delicate tissues like the prothallia.
In connection with this it seemed desirable to state in brief
the method of sectioning and preparation of the tissues for
study. For full treatment of the technique the student is
referred to those works devoted to a wider range of plant
histology.

The collodion method employed in the infiltration of the
tissues as used here is with some slight modifications adapt-
ing it to the delicate prothalline tissue, that described by
M. B. Thomas.

Materials. — The materials needed for the preparation of the
infiltrating substance are as follows : alcohol — what is known
as commercial alcohol with a strength of at least 95 per cent ;
ether — the best should be used; that put up by E, R. Squibbs
& Son, Brooklyn, N.Y., can be recommended. Guncotton,
as it is known to the trade, is used for the base.

Two solutions of collodion should be prepared as follows.
(The quantity of each ingredient given here is that frequently
used in making up the solutions. These quantities can be
varied according to the quantity of solution desired.)

Two per cent Collodion. — Place 6 grammes of guncotton in
a cork-stoppered pint bottle. Pour 150 c.c. 95 per cent alcohol
into a graduate, and add to this 150 c.c. of sulphuric ether.

IOI

102

THE BIOLOGY OF FERNS.

[PART II.

Pour this mixture in the bottle over the 6 grammes guncotton,
cork, and as the guncotton dissolves, invert the bottle so that
the cork will become wetted with the collodion while it is in
place. This leaves a film of collodion on and around the cork
which seals the bottle and prevents the evaporation of the
ether, and consequent thickening of the solution.

Five per cent Collodion. — Place 15 grammes of guncotton in
a cork-stoppered pint bottle and add the same quantity of a
mixture of equal parts of sulphuric ether and 95 per cent
alcohol as for the 2 per cent, and when dissolved seal in like
manner.

Shake each occasionally for a day or two to aid the solution,
when they will be ready for use. Each time that collodion is
used from either solution the cork should be sealed by inverting
the bottle, else the collodion will slowly thicken and be unfit
for use.

Dehydrating Apparatus. Tubes. — For dehydrating a few
prothallia, 10 to 12, tubes 10 mm. to 12 mm. in diameter
and about 6 cm. long are a convenient size. These can be
cut from glass tubing and made in the following way : Cut
a circle from good chamois skin 18 mm. in diameter. Coil
elastic wire twice around a tube 8 mm. in diameter, cut off the
ends, and bend them inward so they will not cut the skin. Place
the circle of chamois skin over the coil of wire and press it
into one end of the tube, being careful not to cut the skin.

Some larger tubes will be necessary for dehydrating the
coarser and bulky tissues, and for use occasionally with the
smaller ones. A convenient size for these tubes is 2 \ cm. in
diameter by 8 cm. to 10 cm. long. Chamois skin of sufficient
size is inserted as described for the smaller tubes.

Dehydrating- jar. — A modified form of Schultze’s apparatus
can be made as follows : Prepare a circular diaphragm of
plaster paris, 18 cm. in diameter by 8 mm. to 9 mm. thick, with
perforations of a size to easily admit the large tubes. Support
this diaphragm in a Whitall & Tatum museum jar, about 20

I-]

NOTES ON TECHNIQUE.

103

cm. in diameter (in the clear) by 25 cm. in height, so that the
diaphragm rests at about two-thirds the height of the jar.
While the diaphragm is being made, three glass rods of suffi-
cient length to support the diaphragm at the proper height can
be inserted as legs. Pour in sufficient 95 per cent alcohol to
reach the diaphragm. Place rubber bands around the larger
dehydrating-tubes so that they can be plunged in the alcohol
and be adjusted to any desired level.

Dehydrating and Orienting the Firmer and Older Tissues. —
Place segments of the stems, roots, or leaves in 50 per cent
alcohol, sufficient to cover them, in a large dehydrating-tube.
This is then sunk through a perforation in the diaphragm of
the dehydrating-jar to such a depth that the two liquids are at a
common level, where it is held in place by adjusting the rubber
band. It is left for twelve to twenty-four hours, according
to the tissue. The 95 per cent alcohol can be kept at the
proper strength by adding from time to time some calcium
chloride. Where these tissues of the stem, leaf, and root are
young and delicate, it is safer to dehydrate them as is described
below for prothallia.

After the tissues are dehydrated they are removed from the
alcohol to sufficient 2 per cent collodion to cover them, for
about twelve hours, and then in 5 per cent collodion for an
equal period.

The segments are then cemented to corks with 5 per cent
collodion. They can be oriented in various positions perpen-
dicular to the plane in which it is desired to cut the sections.
Where segments are placed perpendicular to the surface of the
cork, it may be useful sometimes to cut a shallow hole or slit in
the end of the cork. The 5 per cent collodion can then be
placed on with a camel’s-hair brush, or poured on in small drops
from a vial. First place a small drop on the surface of the
cork, and immediately insert the segment oriented in the de-
sired position. Allow to dry a little. Drop by drop, or with
successive applications with the brush, cover the segment with

104

THE BIOLOGY OF FERNS.

[PART II.

the collodion, allowing each application to dry somewhat before
the next is made. When well covered, allow to dry a very few
minutes, then plunge in So per cent alcohol. In a few hours
it will be ready to section.

Notes on the sectioning and preparation for study are given
in the paragraph for the study of the prothallia, and some gen-
eral comments only will be made here. Sliding cuts should be
made with the knife, and it is usually better to draw the knife
slowly through the tissues, but sometimes in delicate tissues
very thin sections can be made to better advantage by a rather
quick stroke of the knife. The usual directions for fixing the
sections to the glass slip are to use dry ether vapour, which is
blown on the sections from a modified wash bottle. The exit
tube does not come in contact with the ether, and is filled part
way with broken pieces of calcium chloride to dehydrate the
vapour. I have always applied the ether direct, drop by drop,
from a dropping-tube. This melts the collodion, and, as the
ether evaporates, fixes the sections to the slide, 95 per cent
alcohol being floated on as the ether is evaporating. Some
objections to the direct application of the ether may be offered.
If too much is applied, small sections are apt to float out of
their serial order. Also, free parts of sections are apt to float
out of position. In such case it may be well to use the ether
vapour. In any case the operator might use whichever method
is preferred. The free parts of sections are sometimes held in
place, while sectioning, by coating the object each time before a
cut is made, with 1 per cent collodion, applying it with a camel’s-
hair brush. The object is then kept dripping with alcohol while
being cut.

After the sections are fixed they are washed by floating water
over them, stained, washed again with water, dehydrated with
alcohol, cleared with the clearing mixture, and mounted in bal-
sam, when they are ready for study.

A clearing mixture which has been found to be useful is
made by mixing three parts of turpentine and two parts of

NOTES ON TECHNIQUE.

105

melted carbolic acid crystals. If it crystallizes in cold weather,
keep it in a warm place while using.

A tray made by cementing glass rods on a rectangular plate,
for supporting the glass slips during the process of washing,
staining, etc., will be useful.

Two vessels upon a shelf above the work table, one for
alcohol, the other for distilled water, with siphon in each
for floating alcohol and water upon the preparations, and
alcohol upon the knife while cutting, should be provided.
Within easy reach the lower end of the siphon, if of glass
tubing, can be connected with a delivery jet drawn out from
a short section of glass tubing, by a rubber tubing. Upon
this section of rubber tubing place a Mohr pinch cock to
control the delivery of the liquid. In the alcohol flask the
short tube inserted to permit the entrance of air can be partly
filled with calcium chloride, so that the moisture in the air
will not in the least dilute the alcohol.

II.

GAMETOPHYTIC PHASE.

DEVELOPMENT OF FROTH ALLIA.

