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Reprinted from Zhe Botanical Gazette, 41, 109-138, February, 1906

THE EMBRYOLOGY AND DEVELOPMENT OF RICCIA
LUTESCENS AND RICCIA CRYSTALLINA.*

CHARTES Ey Lewis.
(WITH PLATES V-IX)

In June 1903, while collecting liverworts in the vicinity of Ithaca,
N. Y.,an abundance of material of Riccia lutescens was found growing
around the edges of dried-up ponds. In some cases the plants
formed beautiful rosettes, but usually they grew in irregular clusters,
often being so closely crowded together as to cover the ground for
several square centimeters. | |

The individual plants vary greatly in shape and size. The
younger light green plants consist of a narrow, thin, ribbon-shaped
thallus which has a longitudinal median groove. In the older plants
the fore part of the thallus is thickened, very large air cavities being
formed. The thallus is attached to the soil by numerous rhizoids
from the older part, the apical end being free. On the under side
are numerous colorless lamellae.

As the fruiting plant is unknown there is doubt as to the rela-
tionship of this species, authorities differing widely as to its status.
LINDBERG (21) claimed that it was merely a sterile terrestrial form
of Ricciocarpus natans. UNDERWOOD (30) says of it: ““approaches
certain terrestrial forms of Ricciocarpus natans, and possibly derived
from that species, but better kept distinct.”” STEPHANI (28) states
that it is probably not a Riccia but a sterile marchantiaceous hepatic.

For the purpose of determining the true relationship of the species,
Professor ATKINSON suggested the desirability of following the
development of the plant through the summer and autumn, and
of securing fruiting specimens if possible. He had found young
antheridia in plants collected several years before, but had not traced
the development further. It also seemed desirable to study the

embryology and cytology of the plant if material could be obtained,
because comparatively little has been done on these phases of the

life history of Riccia.
t Contribution no. 106, from the Department of Botany, Corncll University.

109] [Botanical Gazette, vol. 41

110 BOTANICAL GAZETTE [FEBRUARY

BISCHOFF (2) investigated a number of species and settled beyond
a doubt the function of the sexual organs. His work was followed
the next year by LINDENBERG’S monograph (20) which added little
that was new. | |

The study of the development of Riccia really begins with Hor-
MEISTER (15), who gave an account of the development of the thallus,
sexual organs, and fruit of Riccia glauca.

Kny (19) made a careful study of the apical cells and the method
of growth of the thallus. He did not secure plants developing from
spores but used delicate thalli which had grown crowded together
and did not bear sexual organs in the younger parts, so that the
regular order of cells was not disturbed. He discovered the origin
and manner of growth of the ventral scales and described the develop-
ment of the sexual organs. Although HOoFMEISTER believed that
young antheridia and archegonia could not be distinguished, Kny
points out that they are distinct after the first walls are formed.

LEITGEB (22) gives a complete account of the method of growth
of the thallus in the Ricciaceae. His study of the sexual organs
and fruit was in many cases incomplete on account of insufficient
material.

BIOLOGY OF RICCIA LUTESCENS.

The account of the biology of Rzccza lutescens given here is based
on field observations extending through two years, together with
experiments and observations upon plants kept growing under
favorable conditions in the greenhouse and laboratory.

The first observations were made late in June. At that time
the plants were growing upon the mud around the edges of ponds.
Some of the thalli were very small and delicate, appearing merely as
green specks on the mud, while others, which seemed to be older, had
the ribbon-shaped form and thickened apical end already described
(figs. 1-3).

Material was collected and examined from time to time during
the summer and autumn, with the expectation of finding plants
bearing the sexual organs, because the statement is usually made
that the species of Riccia fruit in summer and autumn when growing
on the soil. The plants continued to grow well vegetatively through-
out the summer, when they were in such a location that they were

1906] LEWIS—DEVELOPMENT OF RICCIA BIT

supplied with sufficient moisture. In some cases the mud became
so dry and hard that the plants were killed, but whenever they were
sheltered by a stone or other object, or were growing on the sides
of holes, such as cattle tracks, they grew well.

In October all but the youngest and most crowded plants showed
the typical Riccia lutescens form. At this time young antheridia
were found. Material was now collected and fixed from time to
time for the purpose of studying the development of the sexual
organs. In very few cases were archegonia found in plants collected
in autumn. A few young stages were found in plants collected
late in November, at which time the older antheridia were almost
mature. No further development took place out of doors until
spring, because the plants became covered with snow, or with water
by the filling up of the ponds, and remained so until April. A
quantity of the plants were kept growing on the soil in the green-
house through the winter, and developed mature sexual organs
long before spring. Plants taken from under water in March, just
as the ice was going out of the ponds, showed exactly the same form
_ as in November, and little or no further development had taken
place. So it seems that the development depends to some extent
on temperature, and might be expected to vary with different con-
ditions of climate. A warm winter, in which some growth might
take place, would in all probability hasten the development of the
sexual organs. Another point of interest is that the submerged
plants did not seem to have been injured.

A quantity of material still attached to the soil was taken from
under water late in March, and was kept growing in shallow pans
in the laboratory so that it could be kept supplied with a sufficient
quantity of water for growth but not enough to flood the plants.
This was done in order to determine whether the plants would con-
tinue the development of sexual organs and fruit in the same way
when supplied with a limited amount of water and growing on the
soil, as when supplied with a large amount of water which would
tend to cause them to break loose and float. It was found that the
plants growing on the soil did produce fruit abundantly and at
the same time as those growing under natural conditions. The
archegonia begin to develop in April in the same thalli which have

112 BOTANICAL GAZETTE [FEBRUARY

produced antheridia, and all stages are found by May 1. About —
this time fertilization takes place, and by May 25 all stages of sporo-
phyte are found. The arrangement of the sexual organs in the
thallus is shown by figs. 7-11.

The vegetative growth is very rapid during April and May, the
thallus becoming broad and branched by the increase in the number
of growing points. The narrow older part by which the thallus is
attached decays, and the younger part bearing the sexual organs
and sporophytes is set free and floats upon the water. When the
plants are supplied with a large amount of water changes take
place in the lamellae. They grow to great size and become purple.
In the floating thallus decay of the older part continues; the part
bearing the antheridia first disappears, then the part bearing the
sporophytes, and finally the growing points may be separated, one
thallus thus giving rise to several new individuals. In most cases
observed the decay of the older parts in floating plants did not advance
so far. The plants were carried up around the edge of the pond
by the waves, and as the water went down were left stranded upon
the mud. When the thalli settle down upon the mud, the large
ventral plates wither, and rhizoids are put forth which in a few
days attach the thallus to the soil. Growth now continues at the
growing points, so that new branches are produced which form
rosettes.

