Marcu 4, 1897 | 
WATURE 
425 
question. 
But let us for a brief space confine our attention to the full 
and most complex life-history of which it is suggested to be an 
explanation. The fertilised archegone of the prothallus of the 
fern does not become detached from the prothallus, but, on the 
contrary, establishes a closer relation with it by the formation of 
a sucker or foot, which communicates with the tissues of the 
prothallus, and draws from them nourishment for the young 
cormophyte in the course of its growth. When the prothallus 
has thus performed its functions, it withers away. There 
has thus never been any physical severance of continuity 
between the prothallus and the cormophyte, and from the first 
to the last moment in the life-history of the fern there has been 
a continuous physical relation. Now arises the question whether 
the death of the prothallus is like the death of a parent, or the 
death of part of an organism—that kind of death without which 
there can be no life. Is it anything more than the casting off ot 
the leaf in autumn, or of the stipules and bracts in the spring, or 
of the corolla and the stamen and pistil when their part has been 
done, or the withering of the cotyledons? Again, I believe 
that I am right in holding that the prothallus has no adapta- 
tion to independent existence; that if the archegone be not 
fertilised, it does not long maintain its life, and that it is 
thus in no way fitted for an independent existence. If the 
view with regard to the meaning of a generation, which I 
have before suggested, be correct, it would seem that we have 
no true alternation of generations in the life-history of a fern 
any more than of a moss ; and that, asin the mosses, the sexual 
union ends in the reproduction of a new individual, not directly, 
but indirectly only, or (according to another view) in the pro- 
duction of a new part of the existing organism. 
A comparison of the life-histories of the mosses and of the 
ferns discloses, as we have seen, the remarkable fact that in the 
former the cormophyte is an oophore, and in the latter a sporo- 
phore, or, as stated by Hofmeister: ‘‘ The leafy plant in the 
mosses answers, therefore, to the prothallium of the vascular 
‘cryptogams ; the fruit in the mosses answers to the /evv, in the 
common sense of the word, with its fronds and sporangia” 
{*‘On the Germination, &c., of the Higher Cryptogamia,” 
Eng. Tr., p. 435): 
cormophytes of the two groups have no connection and no 
relation of descent, for if the fern plant were a modified moss 
plant, it would obviously belong to the same generation. It 
follows then that the leaves, the stem, and the whole vegetative 
structure of the mosses have no genetic connection with those of 
ferns or of the phanerogams. ‘‘The chasm which divides 
them,” says Prof. Goebel (Zuzc. Brit., s.v., Muscinee, vol. xvii. 
p- 74), speaking of these two classes of plants, ‘‘is the widest 
with which we are acquainted in the whole vegetable kingdom.” 
On this hypothesis then it follows that the mosses are to be 
vegarded as the highest point reached by that line of develop- 
ment in which the cormophyte is the oophore, or, in other 
words, in which the chief vegetative growth is also productive of 
the ovum, or sexually produced cell; and that the ferns are the 
first and lowest example of that line of development in which 
the cormophyte is the sporophore, or, in other words, in which 
the chief vegetative growth produces only the spore or asexual 
cell. The mosses, therefore, appear before us without de- 
scendants, and the ferns without ancestors. 
This conclusion seems improbable in itself, but it becomes 
more strange when we consider the fact that the Hymen- 
ophyllaceze present themselves very much as if they were a link 
between the mosses and the other ferns; a view which has been 
long, and still is, maintained by the foremost students of these 
plants (Bower, ‘*Some Normal and Abnormal Developments 
of the Oophytes in Trichomanes,” i. 4i7. Bot., 269,270). The 
leaves recall those of mosses, not only in their generally delicate 
‘character, but in that they often consist of only one layer of 
cells, and that, except in one genus, Loxsoma, they are 
without stomata. Again, as far as is known, the product of 
the spore of the Hymenophyllacee is not a prothallus, as in 
most ferns, but a protonema, as in the mosses. We have 
already seen that in many cases the protonema of the Hymen- 
sophyllaceze acts like that of the moss, viz. that it produces a 
NO. 1427, VOL. 55] 
If this be correct, it follows that the | 
bud which produces a cormophyte: and this apogamy appears 
to be commoner in this group than in any other of the Filices. 
_If, instead of regarding the successive phenomena of the life- 
history of the moss and the fern as divided into two distinct 
generations, we regard them merely as successive events in 
the history of one and the same organism, and further admit the 
possibility of a variation in the order of these events, then we 
can conceive that a moss was the ancestor of the filmy fern. 
We shall hereafter find other cases in which it appears that the 
order of succession of events has been changed in allied 
organisms. 
Perhaps this variation in the order of the events may be due 
to, or at least may be associated with, the different methods 
adopted by mosses or ferns respectively for retaining that 
moisture in the presence of which alone the act of fertilisation 
occurs. The moss is adapted to retain the dew and the rain 
amongst its leaves and in its perichzetal growths; and the long 
translucent hairs, which characterise the leaves of many of the 
mosses which especially affect dry situations, are probably of 
use in retaining this moisture. Mosses are for the most part 
habitually damp. In the ferns, on the other hand, the presence 
of moisture during fertilisation is assured by an entirely 
different method ; here we have a plate-like expansion of the 
prothallus, clinging closely to the damp soil and the archegones 
and antherizoids situate usually upon the under or damp 
surface. If these different classes of plants are to retain moisture 
at differenc stages of their life-history, it willseem to follow that 
fructification which requires this moisture must follow in the 
order of events this act of retaining moisture. It may be that 
the order of succession in the events of plant life depend, not 
on obedience to some inherent law or antetypal form, but on 
physiological necessities of life. 
Rhizocarpee.—In this group, as is well known, we find, for 
the first time, the presence of two kinds of spores (so called). 
The life-history is briefly this. The cormophyte (which is a 
sporophore) produces two kinds of sporanges—the megasporange 
and the microsporange. The megasporange produces megaspores, 
and the microsporange produces microspores. The megaspores 
are female and without fertilisation produce a_prothallus, 
which bears archegones ; and these archegones are fertilised by 
antherizoids, proceeding from the microspores. From the 
archegones thus fertilised, the new cormophyte is produced. The 
life-history may then be thus summarised :— 
( Cormophyte 
Saree oo | = == 
| Megasporange Microsporange 
( Meee rare wera 
Prothallus Antherizoid 
Oophore ...+ Aeenedore 
| 
| 
Cormophyte (a Sporophore) 
In the foregoing statement a difference as regards the pro- 
thallus will be observed between the megaspores and the micro- 
spores. The female prothallus is developed as a substantive 
growth, but in the case of the microspore this appears to be 
much less clear. ‘*In Marsilea and Pilulalaria the antherizoids 
are produced in the interior of the microspores themselves.” 
In Salvinia each microspore emits a tube which pierces 
the wall of the sporangium and divides into two parts, 
of which the terminal part is developed into antherizoids, 
leaving the single cell of the hinder part as the so-called pro- 
thallus (Sachs, Text-book by Bennett and Dyer, 384). It may 
be permitted to doubt whether that single cell can be regarded 
as a true prothallus ; but even if it be, this is absent in Marsilea 
and Pilularia, so that here, on the male side, the prothallus has 
dropped out of the series of events. 
Another point must be considered. In the case of the moss 
and the fern passing through the full circuit of their life-history, 
there are two points at which the whole future of the plant has 
been thought of as wrapped upin a single cell, viz. in the spore 
and in the fertilised archegone: in the case of the rhizocarps 
and all plants which follow their scheme of growth, including the 
phanerogams, the future of the plant is gathered into a single 