Sowing the Spores. — Spores of most ferns, the Hymeno-
phyllaceae and Osmundaceae excepted, require a period of several
months’ rest before they will germinate. They have been
known to germinate when several years old. When possible,
for the study of native species, material should be collected
in quantity at maturity of the sporangia, and when dehiscence
has only begun. The material can be dried in papers in the
usual way for herbarium specimens. In lieu of material col-
lected for the purpose, it can be obtained in many cases from
the herbarium if not too old. Spores of the Osmundaceae
and Hymenophyllaceae should be sown as soon as mature,
since they possess chlorophyll, and will not germinate after
a period of rest and dryness.

Where dried material is not at hand, spores can be obtained
from ferns in the conservatories. The material can be sown,
directly by scraping off the sporangia from the leaf, or the
material can be collected in advance at maturity, as described
above. If sown directly from the leaves, considerable variability
will follow in the germination, as some spores will probably
have already passed through a resting period, and will germi-
nate in a few days, while others must yet pass through this
period.

The spores should be sown on some porous soil, which can
be kept moist from below, but not too wet. The soil can be
placed in pots or beds, and be kept covered by a bell jar or

106

II.]

GAMETOPHYTIC PHASE.

IO/

in a Wardian case. The soil should first be sterilized, prefer-
ably by steam or hot water, and the plants will need airing
occasionally. Mr. Shore, head gardener in the botanical con-
servatories at Cornell University, prepares the soil in the fol-
lowing way : —

The pots used are about four inches in diameter at the top.
Drainage is supplied in the usual way by placing coarse pieces
of cracked pottery in the bottom, covered by finer pieces, the
bits of pottery filling the pots about one-half way. Upon
this is placed a layer of peat moss, followed by a layer of
coarse peat soil sufficient to fill the pot to within one inch
of the rim. This is pressed firmly down. Fine peat soil,
obtained by running peat soil through a sieve, with a little
admixture of fine sand, is then pressed firmly over this about
one-half inch deep. Boiling water is then sprinkled on with
a fine rose watering-pot. The soil is allowed to settle and
cool, and the spores are scattered over the surface. A few
small bits of cracked pottery can be placed about on the soil
before sowing the spores. The spores falling on these afford
clean examples for studying germination and the early develop-
ment of the prothallia. Too much sand should not be added
to the fine peat soil, since it will hold too much moisture and
endanger the prothallia being killed by “damping off” fungi.
The pots are then placed in a saucer which will hold water,
and all watering is done from below. The pots so prepared
are set away in a box covered with glass to conserve moisture,
some admission of air being provided for, and the box is farther
protected from the sun.

The spores should not be sown too thickly ; for if crowded,
the prothallia develop irregularly, though it would be well to
strew the surface of the soil with them. At the time of germi-
nation they can be thinned, and the removal of material for the
study of germination will thin them to some extent. It might
be well to sow some spots very thickly, and by the use of some
loose material have the spores raised somewhat from the sur-

io8

THE BIOLOGY OF FERNS.

[PART II.

face of the soil. In such cases male prothallia are apt to pre-
ponderate, and simple rudimentary protonemal prothallia are
developed in profusion, which offer excellent material for the
study of the antheridia in a fresh condition.

While waiting for the spores to germinate, the student can
take up some other part of the work, but it may be well to
study the character of the spores which have been sown. It
is also convenient to have some material sown two or three
months ahead to provide old prothallia and embryos.

Structure of the Spores. — Mount some of the spores in
water. Make descriptive notes and illustrations of their
shape ; the character of the exospore ; the mark of the three-
rayed fissure on one side.

Press on the cover glass, moving it about gently, but with
sufficient pressure to rupture some of the spores. Note the
ruptured exospore ; the thin endospore ; illustrate.

Stain with iodine ; note results.

Germination of the Spores. — In the course of one week to
ten days, begin to make examinations of the material for the
germinating spores. Tease out some of the spores in water,
and cover with a cover glass.

Make descriptive notes and illustrations of the different
stages of germination.

The swelling of the spore in germination causes the exospore
to rupture. In some cases, especially in Onoclea , as Campbell
has found, the exospore is entirely cast, and in germination it is
thus quite easy to demonstrate the third coat of cellulose which
is formed on the spore at this time. The endospore will be
seen to split as the rhizoid or first cell of the prothallium
protrudes through it.

Note the development of a protonemal thread of a few cells,
or, in some cases, a plate of cells. (See text.)

Note contents of cells and the distribution of the various
substances.

In very young prothallia note the chlorophyll grains in various

n.]

GAMETOPHYTIC PHASE.

IO9

stages of division. Search for minute starch grains in the
chlorophyll grains. To demonstrate them, place the young
prothallia in absolute or 95 per cent alcohol, in the sunlight if
necessary, to bleach the chlorophyll grains ; transfer to potas-
sium hydrate, wash with water, and stain with iodine.

Prothallia. — When the material is a little farther grown, if
expanded prothallia were not present when studying germina-
tion, tease out some of the young prothallia in water, and
mount.

Make descriptive notes and illustrations of different stages
of development.

Note the expanded plate of cells at one end of the short
protonemal thread.

Demonstrate, if possible in young specimens, that this begins
and grows for a time usually from a V-shaped, apical cell.

Mount some of the larger prothallia in an inverted position.
Note that they are heart-shaped. At the sinus observe the
meristematic cushion. Search for archegonia and antheridia
and rhizoids. Sketch. (See text for details if not familiar with
them.)

Abnormal Prothallia. — From some of the places where the
spores were sown very thickly, mount material and search for
longer and branched protonemal threads and abnormal pro-
thallia. Sketch and annotate.

If possible, study several different species in the same way,
and compare the results.

DEVELOPMENT OF SEXUAL ORGANS.

Selection of Prothallia for Sectioning. — In selecting prothallia
for sectioning, great care should be exercised to avoid tearing,
bruising, or drying, since the tissue is very delicate. In remov-
ing them from the pot where they are grown, it will be well to
keep them attached to a small portion of the substratum in a
moist chamber ; or, if separated from the substratum, keep them

I IO

THE BIOLOGY OF FERNS.

[PART II.

in a thin film of water in a moist chamber, unless the operator
can take the pot to the table during the selection.

If the prothallia are not growing well separated, place a group
of them upon the glass slip in a thin film of water. With the
needles carefully separate them, placing the points of the
needles among the rhizoids, and directed horizontally along the
prothallia, being very careful not to puncture them. Invert the
prothallia which promise to be good specimens, and examine
them by direct light with a low power of the microscope, to be
certain that they are not torn nor bruised. Search the cushion
of tissue near the sinus for archegonia. They will appear as a
group of small, columnar objects, slightly curved toward the
posterior end of the prothallium, and consisting of four rows of
cells. They will not be readily mistaken for antheridia, since
the latter are quite short. Select only those prothallia which
show quite a number of archegonia. Place the needle under
them, and transfer to the small, dehydrating-tube, which should
be partly filled with water, and resting in a small vessel itself
containing water. Distilled or pure water should be used for
both vessels. In like manner select the number of prothallia
desired. One or two rather young ones, with numbers of
young antheridia, might be selected to insure obtaining the
very young stages.

Now place the dehydrating-tube containing the prothallia in
a small vessel partly filled with 50 per cent alcohol of such a
depth that the liquid in each vessel will be at a common level
at the start. The tube should be supported in such a way that
the bottom does not touch the bottom of the vessel containing
it, in order that there may be free circulation for the liquids.
If possible, agitate the apparatus gently about once every three
hours to assist the prothallia in settling in the liquid. In eight
to twelve hours remove the tube from the 50 per cent alcohol,
and quickly place it in a vessel containing 95 per cent alcohol,
and allow to remain here under like conditions for eight to
twelve hours.

II.]

GAMETOPHYTIC PHASE.

