44 BOTANICAL GAZETTE [july 



oogonium, the phenomenon appears lust the same 



are stirred up with the point of a needle before being germinated, 

 so that the original positions are entirely changed. 



The direct cause of such orientations is probably the same as 

 that responsible for those produced by light. At least the results 

 of the stimulations are identical, and it seems probable that the 

 ultimate factor is the relative rate of the oxidations proceeding 

 along an axis of the spore. It follows that the 



energy 



determine this oxidation gradient in unilaterally illuminated 



m 



different 



m 



librium and produce the same sort of a gradient. Rosenvinge 



theory that the phenomenon was produced by a 



m 



on the two sides of the spore. He thought the rhizoid forms on 

 the side toward the center of a group or toward another egg, 

 because as a result of the latter's metabolism the water on that side 

 is less rich in the active substance than on the outer side of the 

 spores. Winkler, however, working with Cystoseira barbata, found 

 that a difference in oxygen concentration which he produced arti- 

 ficially had no such effect on the spores. 



This phenomenon, group orientation, is found in cultures 

 germinated in light as well as those in darkness, although not so 

 conspicuous in the former, because the light may be the stronger 

 stimulus for many spores which in its absence would be affected by 

 the orienting stimulus from adjacent spores. Yet the fact that it 

 is always found in cultures germinated in unilateral light, although 

 limited to those spores and groups of spores within a very short 

 distance of each other, shows that within this distance the influence 

 of neighboring spores is stronger than that of light, at least of lights 

 with the intensities of those used in these experiments. In other 

 words, no light was powerful enough to overcome for the more 

 closely grouped spores the chemical stimuli originating in them- 

 selves. The relative number of spores oriented by light depends 

 therefore on the intensity and wave-length composition of the light 

 source and the distribution of the spores in the culture. In many 



