1916] GRAVES—CHEMOTROPISM IN RHIZOPUS 345 
these last two lines, were then called A, B, C, and D, with orienta- 
tions as shown in fig. 1. The hypha was then classed as A, B, 
C, or D, according to the quarter in which it grew. 
If the hypha curved markedly, only its tip was considered, since 
the ultimate effect of the reaction was expressed in this portion. 
In this case, the point of intersection of the two lines at right 
angles was located at the tip, this having been connected to the 
Fie. t Fic. 2 
GS. 1 and 2.—Diagrams showing methods of locating directions of hyphae: 
fig. 1, where the hypha is fairly straight; fig. 2, where it curves markedly. 
center of the hole by a straight line, as before. The hypha was then 
classified according to the quarter into which the tip pointed (fig. 2). 
In the few cases where the hyphae curved considerably up or down 
from their original plane, that is, above or below an optical section 
of the medium, their direction was taken as that which they would 
assume if projected on their original plane. Those growing ver- 
tically up or down in the medium were neglected. 
The holes in the mica plates were examined in regular succes- 
sion, one row after the other, in order that no subconscious selec- 
tion could be made of those that appeared more favorable to the 