1 1 1

Now pour the prothallia into a flat-bottomed vial with a wide
mouth. If they do not flow out at first, pour more alcohol over
them from the larger vessel, agitate, and pour quickly into the
vial, repeating, if necessary, until all have been transferred.
Decant the alcohol from the prothallia, and add sufficient 95 per
cent alcohol to cover them well. After one or two hours decant
this, allowing it to drain out quite well.

Infiltrating with Collodion. — Add 2 per cent collodion to the
prothallia in the vial, sufficient to cover them. Cork the vial,
and invert two or three times to seal the cork with collodion
from inside. Allow to infiltrate for six hours. Decant the 2
per cent collodion, and add 5 per cent collodion, sufficient to
form a thin film of collodion over the bottom of the collodion-
ized paper box when poured in. Cork the vial, and set away in
an inverted position for six hours.

Imbedding the Prothallia in Collodion. — Prepare collodionized
paper trays as follows : A convenient size is 2 cm. to 3 cm., by
4cm. to 5 cm., and about 1 cm. deep; but the size must, to a
certain extent, depend upon the number of prothallia to be
imbedded. Wet the inner surface of the tray with 95 per cent
alcohol. Into the bottom of the tray then pour a thin film of 5
per cent collodion, allowing it to dry until it reaches nearly
the consistency of hard soap. In like manner add 5 per cent
collodion, until the bottom has a layer from 1 mm. to 1.5 mm. in
thickness. Pour over the surface 95 per cent alcohol, and allow
to stand about fifteen minutes. Decant the alcohol, and allow
the wet surface to evaporate until it is just moist, not at all wet.

Now, holding the inverted vial containing the prothallia in
5 per cent collodion over the centre of the tray, remove the
cork. With the needles quickly and gently guide the prothallia
to rest over the bottom, if possible in an inverted position.
Arrange them so that an antero-posterior line through them
will run perpendicularly across the tray. This will insure
accuracy of blocking and orienting on cork in a position to
obtain longitudinal or transverse sections.

1 12

THE BIOLOGY OF FERNS.

[PART II.

Allow the collodion to dry to nearly the consistency of hard
soap, being careful that it does not dry too much on the pro-
thallia, since the layer there is thin. From a vial add more
5 per cent collodion drop by drop, until the prothallia are cov-
ered about i mm., allowing each addition to thicken as before.
Then nearly fill the tray with 95 per cent alcohol ; set aside in
a covered vessel for one or two hours. Decant the alcohol,
strip off the paper from the collodion, avoiding the bending of
the sheet of collodion, which might bruise the prothallia. With
a scalpel cut the collodion in blocks enclosing the prothallia,
by sections parallel and transverse to their antero-posterior axis.

Orienting the Prothallia. — Pour a drop of 5 per cent collo-
dion on the smooth end of a cork. Orient the block containing
the prothallium in this drop, so that the prothallium will stand
on one wing. If the blocks are cut with perpendicular edge,
and in other ways according to directions given above, by thus
cementing one cut edge next a wing of the prothallium, it will
be in a position to get good antero-posterior sections.

If the blocks of collodion do not readily adhere to the fresh
collodion, melt the edge of the block by the application of a
little ether, when the block will adhere without any trouble.

As the collodion in which each block is cemented thickens,
add more 5 per cent collodion, until it is firmly cemented to
the cork. Float the corks in 80 per cent alcohol, and in ten
to twelve hours they will be ready for sectioning.

In dehydrating the prothallia, if the apparatus is properly
prepared, and the prothallia are agitated about every one to two
hours, six hours in 50 per cent alcohol and the same length of
time in the 95 per cent alcohol, with one to two hours in 95 per
cent alcohol when transferred to the vial, will be ample time.
But, on the whole, it may be safer to extend the time some-
what. Frequently good results are obtained by lowering the
small dehydrating-tube containing the prothallia with pure
water, into 50 per cent alcohol in a larger tube, which in turn
is lowered into the dehydrating-jar containing 95 per cent

II.]

GAMETOPHYTIC PHASE.

113

alcohol. After twenty-four hours, having agitated the appa-
ratus a few times, pour into the infiltrating-vial, and allow to
remain for an hour or two in fresh 95 per cent alcohol, and
proceed as before. The smaller dehydrating-tube should not
rest nearer than one-half inch from the membrane in the larger
tube, and the liquids in all cases should be at a common level
at the start.

Sectioning Prothallia. — For antero-posterior sections, fasten
a cork with its prothallium in the jaws of the microtome, so
that the cut will pass perpendicular to the surface of the pro-
thallium at the centre, and parallel with the antero-posterior
axis. Trim off the surplus collodion around the object.

Unless for some special reason it is desirable to save serial
sections of the entire prothallium, none need be saved except
in the region of the archegonia. In making sections through
this region, usually a sufficient number of antheridia will be
secured for study. If this should not be the case, section one
or two prothallia having a number of young antheridia.

The sections should be made with some instrument of pre-
cision like a microtome, in order to obtain uniformity of thick-
ness, and to save with as great a degree of certainty as possible
all the sections. The knife should be very sharp ; a good razor
is excellent. The tissues are very delicate and easily torn.
Keep sufficient alcohol on the knife to float the sections, in
order that they may not tear nor fold. With the knife at an
angle of thirty to forty-five degrees with the stroke, start the
sections near the edge of the prothallium. Cut with a steady
and rather quick stroke, but not with a jerk. With a needle
or camel’s-hair brush lead each section at a short distance on
the blade, so that successive ones will not fold upon them.
Having cut three or four sections, float them on a glass slip,
and while wet with alcohol examine them with the low-power
microscope. If the region of the archegonia has not been
reached, discard them and cut a few more, and so proceed until
the sections begin to enter the cushion bearing the archegonia.

THE BIOLOGY OF FERNS.

[part ii.

If the prothallium can be seen in the block, the sections can
be made quite thick through the wing until near the meriste-
matic cushion. At any rate, they can be made much thicker
while approaching the cushion. A little experience will be
necessary to determine the thickness of the sections, since
some prothallia are coarser than others, and the sexual organs
are apt to vary in a corresponding degree.

Through the cushion bearing the archegonia my sections
vary from 25 /x to 50 /x ; more frequently they are about 40 /x in
thickness.

Having transferred to the glass slip the number of sections
desired, or such a number as can be conveniently covered with
the cover glass used, proceed to arrange and fix them. Having
kept them in serial order while transferring them to the glass
slip, arrange them as closely as desired, so that they will read
in successive lines, either transversely or longitudinally with
the slip, some uniformity being preserved in this matter in
order to avoid confusion at a later period. During the entire
process of transfer and arrangement they must be kept wet
with alcohol, and should not be allowed to dry at any subse-
quent stage.

Fixing the Sections to the Glass Slip. — Now permit the alco-
hol to evaporate (or draw it off with absorbent paper) until the
sections begin to dry. Then with a dropping-tube place on a
drop of ether to melt the. collodion, and fix the sections to the
slip. The ether will quickly evaporate, but before the sections
become dry and white float on alcohol. In a few moments
wash with water.

Stain with haematoxylin ; wash again with water.

Float on 95 per cent alcohol for fifteen to thirty minutes,
followed by the clearing mixture for an equal time. Remove
excess of clearing mixture and mount in balsam.

If trouble is experienced in preventing the sections from
floating far out of position, a less amount of ether can be added
at one time, followed by successive applications just as the

II.]

GAMETOPHYTIC PHASE.

previous one is disappearing, until the collodion is sufficiently
melted and the sections are fixed. It is sometimes advanta-
geous to fix the sections, three or four at a time, as they are
transferred from the knife to the glass slip, especially where
a large number of serial sections are to be fixed for a single
mount.