When the thallus is injured at this time new plants are imme-
diately produced from the cells of the apical region. This was
first observed in plants injured by being covered with mud, in which
case slender delicate outgrowths were produced (fig. 4). Other
plants injured by snails soon developed long slender plants (fig. 3b).
Thalli were cut into pieces to determine whether other cells would
show the same plasticity, but new plants were produced only from
cells near the growing point. V6OcHTING (33) found in Lunularia
that regeneration takes place from cells in various parts of the thallus,
but this does not seem to be true of Riccia natans under the conditions
in which I have studied it. Large numbers of the plants which
were left upon the mud when the water went down were injured
by cattle coming down to the ponds to drink. Later in the season
the cattle tracks were lined with young, green, ribbon-shaped plants

1906] LEWIS—DEVELOPMENT OF RICCIA Bi

which were outgrowths from the growing points of the older plants.
The cattle tracks serve a good purpose, as the young delicate plants
are shaded and protected to some extent during the dry season.
Two forms of the thallus are produced by the different methods of
propagation. In the one case the thallus after it becomes attached
to the soil continues its growth, branches and forms a rosette, while
in the other case the thallus is injured, and very delicate forms are
produced. When large numbers of the floating thalli are deposited
near together and are then injured. we find the irregular clusters
of plants which have been described in the first paragraph.

The thallus of this plant during the floating period bears such
a striking resemblance to Ricciocarpus natans that one is led to the
conclusion that Rzccza lutescens is only a ground form of Rzcctocar pus
natans. Since the beginning of this study and after it was well
under way, a paper was published by GARBER (11) which dealt
with the life history of Rzcciecarpus natans. Several points in the
biology of the plant as given by GARBER differ from thcse found
to obtain at Ithaca, and since the structure of the thallus as well
as the embryology is conclusive proof that the two forms are the
same species, it seems proper to call attention to these differences
and then to give briefly the embryology before taking up the other
phases of the study.

The greatest difference in our observations lies in the relation
of the supply of water to sexual reproduction. GARBER states that
Ricciocar pus natans as it grows at Chicago spends its entire life,
from the germination of the spore to the production of spores, in
the floating state, and that the occasional fruiting plants found
upon the soil in summer are plants in which the sexual organs devel-
oped and the sporophytes began their development while the plants
were floating. He observed no case in which sexual organs were
produced on plants growing upon the soil and states that Ricciocar pus
natans has not yet acquired the power to reproduce sexually when
growing upon the soil. The sexual organs develop in April.

The plants at Ithaca, however, spend the greater part of their
life upon the soil and only float upon the water for a few weeks at
the fruiting period. The sexual organs begin to develop in autumn
while the plants are on the soil and plants kept on the soil and sup-

114 BOTANICAL GAZETTE [FEBRUARY

plied with a limited amount of water developed fruit. At the time
when the antheridia begin to develop the gametophyte is under
favorable conditions for vegetative growth, but is not supplied with
an abundance of water. The soil is moist and the conditions are
such as would favor the growth of a terrestrial form like Marchantia.

The plants seem especially adapted to spend the winter submerged
and do not perish under such conditions. The fore part of the
thallus contains very large air cavities and thus the tissue is aerated.
It is well known that certain higher plants which grow in wet situa-
tions have large air spaces in the tissue, and GANONG (12) calls
attention to the fact that those marsh plants which are submerged
for a portion of the year are able to survive on account of their capacity
for air storage. About May 1 the older part of the thallus, which
is narrow and thin, has decayed, and the younger parts, bearing
the sexual organs, is set free and floats. GARBER points out that
when land forms are placed upon the water only a small portion
of the apical end remains above the surface, while the older part
of the thallus extends into the water and decays. This is true of
plants taken from the soil in summer, but in the spring when the
free part of the thallus is thick and contains large air cavities, it
floats readily. The length of the floating period depends of course
upon the conditions of the pond. In some cases the plants may
very soon be carried up around the edge of the pond and deposited
on the mud, but floating forms are usually found until the ponds
are almost dry. In the case of ponds which do not become dry
in summer, both forms would be found. The floating period affords
an excellent means for distribution.

When the plants grow upon the soil and are not protected during
the winter by a covering of snow or water, they are usually killed
by freezing, but in some cases plants which were brown and seemed
to be dead produced new thalli from the growing point. The young
delicate thalli are well adapted to tide over the dry season, because
they can live with a less supply of water than would be needed by
the older plants.

RELATIONSHIP OF THE SPECIES.

The form usually described as Riccia lutescens should be regarded

as a ground form of Ricciocarpus natans. Both in the field and in

1906] LEWIS—DEVELOPMENT OF RICCIA 115

cultures in the laboratory the forms have been observed showing
the transition. There can be no doubt that the plant which I have
described is the true Ricciocarpus natans, and the description of
the ground form as a distinct species came about naturally from
the conditions of its growth. In such ponds as have been observed
here, the water is high in April and May, so that the floating plants
are carried up around the edge and left on the soil. In June or
July the water has entirely disappeared from the pond and the only
plants found are the slender ribbon-shaped ones which have developed
from the floating form. In my first summer’s collecting, when
the ponds were dry by the last of June, I saw not a vestige of the
old Ricciocarpus natans, and felt sure that the plants collected were
Riccia lutescens. It seems possible that the plant was first described
as a distinct species from material collected under similar conditions,
because it is said to occur in dried up ponds and ditches. If in
summer and autumn some water were present, so that some of the
typical Ricciocarpus natans would be found floating, the origin of
the ground form might readily be seen, but in such a case there
might be failure to associate the ground form with Rzccza lutescens.
Only by following the development and observing the transition of
one form into the other under different conditions of growth can
the true relationship be determined. My observations have con-
vinced me that Riccia lutescens is only a ground form of Ricciocar pus
natans and should not be regarded as a distinct species.’

The plant now known as Ricctocarpus natans was formerly
regarded as a Riccia. In the structure of the thallus Ricciocarpus
is more complicated than the species of Riccia. ‘The most important
taxonomic characters, however, have been the arrangement of the
sexual organs and structure of the sporophyte.

Hooker first found fruiting plants in dry specimens sent to him
by Torrey from New York in 1824. BiscHorr found fruiting
plants in the autumn of 1829 near Heidelberg, and describes anthe-
ridial plants, but his figure of the antheridium is not very convincing,

2 Having determined the ground form as Riccia lutescens, specimens were sent to
Professor A. W. EVANS in October 1904. He considered that we were right in refer-

ring the plants to that species, but stated the views of different authorities in regard
to the status of the species.

116 BOTANICAL GAZETTE [FEBRUARY

as it looks more like the mass of tissue which projects up as a ridge
into the median groove, the cells being quite too large for those of
' an antheridium.

Although HooKeEr considered that the plant should remain in
the genus Riccia, CorDA placed it in a new genus, Ricciocarpus,
on the basis of HooKER’s description and figures which were taken
from dried material. Corpba’s figures are copies of HooKER’s.
BiscHorF held that there was no real basis for the change, as the
mature sporophyte does not differ from that of other Riccias, the
separation being based on the mistaken notion that the capsule
walls disappear entirely at maturity, and that the genus Riccia
should not be divided on account of differences in the thallus brought
about by the different conditions under which the plant grows, since
the method of fruiting is the same in all the species.

LEITGEB regarded Ricciocarpus as a distinct genus, on account
of the more complex structure of the thallus and the grouping of
the sexual organs. He thought that the antheridia were collected
into groups similar to those in the Marchantiaceae, but GARBER’S
results and my own show that LEITGEB was not correct, and that
the antheridia actually form only one group. The archegonia are
also arranged in a definite part of the plant in one group.

