140 MOVEMENTS OF CURVATURE 



It is evident from the above that the movements of pulvini are not 

 produced in such a simple manner as Bert 1 supposed. This author con- 

 cluded that they were the direct result of the changes of turgor due to the 

 accumulation of the glucose produced by photosynthesis during the day- 

 time, and its gradual removal at night. The mere facts that the daily 

 movements continue in air deprived of carbon dioxide, and that the 

 periodic movements are repeated several times in continued darkness, are 

 sufficient to disprove this supposition. 



PART V 



THE INFLUENCE OF THE EXTERNAL CONDITIONS UPON 

 AITIONASTIC CURVATURE 



SECTION 30. Special and General Actions. 



Since modifications of growth and of the tissue-strains are more obvious 

 when they find expression in curvature, reactions of this kind serve especially 

 well to demonstrate the influence of the external conditions. It is easy to 

 see, for instance, that the movements of Mimosa pudica and of the stamens 

 of Cynareae take place most rapidly and actively at a certain optimum 

 temperature, and cease at high and low temperatures, owing to the onset 

 of cold or heat rigor. Provided that the unfavourable temperature is not 

 too severe or too prolonged in duration, the power of reaction is more or 

 less rapidly regained at a favourable temperature as the inhibitory after- 

 effect of the previous exposure disappears. Similar results are produced 

 by the partial or complete withdrawal of oxygen, by the excessive loss of 

 water, and by the action of ether or chloroform. It is, however, worthy of 

 note that the excitation of the pronounced seismonic movements of Mimosa 

 pudica is not essential to its growth and normal development, while the 

 tone of this plant and of plants in general is not only affected by the 

 temperature but also by substances such as chloroform and ether, which 

 the plant never encounters under natural conditions. 



It is in some cases possible by special treatment to inhibit certain 

 partial functions, and in this way to obtain some insight into the relationship 

 between the sensory and motory processes. Thus the repeated shaking of 

 Mimosa pudica causes the suspension of the seismonic irritability alone, 

 as also do low temperatures and anaesthetization, whereas the autonomic 



1 Bert, Compt. rendus, 1878, T. LXXXVII, p. 421 ; also in Mem. de la Soc. d. sci. phys. et 

 nat. de Bordeaux, 1870, T. vm, p. 53. Cf. also the reference in Bot. Ztg., 1879, p. 187. The 

 speculations of G. Kraus (Flora, 1877, p. 73) are of no importance. 