Immediately after fixing with ether, when covered with alco-
hol, if the sections or the collodion still on the slip should
appear whitened or cloudy, add a drop of ether while the objects
are wet with alcohol. Then quickly float on more alcohol just
as the cloudiness is disappearing, in order to prevent the ether
from loosening the sections again.

Experience will determine the length of the time for the
working of the stain, also for dehydrating and clearing the
stained objects. To hasten the dehydration, the first applica-
tion of alcohol can be poured off in a few minutes and fresh
alcohol be floated on a second time. The clearing can also be
accelerated in the same way.

Should cloudiness appear after mounting in balsam, there has
been some want of care at some stage of the process. Some-
times this can be remedied by removing the cover immediately
and adding fresh clearing mixture again.

Archegonia and Antheridia. — (In connection with this see
text descriptive of the sexual organs.) In the sections from a
single prothallium, if care was used in the selection, several
different stages of development of the archegonia and anthe-
ridia will be found. In studying the sections, search for the
very earliest stages and note the succession of cell division
as the organs become more mature.

Make careful descriptive notes and drawings of various stages
of young antheridia and archegonia ; stages of division of the
central cell and spermatozoids in the antheridia.

The central cell, ventral, and neck canal cells of the arche-
gonia.

Study open antheridia and open archegonia.

ii 6

THE BIOLOGY OF FERNS.

[PART II.

Search for various stages in fertilization, spermatozoids
caught in the slimy protoplasm of the canal cells at the mouth
of the archegonia and in the canal.

Several prothallia should be prepared and examined in order
to get a good representation of the different stages.

Search for different stages of the rhizoids.

Study the structure of the prothallia in section.

Antheridia in a living condition can be studied by mounting
simple male prothallia in water. The rupture of the cap cell
and expulsion of the spermatozoids should be noted ; note also
the quiet condition of the spermatozoids at first, but that soon
they whirl away. Usually it requires a good homogeneous im-
mersion lens to see the cilia.

For the study of fertilization it will be well to fix the ma-
terial after the selection of the prothallia in a i per cent solution
of chromic acid. The prothallia should be then soaked in water
to remove the dark stain ; then dehydrated, infiltrated with col-
lodion, and prepared for study in the usual way.

After dehydration it may also be convenient sometimes to
stain the prothallia in bulk before the infiltration with collodion.

DEVELOPMENT OF THE EMBRYO.

Selection of Prothallia. — The prothallia should be examined
for a small protuberance from the under side of the meriste-
matic cushion. Usually accompanying this will be an increased
development of rhizoids from this region. A few prothallia
should also be selected, showing the very young cotyledon rising
to pass through the sinus at the anterior end. To observe the
very early stages of the embryo, select prothallia with old
archegonia, upon which there is no external appearance sug-
gesting the embryo.

These should be prepared for study the same as described
above. Make notes and drawings of as full a series of the
embryo as can be obtained. Note the basal and transversal

II.]

GAMETOPHYTIC PHASE.

ii 7

walls, if such young stages are obtained, dividing the embryo
into the stem, leaf, root, and foot segments ; the apical cell
of stem and leaf ; apical cell and root cap of young root. (The
text on the development of the embryo may be consulted here.)

In preparing sections for the study of the archegonia, young
embryos will sometimes be obtained, and also good archegonia
will frequently be obtained in sectioning for embryos.

Cases of apogamy should be looked for. They can be easily
obtained by sowing the spores of Pteris cretica.

III.

SPOROPHYTIC PHASE.

MACROSCOPIC STUDY.

For the general morphology of the sporophyte the choice
may fall on almost any of the medium-sized ferns. The ease of
obtaining material in good condition should govern the selec-
tion rather than the insistence on any one species. There are
several species, however, which, both for their wide distribution
and for their convenience in collecting, can be recommended
for study. Of these, Pteris aquilina , Adiantum pe datum ,
P olypodium vulgare , Onoclea sensibilis , or their near relatives
are convenient for the study of the stem, since the leaves are
not crowded. Various specimens of Aspidium or Asplenium
provide material for the study of crowded leaves representing
a more complicated phyllotaxy.

Wherever possible, several of these should be obtained in
order to make a comparative study. With this in view species
of Lygodium , Schizcea, or Hymenophyllum , offer the single
central bundle which is interesting to compare with the other
arrangements found to prevail in the species mentioned above.
Species of Botrychium or Ophioglossum will also repay study.

The plants should be removed from the substratum with
care to avoid injuries to the bud or growing end, and to pre-
serve as many roots free from injury as possible, especially the
root tips. If it is necessary to collect them some time in
advance, the parts may be preserved in 80 per cent alcohol,
having first dehydrated them by passing successively through
50 per cent, 75 per cent, and 95 per cent alcohol ; but it is

118

III.]

SPOROPHYTIC PHASE.

II 9

always better when possible, especially for microscopic study
of the more delicate tissues, to collect and prepare for use as
indicated under the paragraph on microscopic study.

The Stem. — Descriptive and comparative notes, and draw-
ings when useful, should be made of the general morphology
of the stem ; the branching ; terminal bud or growing end ;
the dying end ; peculiarities of form ; protective covering of
certain parts ; leaf scars, or bases of attached leaves.

Root. — Observe the succession of the roots, character of
their branching, position of the root hairs, the root tip.

Leaf. — (Herbarium material will answer for macroscopic
study.) Note the attachment of the leaves to the stem ; com-
pare the relative position and number in different species. In
such forms as Aspidium acrostichoides , Asplenium angustifo-
lium , Onoclea , sensibilis , etc., note the greater or lesser differen-
tiation of the fertile and sterile leaves. If conservatories are
convenient, note the differentiation of leaves in the case of
some of the epiphytic ferns. (See text.)

Parts of the Leaf. — The stalk and lamina, the latter usually
farther differentiated into the rachis and pinnae. Sketch.

The Stalk. — Note form; compare extent with that of the
lamina ; observe character of the surface, colour, texture.

The Lamina. — From herbarium material, note the simple
character of the lamina in such ferns as Scolopendrium vulgare
and Camptosorus rhizophyllus. In other ferns, compare the
various degrees of complexity in the division of the lamina into
rachis and pinnae, and the various forms presented. Sketch
forms of pinnae and pinnules, and note carefully the character
of the venation.

The Reproductive Bodies. — On fertile leaves, or fertile parts
of leaves, observe the “fruit dots,” or sori. From herbarium
material, if fresh material is not at hand, compare position,
form, exposure, or covering (indusium), of the sori of several
different species. (Consult text.) Sketch various forms, and
make comparative annotations ; with a pocket lens observe the

THE BIOLOGY OF FERNS.

120

[part ii.

stalked sporangia forming the sorus, and the form of the indu-
sium when present.

MICROSCOPIC STUDY.

The Stem. — To prepare stems for sectioning, cut several
segments about 6 mm. long containing the bud or growing end ;
without injuring the bud, mark the base of the segment in some
way, so that the perpendicular (to ground when the stem is in
natural position) and horizontal diameter can be determined in
orienting the segment for sectioning.

Dehydrate and infiltrate with collodion. It will require a
longer time to dehydrate the stems than the thinner and more
tender leaf and prothalline tissue. Twelve hours in the 50 per
cent alcohol, and an equal time in the 95 per cent, or the older
parts of the stem may be put directly in the 50 per cent alcohol
in the dehydrating-tube, and this sunk in the 95 per cent
alcohol for twelve to twenty hours. If it is necessary to collect
the material some time before it can be studied, these segments,
after having been dehydrated, can be allowed to stand in 80 per
cent alcohol, or they can be carried through the collodion, ori-
ented on corks, and stored in 80 per cent alcohol, until ready
for use. As a last precaution, I have found it well to place the
material in a small quantity of fresh 95 per cent alcohol for an
hour or so before placing in the 2 per cent collodion. If the
material is stored in 80 per cent alcohol after dehydrating,
when ready for later use it must be again placed in 95 per cent
before placing in the collodion. Allow the segments of the
stem to remain in the 2 per cent and 5 per cent collodion
twelve hours respectively. The segments of the stem, being
convenient to handle without injury, can be oriented on the
corks directly. Some of the shorter ones can be oriented in
a horizontal position, segments of the buds, or growing ends,
being so placed that some will section in a longitudinal horizon-
tal plane ; others in a longitudinal vertical plane, to obtain

III.]

