XI] TELEGRAPH PLANT 115 



Strictly speaking, these nutations belong to the same 

 order of phenomena as the curvatures of the growing leaf 

 in the bud, and as they emerge from the bud state, but 

 they may be conveniently regarded here because they 

 result in definite up and down (and even side to side) 

 movements of leaves which are already nearly fully de- 

 veloped. 



Some leaves, and especially those of certain Leguminosce, 

 Oxalidce, Marantacece, Marsiliee, &c., exhibit quite a 

 different set of periodic movements, however, and it is 

 to these alone that the term spontaneous can be applied 

 with any approach to accuracy ; though even here the 

 term is only applicable as an expression of our ignorance 

 of the internal causes which induce the movements. 



In the cases referred to, the leaves, or leaflets, describe 

 jerking nutating movements, at intervals of a few minutes, 

 day and night, provided the temperature and other con- 

 ditions of the environment are not unfavourable to the 

 general welfare of the plant. 



In Desmodium gyrans, the Telegraph Plant, one of 

 the best examples, the two small lateral leaflets oscillate 

 in such a way that their midribs describe an inverted 

 conical surface in from two to five minutes at intervals. 

 The movement is jerky, and often very irregular in 

 character, even in darkness or in a light of constant in- 

 tensity, and is due to periodic differences of turgescence 

 of the upper, lower, and lateral cells of the pulvinus, 

 possibly induced by periodic alterations in the character 

 of their osmotic contents. In most of the other plants 

 referred to, the leaves simply move up and down. 



It is clear that we do right in classifying this set of 

 periodic spontaneous movements apart, for the time being; 

 but it is also very probable that the only essential difference 

 between them and the movements brought about by 



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