46 BOTANICAL GAZETTE [JULY 
case in daylight. The result will be a movement towards light, 
or as it is generally termed positive phototaxis. That sucha 
phenomenon really exists among the Diatomacez everyone knows 
who has observed the pools containing these alge in a summer 
day. And this kind of phototaxis, which the Diatomacez have 
in common with the great part of unicellular organisms contain- 
ing chlorophyll, is without doubt of use to them, for moving 
towards the light places the cells in the most advantageous con- 
ditions for assimilation. | 
CHICAGO. 