SPOROPHYTIC PHASE.

I 2 1

different views of the apical cell. To orient the segments for
transverse sections, cut a shallow hole in the end of a cork to
receive one end. Segments of the buds should be similarly
mounted in order to obtain transverse sections of the apical
cell. The segments can be cemented to the corks in the same
manner as described for the collodion blocks containing pro-
thallia.

Cutting the Sections. — Cut the sections of the various speci-
mens, fix with ether, harden with alcohol, wash with water,
stain with haematoxylin, wash with water, dehydrate with alco-
hol, clear with the clearing mixture, and mount in balsam.

In longitudinal sections of the bud, serial sections should be
carefully saved through the middle in order to obtain the apical
cell. In transverse sections of the bud, serial sections must be
carefully saved from the very first entrance into the tissue until
the apical cell shall have been passed.

Longitudinal sections of the older portions of the stem
should contain the greatest diameter of some of the bundles.
In specimens like Botrychium or Adiantum a long and com-
plete series of transections should be preserved, showing the
transition from one leaf trace to another. Quite a long series
can be preserved on a single glass slip by using long rectangular
cover glasses.

In Pteris , Poly podium , Onoclea, etc., a few transections will
suffice.

Study. (See text for reference.)

Apical Cell. — From longitudinal and transverse sections of
the bud make out the form of the apical cell.

Note the successive oblique divisions on each side of the
apical cell ; the stratified condition of the tissues for some
distance ; the outline of the end of the bud in longisection ;
the protective scales.

In such forms as Adiantum , Onoclea , Botrychium , etc.,
note the young leaves coiled over the bud. Search for very
young leaves, shown by the arching of tissue near the apical

122 THE BIOLOGY OF FERNS. [part ii.

cell in longisection. Frequently the apical cell of the leaves
can be seen in these sections. Look out for longitudinal and
transverse sections of young roots in various stages of develop-
ment, not yet emerged from the stem. They can be deter-
mined by the apical cell and root cap. Note the change of
form in cells at varying distances from the apical cell. Some
elongate, gradually lose their protoplasm, and become tracheides
of the vascular bundles.

Trace the connections of these transforming cells in stem,
leaf, and root. Sketch the various features and make full
annotations.

Structure of the Stem. Transection. — With the low power
of the microscope study the arrangement of the various, tissues.
The things to be observed are —

Sclerenchyma, dark brown tissue, with thick cell walls. Note
its arrangement. If several species are examined, note its
varying distribution and occurrence.

Vascular Bundles, groups of large, empty cells with stout
walls (xylem), surrounded by smaller cells, usually with proto-
plasmic contents (phloem), this surrounded by a chain of cells
(bundle sheath). Such a bundle is concentric.

Parenchyma. — Thin-walled, large cells, with prominent in-
terspaces.

Leaf Traces and Origin of Roots. — These are beautifully
shown in a series of sections of the stem of Adiantum pedatnm.
The leaf trace, C-shaped, opens against a larger C-shaped
bundle in the stem, while the root bundles fork off from the
outside of the stem bundle without opening it. Study the
changing form of the bundle in a series of sections.

Starch Grains, in cells of parenchyma and sclerenchyma.

Sketch in outline the grouping of tissues in transection of
the stem. Annotate.

With the high power of the microscope study the markings
and other characters of the thick-walled sclerenchyma.

Vascular Bundles. — In the centre of the bundle note the

III.]

SPOROPHYTIC PHASE.

123

character of the thick-walled xylem cells (tracheides) ; the thin-
walled cells (parenchyma) intermingled with them ; outside of
this xylem a ring of smaller cells with slightly thickened walls,
which stain quite deeply with haematoxylin (bast), intermingled
with larger thin-walled cells (parenchyma), the whole forming
the phloem portion of the bundle. Surrounding the bundle
note a chain of usually narrow cells, the bundle sheath; just
inside of this a row of larger cells, the phloem sheath.

Longisection. Vascular Bundle. — Detect the various tissues
studied in transection. Certain markings on the cell walls
enable us to differentiate them into —

Scalariform Tracheides, elongated cells with transverse pits.
Where two longitudinal walls meet, note the bordered pits.

Spiral Tracheides, usually smaller cells with spiral markings.

Scalariform Vessels. — -In Pteris aquilina certain of the
oblique walls connecting the ends of the cells are perforated
by pits, forming true vessels.

Xylem Parenchyma, thin-walled parenchyma cells inter-
mingled with the xylem.

Sieve Tubes, elongated cells bordering the tracheides with
sieve plates in their walls.

Bast, narrow, elongated cells bordering usually the sieve tubes.

Phloem Parenchyma, large cells accompanying the bast.

Phloem Sheath and Bundle Sheath in succession.

Sketch a bundle in longisection, showing details of structure.
If possible, compare stems of Botrychium and Ophioglossum.
The bundles here are collateral. (See text for detail.)

Root. Selection of Material. — Short segments 4 mm. to
6 mm. from the larger roots, and segments containing the root
tip of almost any species, can be used. If possible, roots of
Botrychium and Ophioglossum should also be provided. While
the root cap is not so highly developed in these as in the ferns,
the root and tip are large and easily prepared for study, and
serve as excellent material for comparison. The material can
be prepared for study as described for the stems.

124

THE BIOLOGY OF FERNS.

[PART II.

Apical Cell. — From longisections and transections of the root
tip, study the form of the apical cell ; the succession of cells cut
off on all sides ; the stratification of the cells ; the transition of
these cells into the various tissues ; note the root hairs, and
compare with the Ophioglosseae. Sketch the study and annotate.

Structure of Root. Transection. — Note the epidermis; cor-
tical parenchyma, sometimes brown ; sclerenchyma inside this
forming a ring around the single, radial, vascular bundle; bundle
sheath ; xylem ; scalariform tracheides, usually arranged in two
opposite groups, which in old roots are sometimes connected.
In younger roots note very large, thin-walled cells in the centre
separating the two xylem groups. These in age change to
tracheides, thus connecting the two groups.

Phloem, alternating with the xylem groups ; note soft, thick-
walled cells which take a deep stain from the haematoxylin.

Parenchyma. — Between the xylem and phloem. This is
gradually changed to xylem and phloem in age.

Sketch and annotate the study.

Leaves. Preparation of Material. — The structure of the leaf
can be studied from the same material which is used for the
development of the sporangia, though it may be well to put up
some material representing sterile parts of the lamina.

Material to be used for the study of the development of the
sporangia and spores should be selected from fertile leaves ;
some from material bearing very young sori, and some with sori
bearing sporangia in the final stages of development.

Dehydrate with alcohol, and infiltrate with collodion as de-
scribed for the prothallia.

Orient on corks in such a way as to obtain transections of
the leaf through the sorus. Portions of the sterile leaves can
be oriented so as to obtain both longitudinal and transverse
sections. Section and prepare for study.

Structure of Leaf. — In transections of the leaf, descriptive
notes and drawings should be made of the structure of the leaf,
showing mesophyll, epidermis, and vascular bundles.

III.]

SPOROPHYTIC PHASE.

125

Epidermis. — Surface views of the epidermis can be best
studied from fresh material. With fine-pointed forceps pick
the lower epidermis, and tear off a strip and mount in water.
Note irregular form of cells; the stoma and guard cells;
chlorophyll in the epidermal cells. Stain with iodine. Sketch
and annotate.

