No. 463.] STUDIES ON PLANT CELL.— VI. 457 
I refer to many lower alge such as Ulothrix, forms of the 
Volvocacex, CEdogonium, Coleochzte, and many others. How- 
ever, the homologies of primitive gametes and their origin from 
types of asexual zoóspores is very clear in a number of groups. 
We can see nothing in the morphology and mode of develop- 
ment of these reproductive cells to suggest reduction phenomena 
when gametes are produced. The primitive gamete is generally 
somewhat smaller than its homologue the zoöspore, often because 
the protoplasm of the gamete mother-cell becomes distributed in 
a greater number of daughter elements. It is well known that 
the conditions that lead to conjugation are exceedingly variable, 
depending upon environmental factors and one often cannot tell 
at the time whether a swarm spore will show sexual habits or 
germinate without conjugation. The most satisfactory theory 
of the origin of sex in plants regards primitive gametes as 
weaker or lacking in certain potentialities of vegetative growth 
and the conjugation as a mutually coóperative process resulting 
in a rejuvenescence of the protoplasm. The fact that many 
simple types of gametes will germinate without fertilization and 
produce small and weak sporelings shows that vegetative possi- 
bilities are not entirely lost. Investigations on the chromosome 
history among these forms, difficult though they be, are some of 
the most interesting subjects of botanical research. We know 
some general principles of the origin and evolution of sex in 
plants (Davis, :oıb, :03a) but of the chromosome history in the 
simplest types of gametogenesis nothing is known. 
With respect to the history of the chromosomes in the sim- 
plest sporophytes we are also as ignorant as in the simplest 
types of gametogenesis. We have excellent reasons for believ- 
ing that the sporophyte generation is represented among the 
thallophytes in a number of very simple conditions. Numbers 
of zygospores and oöspores (^. £. Ulothrix, CEdogonium, forms 
of the Conjugales and Volvocacez, etc.) give rise on germination 
to several daughter cells. In higher forms this growth period is 
lengthened to the formation of a reproductive tissue (Coleochzte) 
and in the great groups of the Rhodophycez, Ascomycetes, and 
Basidiomycetes there is present an extensive development from 
the fertilized female cell (or its equivalent when apogamy obtains) 
