THE PLANKTON OF SHA\VNEE CAVE. 



397 



TABLE II. 

 SHOWING INFLUENCE OF FLOOD UPON TEMPORAL DISTRIBUTION. 



be carried through the cave that would succumb to the cave en- 

 vironment at ordinary stream levels. The first and third of these 

 effects of excessive rainfall are therefore positive and the second 

 negative. 



The cycle of pond life in this region is not well known, but is 

 being investigated. It is very probable that in its main outlines 

 it resembles that of lakes in the same latitude. 



The minimum of February was due to two things, the small 

 number of organisms produced in the pond and the great dilution 

 by rain water. 



The increase in the amount of plankton after the heavy rains 

 of May and August was due to the fact that the amount con- 

 tributed was so great that the dilution was insufficient to reduce 

 it to the amount per gallon previously present in the cave. The 

 increase in the number of species was caused by the rapid current 

 carrying through many of the forms that would have succumbed 

 to the destructive influences of the cave environment at lower 

 stages of the water. The subsequent gradual decrease in amount 

 and number of species was due to the destructive cave environment. 



The temporal distribution of the plankton in this cave depends 