Prepare a strip from the upper epidermis in the same way.
Sketch and annotate.

Development of the Stomates. — Excellent preparations show-
ing the developmental stages of the stomates can be prepared
as follows : Select terminal portions of the young leaves which
are just unrolling. (I used Pteris aquilina .) Cut a segment
4 mm. to 6 mm. long from the ends of several leaves. Dehydrate
and infiltrate in the usual way. To orient, allow a drop of col-
lodion to stiffen on the end of a cork. Place the young leaf
segment horizontally on this with the lower epidermis upper-
most. Section and prepare for study. Though it will be well-
nigh impossible to get the entire epidermis, or any very large
portion of it, in a single plane, at the edges of many of the
sections will be found considerable portions of it.

Observe that the epidermal cells are much smaller than in the
mature leaf, and that their form is more simple. Note semicir-
cular walls in the side of some, forming mother cells for the
guard cells. Note various stages of development of the guard
cells ; the abundance of protoplasm in the young epidermal
cells and large nuclei in different stages of division. (Consult
text.) Sketch and annotate.

Development of Sporangia and Spores. — (Consult text.) Note
placental region ; its proximity to a vascular bundle. In sec-
tions of the younger sori search for the earliest origin of the
sporangia as epidermal outgrowths from the placental region.
By searching among the different young sporangia trace the
successive cell divisions to produce young sporangial wall ;
tetrahedral archesporium ; tapetal cells ; tetrahedral primordial
mother cell of the spores ; successive bipartitions of this into

126

THE BIOLOGY OF FERNS.

[PART II.

sixteen mother cells of the spores with large nuclei ; the disso-
lution of the tapetal cells.

Spores. — Search for mother cells, the nuclei of which show
the nuclear spindle, and various stages of its formation and
division producing primary bipartition of the nucleus. Search
for mother cells showing the farther division of the nuclei into
four nuclei. Search for successive stages in the farther devel-
opment of the spores and formation of the walls. Sketch and
annotate.

In mounting dry sporangia the collodion should be allowed to
dry quite hard at each application, so that the objects will not
pull out of position by the knife.

Dehiscence of Sporangia. — If recently matured sporangia
can be procured, proceed in the order of paragraphs from i to
io. If not, then with dry material proceed in the following
order of paragraphs : 7, 1, 8, 9, 3, 4, 5, 6, 10.

1. PolypodiacecE. — To note the first dehiscence and disper-
sion of the spores, specimens should be selected the sporangia
of which are mature but not yet open. Take a pinnule or
portion of leaf of any species the sporangia of which are free
or project from underneath the indusium. Invert upon a glass
slip and examine with a low power of the microscope by direct
light. If movement does not promptly begin, hold the slip a
moment over a low flame and quickly return to the stage of the
microscope. Note the slow elevation of the distal end of the
annulus as it straightens, and that the mass of spores is held
near the end between adherent portions of the lateral walls.
Keep the attention fixed upon the annulus until it is completely
everted, the ends usually meeting, when with a sudden flip it
scatters the spores and returns to nearly its former position.

In some of the sporangia note that before the annulus is
completely everted it snaps for a short distance, at the same
time continuing to evert, until by several successive snaps it
eventually comes to rest somewhere between a nearly straight
line and the closed position.

III.]

SPOROPHYTIC PHASE.

12 /

2. Now scrape some of the mature unopen sporangia from
the leaf to the glass slip. In a dry condition cover with a
cover glass and examine with the low power of the microscope
by transmitted light, heating very gently if necessary. When
the annulus begins to move, note that the rift in the sporangium
begins at the stomium between the lip cells, and continues,
after parting them, irregularly across the lateral walls. The
movement can now be more easily observed, but the cover
interferes somewhat with the dispersion of the spores. Sketch
different positions of the annulus and sporangium.

3. After movement has ceased, run water under the cover
glass and note quickly that within each cell of the annulus
of the dehiscent sporangia is a sphere of air. Focus the high
power on some of these and note that the spheres gradually
grow smaller until, with a sudden whiff, they one by one vanish,
having been absorbed by the water under endosmotic pressure.
Sketch different appearances.

4. Now place a small drop of glycerine on the slip by the
side of the cover and with absorbent paper draw off the water.
As the stream of glycerine comes in contact with the sporangia,
note that the effect on the annulus is the same as that produced
by drying. After the annulus has sprung, note that each cell
is again occupied by a sphere of air.

5. Remove the cover and with a needle move the sporangia
to one edge of the glycerine; wash them once or twice with
water quickly. Add fresh water and cover with the cover glass.
Observe the disappearance of the air spheres again. Add
glycerine a second time and note results.

6. With fresh material, instead of glycerine, use alcohol^
or strong solutions of potash, chloriodide of zinc, or other sub-
stances which absorb water.

7. Dry Material. — (Material should be selected which is
mature, but which has not weathered by long exposure to
weather after maturity.) From the herbarium or from material
collected after the sporangia have opened take a small portion

128

THE BIOLOGY OF FERNS.

[PART II.

of leaf or pinnule, and after moistening the sporangia with
water invert on a glass slip. Dry by gentle heat, and note
movement of the annulus as described in paragraph i.

8. Scrape some dry sporangia to the glass slip, moisten with
water, aiding the absorption of the water by gentle pressure
from a scalpel or spatula. Now by gentle heat evaporate the
water, and just as the moisture is disappearing examine with
the low power.

9. Make a similar preparation, but after adding the water,
place on a cover glass. Now quickly note the air spheres in
the cells of the annulus, and proceed as directed in paragraphs
3, 4, 5, 6, and 10.

10. Try material from very old herbarium specimens.

BIBLIOGRAPHY.

The following bibliography includes the more important papers and works

consulted in connection with the study. Systematic works are not included,

since they bear a less important relation to the present subject than those

on development.

Atkinson, Geo. F., Symbiosis in the Roots of the Ophioglosseae ; Bulletin
Torrey Botanical Club, XX., 1893, p. 356.

Unequal Segmentation and its Significance in the Primary Division of

the Embryo of Ferns ; Bull. Torr. Bot. Club, XX., 1893, p. 405.

Two Perfectly Developed Embryos on a Single Prothallium of Adian-

tum cuneatum ; Bull. Torr. Bot. Club, XX., 1893, p. 407.

The Extent of the Annulus, and the Function of the Different Parts

of the Sporangium of Ferns in the Dispersion of Spores; Bull. Torr.
Bot. Club, XX., 1893, p. 435.

De Bary, A., Comparative Anatomy of the Phanerogams and Ferns, 1887
(English translation).

Ueber die von Farlow zuerst beschriebene Bildung beblatterter Sprosse

an Farn-Prothallien ; Tageblatt der 50 Versammlung deutscher Natur-
forscher und Aertze, p. 200.

Bauke, H., Entwickelungsgeschichte des Prothalliums bei den Cyatheaceen
vergleichen mit derselben bei den andern Farnkrautern ; Jahrb. f. wiss.
Bot., X., p. 49 (J- J. B., V., 1887, p. 282).

Behrens, J. W., A Guide to the Microscope in Botany; 1885. English
edition*

Bennett and Murray, Cryptogamic Botany ; 1889.

Berggren, Ueber Apogamy des Prothalliums von Notochlaena distans ;
Bot. Centralb.. XXXV., p. 183.

Bessey, C. E., Botany.

Bower, F. O., Preliminary Note on the Formation of Gemmae on Tri-
chomanes alatum ; Ann. Bot., I., 1887-88, p. 183.

On Some Normal and Abnormal Developments of the Oophyte in

Trichomanes ; Ann. Bot., L, 1887-88, p. 269.

