Chromosomes in Living Organisms . 285 
the sexual product of the first generation can be actually 
traced step by step phylogenetically. The first indication of 
this development is apparently to be found in the Algae : at 
least the life-history of Oedogonium, Coleochaete , and the 
Florideae, may be interpreted in this sense. In Oedogonium , 
four swarm-spores are formed from the fertilized ovum ; 
whilst in Coleochaete a small multicellular body is developed, 
from the cells of which swarm-spores are formed : in both 
cases the swarm-spore gives rise to the first generation. In 
the Florideae the cystocarp is developed from the fertilized 
ovum, and the spores of the cystocarp give rise to individuals 
of the first generation. The Muscineae and the Pteridophyta 
can readily be traced to the Chlorophyceae : in the Muscineae 
the fertilized ovum gradually developed into a sporogonium, 
and, in the Pteridophyta, into a sporangium-bearing cormo- 
phytic plant. 
In the consideration of the alternation of generations ob- 
taining in all the higher plants, importance is chiefly attached 
to the sexuality and asexuality of the two alternating genera- 
tions respectively. But, as a matter of fact, it would be more 
accurate to lay emphasis on the mode of origin of the two 
generations : from this point of view the sexual generation 
would be characterized as the gamogenic or sexually-developed 
generation. 
Our insight into the nature of the process of fertilization 
was very materially promoted by the discovery, made by 
Edouard van Beneden 1 , that the number of the chromosomes 
is the same in both the conjugating nuclei. Further investi- 
gations established the fact, for both animals and plants, that 
a reduction to one-half of the number of the chromosomes in 
the generative nuclei precedes the sexual act, and that, in 
consequence of the coalescence of the male and female nuclei, 
the nucleus of the fertilized ovum possesses the number of 
chromosomes characteristic of a vegetative cell. 
Basing myself on the observations which had been made 
1 Rech. sur la maturation de l’ceuf, la fecondation, et la division cellulaire, 
Arch. d. Biol. IV, 1883, p. 403 
