

46 BOTAXICAL GAZETTE [july 



but arises as the result of the differential action of factors external to the 

 protoplasm, cell, or cell mass acted upon. If, for example, an undifferentiated 

 cell or cell mass is stimulated at some point by the action of a factor external 

 to it, the resulting increase in metabolic activity is not limited to the region 

 immediately affected, but a wave of change spreads or is transmitted over or 

 through the protoplasm with decreasing energy, intensity, or physiological 

 effectiveness, until, if the mass be large enough, it becomes inappreciable at 

 a greater or less distance from the point of origin. 



In the case of determination of the polarity of a spore by the 

 direction of its illumination, it might be said, therefore, that a 

 gradient is established within it by virtue of the fact that the 

 oxidation reactions proceed more rapidly on the side receiving 

 the greater amount of light energy. This side would become the 

 apical end, if Child's supposition is correct that the higher rate is 

 toward the apex, or head, and that in the posterior parts, or in the 

 rhizoids of algae, the rate is least. Thus it might be said that the 

 disturbance of equilibrium within the spore due to the reception 

 of unequal amounts of light energy over its surface produces an 

 oxidation or metabolism gradient which establishes the polarity 

 of the young plant. The spindle is oriented in some unknown 

 way, and the less active of the two cells resulting from the first 

 cleavage is the rhizoidal cell. 



Why only the rays of the blue end of the spectrum should have 

 this action is not clear. Possibly the cells exercise a selective 

 absorption such as that described by Bovie (2) as possessed by 

 Paramoecium when acted upon by ultra violet light. Then the 

 differences in the effects of monochromatic lights on Fucus spores 

 would be due to differences in penetrating power rather than to 

 u any action specific of wave length." Possibly the energy becomes 

 available to the cell for its effect on oxidations through some photo- 

 sensitive substance which responds only to the actinic rays. 



Child has recently found a metabolic gradient or oxidation 

 gradient in these germinating spores, and he finds that the region 

 of highest susceptibility, w r hich he takes to be the region of highest 

 oxidation, is at first at the rhizoidal end, suggesting that the 

 original effect of the light is an inhibition of reactions on the 

 exposed side of the spores. A letter written to the author regard- 

 ing this point contains the following: 