On Apospory and Allied Phenomena; Trans. Linn. Soc., London,

2 ser. Bot., II., 1887, p. 301.

129

130

THE BIOLOGY OF FERNS.

Bower, F. O., Comparative Examination of the Meristems of Ferns as a
Phylogenetic Study; Ann. Bot., III., No. 2.

Campbell, D. H., A Third Coat in the Spores of the Genus Onoclea ;
Bull. Torr. Bot. Club, XII., 1885, P* 8.

The Development of the Prothallia of Ferns; Bull. Torr. Bot. Club,

XII. , 1885, p. 355.

Development of the Root in Botrychium ternatum; Bot. Gazette, XI.,

1886, p. 49.

The Development of the Antheridium in Ferns; Bull. Torr. Bot. Club,

XIII. , 1886, p. 49.

The Development of the Ostrich Fern; Mem. Boston Soc. Nat. Hist.,

IV., 1887, p. 17.

Zur Entwicklungsgeschichte der Spermatozoiden ; Ber. d. deutsch. Bot.

Gesells., V., 1887, p. 120.

On the Affinities of the Filicineae ; Bot. Gaz., XV., 1890, p. 1.

Notes on the Apical Growth of Osmunda and Botrychium; Bot. Gaz.,

XVI., 1891, p. 37.

A Study of the Apical Growth of Ferns with Reference to their Re-
lationships; Bull. Torr. Bot. Club, XVIII., 1891, p. 73.

Notes on the Archegonia of Ferns; Bull. Torr. Bot. Club, XVIII.,

1891, p. 16.

On the Relationships of the Archegoniata ; Bot. Gaz., XVI., 1891,

P- 323.

On the Prothallium and Embryo of Osmunda claytoniana and O.

cinnamomea; Ann. Bot., VI., 1892, p. 49.

Cramer, Ueber die geschlechtlose Vermehrung des Farn-prothalliums ;

Denkschr. Schweiz. Naturf. Gesells., XXVIII., 1880.

Drury, C. F., Observations on a Singular Mode of Development in the
Lady Fern; Jour. Linn. Soc., London, XXL, p. 354.

Further Notes on a Singular Mode of Reproduction in Athyrium filix-

foemina, var. clarissima ; J. L. S. L., XXL, p. 358.

Farlow, W. G., Asexual Growth from the Prothallium of Pteris cretica;

Quar. Jour. Micr. Soc., 1876, p. 266.

- — — Apospory in Pteris aquilina ; Ann. Bot., II., 1888, p. 383.

Goebel, K., Entwickelungsgeschichte des Prothalliums von Gymnogramme
leptophylla ; Bot. Zeit., 1877, Nos. 42-44.

Zur Embryologie der Archegoniaten ; Arb. d. Bot. Inst. in Wurzburg,

II., 1880, S. 437.

Morphologische und Histologische Notizen; Ann. d. Jard. Bot. d.

Buitenzorg, VII., 1887, S. I. (J. J..B., XV., I., 563).

Outlines of Classification and Special Morphology of Plants.

BIBLIOGRAPHY.

131

Heinricher, Beeinflusst das Licht die Organ Auflage am Farn Embryo?

Mitth. d. Bot. Inst. z. Graz, II., S. 239.

Hoffmeister, Higher Cryptogamia ; 1862.

Holtzman, C. L., On the Apical Growth of the Stem and the Develop-
ment of the Sporangium of Botrychium virginianum ; Bot. Gaz.,
XVII., 1892, p. 214.

Kienitz-Gerloff, F., Ueber den genetischen Zusammenhang der Moose
mit den Gefasskryptogamen und Phanerogamen ; Bot. Zeit., 1876,
Nos. 45-46.

Untersuchungen Uber die Entwickelungsgeschichte der Laubmooskapsel

und die Embryoentwickelung einiger Polypodieen ; Bot. Zeit., 1878,
Nos. 3-4 CM- B.,VI., I., 1878, 535).

Kny, L., Keimungs- und Entwickelungsgeschichte von Ceratopteris ; Nova
Acta d. K. Leop. Carol. Deutsch. Akad. d. Naturf., XXXVII. (J. J. B.,
i874 ? 385)-

Die Entwickelung der Parkeriaceen, dargestellt an Ceratopteris thalic-

troides; Ibid. (J. J. B., 1875, 333).

Kundig, J., Beitrage zur Entwicklungsgeschichte der Polypodiaceen Spo-
rangium; Hedwigia, 1888, p. 1.

Leclerc du Sablon, Recherches sur la dissemination des Spores chez
les cryptogames Vasculaires ; Ann. d. Sc. Nat. Bot., 7th ser., Tom.

11., 1885, p. 5.

Leitgeb, Zur Embry ologie der Fame ; Sitzungsb. d. Mathem. Klasse d.

k. Akad. d. Wiss. zu Wien, LXXV., 1878 (J. J. B., VI., I., 5).

Ueber Bilateralitat der Prothallien ; Flora, 1879, S. 317 (J. J. B., VII.,

1., 409).

Lyon, F. M., Dehiscence of the Sporangium of Adiantum pedatum ; Bull.
Torr. Bot. Club, XIV., 1887, p. 180.

Prantl, K., Die Mechanik des Rings am Farn-Sporangium ; Tagebl. d.
52 Versaml. deutsch. Naturforscher u. Aertze in Baden Baden, 1879,
S. 213.

Ibid.; ber. d. Deutsch. Bot. Gesells., IV., 1886-87, S. 41.

Ueber den Einfluss des Lichtes auf die Bilateralitat der Farnprothallien ;

Bot. Zeit., 1879, S. 697 and 713.

Rauwenhoff, De Geslachtsgeneratie der Gleicheniaceen ; Verh. d. konikl.
Akad. van Wetensch. te Amsterdam, 1889 (J. J. B., XVII., I.,
718).

Rees, Sporangien; Pringsheim’s Jahrb. Wiss. Bot., 1867, p. 217.

Sachs, The Physiology of Plants.

Schinz, Untersuchungen liber den Mechanismus des Aufspringens der Spo-
rangien und Pollensacke ; Zurich, 1883.

132

THE BIOLOGY OF FERNS.

Schrenk, Joseph, Dehiscence of Fern Sporangia; Bull. Torr. Bot. Club,
XIII., 1886, p. 168.

Schrodt, Das Farnsporangium und die Anthere ; Flora, 1885.

Der mechanische Apparat zur Verbreitung der Farnsporen; Ber. d.

Deutsch. Bot. Gesells., III., 1885-86, p. 396.

Neue Beitrage zur Mechanick der Farnsporangien ; Flora, 1870, p. 70.

Sedgewick AND Wilson, Biology ; 1886.

Smith, W., Longevity of Spores ; Gard. Chron., 1889, II., p. 140.

Smith, J., Historia Filicum ; 1875.

Strasburger, E., Ueber Befruchtung und Zelltheilung ; 1878.

— — ; Botanisches Practicum, 1884.

- - Histologische Beitrage, I .-IV.

and Hillhouse, Handbook of Practical Botany, 1887.

Thomas, M. B., The Collodion Method in Botany; Bot. Gaz., XV., 1890.

Ibid.; Proceed. Am. Soc. Microscp., 1890, p. 123.

Underwood, L. M., Our Native Ferns and their Allies.

-Onoclea sensibilis, var. obtusiloba; Bull. Torr. Bot. Club, VIII., 1881,

p. 101.

Vines, S., On the Homologies of the Suspensor; Quar. Micros. Jour*, 1877,
p. 58.

Vouk, F., Die Entwickelung des Embryo von Asplenium shepherdi ; Sit-
zungs b. d. k. k. Akad. d. Wiss., LXXVI., I., 1877 (J. J. B., V.,
p. 280).

INDEX TO PART I.

