1909] COULTER—EVOLUTION AMONG GYMNOSPERMS 95 
THE MALE GAMETOPHYTE 
It is perhaps impossible as yet to determine the character of the 
male gametophyte of the Paleozoic gymnosperms. The evidence 
is accumulating that it comprised many more cells than do the game- 
tophytes of most living gymnosperms; but it is not demonstrable 
whether these supernumerary cells were vegetative or spermatogenous. 
There are instances of supernumerary cells of both kinds among 
living gymnosperms, so that they furnish no clue; and the same is 
true of heterosporous pteridophytes. The balance of probability, 
however, is in favor of the view that they were in the main sperma- 
togenous. : 
In any event, starting with the known condition among hetero- 
sporous pteridophytes, the tendency among gymnosperms has been 
to reduce and finally to eliminate the vegetative (prothallial) tissue; 
and to reduce the sperm mother cells to two. 
In certain groups (as Abietineae) the prothallial cells are two in 
number; in others (as cycads) there is one prothallial cell; and 
in still others (as Taxodineae, Cupressineae, and Taxineae) prothal- 
lial tissue has been eliminated. Such prothallial cells as do appear 
are sometimes persistent and sometimes ephemeral; so that the evi- 
dence of a disappearing tissue is complete, and it actually has dis- 
appeared in what are recognized as the most modern groups. The 
situation common to Podocarpineae and Araucarineae is usually 
cited as an illustration of a more extensive and therefore a more 
ancient prothallial tissue, which connects directly with the “ multi- 
cellular” pollen grains of Cordaitales. This may be true, but all of 
the extra cells are derived from two primary ones, which hold a definite 
place in the ontogeny of the gametophyte; and therefore may repre- 
sent a secondary tissue that holds no phylogenetic relation to the more 
extensive prothallial tissues of older forms. In any event, it is 
ephemeral, breaking down and liberating its nuclei. 
The number of sperm mother cells is so rigidly two, that this reduc- 
tion may be said to have been accomplished by all living gymno- 
sperms, whatever may be the fact in reference to the Paleozoic gymno- 
sperms. It is interesting to note that the very few instances of a 
greater number of sperm mother cells occur in one group character- 
ized by its retention of ancient features (Cycadales), and in another 
