744 Wisconsin Academy of Sciences , Arts, and Letters. 
ters are particularly striking; their rays are like short, stiff 
bristles, and densely stained. There is the same colorless space 
between the center and the darkly-stained spindle fibers as in. 
the two preceding divisions (Fig. 10). This whole stage of 
spindle formation bears a very close resemblance to the same 
stage in Erysiphe (6). 
There are eight chromosomes on the equatorial plate and 
many more in the metaphases. The astral rays grow longer 
and become much finer, and, as the spindle often lies close to 
the ascus wall, they may be seen bending away from the wall 
toward the interior of the ascus. A small light zone still ap¬ 
pears at each pole of the completed spindle. 
The process of spore formation in Microsphaera alni is en¬ 
tirely like that described by Harper in detail for Erysiphe 
communis (11), and more recently for Phyllactinia suffulta 
(13), and corroborated by various authors (8, 19) for many 
other Ascomycetes. 
The eight nuclei formed by the third division retain their 
asters; from these there continue to grow out long, fine threads 
which become more numerous. From the beginning the asters 
are turned toward the periphery of the ascus (Fig. 12). With 
the growth of the asters the nuclei become beaked. The cen¬ 
ter is situated at the summit of the beak, and from it chroma¬ 
tin strands run back into the nuclear cavity. During the proc¬ 
ess of beak formation, the nucleus with its aster shifts its po¬ 
sition, so that it lies a little farther in from the ascus wall (Fig. 
12). At this time the rays next the nucleus begin to curve 
back about it; more bend over in the same way, until a cone- 
shaped opening is formed in the midst of the aster. This 
folding back continues until the majority of the fibers lie in 
one plane, which forms a hemispherical covering over the 
beaked nucleus. Some of the fibers bend further, pass below 
this surface, and are finally enclosed within the spore (Figs. 
13 > 15) * 
As yet there is no differentiation of the protoplasm within 
the ascus; the fibers continue to grow in length, cutting 
through a homogeneous cytoplasm. That the lateral fusion 
of the rays begins early, as is shown by the plasmolysis of the 