The question now arises whether this is a more advanced con-
dition of development than is found in species of Riccia. In the
lower species of Riccia, the sexual organs are said to be indiscrimi-
nately scattered over the surface of the thallus, while in Kzccia flusians
a regular alternation of single antheridia and archegonia is described.
CAMPBELL, in discussing the arrangement of sex organs in Riccia,
says that in the two forms which he studied, Riccia hirta and Riccia
glauca, he found as a rule that several of one sort or the other would
be formed in succession. I have observed the same in Riccia crystal-
lina, although the older sporophytes appear scattered in the thallus.
LINDENBERG described the fruit of Riccia crystallina as scattered,
but the antheridia are described and figured as being in a group
along the middle part of the thallus. He described and figured
the fruit in Riccia glauca as being sometimes in rows and sometimes
scattered. Most of the figures show them in more or less perfect
rows along the longitudinal axis.

1906] LEWIS—DEVELOPMENT OF RICCIA ieiy/

In Riccia minima, LINDENBERG (20, p. 429) describes and in
pl. 20 figures the antheridia as arranged in two rows, one on each
side of a median groove. In Riccia bulbosa the antheridia are along
the median groove for its entire length, sometimes in pairs and
sometimes far apart. Riccia Bischoffit has the antheridia in two
or three rows in the thallus.

It seems highly probable that a careful study of a large number
of species of Riccia by modern methods would show that in many
of them there are produced groups of antheridia and archegonia
in distinct parts of the thallus.

Since the characters upon which the genus Ricciocarpus has
been based, with the single exception of the structure of the thallus, .
have been found wanting, it seems to me that there is not sufficient
reason for retaining the genus. The thallus varies in form according
to the supply of water, and when growing on the soil has been called
a species of Riccia. Many plants assume quite different forms
when growing under different conditions, but the different forms
are not regarded as species.

We should then write:

RICCIA NATANS L. Syst. Veget. 956. 1774.—Bischoff, Nova Acta
Acad. Caes. Leop. Carol. 17: 2. 1835.—Lindenberg, Nova Acta
Acad. Caes. Leop. Carol. 18:—1836.—Sullivant, Gray’s Manual
2ed. 1856.

Ricciocarpus natans Corda, Opiz Naturalischentausch. 1829.—Leitgeb, Die
Riccien, Unters. Lebermoose 4:1879.—Lindberg, Revue Bryol. 9:82. 1882.
(Includes Riccia natans L. and Riccia lutescens Schw.)—Schiffner, Engler and
Prantl. 1893.—Campbell, Mosses and Ferns. 1895.—Underwood, Systematic
Botany of North America. Hepaticae. 1895.—Garber, Bot. GAZETTE 3'7:101-
177. pls. Q-10. 1904.

Riccia lutescens Schw. Specimen Fl. Amer. Sept. Crypt. 26. 1821.—Linden-
berg, Nova Acta Acad. Caes. Leop. Carol. 18: pl. 26. 1836.—Sullivant, Mem.
Amer. Acad. II. 4: fl. 4. 1849.—Sullivant, 2d ed. Gray’s Manual 684. 1856.
—Underwood, Systematic Botany of North America, Hepaticae. 1895.

Riccia velutina Hooker (in part) Ic. Pl. pl. 149: founded on sterlile thalli of
Riccia lutescens and fertile thalli of Riccia crystallina, according to Sullivant,
Gray’s Manual, 1856.

EMBRYOLOGY.

Material for study was collected during the autumn and spring,
and fixed very satisfactorily in 1 per cent. chromacetic acid or in
chromosmacetic.

118 BOTANICAL GAZETTE [FEBRUARY

The large air cavities prevent the penetration of the fixing fluid,
to overcome which the pieces were submerged by means of cotton
plugs. After dehydration the material was passed through chloroform
into paraffin. Sections were stained with the triple stain of Flem-
ming or with Heidenhain’s iron-alum haematoxylin.

SEXUAL ORGANS.

Young antheridia were found in October. ‘They begin to develop
while the plants are young and growing on soil not supplied with a
large quantity of water, although the conditions for vegetative growth
are good. At this time the thallus is ribbon-shaped, with a thick-
ened apical end and a longitudinal median groove, the thallus in
cross-section having about the shape of an inverted Y with a ridge
of tissue between the arms (fig. 9). Very few plants are found
which do not produce antheridia. The archegonia develop later
in the same thallus. At first there seemed to be in this a distinction
between Riccia lutescens and Ricciocar pus natans, because Ricciocar-
pus natans has been described by SCHIFFNER, LEITGEB, and CAmp-
BELL as being strictly dioecious, but the work of GARBER shows
conclusively that it is monoecious. The earlier observers state that
Ricciocarpus fruits in autumn, so it seems probable that their material
was collected after the older portion of the plant had decayed, leaving
only the portion bearing sporophytes.

The antheridia are produced in acropetal succession in three to
five rows (jigs. I0, IT).

The antheridium develops as has been described for other species
of Riccia. A superficial cell on the floor of the dorsal furrow just
back of an apical cell protrudes above the surface and is cut off by
a horizontal wall. The cuter cell increases in size, and is divided
by three or four cross walls, then a longitudinal wall is formed divid-
ing the young antheridium into two equal parts: this is followed
by a second longitudinal wall perpendicular to the first. ‘Then
periclinal walls are formed which cut off the single layer of cells
which form the wall of the antheridium. The cells in the center
now undergo repeated divisions until a very large number of cells
is formed. Each of these cells is almost cubical in form and in
Riccia has been described as producing a single spermatozoid,

1906] LEWIS—DEVELOPMENT OF RICCIA 11g

Kyny (19). The mature antheridium is a short stalked oval body
with a conical apex.

As the antheridium develops, the vegetative tissue grows up and
surrounds it so that it is enclosed in a cavity which opens into the
dorsal furrow. This cavity is formed in the same way as the air
spaces of the thallus. The apex of the antheridium is a little below
the floor of the dorsal furrow and the sperms escape through the
neck formed by the surrounding tissue. Although the antheridia
begin to develop in autumn, they are not mature until the following
spring, because the growth is checked by the cold. Plants kept in
a warm place produced mature antheridia during the winter.

A series of archegonia is developed which is a continuation of
the series of antheridia (fig. 7). The archegonium is at first super-
ficial on the floor of the dorsal furrow. Later it becomes enclosed
in a cavity by the upward growth of the vegetative tissue as in the
case of the antheridium except that the neck of the mature arche-
gonium protrudes above the bottom of the furrow. The origin of
the archegonia side by side at the bottom of the dorsal groove is
shown in figure 9. In this way three to five rows are formed and
later a large number of sporophytes are found in each thallus.

The archegonium develops in general as has been described by
JANCZEWSKI (17). My observations confirm the account given by
GARBER for Ricciocarpus natans, as a comparison of the figures
will show, so it is unnecessary to describe the development here.

