428 Lawson. — The Gametophytes , Fertilization and 
ordinarily occurs after mitosis. The result of this is that the prothallium 
passes through a stage when the majority of its cells are binucleate. 
When first formed, the membranes surrounding the pairs of nuclei 
appear round or oval in section. As hundreds of them are formed they 
become more or less crowded and the walls become flat where they press 
upon each other. As they crowd against one another, the neighbouring 
walls become fused together, and this gives the appearance of ordinary 
cellular tissue. Fig. 33 shows a portion of the prothallium soon after this 
division. There are two distinct nuclei in each cell. 
As far as I am aware such a peculiar method of endosperm-formation 
has not been recorded. Indeed I do not know where such a type of free 
cell-formation occurs in the plant kingdom. The nearest parallel to it is 
that which Harper (’97 and ’00) has described in the development of 
the ascospores in the ascus of Erysiphe and Pyronema. In these Fungi, 
after the last division of the spore-mother cell, the kinoplasmic fibrils which 
radiate out from the centrosome bound off the ascospores by a process of 
free cell-formation. These fibrils increase in number, and as they grow in 
length they curve around the nucleus. By fusing together laterally the 
fibrils are converted into a complete membrane which surrounds the young 
ascospore. Between this process and that which I have described in the 
endosperm of Cryptomeria , there is a striking similarity ; the main differ- 
ence being that it is the astral rays in Erysiphe and Pyronema which 
form the membrane, while in Cryptomeria it is the continuous fibrils of the 
spindle which are converted. They also differ in the absence of the 
centrosome in Cryptomeria , and also in the enclosure of two nuclei instead 
of one. 
The earlier stages in the development of the female prothallium in 
Cryptomeria agree very closely with those reported for many other Conifers, 
but this later stage, where such a peculiar form of free cell-formation 
precedes the formation of the permanent endosperm-tissue, is unlike any- 
thing that has heretofore been described. That it is normal in Cryptomeria 
I feel tolerably certain. It was found in a large number of preparations of 
material collected from several different trees and during both years, 1902 
and 1903. Whether or not it occurs in other Conifers can only be learned 
from future investigations. 
After the binucleate cellular tissue has been thoroughly established in 
the endosperm, nuclear division proceeds in the usual way and the cell- 
plates are formed between the daughter-nuclei. Some preparations, 
however, showed binucleate cells in the endosperm as late as the early 
stages of the embryo. 
