Mast, Light Reactions in Lower Organisms. 179 



colonies or spores, collect to the right of the region in the jars 

 nearest the source of light; those without daughter-colonies or 

 spores or with small ones collect nearest the source of light, but 

 they spread out considerably both to the right and left. A 

 majority of all the colonies are, therefore, usually found in that 

 part of the jar to the right of the region of strongest illumination. 



22. The cause of this collection to the right is found in the 

 fact that when the specimens containing large daughter-colonies 

 strike the wall of the jar, in swimming toward the source of light, 

 they usually turn to the right. This is caused by the effect of 

 gravitation, rotation, and contact stimulation. 



23. Since the ratio between the difference in light intensity on 

 opposite sides, which is sufficient to induce a reaction, and the 

 intensity on either side is nearly the same for different degrees of 

 illumination, Weber's law holds approximately for the light 

 reactions of Volvox. 



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