IgI0] SHATTUCK—HETEROSPORY IN MARSILIA 29 
time, plants in the same tank, in 8 to 12°™ of water, at the same tem- 
perature but shielded from the direct rays of the sun, either blasted 
completely or showed more or less abortion among the megaspores 
and occasionally enlargement of some of the microspores. It is 
evident, therefore, that the plants are dependent on strong light and 
high temperature in order to mature perfect sporocarps, and that 
water at any depth less than 20°™ need not cause blasting unless it 
greatly lowers the temperature or reduces the light below a certain 
minimum. 
Discussion 
A close inspection of this process of blasting brought to light the 
important fact that under the conditions of growth to which these 
plants were subjected the megaspore was the first to show signs of 
abortion. It might be added that through a long list of experiments 
on the younger stages of sporocarps this was the invariable rule. 
Unfavorable conditions of growth, whether brought about by depth 
of water, lack of light, low temperature, or drought, without excep- 
tion always affected the megaspores more than the microspores. 
Later experiments revealed the fact that in the more mature sporo- 
carps this was not the case. Hard conditions brought on after the 
megaspores are well formed, but about the time the microspores are 
in the mother cell stage, will produce abortion among the microspores. 
The critical period in the life of the spore, whether microspore or 
megaspore, seems to be from the time when the mother cell comes into 
the synapsis stage until the tetrads are well on the way to becom- 
ing spores. This also agrees with Miss PFEIFFER’S observations on 
Azolla (20). However, it proved to be much easier to arrest the 
development of the megaspores than to affect the microspores in 
this way, and when abortion did occur it was much more nearly 
universal in the case of the megaspores than in that of the microspores. 
Excellent examples were secured showing sporocarps without a 
Single megaspore, while I was never able to secure the complete 
blasting or abortion of the microspores alone. Many experiments 
Were made in which both were completely blasted, but if either sur- 
Vived it was always the microspores, though sometimes only a small 
number. It was also noticeable that when the sporocarps were 
subjected to such treatment as to blast the megaspores in their early 
