345 
Nemalion multifidum , Ag. 
diploid condition have arisen simultaneously, and both have become 
extended and amplified through the same cause— a progressive sterilization 
of sporogenous tissue. The' sporophyte structure is antithetic with the 
gametophyte structure, as is the diploid with the haploid condition. 
The situation in the Florideae, however, is more complex. In those 
forms which possess a sporophytic phase, the diploid condition is not borne 
by one sporophyte structure but by two structures — the cystocarp and the 
tetrasporic plant — neither of which in its origin is wholly analogous with 
the sporophyte of the Archegoniates. The cystocarp has arisen as a 
structure antithetic to the sexual plant, and has done so in the same way 
that the sporophyte of the Archegoniates has arisen, namely, by a steriliza- 
tion of sporogenous tissue, having possibly come from a condition similar 
to that found in Coleochaete, where a number of cells (eight) are formed by 
division of the zygote, each of which, however, gives rise to a zoospore. 
By progressive sterilization in the cystocarp, a certain amount of tissue 
formation has come to precede spore formation. We have, therefore, in the 
cystocarp of a form like Nemalion , a structure which we may look upon as 
a spore-bearing epiphytic plant, alternating with the sexual plant and 
bearing an antithetic relation to it. The cystocarp, however, differs in one 
very fundamental respect from the sporophyte of the Archegoniates in that 
it has originated independently of the appearance of a diploid condition. 
In Nemalion and Scinaia the cystocarp is already well developed, although 
the diploid condition has as yet not appeared. The cystocarp, therefore, 
unlike the sporophyte of the Archegoniates in its origin, was not funda- 
mentally sporophytic in nature. 
The only structure in the red algae which is always diploid in 
character is the tetrasporic plant. This, as we have already pointed out, 
is morphologically identical with a sexual plant, but is modified by the 
possession of a diploid number of chromosomes. It resembles the sporophyte 
of the Archegoniates in that it carries the double number of chromosomes, 
but in origin is entirely different from this, since it is not an entirely new 
structure, but only an old one made over. 
We have, therefore, two markedly different situations. On the one 
hand, in the Archegoniates we find a sporophyte appearing simultaneously 
with the diploid condition and representing something as new, morphologi- 
cally, as is the diploid condition cytologically— a structure without a 
phylogenetic ancestry. On the other hand, in certain red algae we have 
a sporophytic phase composed of two separate generations, one of which 
(the cystocarp) is antithetic to the sexual plant, but was in existence before 
the diploid condition made its appearance ; the other of which (the tetra- 
sporic plant) is the morphological homologue of the sexual plant. In the 
Archegoniates two antithetically alternating plants correspond to two 
antithetically alternating cytological phases. In the red algae these 
