490 



S. O, MAST 



colonial organisms appeared in great abundance, especially the 

 green forms, Chlamydomonas, Euglena, Pandorina and the like. 

 In any given pool a given species ordinarily predominated at any 

 given time, but usually there was a succession of species between 

 successive rain storms, depending apparently upon changes in the 



400 



600 



Fig. 3 Curve representing the distribution of energy in the spectrum used 

 in the following experiments. The circles represent the points experimentally 

 established, the ordinates the energy and the abscissae the wave-lengths in aim. 



constitution of the solution. For example, in one particular pool 

 which frequently dried up entirely Chlamydomonas appeared 

 first each time after several rain-storms and became very abun- 

 dant with a few scattered Pandorina colonies. Then after a few 