About the time when the archegonia are mature, cross-sections
of the thallus show numerous, delicate, almost hyaline, club-shaped
hairs extending up from the floor of the median groove. Each
hair consists of a stalk of two or three short, narrow cells with a
much larger cell at the free end. ‘These hairs bear a striking resem-
blance to paraphyses(fig. 78). LEITGEB (22, p.31) describes “‘papillae’’
which grow up from the bottom of the groove and regards it as
highly probable that it was the dried remnants of these which LINDEN-
BERG observed when he wrote: ‘“‘Sporangium vor aussen mit kleinen
unregelmdssigen braunen Schuppen bedeckt ist, die Fragmente
elner zersprengten friitheren Hiille zu sein scheinen.”’ As the hairs
become older they become brown and break down so that they

120 BOTANICAL GAZETTE [FEBRUARY

would give much the appearance described by LINDENBERG. We
know now that the sporophyte has no Hille or sheath.

SPOROPHYTE.

The development of the sporophyte agrees with the account given
by CAMPBELL (3) for Riccia and by GARBER for Ricciocarpus natans.

The first division is usually transverse but may be oblique (jig. 21).
The next wall may be perpendicular to the first so as to form a quad-
rant (jig. 22), or parallel to it, producing a row of cells. Divisions
take place in all directions after this until an almost spherical mass
containing several cells is formed. Then the amphithecium becomes
distinct as a single layer of cells enclosing the spore producing cells.
The growth takes place rapidly but the divisions of the cells are not
simultaneous, usually only a few dividing cells being found in a
sporophyte.

The sporophyte continues its growth until a solid mass of three
to four hundred cells is produced. Then the calyptra and amphi-
thecium expand and the spore mother-cells becoming free separate
from, one another and become rounded. From the surrounding
cells, which are richly stored with food, there is secreted a large
amount of nutritive material which fills the space around the mother-
cells, giving them favorable conditions for growth (jigs. 25, 26).
The spore mother-cells increase rapidly in size and again fill the
cavity. That part of the nutritive material not absorbed by the
spore mother-cells is pressed into thin plates between them. This
material takes a deep blue stain with gentian violet. A fuller dis-
cussion of the spore mother-cells and of their division to produce
the spores will be given in another place.

Before the spores are mature the inner layer of the calyptra
collapses. ‘The amphithecium is distinguishable until the spores
are almost mature. The outer layer persists but the cells are usually
shrunken. ‘The contents of these cells is no doubt used up to supply
the growing spores with nourishment. All of the spore mother-
cells produce spores, there being no sterile tissue in the form of elaters.
In discussing the simple form of sporophyte of Riccia, GARBER
considers that the absence of sterile tissue is to be associated with
the habit of the plants; since there is not much chance for the attach-
ment of an. independent sporophyte, there is no sterile tissue in

1906] LEWIS—DEVELOPMENT OF RICCIA 121

the form of a foot. When we consider the fact that some other
Hepaticae which have the foot well developed grow on very wet
soil and require as much moisture for their development as do some
of the species of Riccia, this theory does not seem entirely convincing.
The sporophyte develops during May and June. A given sporo-
phyte requires about three weeks for its development. ‘

SPOROGENESIS.

Usually the most favorable cells for the study of cytological details
are the spore mother-cells. Their large size, abundant contents
and active growth at the time when divisions are taking place, permit
good results in fixation. Riccia crystallina has furnished the most
satisfactory material.

In July, 1903, an abundance of fruiting Rzccza crystallina was
found growing on the mud on the bottom of a dried up pond not
far from the ponds where the form known as Riccia lutescens was
growing. This species had never been collected in this region
before. Having so determined the plant, I referred specimens to
Prof. A. W. Evans who confirmed my determination. He says:
‘“Apparently this species represents an addition to the hepatic flora
of New York. I find no mention of it in local lists of New York
plants and there are no specimens of it from your state in my
herbarium.”

These plants had been growing under favorable conditions, as
the pond had not contained much water at any time during the
spring. The thalli formed rosettes growing so close together as almost
to cover the ground. ‘The number of fruiting plants was very
striking, as it seemed impossible to find a single sterile plant. All
stages in the development of the sporogonium and spores were
easily obtained, and some stages in the development of the sexual
organs, but changes were taking place very rapidly and the younger
stages were of comparatively rare occurrence. The development
of the sexual organs and fruit agrees with that of other species of
Riccia. Each thallus produces several sporophytes which are easily
recognized when mature as small black spherical bodies imbedded
in the tissue.

These plants continued to develop and produce sporophytes for
only a short time after they were discovered. The month of July

122 BOTANICAL GAZETTE [FEBRUARY

was the most favorable time for the collection of material showing
karyokinesis in the spore mother-cells. During August, the spores
became mature and the thalli broke down. No good specimens
could be collected after August 25. This differs from what has
been observed for some other species of Riccia, which are described
as withstanding long periods of drought, the thalli continuing their
growth again when supplied with moisture. (CAMPBELL, 3.)

During the following winter this pond became filled with water
and did not become dry until late in the summer, so that only a few
plants were found as compared with the large number of the pre-
ceding year. ‘This made a difference in the time of fruiting. In
September the sporophytes were in about the same stage of develop-
ment as in July of the preceding year. This may explain why
different authors give different seasons for the fruiting of Riccia.
It seems that conditions of temperature and water supply exert such
an influence that in the same species and locality the time may vary
considerably from year to year. In general, I think it may be said
that good conditions for vegetative growth will hasten rather than
retard the fruiting of Riccia.

The thallus of Riccia crystallina is small and thin; its surface
presents a series of wide depressions separated by thin lamellae;
and there are no ventral scales. ‘The fixing fluid easily penetrates
and the spore mother-cells are usually well fixed.

The development of the spore mother-cells agrees with the account
given for Riccia natans, but there is not such a large number produced
in a sporogonium. When the spore mother-cells ccme to lie locsely
in the sporogonium, they are surrounded by nutritive material.
The mature spore mother-cells are then generally spherical, but
they may be elliptical or so angular by crowding as to lock like a
tissue. The contents of the spore mother-cells of Riccia has been
described as granular by CAMPBELL (3) but the structure cf the
cytoplasm in Kzccza crystallina is a fine reticulum with the granules
occurring usually at points of intersection of the fine threads of the
network. ‘The older spore mother-cells as well as the mature spores
contain considerable oil.

In the nucleus of the spore mother-cell the chromatin is scanty
and is irregularly scattered on a fine linin network. No nucleolus

as

1906] LEWIS—DEVELOPMENT OF RICCIA 123

has ever been observed (fig. 34). When the nucleus is preparing
for division, the chromatin leaves the linin network and collects into
several bodies which soon move together to form one irregular mass.
I regard this as the synapsis stage. Such bodies of chromatin have
been found often and in cells which seemed to be well fixed so it
seems to represent a stage in the preparation for division and not
to be a result of shrinkage as has been suggested by certain authors
for other plant cells in which the same condition has been observed.
The body of chromatin occupies a position at one side of the nucleus,
and the rather large nuclear cavity appears hyaline. There can
be little doubt that the body described by CAMPBELL (3) as a nucleolus
is really the entire mass of chromatin in the synapsis stage.

From this mass of chromatin a short thread develops which later
segments to produce the chromosomes (fig. 35). The small amount
of chromatin present here makes the details very difficult to deter-
mine. The four chromosomes, easily counted here as well as in
the nuclear plate and on the way to the poles, are very small and
appear almost spherical when on the spindle although they are
short, thick, curved rods.

