

VARIOUS MOVEMENTS IN PLANTS 169 



of their pulvinules is thus found to be more on their upper 

 surface, the very opposite from that of the main pulvinus. 

 Besides these two movements in opposite planes, down and 

 up respectively, we see that the midway pulvini, those 

 of the four main leaf divisions, behave differently again ; 

 for though they may fall a little, their main movements 

 bring all four almost close together from their normal 

 divergent position, so their sensibility must obviously be 

 in each case on their sides, and in right and left pairs. A 

 wonderful leaf-mechanism, with its tri-dimensional con- 

 trast ; yet after all in analogy with that of our own build. 



The leaf thus visualised, and its sensitive working 

 practised on, till we can in various ways not only make a 

 whole leaf fall, and thence all the rest, but also stir a single 

 leaflet, and so compel the fall of the whole leaf, and even 

 thence of other leaves through the plant. We thus prove 

 conductivity of impulse in each direction. We are now 

 ready for finer observation, experiment and interpretation. 

 First the older explanation, still surviving in text- 

 books ; Pfeffer had offered a hydro-mechanical theory of 

 transmission of stimulus, and Haberlandt the very best of 

 microscopic analysts of plant-tissues, since most devoted 

 to applying his observations towards the interpretation 

 of their uses and functionings in detail had offered, and 

 with fairly general acceptance by physiologists, a too simple 

 explanation of the fall of the Mimosa leaf. He compared 

 its pulvinus to an indiarubber tube filled with water and 

 tied in at both ends so having a definite hydrostatic 

 pressure of turgescence, and which, when a pinch is given 

 at one end, of course exhibiting an increase of pressure, and 

 even a certain flow, which are transmitted along the tube 

 as an undulatory wave. 



It is here worth noting clearly that in this contrast 

 of interpretations of transmission of stimulus (i) as essen- 

 tially hydro-mechanical, for most vegetable physiologists 

 hitherto, but (2) as fundamentally ' excitatory ' for Bose 

 that it is our physicist who has here taken up the 



