426 
NATURE 
[Marcu 4, 1897 
cell only once in the life-history, viz. in the fertilised archegone. 
It seems difficult to consider in the latter case that there is more 
than one generation. 
Can it be rightly said that in the case of the Rhizocarps there 
is any true spore or any true sporophore? The answer depends 
on the meaning which we attribute to the word spore. 
Of this word many uses are made, to the confusion of thought 
on such subjects. It is according to the glossary to Kerner’s 
“Natural History of Plants,” as edited by Prof. Oliver, ‘‘a re- 
productive cell which becomes free and is capable of developing 
into a new individual.” De Bary, in like manner, applies the 
term generally to ‘‘ any cell which as a single cell becomes free 
and is capable of direct development into a new organism (Bion) 
without reference to its origin and homology ” (cited by Bower, 
ii. Linz. Ty., 301.) Sachs, on the contrary, would appear 
to confine the term to such a cell when asexually produced. 
‘*The asexual reproductive cells,” he says, ‘‘ usually become 
detached from the mother plant and dispersed (hence called 
spores) in order to produce a new generation at a distance from 
it’ (Bennett and Dyer’s Translation, p. 203): and in the language 
which contrasts oophore and sporophore, I suppose this view 
that the spore is asexually produced is plainly involved. 
Now if we take either of these definitions and apply it to the 
life-history of the Rhizocarps, a curious result appears to follow. 
Inasmuch as the megaspore produces a prothallus of its own 
energy, it may fall under the description of a spore, and may be 
considered as the product of a sporophore and the beginning of 
an oophore. But neither the microspore nor the antherizoid 
of Marsilea and Pilularia falls under such a definition, and there 
seems nothing to separate it from the sporophore as a new 
generation, and yet the archegone of the megaspore is fertilised 
by it. If I follow the matter aright, the sporophoric generation 
on the female side has united with the oophoric on the male side 
for the production of the young cormophyte. If this be true, 
there is certainly no hard and fast line between sporophore and 
oophore, for the cormophyte is the one by one parent and the 
other by the other parent. 
If the capacity to reproduce an organism like the parent be 
essential to the conception of a spore, then neither megaspore 
nor microspore is a true spore, and we have no sporophoric 
generation on either side. 
Lycopods.—In this single group we have a most remarkable 
diversity of schemes of generation. 
The Selaginellaceze (as is well known) produce megaspores 
and microspores, and present substantially the same scheme as 
the Rhizocarps. 
The Lycopodiacez, on the other hand, have a prothallus pro- 
duced by a spore, and itself in turn producing archegones and 
antherizoids, from the union of which arises the cormophyte, 
which is regarded as beingasporophore. This group, therefore, 
presents substantially the same scheme as the Ferns. 
Here, then, we have two groups of plants which botanists have 
agreed in regarding as closely united the one to the other, yet 
pursuing essentially different courses as regards reproduction. 
The two courses are so opposed, that whilst the sexual differen- 
tiation arises in the Lycopodiacec only in the oophore, in Sela- 
ginella it goes back into the sporophore ; or otherwise stated, in 
the one this differentiation begins in the prothallus, in the other it 
begins before the prothallus by the differentiation of the spores 
into two kinds. What is the inference? Is it not this? tha 
neither the modes of reproduction, nor the order of events int 
the life-history are characters of great persistency; or, in other 
words, that the organism is unstable in all these particulars? 
The Lycopods exhibit the phenomenon of short cuts. In Z. 
cernuum it has been found that the root tops (séc) turn into 
root gemmez or bulbs, which produce on germinating young 
plants much like those from the prothalli (Treub., ‘Some 
Words on the Life History of Lycopods,” 47272. Bot., pp. 119, 
122). 
Phanervogans.—The accepted application of the doctrine of 
the alternation of generations to this class of plants may thus be 
stated. 
The cormophyte of the 
Phanerogam is, as in the Ferns, a 
sporophore. 
