486 



Mr. F. Darwin and Miss I). F. M. Pertz. [May 30, 



Care is necessary, at the beginning of the experiment, to prevent 

 more than one secondary root developing • the primary root should at 

 first be uncovered every day, and any young secondaries pinched off. 



The preliminary arrangement takes some time ; thus, for instance, a 

 primary root was amputated February 6, and the tertiary roots were 

 not ready for observation until February 16. 



Fig. 1. 



The method was that of Sachs, which may be illustrated by the 

 following diagram (p. 487). 



Fig. 2, A shows a primary root growing vertically, and giving off, 

 to the left and right, two sets of secondaries, L and E, which have 

 assumed their usual lines of growth somewhat below the horizontal. 

 The trough is now raised at one end, as in fig. B ; the roots L and E 

 are affected in opposite ways by this change, the L roots are now 45° 

 below, while the E's are 45° above their normal line of growth, the 

 consequence is that the L's bend up and the E's down, as shown by the 



