Notes . 
593 
ALTERNATION OP GENERATIONS. — The first thing to be 
considered in this question is the behaviour of the cells. We may 
distinguish two modes of cell-division : (i) the protistoid , where the 
division of the cells is not influenced by their forming part of a complex 
multi-cellular body, and (2) the colonial or metis toid, where the division 
of every cell is dependent on its relations to the other cells of the 
organism at large. In Metazoa and Fucaceae a cycle of metistoid 
cell-division, in the formation of the organism with its buds and 
branches, alternates with a single short cycle of protistoid cell-divisions 
which produce the gametes — the oospheres (or oosphere and polar 
bodies) on the one hand, and the spermatozoa on the other. In 
archegoniate plants, and less visibly in Flowering-plants, there are 
two such alternating cycles of protistoid and colonial cell-multiplication : 
(<2) starting with the zygote, we have the colonial system of the sporo- 
phyte, followed by the protistoid divisions determining the formation 
of the neutral spores ; (b) starting with the spores, we have the other 
colonial formation, that of the gametophyte, eventuating in the protis- 
toid formation of the gametes. We have here a double alternation 
of twofold cycles, which thus cannot be paralleled by anything in the 
life-history of the lower Thallophytes, save in so far as they exhibit 
true tissue-formation and colonial subordination of cells. The 
alleged alternation in Batrachospermum, for instance, is really com- 
parable with larval conditions. That we are justified in the 
comparison of the ill-developed sporophyte in the Muscineae with 
the stately ‘ plant ’ of the higher Archegoniates, is shown by the forma- 
tion of such peculiar organs as true stomata in both ; and that this is 
not a mere case of homoplasy is shown by the fact that the conditions 
under which stomata are needed are found in the Marchantiaceae, and 
that breathing-pores which are not homologous with true stomata are 
here found. Again the phenomenon of nuclear reduction occurs at 
the same stage in both groups, to which we shall refer later. 
The argument put forward that the Moss-sporophyte must be con- 
sidered ‘ part of’ the leafy plant because it is attached to it and never 
becomes free, takes no cognizance of the discontinuity of the oosphere 
at the moment of its fertilization, and the lack of continuity of the 
cell-network of the sporogonium with the leafy plant ; it disregards 
the necessary results of parasitism ; and if applied to the Vertebrata, 
would lead to the most curious jumbling of questions of individuality 
in the passage from oviparity to viviparity, with the varying intensity 
of the parasitism of the embryo on the mother. 