The development of the spindle is not easily observed. Divisions
take place almost simultaneously in all the cells of a sporogonium
and the changes are very rapid. By far the commonest stage of
division is that in which the chromosomes are in the nuclear plate
(jig. 38). Neither centrosomes nor centrospheres occur in the spore
mother-cells of either Riccia crystallina or Riccia natans. Around
the nucleus preceding the formation of the spindle, there is an accu-
mulation of material, apparently composed of fine fibres. ‘The
nucleus elongates, becoming somewhat elliptical but not sharp
pointed. The fibres about the nucleus do not give the appearance
of centrospheres but are like the weft of kinoplasmic fibres described
for certain pollen mother-cells (figs. 36, 37). It has been impossible
to find any nucleus which showed anything resembling a multipolar
spindle. The poles of the spindle are probably determined by the
elongation of the nucleus at an early stage in the spindle formation
The spindle is composed of very fine fibres, some of which extend
from pole to pole, while others extend from the poles into the
cytoplasm, reaching almost to the nuclear plate (fig. 38). The

124 3 BOTANICAL GAZETTE : [FEBRUARY

mature spindle has very broad poles and its formation does not
seem to have been controlled by a centrosome or a centrosphere,
as a comparison of the spindles of the spore mother-cells with those
of the cells of the antheridium makes clear.

The minute chromosomes separate, four going to each pole, after
which a cell plate is formed in the usual way (figs. 40, 41). The
daughter nuclei do not come to a true resting stage. The chromatin
is scattered in almost spherical bodies in the hyaline cavity of the
nucleus, which do not represent the individual chromosomes, as
their number and size vary considerably (jig. 42).

The second division takes place in much the same manner as
the first. The spindles are arranged with their long axes parallel
to the first cell plate, so that the cell plates formed in these spindles
are almost perpendicular to that formed in the first division (figs.
43-47). The latter does not disappear during the second division
but remains and the walls separating the spores are laid down here
(fig. 47). The walls separating the cells of the young tetrad are
thin and delicate, but in the mature spore the outer layer of the
wall becomes thickened and folded. ‘The mature spore is almost
black, and its contents are largely oil. When carried through chloro-
form into paraffin and sectioned, the spores seem to have only scanty
granular contents, due to the fact that the oil has been removed in
the process. The nucleus is very small.

During the winter and spring following their development, unsuc-
cessful attempts were made to germinate the spores. It may be
that they had been allowed to remain dry too long before they were
moistened, for in nature they would not be dry very long even in
tiding over a dry season. :

The spore mother-cells of Riccia natans do not furnish such ,
satisfactory material for study as do those of Riccia crystallina,
because the large air cavities of the thallus prevent the penetration
of the fixing fluid and so the spore mother-cells often shrunk. A
sufficient number of good preparations was secured, however, to
show that the process of division does not differ from that of Rzccza
crystallina.

1906] LEWIS—DEVELOPMENT OF RICCIA 125

SPERMATOGENESIS.

The development of the spermatozoids has been treated by a
number of investigators, among them, CAMPBELL (4), LECLERC DU
SABLON (23), GUIGNARD (14), SCHOTTLANDER (27), and STRAS-
BURGER (29). It will be observed that mest of these papers were
published before methods of preparing material for study were so
well developed as at present. The work of BELAJEFF (1) confirmed
by that of STRASBURGER (29) shows that the spermatozoid in the
Hepaticae consists not only of the metamorphosed nucleus but also
of the cytoplasm.

IKENO (16) not only confirms the view that the spermatozoid
consists of cytoplasm as well as nucleus but also discusses the develop-
ment of the cilia and the homology of the blepharoplast and centro-
some of Marchantia polymorpha.

He finds that the body which becomes a blepharoplast in the
developing spermatozoid appears in the earlier nuclear divisions of
the antheridium and functions as a centrosome. It is, however, not
permanent, but appears at the time of nuclear division and disappears
during the process, so that it is not found in the daughter cells until
about the time for the formation of the spindles of their division.
After the last division which gives rise to the cells that develop into
the spermatozoids, the body does not disappear but remains and
becomes a blepharcplast. IKENO argues from this that the centro-
some and blepharcplast are homologous. He has good grounds for
such an argument in the case of Marchantia polymorpha, because
centroscmes have been reported also in the vegetative cells of that
plant, by MorrTrer (24) and by Van Hook (32). In other plants
which have the blepharoplast, centrosomes are not found, and the
bedy appears in cnly one or two divisions before the formation of
the cells which prcduce the spermatozoids.

MorrTierR (26) in discussing IKENo’s paper raises the question
whether the bedies which IkENo has figured as centrosomes are in some
cases more than ordinary granules such as appear in the cytoplasm
of other cells in which centrcsomes are known to be absent. IKENO
has pointed cut, however, that the cytcplasm cf these cells is very
finely granular, there being no other bodies in the cell which bear
any resemblance to the ones figured as centrcscmes. He also calls

126 BOTANICAL GAZETTE [FEBRUARY

attention to the fact that centrospheres have been described in dividing —
spore mother-cells of Pellia epiphylla, by FARMER (6, 7, 8, 10) and -

by Davis (5). The occurrence of centrospheres here has been
questioned, however, by GREGOIRE (13). In a recent paper, FAR-
MER (Q) reports centrospheres and occasional centrosomes in the
spore mother-cells of Aneura pinguts.

In order to get good results in Riccia natans it is necessary to
fix the material when growing rapidly. About equally good results
were secured with chromacetic acid and with Flemming’s weaker
solution. ‘The sections were stained with anilin safranin and gentian
violet. It was found best to stain deeply in gentian violet and then
to wash out carefully. In this way all details can be brought out
clearly, although IkENo did not find it good for Marchantia.

The development of the antheridium has been described. When
almost mature it consists of a large central mass of cubical cells
surrounded by a wall one cell in thickness (fig. 33). In preparations
from plants in which some antheridia are mature, one finds several
stages in the development. ‘The nuclear divisions do not take place
simultaneously throughout an antheridium but usually all the cells

of one of the segments marked out by the first walls dividing the ~

antheridium, show the nuclei in the same stage of karyokinesis.
In the most favorable preparations, therefore, one may find severa.
stages of division in the same antheridium.

The cells of the young antheridium are almost cubical, with finely
granular cytoplasm. The nucleus is rarely exactly spherical and
has a rather thick membrane. The chromatin is in an irregular
central mass, made up of a number of pieces. A nucleolus cannot
be distinguished. ‘The cavity surrounding the chromatin is large
and hyaline (jigs. 53, 54). In some cases a large number of small
bodies of chromatin were found scattered irregularly in the nuclear
cavity. The number of chromosomes is four. It seems that the
nuclei in the young rapidly growing antheridium rarely come to a
typical resting stage.

The question of the presence or absence of centrosomes in the
cells of the young antheridium was taken up carefully, because
previous observations on the karyokinetic figures in the sporophyte

cells and spore mother-cells have convinced me that no such bedAT.

