1904] DAVIS—SEXUAL ORGANS IN PLANTS 243 
Sporocyst, a unicellular structure producing asexual spores. 
Zoosporocyst, a unicellular structure producing zoospores. 
Gametocyst, a unicellular structure producing uninucleate gametes. 
Spermatocyst, a unicellular structure producing sperms. 
Oocyst, a unicellular structure producing eggs. 
The terms sporangium, gametangium, antheridium, and oogonium, 
which have been applied to the above structures and to others as well, 
have been reserved for more precise usage, as will appear later in the 
paper. 
It should be noted especially that this list includes the sexual 
organs of almost all of the groups of algae, forms which illustrate 
the usual course of sexual evolution. The principal stages and steps 
in the origin and evolution of sex are fairly well understood. The 
writer has recently described them (Davis ’or, ’03@) and will not 
take up the matter further than to emphasize some facts which have 
important bearings on the subject of this ‘paper. 
The gametocyst came into existence with the origin of sex, and was 
derived from a zoosporocyst whose zoospores became physiologically 
sexual. Sex has probably arisen a great many times in the plant 
Kingdom, since it is fundamentally only a physiological condition, 
but so far as we know the origin has always been the same, namely 
through the conjugation of motile cells. 
Vith the gametocyst established, there is sure to follow a tendency 
‘0 differentiate the structure according as the sexual cells assume 
more and more the characters of sperms and eggs. The differentia- 
te of sex is well known to be one of the results of plant evolution 
which has appeared in a number of divergent lines of ascent entirely 
“pendently of one another. The eggs and sperms of widely 
Same es in the algae, as for example those ending in Mods 
pra = oleochaete, and Fucus, can only be related through t 
Rae e the undifferentiated gametes or zoospores of a ae 
seal 0 the mother-cells, oocysts, and Spcreioryer ) re 
a nae are related in the divergent lines among the ag 
ti Sabi, an ancestry from the undifferentiated gametocyst 0 
Th or the sporocyst. gu 
e ook ook Several groups of algae which offer interesting nee 
tons Gani Cture that demand special explanations. In the — 
Jugales we have the union of gametes while still contained 
