The f irat work establishing the nov: km I fact that one- - 



sided illumination will cause the first division plane of a germinating 



J 



spore to be perpendicular to the direction of the incident light 

 s done by Stahl(/f? $"*) on Equi fee turn. He found th?<t the first wall 



is formed perpendicular to & light rays striking the spores on one 

 side only, and that if ? 11 sides ore illuminated by rotating " 



spore? on a clinostat , the formation of ine vrall is retarded or 

 prevented. The cell on tne shaded side of tne s -ore become? the rhi - 

 zoidalfcell. in darkness the formation of the first v/all follov/s 

 no rule and the rhizoids extend 4n every di ection. Stahl refers to 



enrlier v/ork on liar s i 1 ia and n ara. whicn indicates /I that gravity 



a 

 is ton. controlling factor in the otientation of the first division 



A 



plane 





, 

 spore regardless of the light direction. SK ^Je conclude^ that no$T 



A 

 only light but a difference in the concentration of oxygen on the 



two Fides of the spores could determine their pol; rity. He says 

 that as a result of their respiration tne water in the center of 

 the groups of scores is lesn rich in oxygenjand as a consequence 

 the rhizoids^p. are formed on th?>t side. Inlsupport of this theory 

 is the fact th ':. although light can determine the polnrity of all 





Rosenvinge(1889) showed that in Fucus spiralia there is no 



relation between gravity and the first division plane nor did con- 



. 

 tacf with a solid body have any effect. He got tne same orientation 



- 

 to light in Ascophylium and ./ucrus' that Stahl did with Bfruisetum. 



but with puzzling exceptions. There the spores were in groups the 



^k_ /T_xjv-^W - *^ 



cell/ toward the -4e&r, interior of the G r up became; and in the lov/er 

 part of hanging drops the rhizoids appeaWon the upper side of the 



