6 BOTANICAL GAZETTE [JULY 
many instances they become quite irregular, being stretched almost 
to the point of breaking. It is quite possible that irregular numbers 
of chromosomes, which are occasionally reported in plants, may have 
originated by the breaking of an individual chromosome. The micro- 
spores, still within the wall of the mother-cell, quickly assume an 
oval form (jig. 14). 
After a brief period of rest (fig. 15) the nucleus of the microspore 
divides, and the first prothallial cell is formed. It has been deter- 
mined beyond a reasonable doubt that a wall is laid down between 
the two nuclei (jigs. 16, 17), although it is extremely difficult to differ- 
entiate. The prothallial cell is pressed closely against the end of 
the microspore by the growth of the other cell, its nucleus usually 
taking the meniscus form (jigs. 17-22). The other cell, still remaining 
at the center of the spore, enlarges, and dividing (jig. 17) gives rise 
to the second prothallial cell and the antheridium initial (jig. 18). 
The antheridium initial does not appear to be separated from the 
second prothallial cell by a wall, but both nuclei remain in the same 
mass of cytoplasm which originally surrounded the nucleus before 
division (fig. 18). Here again arises a great difficulty in making 
conclusive observations. It may be that a wall is laid down and 
almost immediately resorbed, as Juel (’00) has shown to be the 
case in tetrad formation in Carex acuta, where a cell plate is 
formed and immediately resorbed, leaving the tetrad nuclei free 
within the wall of the mother-cell. It is conceivable that such a 
wall may be laid down, for it must be remembered that the entire 
prothallial region of gymnosperms is undergoing modification, in 
that the prothallial cells are either more or less ephemeral or alto- 
gether wanting; and that when cells are becoming obsolescent the 
wall is the first to disappear, leaving the two nuclei free within the 
common cytoplasm; next, the nucleus occasionally fails to divide; 
and finally no division takes place at all. 
The second prothallial cell becomes flattened because of pressure 
_ due to the growth of the antheridium initial, and its nucleus becomes 
plano-convex or even meniscus-shaped, with its plane or concave 
face turned toward the first prothallial cell (jigs. 18, 20). The nucleus 
of the antheridial cell, still at the center of the microspore, enlarges 
very much (fig. 18) and divides (fig. 19), giving rise to the generative 
