TROPISMS 183 



like the mussel, so that we are ready to understand how he 

 and his assistants can now dissect out a petiole-pulvinus 

 preparation for investigations as definite and complete as 

 those long familiar to physiologists of the nerve and muscle 

 of a frog, and with his present apparatus carry their in- 

 quiries substantially further. 1 He shows in this connection 

 that in Mimosa the conducting power in a transverse 

 direction is only -^ that in the longitudinal direction of 

 the stem. 



We may next take the case of tissues in which the power 

 of conduction is exceedingly feeble ; the contraction caused 

 by direct stimulus remains, in this case, localised. A very 

 remarkable reaction is, however, produced at a distance, 

 which is of a diametrically opposite character and distin- 

 guished as the ' Indirect ' effect of stimulus. The effect 

 of ' Direct Stimulus ' applied immediately on the responding 

 surface is a diminution of turgor, a contraction and a 

 negative electrical variation shown by the galvanometer. 

 The effect of ' Indirect Stimulus ' is, on the other hand, an 

 increase of turgor, an expansion and a positive electric 

 indication. The discovery of this hitherto unsuspected 

 effect of Indirect Stimulus is one of Bose's most far-reaching 

 results ; for many of the apparent contradictions in the 

 responsive movements in plants are shown to be due to this 

 very important factor having remained so long unknown. 



We may next proceed to Bose's special contributions 

 to the understanding of plant-movements. A very im- 

 portant generalisation established by him is the unity of 

 reaction in all plant -organs, growing and non-growing. 

 Most significant of these advances towards the under- 

 standing of the movements brought about by growth, is 

 the conception, experimentally worked out, that the 

 growing organ and its responses are like those of Mimosa 

 pulvinus and its responses. He records the effect of 

 all forms of stimulus on growth, and shows that direct 



1 Transactions of the Bose Institute, vol. i., 1918. 



