a a nn 
~—_ 
1910] SAXTON—WIDDRINGTONIA 37 
The formation of binucleate and multinucleate prothallus cells 
has already been described. It is initiated at about this time, but 
nuclear divisions continue to occur during the earlier phases of 
embryo formation. Two such divid- 
ing nuclei are drawn in figs. 26 
and 27. 
The structure of the mature arche- 
gonium is much like that of other 
Cupressineae, with a large, centrally 
situated oosphere nucleus and a basal 
(or sometimes partly lateral) vacuole 
(fig. 28). The neck cells do not per- 
sist long, the archegonia of the basal 
group finally opening into the pollen 
tube. 
The total number of archegonia 
of both kinds organized in a pro- 
thallus varies considerably. Some- 
times there are only about 25-30,  Siiemmh ss 9 aaa 
usually about 40-70, and occasionally —fyc._ x. —Microphotograph of a 
as many as 100. The microphoto- tangential section of a prothallus in 
graph (text fig. 1) is taken from a yhich about 100 archegonia were 
tangential section of a prothallus in 
which about 100 archegonia were present. About 50 of these appear, 
cut transversely, in this section. A prothallus containing about 50 
in all was sketched in my preliminary paper (10, fig. 15). 
present. 
5. The male gametophyte 
The earliest stages of the germination of the microspore have been 
already described, but the description will be briefly repeated here. 
The mature pollen grain is uninucleate and there is no evidence that 
any prothallial cells are formed. Thus the “pollen grain” is here 
synonymous with the “microspore.” The earliest stage of germina- 
tion usually consists in the formation of a solid outgrowth from the 
exospore, which applies itself closely to the surface of the nucellus, 
sometimes with a tendency to grow down between the nucellus and 
integument. About three pollen grains usually begin to germinate 
