1917] 



LOEB—BR YOPH YLL UM 



37 



iv. Mechanism of geotropic curvature in Bryophyllum 



CALYCINUM 



periments 



definite idea concerning the mechanism of the geotropic ben 

 Immediately after the stems were split, marks were made 



and 



then the stems were suspended horizontally, one-half of the split 

 stems having their cortex below, the others having their cortex 



Fig. 21 



above. Stems with an apical leaf were used for the purpose (like 



17, 20). After 10 days, when the halves with the 



those in figs. 



cortex below had bent strongly, the displacement of the marks 

 was ascertained. It was found that the marks on the halves in 

 which the cortex was above and which had not bent were practically 

 unchanged. The same was true of the marks in the non-bent 

 regions of the other halves, where the cortex was below; while a 

 growth of 15-20 per cent of the original length had taken place in 

 the bent convex region of those stems having their cortex below. 



