SPH ZROTHECA. 109g 
preceding somewhat that of the antheridium. Each consists at first of 
a short oval branch, which is distinguished from the ordinary vegeta- 
tive hyphz only by its denser protoplasmic contents and by standing 
at right angles to the surface of the leaf of the host plant. 
As soon as the odgonium has attained a length equal to two or three 
times its width, and a diameter which is about twice that of a mycelial 
filament, it is cut off from the parent hypha by a cross-wall. At this 
stage it possesses a single nucleus which can scarcely be distinguished 
from the nuclei of vegetative cells. Frequently, before the young 
odgonium is delimited by the cross-wall, the antheridial branch appears 
quite near the base of the former, and grows upward, closely applied 
to its side (Fig. 39, A). The oogonium appears to grow faster than 
the antheridial branch at first, thereby bending over toward the latter, 
Fic. 39.—Sexual organs and fecundation in Spharothect castagni Lm.—(After Harper.) 
A, young odgonial and antheridial branch, odgonium on left. 
B, later stage of same, antheridium delimited by a transverse wall. 
C, copulation of antheridium and oégonium ; the two sexual nuclei in contact in odgonium. 
D, odgonium in which the sexual nuclei have fused. 
E, young ascogonium with two nuclei; wall of perithecium is now several cells in thickness. 
and givirig the impression that the contiguous walls were grown 
together, and that the growth of the oogonium was retarded on the 
side next the antheridium, The antheridial branch is now separated 
from its mycelial filament by a cross-wall which is higher in position 
than the corresponding wall of the oogonium. This cell contains also 
only one nucleus. When the development of the oogonium is com- 
plete the antheridial branch elongates and its nucleus divides. One of 
the resulting daughter-nuclei passes into the somewhat attenuated end 
of the cell, which is cut off from the lower part to form the anthe- 
ridium (Fig. 39, B). While the stalk cell now elongates and the 
antheridium increases in size the oogonium experiences little change; 
consequently, the antheridium is carried upward, and finally comes to 
lie as a cap placed more or less obliquely on the top of the oogonium. 
At this stage the nucleus of the egg-cell is larger than the ordinary 
