40 



BOTANICAL GAZETTE 



[JULY 



germin 

 becomt 



rhizoidal cell is dependent on the reactions within the spore initiated 

 by the short actinic rays; that the long red rays, even though 



much 



stimulation 



very low intensity of white light or its effective 

 Spores left in open dishes in the laboratory rarely 

 themselves in a most conspicuous way with respect tc 

 of the windows, nor do they require bright light. Thi 



com 



enomenon 



as evident in the more dimly 

 arthest removed from windows. 



ery 



more 



general rule. Every worker on this problem 



assuming 



inherent polarity, which as a rule is < 

 ht stimulus. The fact that in absolute 

 normal growth are as rapid as or more 



germi 



evidenced 



in the 



absence of the stronger orienting agents. 



Phototropism 



Winkler (21) first showed that the young rhizoids of Fucus 

 inflatus are negatively heliotropic. With the apparatus designed 

 for the light polarity experiments just described, several questions 

 concerning this phenomenon were easily answered. These were: 

 (1) what wave lengths are responsible for the turning away from 

 a source of white light? (2) is the intensity of the illumination a 

 factor, or is the phenomenon controlled only by the wave lengths 

 acting; in other words, what is the role of the quality factor apart 

 from the quantity of the light stimulus ? (3) do all lights which 

 have any effect at all produce the same negative tropism produced 

 by white light ? 



Although the light emitted by the electric arc was too low in 

 intensity after passing through the dense filters to establish the 



polarity of the young Fucus plants, it was noticed very early in 

 the investigation that behind the blue and violet filters this light 







