Notes . 
377 
According to the view put forward now, namely that alternation of 
generations arose from polyembryony, homology between the two 
generations is inadmissible, for a completely new structure or tissue 
comes into consideration. Throughout the Algae, with the exception 
of Chara, wherever there is an alternation of generations the sporo- 
phore consists of a mass of cells or a tissue which is solely sporogenous. 
It is not till we come to the land-plants, in the Mosses, that some of 
the tissue ceases to be sporogenous and becomes purely vegetative, so 
that we get a new vegetative body altogether, intercalated between 
two sexual individual vegetative bodies, the object of which in the 
first instance is to protect the product of the sexual process, and later 
on to assist in its dissemination. It is therefore because all the new 
tissues arising from this new starting-point can have no phylogenetic 
connection with the tissues of the oophore which arose from another 
and quite separate starting-point, and moreover had arrived at a 
certain amount of differentiation before the tissues of the sporophore 
began to be formed at all, that no homology between the tissues and 
organs of the sporophore and oophore can be allowed to exist. 
To consider a particular case, Coleochaete produces asexual re- 
productive cells on the sexual body, the oophore ; these asexual 
reproductive cells cannot be allowed to be homologous with the 
asexual reproductive cells formed by the division of the oospore, 
assuming my view to be correct ; hence it follows that the spores of 
Riccia produced by the sporophore, that are homologous with those 
produced by the division of the oospore of Coleochaete , are not 
homologous with those produced by the sexual Coleochaete plants on 
plants with the sexual form. The same will hold good for the spores 
produced by the sporophore of all the Mosses, Ferns and Flowering- 
plants. Consequently Sachs ’ 1 distinction between true spores and 
gonidia is held to be eminently a sound one, as expressing a great 
and fundamental difference between two kinds of asexual reproductive 
cells. 
And as all the tissues of the sporophore of the higher plants are 
derived in the first instance from the cell-mass of sporogenous tissue 
which constitutes the sporophore of Coleochaete by a process of 
sterilization, any cell in the sporophore of any of the higher plants 
may be said in a certain sense to be homologous with a spore of 
Coleochaete , for they are each of them a segment of the oospore. 
1 Sachs’ Lehrbuch. 
