tort] LEWIS—SPORES IN PLEURAGE 371 
takes place, and this is followed quickly by two succeeding divi- 
sions, so that 8 cells are formed in the ascus in the usual way. 
These cells lie quite close together near the upper end of the ascus, 
are very small, and there is an abundant epiplasm (fig. 4). These 
are the primary sporogenous cells which later give rise to the fertile 
cells of the spores. They are cylindrical, hyaline, and the cyto- 
plasm is more dense than the epiplasm surrounding them. The 
ascus has not at this time reached its mature size, and the spores 
appear as very minute cells in its upper end (fig. 4). 
Further development from the primary cells was found to be 
quite variable in any one perithecium. In all cases, however, the 
sporogenous cell begins to elongate and to enlarge in all directions. 
It most frequently happens that the growth takes place faster on 
one side than on the other, so that the cell becomes somewhat 
crescentic in shape. It is also slightly bulged out near its middle 
(figs. 5, 6). It often happens that the nucleus of the young spore 
divides before the cell has grown to more than two or three times 
its original length (fig. 5), but this is by no means always the case. 
Frequently the nucleus remains undivided even after the cell has 
reached the length equal to half that of the ascus. In a few cases 
it was observed that the nucleus did not divide at all. As the cell 
elongates, its cytoplasm becomes vacuolate and more resembles 
the epiplasm from which it is derived. The nucleus usually 
divides, and after the daughter nuclei have moved apart, succeeding 
divisions take place until a number of free nuclei are present in the 
spore (figs. 6-10). The filamentous cell grows in length until in 
many cases it becomes longer than the ascus, and is consequently 
compelled to assume a spiral position. It is at this time almost 
uniform in diameter throughout its length, and the nuclei are dis- 
tributed along the entire filament. The cytoplasm contains many 
vacuoles and the epiplasm is greatly reduced. The formation of 
Cross-walls may or may not take place. Both types of asci occur 
in the same perithecium, but one type usually predominates in 
any one perithecium. In the cross-walled type the walls are usually 
formed at about the stage shown in fig. 6. Stages such as shown in 
figs. to and 11 never form cross-walls. In some perithecia there 
may be only a single ascus of the cross-walled type, while in others 