The ovule 
The embryo sac 
The endosperm 
the megasporange. 
the megaspore. 
the female prothallus. 
Hou wwe neal 
The pollen sac microsporange. 
The pollen grain microspore. 
The pollen tube antherizoid. 
NO. 1427, VOL. 55| 
According to this view, the life-history of a. Phanerogam may 
be thus stated :— 
| Cormophyte 
Sporo- Ovule 
phore \ (Megasporange 
Pollen sac 
(Microsporange) 
Pollen grain 
(Microspore) 
Embryo sac Pollen tube 
(Megaspore) (Antherizoid), 
| 
Oophore Endosperm 
(female prothallus) 
| 
Cormophyte (a Sporophore) 
So that the dividing line between the two generations is, according 
to the theory in question, drawn in the same way as in the 
Rhizocarps, and seems open to the same observation of the 
mingling in pollination of two generations. 
With regard to phanerogams, no fact is more familiar than 
that the embryo, z.e. the young oophore, is intimately connected 
with and is nurtured by the cormophyte, z.e. the sporophore, 
and thus the two so-called generations coexist in close physical 
union ; and, furthermore, it is familiar that the fertilisation of 
the embryo sac (or megaspore) by the pollen tube (or antheri- 
zoid) often produces great changes in the carpels and the 
other parts of the perianth, and, in fact, in the whole flower- 
bearing axis; so that the fertilisation of the mother of a future 
organism is followed by great physical alterations in the 
structure of the grandmother. 
Another familiar fact is this. In Gymnosperms the endo- 
sperm is formed long before fertilisation, whereas in the Angio- 
sperms it is formed after that event. Now, as in the Rhizocarps 
so in the Phanerogams, we have only the supposed female pro- 
thallus left, for the pollen is formed without prothallus; and 
now, in the Angiosperms, we find the prothallus not coming 
into existence till after the formation of the ovule (or mega- 
sporange) and the embryo sac (or megaspore), and the fertilisa- 
tion of this by the pollen (or microspore). What was regarded 
asa fro embryo is now a fost embryo: the parent has become 
the child. The prothallus has, therefore, according to the 
theory in question, lost its old position of a growth preceding 
the sexual or, at least, the female organs, and does not arise til 
after these; it has lost its old function of producing thes 
organs ; and, one may add, it has lost its old form, for it i 
no longer a prothalloid growth and no longer a substantiv 
organism, but is reduced to a part of the seed. 
In the case of the Cryptogams, the prothallus for the mos 
part shows its true place in the order of events by gradually 
withering and dying away when the cormophyte has been 
started ; but in the Phanerogams the endosperm is only enter- 
ing on its functions when the development of the embryo begins, 
for it then becomes filled with nutriment, and increases in size. 
In a word, its duties are essentially connected with the life and 
growth of the embryo, so that it is functionally, as well as 
physically, part of the seed. 
If the homology-of structures so different in form, function, 
and order of succession, as the prothallus of Cryptogams and the 
endosperm of Phanerogams is to be maintained, cogent evidence 
ought, one would think, to be forthcoming. 
The Phanerogams, no less than the other groups which we 
have been considering, give abundant evidence of short-circuit- 
ing. It will be enough, briefly, to refer to some instances. 
The gemme which are found growing on the margins of the 
leaves of the Malaxzs paludosa recall curiously the similar, 
though less complicated organised, structures in the Zetraphzs, 
the Orthotrichiwm, and other mosses. 
Bulbils are found in many cases on the stem in the axils of 
the leaves.  anwnculus ficaria, Dentaria bulbifira, Lilium 
bulbiforwm are amongst the plants which present this fact. 
Small young plants arise directly on the leaf in certain cases, 
as in Cardamine palustris, where the young plant arises at the 
bifurcation of the vascular bundles : and in many other cases they 
arise from the leaves upon the severance of the leaf from the 
plant, so that an injury to the parent leads to reproduction. 