1906] LEWIS—DEVELOPMENT OF RICCIA 127

appears there. On the other hand centrosome-like bodies appear
in the cells of the older antheridia at the time of nuclear division.
There can be no doubt that these are distinct bodies, and they cannot
possibly be interpreted as accidental granules in that position. In
some of my preparations hundreds of cells showing them are found
on a single slide, and they are so distinct that the preparation could
easily be used for class demonstration. ‘These bodies appear in
the cells of the antheridium in early stages of its development. I
have been unable to determine whether they appear in the earliest
cell divisions but they appear in the antheridia which consist of only
a few cells. They are not permanent, but disappear and arise anew
with each division.

IKENO regarded it as highly probable (though unable to state this
positively) that in Marchantia these bodies were of nuclear origin.
He figures a small spherical body inside the nuclear membrane,
which in a later stage is found outside the membrane. This body
then divides into two, which arrange themselves on opposite sides of
the nucleus. If the bodies. have their origin as one, which later
divides as described, they act as do the centrosomes which have
been described for other plants.

In Riccia natans, nothing has been observed to indicate that the
body is of nuclear origin, except that it stains in much the same
way as the mass of chromatin in the nucleus. In some of my pre-
parations a single body has been observed near the nuclear membrane
(fig. 53). These bodies have never seemed so distinct as the ones
which appear at the cpp<site ends of the nucleus and in the poles
cf the spindle. There is a dark central part, surrcunded by a mass
cf cytcplasm which is more or less irregular but does not give the
appearance cf distinct radiations such as are described in the centro-
spheres cf certain plants.

When these single bodies were discovered, a careful search was
made cf the same preparations and of others in which the two bodies
were on the cppcsite sides cf the nucleus, in order to discover if
pessible the intermediate stages which it would seem should appear
in such preparations. In cases in which two bodies have been
observed, they have always been on opposite sides of the nucleus,
cr so nearly cppcsite that the spindle devel-ping between them

128 BOTANICAL GAZETTE [FEBRUARY

might take the curved form shown in fig. 60. The origin of the
two bodies is of importance in determining the homology of the
centrosome and blepharoplast and will be discussed later.

Starting with the stage in which the centrosome-like bodies are
on opposite sides of the nucleus, the nuclear division takes place
in the following manner. At first the bodies are at a little distance
from the nuclear membrane, then the nucleus elongates so that the
membrane closely approaches the bodies, becoming somewhat
pointed. At the same time one observes that there is a collection
of kinoplasm at the poles of the nucleus and extending along the
nuclear membrane for some distance. At this time the bodies at
the poles do not show radiations in any direction, but are very distinct
(jig. 54). The spindle is formed from the kinoplasm which has been
described, and when formed consists of a few thick fibres which
converge at the poles, so that the centrosome-like bodies occupy the
position of true centrosomes. About the time when the spindle
develops, the chromosomes are formed from the central mass of the
nucleus and become arranged in the nuclear plate. They are closely
crowded together in this stage, and not so easily counted as when
they have moved to the poles. The photograph (jigs. 75, 76) shows
the dense mass formed by the chromosomes when arranged in the
nuclear plate. It was impossible to determine how the division takes
place in the chromosomes as they move to the poles. The changes
take place so rapidly that stages are rarely found in which the chromo-
somes are on their way to the poles.

The centrosome-like bodies disappear during the division, but
it is difficult to say at just what point. Fig. 56, a cell taken from
an antheridium in which only one or two more divisions will take
place, shows the centrosome-like bodies quite distinctly when the
chromosomes are almost at the poles, but by the time the chromosomes
are at the poles and before the daughter nuclei are formed, the bodies
disappear (jig. 57).

These bodies are best seen in preparations which have been over-
stained and washed out. In some cases my preparations were
stained deeply enough to show the spindle and chromosomes well,
but only an cccasional spindle showed the bodies at the poles. When
these slides were over-stained and carefully washed out, the bodies
were brought out very distinctly in all cases.

1906] LEWIS—DEVELOPMENT OF RICCIA 129

After a large number of divisions has taken place the antheridium
consists of nearly cubical cells, each of which has been considered
by earlier investigators to produce a single spermatozoid. STRAS-
BURGER (30, p. 482) says of Marchantia polymorpha: “ Die Spezial-
mutterzellen der Spermatozoiden sind durch fortgesetzte, sich
rechtwinklig schneidende Teilungsschnitte angelegt worden.” CAmp-
BELL (4) describes and figures the spermatozoid mother-cell of Pellia
as producing two spermatozoids. IKkENO (16) discovered that in
Marchantia each of the cubical cells undergoes another division in
which the spindles are arranged diagonally, in the earlier divisions
the long axis of the spindle being parallel to the long axis of the cell.
In this last diagonal division no cell wall is formed between the
daughter cells, each of which develops into a spermatozoid. ‘Thus
each of the cubical cells produces two spermatozoids instead of one.
IKENO cites several cases in which two spermatozoids are produced
from a single mother-cell and thinks that this is probably general
in the liverworts and mosses.

JoHNsON (18) has described a diagonal division of the cubical
cells of Monoclea, but he figures a wall separating the two parts of
the cell and regards each three-cornered cell as the mother-cell of
a spermatozoid. He dces not give the details of nuclear division
in the earlier stages of the antheridium nor in the formation of the
spermatozoid mother-cells.

In the last division of the cells in the antheridium of Riccia natans
the spindles are arranged diagonally asin Marchantia. This arrange-
ment of the spindles is quite striking. ‘They are larger than in the
earlier divisions and the bodies at the poles are very distinct. In
some cases the spindles are curved (figs. 58-60).

No wall is formed between the daughter cells, each of which
develops into a spermatozoid. The centrosome-like bodies do not
disappear after this division (fig. 61). "They remain in the cells, at
first near the nuclei. The daughter cells are contracted, occupying
the central part cf the cell cavity (figs. 62, 63). Soon the centrosome-
like body moves away from the nucleus toward the end of the cell.
Those in the two spermatids may be at the same end or at opposite
ends (jigs. 63-67). When the spermatid has become somewhat
rounded, the centrosome-like body has taken its position in contact

130 ‘ BOTANICAL GAZETTE [FEBRUARY

with the cell membrane (fig. 68). When the cilia appear they are
inserted in this very small body so that it comes to function as a
blepharoplast. Its small size as compared with that of the cilia of
the mature sperm makes it seem probable that some of the material
for the growth of the cilia must be drawn from another source than
the blepharoplast itself, although it disappears to such an extent
that in the mature sperm it cannot be recognized as the point of
insertion of the cilia.

The developing spermatozoids of Riccia natans do not remain
enclosed in the mother-cells until they are mature, but at about
the stage represented by jigs. 70, 71 the walls break down and the
young spermatozoids lie free in the cavity of the antheridium. Here
they seem to undergo considerable growth. The material for this
growth is probably derived from the surrounding cells as they become
collapsed in old antheridia.