Adiantum, leaves, 45 ; fructification, 50.

Adiantum concinnum, 14, 19; embryo,
25, 26, 28.

Adiantum cuneatum, 8, 10, 14, 16, 21;
embryo, 23, 29, 31, 32; gametophytic
budding, 83.

Adiantum pedatum, 33, 36; stem bundle,
39; root bundle, 44; leaves, 46, 47.

Anatomy, Stem, 34; root, 43; leaves, 46.

Aneimia, stomates, 47; sporangia, 64,
65, 66.

Annulus, mechanism, 75.

Antheridia, 10, 15, 16, 20.

Apogamy, 84.

Apospory, 84.

Archegonia, 10, 12, 14.

Archegoniophores, 12.

Aspidium, 4 ; leaves, 45, 46, 48; fructi-
fication, 51.

Aspidium acrostichoides, 34, 36; leaves,
48; fructification, 51; sporangia, 59,
69, 70, 71.

Aspidium bootii, 71.

Aspidium cristatum, 71.

Aspidium erythrosorum, 83.

Aspidium falcatum, 84.

Aspidium filix-mas, 83, 84.

Aspidium goldianum, 71.

Aspidium marginale, 71.

Aspidium spinulosum, 71.

Aspidium thelypteris, 71.

Asplenium, 45, 46, 48; fructification, 51.

Asplenium angustifolium, 48, 71.

Asplenium bellangerii, 81.

Asplenium bulbiferum, sporangia, 54, 55,
57; sporophytic budding, 77-82.

Asplenium celtidifolium, 81.

Asplenium decussatum, 81.

Asplenium ebeneum, 71.

Asplenium filix-foemina, stem bundle, 39;
vessels, 43; sporangia, 71 ; sporophytic
budding, 83; apospory, 84.

Asplenium thelypteroides, 71.

Asplenium trichomanes, 71.

Asplenium viviparum, 81.

Bolbophyllum, 50.

Botrychium, 87, 97.

Botrychium lanceolatum, 97.

Botrychium lunaria, 88, 90, 97.

Botrychium lunarioides, 91.

Botrychium matricarisefolium, 94, 97.

Botrychium rutaefolium, 88, 94.

Botrychium subbifoliatum, 97.

Botrychium ternatum, 97.

Botrychium virginianum, 87; stem bun-
dle, 88, 89; leaf bundle, 89, 90, 91, 93;
root, 93, 94, 95, 97.

Blechnum hastatum, 83.

Camptosorus rhizophyllus, leaves, 46;
sporophytic budding, 83; fructifica-
tion, 51.

Ceratopteris thalictroides, 21, 31.

Cibotium chamissoi, 60, 61, 62.

Cyathea brunonis, 60, 61, 72.

Cyatheacese, 4, 11, 34, 58; structure of
sporangia, 60 ; dehiscence of sporangia,
72 -

Cycle, life, of ferns, 3, 77.

Cystopteris bulbifera, 4 ; fructification,
51; sporophytic budding, 78, 81, 82,
83, 84.

Dicksonia, 52.

Dimorphism, prothallia, 10 ; leaves ?

48.

Embryo, 24.

Endospore, 4, 5.

Epiphytic ferns, 49.

Exospore, 4, 5.

Fertilization, 20.

Fructification, 50.

Fruit dots, 50.

Gametophyte, 3, 77; gametophytic bud-
ding, 83.

Gleichenia emarginata, 63, 64, 73, 74.

134

INDEX TO PART I.

Gleichenia, stem bundle, 40 ; gameto-
phytic budding, 83.

Gleicheniaceae, 4, 5, 11 ; structure of
sporangia, 63; dehiscence of sporan-
gia, 73 -

Gymnogramme leptophylla, II, 12, 83, 87.

Helminthostachys, 87, 91.

Hemitelia speciosa, 61.

Hymenophyllum demissum, 62, 63.

Hymenophyllacese, 4, 5, 12, 34, 40; root
bundle, 44; spores, 58; structure of
sporangia, 62; dehiscence of sporan-
gia, 72.

Indusium, 50.

Leaves, morphology, 45; anatomy, 46;
dimorphism, 48.

Lygodium, leaves, 49; sporangia, 64.

Lygodium palmatum, 35; stem bundle,
39, 40, 41 ; sporangia, 65.

Morphology, stem, 33; root, 41 ; leaves, 45.

Niphobolus, 4, 6, 10, 11, 18.

Notochlaena distans, 84.

Onoclea, 5.

Onoclea sensibilis, 33; stem bundle, 39;
root, 43; leaves, 49; fructification, 52.

Onoclea struthiopteris, leaves, 46; sporo-
phytic budding, 83.

Oosphere, 12.

Oophyte, 3.

Oophytic budding, 84.

Ophioglossese, 87; stem, 87; leaf, 89;
sporangia, 91, 93; roots, 92; symbi-
osis, 96.

Ophioglossum, 87; leaf bundle, 89.

Ophioglossum lusitanicum, 97.

Ophioglossum palmatum, 97.

Ophioglossum pendulum, 97.

Ophioglossum vulgatum, 96, 97.

Osmundacese, 4, 5, n, 58; stem bundle,
40; spores, 58; sporangia, 66, 67.

Osmunda, 22; prothallia of, 9, 11; an-
theridia of, 20; embryo of, 25, 31 ;
leaves, 49.

'Osmunda regalis, 73.

Pellsea atropurpurea, 48, 71.

Platycerium alcicorne, dimorphic leaves,
5 °*

Polypodiaceae, 4, 5, 10, 11, 33, 50, 56;
sporangia, 58; dehiscence of sporan-
gia, 68.

Polypodium, dimorphic leaves, 49; fruc-
tification, 50.

Polypodium lingua, 47.

Polypodium vaccinifolium, 36.
Polypodium vulgare, 4, 33, 34 ; stem
bundle, 39, 41; leaves, 46; fructifica-
tion, 57; sporangia, 57, 71, 72.
Polystichum angulare, 84, 85.
Prothallium, 6; dimorphism of, 10.
Protonemal, 6, 7.

Pteris, fructification, 50.

Pteris albo-lineata, 57.

Pteris aquilina, 33, 34; stem bundle, 35,
37, 38, 41; root bundle, 48; vessels,
48; leaves, 45, 46; sporangia, 47;
sporophytic budding, 83; apospory,

85-

Pteris cretica, 84, 85.

Pteris serrulata, 7, 13, 14, 15, 16, 21-5
embryo of, 23.

Rhizoid, 5.

Rhizome, 33.

Root, 41.

Salviniaceae, 16.

Schizaea, sporangia, 64, 65.

Schizaeaceae, 4, 11, 58; stem bundle, 40;

structure of sporangia, 64.

Schizaea pusilla, 4; leaves, 49.
Scolopendrium vulgare, leaves, 46; fruc-
tification, 51.

Sorus, 50.

Spermatozoids, 17.

Sporangia, development, 53; structure,
58, 74, 75; dehiscence, 68, 74, 75.
Spores, 3, 4; germination, 5; develop-
ment, 56, 58; dispersion, 69.
Sporophyte, 3, 23, 77.

Sporophytic budding, 78.

Stem, 33.

Stomates, 47, 48.

Substitutionary growths, 77.

Todea africana, 84.

Todea rivularis, 66.

Tree ferns, 34.

Trichomanes, root bundle, 44; apospory,

85-

Trichomanes alatum, 84, 86.

Trichomanes pyxidiferum, 12, 83.
Woodsia, fructification, 52.

Woodwardia, fructification, 51.

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to select the most important aspects of the topic discussed, the essential facts being
presented in clear and untechnical language, while the subject is not overburdened
with detail.” — Popular Science Monthly.

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Full text of "The study of the biology of ferns by the collodion method. : for advanced and collegiate students"

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