78 PLANT RESPONSE 



Style of Datura alba. Experimenting with the style has 

 the special theoretical advantage that, owing to the soft 

 nature of the tissue, the effect recorded is purely of 

 longitudinal contraction. In specimens which have not 

 this characteristic to the same extent, and which may be 

 anisotropic, like the filaments of Cynerecs, the contraction is 

 not always purely longitudinal. There is a tendency, owing 

 to differential contraction, to the production of curvature. 

 ""' For these reasons, a limp and thread-like 



style fulfils the ideal requirements of an 

 experiment for obtaining true longitudinal 

 contraction. With this specimen of Datura 

 I applied thermal stimulus at intervals of 

 Fig. 38. Photo- ^^^'^ minutes, in the manner already de- 

 graphic Record of scribed. The records show how extremely 



Responses of Style -r 1 



oi Datura aiha xo uniform the responses are (fig. 38). The 

 Thermal Stimula- ^^^^ longitudinal Contraction may also be 

 obtained from plants other than phanero- 

 gams. On applying electrical stimulus to the stalk of the 

 fungus Agaricus 1 obtained a contraction of 2 per cent, of 

 the original length. 



Remarkable extent of contraction in coronal filaments 

 of Passiflora. — There are some plants, again, in which the 

 extent of the excitatory contraction is very great. For 

 instance, the filamentous corona of Passiflora qiiadrangiilaris 

 often gives a contraction of as much as 20 per cent. 



It will thus be seen that not only is the phenomenon of 

 longitudinal excitatory contraction present in all plants, but 

 that such excitatory movements in some which are supposed 

 to be insensitive, rival in extent those of the typically sensi- 

 tive filaments of Cynere(£^ which are said to exhibit a con- 

 traction of from 8 to 22 per cent. 



In order to obtain a suitable record a magnification of 

 only twenty to thirty times is necessary in the case of the 

 highly excitable tissue of the corona of Passiflora. In less 

 excitable specimens, a magnification of 100 would be enough. 

 The advantage of relatively high magnifications in general 



