76 



REGENERATION 



of the net were squares with a side of 3^ inch and the squares of 

 the wire netting made it easy to follow and measure the slope of 

 geotropic curvature from day to day. It was found that under 

 proper conditions this curvature increases with the mass of the 

 leaf as intimated in Fig. 54. Three stems (a, h, c) were selected, 

 each having a leaf at the apex. The leaves in h and c were partly 

 cut off so that the mass of the leaves in a, h, and c was roughly in 

 the ratio of l'.}i'./^i. The drawing was made after 11 days. 

 The figure shows that the degree of geotropic curvature in the 



Fig. 55. — Stem split lengthwise, one piece having a whole, the other only half of 

 a leaf at apex. Curvature is greater in stem with whole leaf. May 8 to 11. 



three stems increased with the mass of the apical leaf, being a 

 minimum in c and a maximum in a. When the stem contains no 

 leaf the curvature is a verv slow process. 



It seemed more accurate to modify the experiment by always 

 comparing the rate of curvature of two halves of a stem split 

 longitudinally as in Fig. 55, a and h. A stem with a pair of apical 

 leaves was split as accurately as possible in the middle between 

 the two leaves and each half was suspended as shown in the 

 figure. The leaf was on the lower side of the stem as in the pre- 

 ceding experiment, but while one leaf remained intact, part of the 

 other was cut off, so that its mass was only about one-half that 



