Sands—Spore Formation in Microsphaera Alni. 741 
The asciis grows rapidly, at first mainly in the region far¬ 
thest from the nuclei, so that these come to lie in the smaller 
end of the cell. The nuclei also increase in size, but not in 
proportion to the growth of the ascus. When the ascus has 
reached about one-third its mature size, the nuclei come in 
contact preparatory to fusion. They are sometimes elon¬ 
gated and may lie one a little above the other, or in any other 
position. Finally the walls between break down, and fusion 
occurs. A late stage in the fusion of the nuclei is shown in 
Figure 7. The two centers with their respective chromatin 
systems are still separate. (The one on the left is cut 
through). The nucleoli have already fused into one large nu¬ 
cleolus. The ascus at this stage is about half-grown. It is 
well rounded out except where it presses against an adjoining 
ascus. The fusion nucleus is about the size of the average 
primary nucleus. 
The most frequent and conspicuous stage foimd in Micro¬ 
sphaera is that of the primary nucleus. It persists from the 
time of the relatively early fusion in the young ascus, until 
the ascus has reached its full development. It grows very lit¬ 
tle after fusion is complete. There is an abundance of chro¬ 
matin, which readily stains a dense blue. This is at first ar¬ 
ranged in irregular strands which occasionally appear double, 
and always cross and interweave in a tangled net. A large 
nucleolus is always present, most frequently slightly flattened 
against the nuclear membrane. The center is most difficult of 
demonstration, partly because the chromatin stains so heavily 
and is so abundant as to hide the center. Moreover, metachrm 
matic bodies are particularly abundant at this stage, espe¬ 
cially in cases of poor fixation. These bodies occur just out¬ 
side the nucleus, often at a point where two or more chromatin 
strands touch the nuclear membrane, and may obscure the 
central body. Faull believes that these metachromatic bodies 
are normal cell products, since they are always present about 
the primary nucleus but disappear in later stages. However, 
this disappearance may indicate merely that fixation is more 
perfect at these later stages. 