The nucleus of the developing spermatozoid takes a position at
one side of the cell and becomes homogeneous. It seems probable
that other material than the chromatin of the spermatid nucleus
must enter into this part of the spermatozoid, because it is very
evident that the body contains more material than would be obtained
from the chromatin alone. Soon the nucleus elongates, following
the outline of the cell and becoming crescent-shaped (jigs. 71-73).
In some cases, a distinct vacuole occurs in the cytoplasm although
this is not always the case (figs. 71, 72). The mature spermatozoid
becomes long and slender and consists of the nucleus, the material
of which seems to have increased in amount, a small amount of
cytcplasm, and the cilia which are derived from the blepharoplast
and in all probability from a part of the cytoplasm surrounding it.
IkENO describes a spherical body which appears in the spermatids
of Marchantia before the cilia begin to develop and disappears about
the time that changes take place in the nucleus. It has been impos-
sible to find such a body in Riccia, although it would seem, judging
from IKENO’s figures, that it could easily be seen if present.

The question of the homology of the blepharoplast and centro-
some is one which it seems to me has not yet been settled. In Mar-
chantia, where centrosomes have been reported in the vegetative
cells as well as in the antheridium, the evidence seems good that the

1906] LEWIS—DEVELOPMENT OF RICCIA ie a

centrosome and the blepharoplast are homologous, and this is the
conclusion of IxENo. In all other plants in which blepharoplasts
are known to occur, centrosome-like bodies are not present in any
cell divisions except those immediately preceding the formation of
the sperms. That centrosomes occur in liverworts in cells outside
the antheridium is open to question. The conflicting reports of
those who have investigated Pellia epiphylla make it clear that no
distinct body occurs there which can be regarded as a centrosome,
although aggregations of kinoplasm, called centrospheres by most
authors, do occur.

In Riccia natans, it seems very evident that centrosomes do not
occur in the divisions of the spore mother-cells. The spindle poles
are bread, and there is not even a suggestion of a centrosphere such
as has been described for Pellia. In the cells of the sporophyte
GARBER reports centrospheres but no centrosomes. I have never
been able to observe them in my preparations. When the spindle
is fully formed there are no fibres radiating into the surrounding
cytoplasm (jigs. 45-52).

Although the thallus of Riccia naians does not present favorable
material for cytological study, a number of cells showing nuclear
division in the gametophyte have been observed near the growing
point. The greatest difficulty here is the presence of numerous
deeply staining granules in the cell. In some cases granules resem-
bling centrosomes appear at the poles of the spindle, but they do
not differ in appearance from the other granules of the cell, and it
seems probable that their occurrence here is accidental.

Summing up, we find that in Riccia natans centrosomes are not
found in the cells of the gametophyte, sporophyte, or spore mother-
cells, but that bodies occur in the dividing cells of the antheridium
which seem to function as centrosomes. In Riccia and Marchantia,
the blepharoplasts certainly have much more the appearance of
centrosomes than in any other plants in which blepharoplasts have
been described. ‘The bodies have every appearance of centrosomes
when at the poles of the elongated nucleus or at the poles of the
spindle. Perhaps the strongest objection to regarding these bodies
as centrosomes lies in the fact that in Riccia natans they occur only
in the cells of the antheridium, while the blepharoplasts reported

122 BOTANICAL GAZETTE [FEBRUARY

in other plants appear only in the last two generations of cells con-
cerned in the formation of spermatozoids.

Those who argue in favor of the homology of the centrosome
and blepharoplast certainly find their best evidence so far in the
liverworts, but it seems to.me that this evidence is not conclusive
when the bodies occur only in cells of the antheridium.

In those plants in which centrosomes are known to occur, a single
body divides to produce two, which arrange themselves on opposite
sides of the nucleus (MOTTIER, 25). IKENO has reported a similar
condition in Marchantia. In Riccia natans, however, the evidence
seems to favor the view that the two bodies arise anew with each
division, appearing on opposite sides of the nucleus at the same
time. In this respect they behave more like blepharoplasts.

MottiER (26) in discussing this question has called attention
to the fact that it is questionable whether we can speak of organs
as homologous which, as such, are without genetic continuity. The
question as to whether true centrosomes have genetic continuity
has not yet been decided, but it is probable that they do not in all
cases.

SUMMARY.

1. Kiccia lutescens and Ricciocarpus natans are forms of the same
plant, the former occurring on the ground in summer and autumn
when the ponds are dry, and the latter as a floating form. Either
form can be changed into the other by altering the supply of water.
Therefore, Riccia lutescens should not be regarded as a distinct
species.

2. The genus Ricciocarpus has been based largely on characters
which do not exist. In my opinion, the only real basis for separating
it from Riccia is the more complex structure of the thallus. BISCHOFF
did not regard this as a good character for the separation of the genus.

3. The plant is monoecious, antheridia and archegonia being

produced in definite groups in the same thallus. The sexual organs |

appear in autumn when the thalli are growing on the ground and
complete their development the following April. Abundance of
water is not essential to sexual reproduction, as the plants fruit when
kept growing on the soil and supplied with a limited amount of

1906] LEWIS—DEVELOPMENT OF RICCIA 133

water; therefore the ground form is not sterile, as was the opinion
of LINDBERG and GARBER.

4. Plants which have been growing attached to the soil and have
been submerged by the filling up of the ponds do not necessarily
perish, but are adapted to spend the winter under water and then
to break loose by the decay of the older part of the thallus and float
upon the water in the spring.

5. The plants are propagated vegetatively by the separation of
branches of the thallus, by the decay of the older part, and also by
the growth of new plants from cells in the apical region.

6. The sexual organs and fruit of the two species studied agree
in their development with the accounts given for the other species
of Riccia. There is no rudimentary integument surrounding the
archegonium or sporophyte of Riccia natans. ‘The sporogonium
of Riccia natans is larger than that of Riccza crystallina and produces
a larger number of spores. The only sterile tissue in either is the
amphithecium, a single layer of tabular cells surrounding the mass
of spore mother-cells. |

7. Centrosomes are not present in cells outside the antheridium
nor would I interpret any structure observed in the cells of the sporo-
phyte or the spore mother-cells as a centrosphere.

8. Bodies which resemble centrosomes, and which are con-
sidered to be true centrosomes by certain authors, occur in the cells
of the antheridium. These bodies do not have genetic continuity,
but arise de novo with each division. ‘They do not disappear after
the last division cf antheridial cells but remain in une spermatids
and later become blepharoplasts.

9. In the earlier divisions of cells in the antheridium, the spindle |
is arranged parallel to the long axis of the cell, but in the last division,
the spindle is placed diagonally in the cell. No wall is formed
between the two cells produced by this division, each of which becomes
a spermatozoid. Thus two sperms are produced from each cuboidal
cell.

10. In the developing sperm, the Been arople takes a position
on the membrane of the cell and the two cilia grow from it, the nucleus
becomes almost homogeneous in structure and crescent-shaped,
almost enclosing the cytoplasm. The mature sperm consists of the

134 BOTANICAL GAZETTE [FEBRUARY

nucleus, the cytoplasm, and cilia which have received material for
their growth from the blepharoplast and probably also from the
material surrounding it. 7

11. The amount of chromatin in the nucleus is small. There
is no nucleolus present unless the masses of chromatin which are
found in nuclei which are undergoing repeated division be inter-
preted as nucleoli.

12. The number of chromosomes is four for the gametophyte
and eight for the sporophyte.

13. The cytoplasm of the spore mother-cells appears to be a
fine reticulum, in which are numerous granules usually located at
the point of intersection of the fibres of the reticulum.

