42 BOTANICAL GAZETTE [july 



when the arc was used. Then the experiment was repeated with 

 diffused light. The boxes were placed in an east window for 8 



hours. 



the 



response, but in addition a considerable but much smaller number 

 were affected in the same way behind the green filter. Later the 

 experiment was repeated with the second set of three filters with 



periments 



first 



ght from a north window. Here the neg 



ism 



-ame 



behind the red. Thus the 

 have the power of establishing the polarity of the germinating 

 spores were also the ones which produced the rhizoidal photo- 

 tropism (table II). As explained previously with reference to these 



than the shorter but more 



Angstrom 



many times 

 ^ngths. Just 



lm 



found that the phototropism occasionally occurred behind the 



erreen 



It is probable, there- 

 experiments the blue 



4000 to S200 Angstrom 



enomenon 



from the violet 



spectrum, losing its power at ordinary 



somewhere around <r6oo A 



remains 



still longer rays can be made to produce the same effects by 

 increasing their intensity. 



Only the growing tips of the rhizoids are sensitive to light. 



results in a sharp angular turn if the direction of 

 is changed through 90 or 180 . As pointed out by 



illumination 



isms 



chemical 



growing tip. The first protuberance of the germinating spore 



illuminated 



triking it from the side; and if it is so 



first bend occurs at the cross-wall separating it from the next 







