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at all times of the year, a secondary maximum occurring in September 
and October. In the years with heavy autumn rains this is especially 
marked. The temperature as a control of the germination of algal 
spores has probably been overestimated. The spores of many species 
will germinate at all the ordinary water temperatures. There is still 
less reason for speaking of the germination as coincident with "rising" 
or "falling temperatures." The data in hand point rather to the con- 
clusion that all those factors which contribute to the germination of 
seeds are also operative here. Increased oxygen content of the water, 
increased mineral content, and induced changes in the permeability 
of the spore coats are probably the controlling factors, the speed of 
germination being retarded or accelerated by the temperature. 
Length of the Vegetative Cycle. — ^So far as I am aware this has 
received scant attention among experimenters. In some forms like 
Pithophora and Vaucheria it is probably of no consequence for they 
may be induced to fruit immediately upon germination. But in other 
forms like the Zygnemales and Oedogoniales it is probably of vital 
importance in the interpretation of experimental results. In these 
forms the vegetative cycle is a period of the formation of the filament 
by cell division, and the period of accumulation of nutrient and other 
materials. During this period photosynthesis, proteinsynthesis and 
assimilation are active on the one side, while respiration, accumulation 
and growth are active on the other. Field observations and experi- 
mentation indicate that this must go on for a certain length of time 
before reproduction is possible. They also indicate that the speed 
of the metabolic processes must attain a certain minimum rate or 
reproduction fails to close the vegetative cycle. A number of factors 
may limit the speed of metabolism ; light of low intensity is obviously 
one that operates so effectively, that algae in shaded portions of streams 
may never reproduce, or even be able to maintain more than a tem- 
porary existence. It is probable that excessively high temperature 
may also prevent the normal development of the algae. Higher tem- 
peratures accelerate and lower temperatures retard the completion of 
the vegetative cycle. These results are just as clearly indicated by 
field observations as by experiment. The amounts of available oxygen 
and carbon dioxide in the water also act as limiting factors to these 
processes. 
The length of the vegetative cycle is so regular from year to year, 
that, given the conditions, it is not difficult to predict the order in 
