Sands—Spore Formation in Microsphaera Alni. 743 
The two centers with their asters probably originate here as 
elsewhere from the division of the single central body of the 
resting lindens, and of a single aster developed earlier in the 
prophase. The two sets of fibers meet below the center of the 
nucleus, where they cross and interlace; some of the fibers ap¬ 
pear to be continuous from one center to the other. At the nu¬ 
clear membrane, where the broad centers are attached to the 
intranuclear bundles of fibers, there is a conspicuous non-stain¬ 
ing region. Some of the peripheral fibers can be traced to the 
disc, but most of them fade abruptly just before reaching the 
-central body, leaving an apparent space (Fig. 81. The so- 
called “achromatic” fibers at this stage stain quite as densely 
as the chromatic parts of the nucleus, so that the chromosomes 
cannot be clearly distinguished. I have not found the later 
stages of this division. 
The binucleated stage of the ascus following the first divi¬ 
sion is easily distinguished from the binucleated condition be¬ 
fore fusion, both by the mature size of the ascus, and by the 
older appearance of the whole perithecium. The two* outer 
cell layers on the upper side of the perithecium have thick 
brown walls, and the appendages have nearly reached their fi¬ 
nal length. 
A resting nucleus at this stage has a prominent center to 
which the chromatin is plainly attached; the center is always 
readily seen as a little cap just outside of, and closely pressed 
against, the nuclear membrane. 
One of the most common division figures in my material is 
the equatorial plate stage of the second division. The spindle 
usually lies transversely in the ascus, with eight chromosomes 
arranged on the equatorial plate. The asters are inconspicu¬ 
ous, with fine, delicate rays that fade into the cytoplasm. Bie- 
tween the centers and the spindle poles, light areas are found 
as in the first division. The four nuclei resulting from this 
division do not differ from those of the two-nucleated stage, 
except that they are somewhat smaller (Fig. 11). 
The third division is ushered in by a division of the center. 
Most frequently the centers are far apart-—100° or 120°— 
when the asters and spindle fibers are well developed. The as- 