14. The mature spore contains a large quantity of oil together
with a small amount of granular matter. The nucleus of the spore
is very small.

In conclusion I wish to thank Professor Gro. F. ATKINSON and
Dr. E. J. Duranp for valuable advice and assistance during the
progress of this study.

LITERATURE CITED.

1. BrLAjJEFF, Ueber Bau und Entwickelung der Antherozoiden. Heft I,
Characeen. 1892 (Russian). German translation, Flora '79:1-48. 1894.

2. BiscHorr, Bemerkungen iiber die Lebermoose vorzuglich aus den Gruppen
der Marchantieen und Riccieen. Nova Acta Acad. Caes. Leop. Carol.
Nat. Am. 17:part 0. 1835.

3- CAMPBELL, D. H., The structure and development of mosses and ferns.
jigs. 1-7. New York. 1895.

, Zur Entwickelungsgeschichte der Spermatozoiden. Ber. Deutsch.
Bot. Gesells. 5:120-127. pl. 6. 1887.

5. Davis, B. M., Nuclear studies in Pellia. Annals of Botany 9:147-180.
pls. To-II. 1805.

6. Farmer, J. B., On spore formation and nuclear division in the Hepaticae.
Annals of Botany 9: 469-523. pls. 16-18. 1895.

7. , The quadripolar spindle in the spore mother-cell of Pellia epiphylla.
Annals of Botany 15: 431-433. Igol.

8. ———,, On the interpretation of the quadripolar spindle in the Hepaticae.
Bot. GAZETTE 3'7:63-65. 1903.

9. ——— and Moorg, J. E. S., On the maiotic phase (reduction divisions) in

animals and plants. Quart. Jour. Mic. Sci. 48:489-557. pls. 34-41.
1905. -

1906] LEWIS—DEVELOPMENT OF RICCIA 135

Io.

If.

I2.

13.

14.

z5.

16.

17.

18.

IQ.

20.

21.
PP AC

23.

24.

25.

26.

D7.

28.

29.

30.
3i-

and REEvEs, J., On the occurrence of centrospheres in Pella
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LINDENBERG, Monograph. Nova Acta Acad. Caes. Leop. Carol. Nat.
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EXPLANATION OF PLATES V-IX.

All drawings, except fig. 7, were made with camera lucida. Figs. 8—52, with
Bausch & Lomb oculars and ee: as follows: Figs. 8, 10, II, I in. hie
2 objective; 9 and 25 2 in. oc., $o0r; ; IQ, 21-24, 26, 32, 33; 2 Muoc., 7. .enie
12-18, 20, 27-31, 34-52, I im. oc., yy obj:; Figs: 53-73 with Zeiss. oc. 7 ou
apochromatic objective, 1.40 aperture.

The figures of plate VI were reduced slightly more than one- ee | in repro-
duction.

All figures are of Riccia natans except the spore mother-cells (figs. 34-47)
which are of Riccia crystallina.

PLATE V.

Fic. 1. Rosette of plants growing on the soil; a, natural size; 0, enlarged.

Fic. 2. Land plants growing in regular clusters.

Fic. 3. Two plants growing on soil, one of which has been injured and has
grown out in an irregular way from the growing point.

Fic. 4. New plants growing from apical cells of old thalli.

Fic. 5. a, Decay of older part of thallus of the land form to give the floating
form; 0, plants collected in May. If these thalli should become stranded on the
mud and growth should continue rosettes would be formed.

Fic. 6. Plants decolorized in alcohol. The sporophytes appear as chains of
dark bodies in the thallus.

PLATE VI.

Fic. 7. Longitudinal section of thallus parallel to the dorsal furrow, showing
arrangement of sexual organs.

Fic. 8. Cross-section of thallus showing archegonia.

Fic. 9. Cross-section of thallus, showing the origin of archegonia in rows on —
floor of dorsal groove.

Fic. to. Cross-section of thallus, antheridia.

Fic. 11. Longitudinal section of thallus parallel to surface, showing the
arrangement of antheridia. Archegonia have not begun to develop.

Fics. 12-18. Stages in development of archegonium.

Fic. 19. Archegonium in which egg-cell has not been fertilized and is
shrunken.

Fic. 20. Cross-section of neck of archegonium.

Fic. 21-25. Stages in development of sporophyte.

Fic. 26. Spore mother-cells.

Fics. 27-33. Development of antheridium. Figs. 27-31, from material
collected in October.

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PLATE VI.

Fic. 34. Spore mother-cell in resting state. Chromatin on a fine linin net-

Fic. 35. The chromatin is in the form of an irregular thread.

Fic. 36. Chromosomes formed; weft of delicate fibres about the nucleus.

Fic. 37. Nucleus elongated and showing a weft of fibres.

Fic. 38. Spindle with chromosomes in plate. No centrosome.

Fic. 39. Chromosomes moving to poles of spindle.

Fic. 40. Chromosomes at the poles, thickening of spindle fibres to form cell
plate.

Fic. 41. Daughter nuclei.

Fic. 42. Cell plate. Daughter nuclei contain numerous spherical bodies of
chromatin which stain bright red with safranin.

Fic. 43. Daughter nuclei preparing for division.

Fic. 44. Daughter nucleus with chromosomes in plate. Neither centro.
sphere nor centrosome.

PLATE VIII.

Fic. 45. Chromosomes moving to poles.

Fic. 46. Daughter nuclei with chromosomes at the poles to form nuclei of
spores. The cell plate formed in the first division persists.

Fic. 47. Second division completed.

Fics. 48-52. Stages in the division of a sporophyte cell. No centrosome.
Fig. 48 shows slight radiation of cytoplasm from the poles of the elongated nucleus.

Fic. 53. Cells of antheridium which show a single rather irregular body near
the nucleus.

Fic. 54. Cells of antheridium which shows the distinct centrosome-like
bodies at the poles of the elongated nuclei. Compare fig. 74.

Fic. 55. Spindle with centrosome-like bodies at the poles.

Fic. 56. Centrosome-like bodies present when the chromosomes are almost
at the poles.

Fic. 57. Cell from young antheridium. Chromosomes at poles. No
centrosome can be distinguished.

Fic. 58. One cell preparing for last division, while the adjoining cel] has the
spindle formed and arranged diagonally.

Fic. 59. Diagonal arrangement of spindles in last division of cells in the
antheridium.

Fic. 60. Curved spindles.

Fic. 61. Daughter nuclei formed after diagonal division; centrosome-like
bodies present.

Fic. 62. Cells of antheridium after last division.

Fics. 63-67. Spermatids in mother-cells.

Fics. 68-73. Stages in the development of the spermatozoids.

138 BOTANICAL GAZETTE

PLATE IX.

Fic. 74. eiheaauam in which the nuclei are elongated and preparing
division. :
Fic. 75. Portion of section of an antheridium showing the spindles ake .
dense chromosomes in the plate and in some cases the centrosome-like bodies he
the poles.
Fic. 76. Two cells of the same section enlarged three times.
Fic. 77. Chromosomes at the poles of the spindles. a
Fic. 78. Cross-section of thallus showing the hyaline hairs which extend ED.
into the median grooves.

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