1026 ELLIOT ROWLAND DOWNING 
discard these forms as pathways of ascent and adopt the Phaeo- 
phyceae as the most likely progenitors of the higher plants. Still 
others believe some common ancestors of these groups, a form now 
extinct, to have been the starting point of the archegoniates. 
Disagreeing over the probable course of evolution, they are equally 
at variance on the moot point mentioned above. 
Insuperable difficulties seem, so far, to stand in the way of 
tracing the evolution of the sporophyte of higher plants from the 
so-called rudimentary sporophyte which develops from the fertil- 
ized egg of such forms as Oedogonium, Ulothrix and Coleochaete. 
In these forms the egg, after fertilization, breaks up into a num- 
ber of separate cells, each of which gives rise to a new plant, thus 
functioning in a way suggestively like the asexual spores of the 
archegoniates. In Coleochaete, the only one of the lot that 
approaches the Hepaticae in structure sufficiently to be considered 
a probable ancestor, this structure can not be considered a sporo- 
phyte unless it be one with the x number of chromosomes instead 
of the 2x, in which ease it is difficult to see how it gives rise to 
the sporophyte of the higher forms, which is usually character- 
ized by the 2x number. 
In quite as many algae, Sphaerella, Volvox, Vaucheria, Chara, 
Fucus, Dictyota, etc., the fertilized egg, possibly after a rest period 
develops directly into the spore-bearing generation. It may 
be invidious for a zoologist to suggest that the sporophyte of the 
higher plants has arisen from this class of algae, by the inclusion 
of the spore-bearing generation of an alga within the gamete- 
bearing generation, somewhat as in Volvox one individual is 
included within the other. And I will not even venture the sug- 
gestion but will merely call attention to the fact that botanists are 
still not in sufficient agreement as to the course of the origin of 
the sporophyte in the archegoniates to prejudice, by their plant 
evidence, a zoologist against a theory along this line for animals. 
It is such a point of view that I take, namely, that in animals, 
and possibly also in plants, the spore-bearing and gamete-bearing 
generations of the protozoa (and algae) are phylogenetically con- 
tinuous with the sporozoon (or sporophyte) and the gametozoon 
(or gametophyte) of the higher forms. 
