ir olvox reported in the third part of this parer that with a^greater ^ 

 intensity, the rays of the red end of the spectrum might caWse the sane 

 negative phototropism. *&? 



Only the growing tips of the Jifrhizofds are sensitive to light^, 

 m his results in a sharp angular turn if the direction of illumination 

 is changed through 90 or 180 degrees, or if the plants be brought 

 from darkness into unilateral light. As pointed out by Loeb and others 

 tropismJla uncftubljunliy due to the di ference in the speed of the 



chemical reactions going in the two dides of the growing tip. 



T he first protuberance of the germinating spore is not affected 

 by light striking it from th'i side; and if it is so illuminated 

 during the early stage of elongation of this cell, the first bend 

 occurs at the cross wall separating it from the next rhizoidal cell. In 



s~* 



other words, the firs t rhizoidal /^elongation continues in the orig- 

 inal direction established by the first cleavage plane. and the wall 

 separating it from the next cell of the growing ehizoid appears as the 

 axis of the tropism. 



In every culture of Pucus evanescens whether germinated in 

 darkness or in strong unilateral light a most striking orientation of 

 the first cross-wall with reference to adjacent spores appears, ^her- 

 e-teer a group of spores are lying within about 0.2 mm. of each other, 

 the first cleavage plane is perpendicular to the direction of the cen- 



t^er of the group. THe cell toward the interior invariably becomes 



C ) 



the rhizcidal cell. This phenomenon was reported by Fosenvinge in 



--" 



other species of Fucus and in Ascophyllum. 



^ 



A study of this phenomenon ^pfs madeM'to determine the strength , 



compared to *^'**^' 



of the stimulus producing this effect, **- that of light. in 



A 



A 



