SIGNIFICANCE OF THE SEXUAL PROCESS. 53 
gontum, Coleochete and, as the researches of Oltmanns seem to 
indicate (See Chapter IV), certain Rhodophyce@. From the fecun- 
dated egg of Q@dogonzum four swarm-spores are developed, while in 
Coleochete a multicellular body is developed, from the cells of which 
asexual swarm-spores are formed. In both cases the swarm-spores 
give rise to sexual plants, or the first generation. The product of the 
fecundated egg in Coleochete bears a striking resemblance to the 
sporophyte of such liverworts as Aéccza. The fundamental differ- 
ences lie chiefly in the fact that the covering of the sporophyte in 
Coleochete is derived from vegetative branches of the thallus, the 
odgonium being unicellular, and that the asexual spores are motile, a 
correlation with the aquatic habit of Coleochete. In the Rhodo- 
phycee the cystocarp or cystocarps are the product of the fecundated 
egg, and the spores give rise to the first generation. This is made all 
the more probable by the researches of Oltmanns, which go to show 
that the fusion of the cells of the sporogenous filaments with auxiliary 
cells is merely a nutritive process. It is of interest to note further 
that a similar condition is preserved in certain Ascomycetes in which 
Harper has proved that wxquestioned sexuality exists. Such alge 
as Coleochete, therefore, seem to point out more or less clearly the 
phylogenetic road along which the ancestors of the Archegoniates have 
passed. 
Research upon the process of fecundation and indirect nuclear 
division, especially in reproductive cells, during the past twenty years, 
has given a new insight into the significance of sexuality and the alter- 
nation of generations in plants. Our knowledge along this line was 
very materially advanced by the discovery of Van Beneden (’83) that 
the number of chromosomes is the same in both conjugating nuclei. 
Further investigations have established the still more important fact 
that, in both plants and animals, a reduction to one-half of the number 
of chromosomes in the sexual nuclei preceded the sexual act, and that, 
as a consequence of the fusion of the male and female nuclei, the 
number of chromosomes in the fecundated egg is doubled. 
In all the higher plants it is a well-established fact that the numeri- 
cal reduction of the chromosomes takes place in the spore mother-cell, 
and that in the cells of the gametophyte arising from the spore the 
reduced number persists. In cells of the sporophyte, resulting from 
the fecundated egg, the increased number obtains until the differentia- 
tion of the spore mother-cells. It will thus be seen that the funda- 
mental characteristic of both sexual and asexual generations lies in the 
number of the chromosomes, and upon this phenomenon rests the 
sexual differentiation of cells. 
