80 



TROPISMS 



The problem now resolves itself into the construction of an angle about 

 OC as a bisector, which shall be of such a magnitude that equal dis- 



Fio. 30. Diagram for constructing direction of motion of larvae under influence of two 

 lighta of different intensity. (After Patten.) 



tances on its opposite sides shall have projections on the line AB of 

 the ratio of two to one. 



Construction : From a point D on the line OC draw Dh perpendicular 



