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THE CAUSES OF FLUCTUATIONS IN TUKGESCENCE 



action 



along the pinnules of the same secondary rachis, convergence of th 



one or 



it may be of all the other secondary petioles, rapidly spread 

 the course of one, two or all the other secondary rachises, 



d 



fugal action alonjr 



aximal action in th 



primary pu 



leading to the fullest dep 



of the primary petiole. But wl 



soil and air are alike damper, the extension and rapidity of movements steadily di 



and when 



approached 



minimum 



of 



m 



attained 



pt unde 



action of other factors than mere escape of liquid from the tissues. 



During periods 



of 



excessive moisture the injury to the pinnule prod 



no 



ediate movement even 



,11 y, gradual 



dat 



appear 



conspicuously at the site of section, and this is 



presently followed by slow gradual 



of the injured p 



In some cases no 



effect whatever foil 



others, movements 



and 



m 



still 



others, 



7 



ow 



and imperfect ele 



confined to the opposite pinnule 



of 



a certain number of 



other pinnules in the distal half or third of the same pinna occurs. Both rate, 

 >unt and extension of movement most unequivocally bear an inverse relation to 

 conditions of soil and atmospheric moisture ; where soil — and atmospheric moisture are 



am 



pr 



esent in maximal degree, the movements following section attain their 

 gard to rate, amount and extension ; where soil and atmospheric 



minmmm in 



moisture reach the 



lowest level at whicl 

 position by the pin 

 velopment. 



they d 



■ 



not lead to permanent 



pt 



of th 



e 



octurnal 



the 



movements following section attain their maximal de 



The same holds good in regard to movements originating in connection with 

 other influences. The movements which follow the application of heat to the tissues 

 are normally more extensive than those following section, but their extent and rapidity 

 are equally affected by the existing conditions of atmospheric and telluric moisture. 

 The application of an open flame to the tip of a distal pinnule of 

 is' in hot dry weather followed by immediate 



a 



distal 



pinna 



action, spreading rapidly 



over the 



entire leaf, and in many cases succeeded by action in many more leaves on the same 



axis 



both 



in 



the centripetal and centrifugal direction. 



But, 



where conditions ap- 



proaching saturation prevail, similar treatment is followed by action which is both of 



a more gradual character, and which does not extend 

 directly injured pinna (Appendix D). 



beyond the pinnules of the 



The above facts clearly show that the capacity for movements, the rate at which 

 they are conducted, and the extent to which they are propagated, bear a direct rela- 



can occur; and the question 



irritability and 



tion to the extent to which rapid general loss of liquid 



arises is whether this is to be 



regarded 



indicating increased 



favouring general loss of liquid from the 



contractibility in the protoplasts of the motor organs under the influence of conditions 



tissues, or as evidence that the movements 

 are dependent on losses in tumescence directly connected with the loss of liquid itself. 

 Now, there is no independent evidence that conditions of atmospheric humidity are capable 

 of acting directly upon the irritable and contractible functions of the protoplasts of the 



motor organs 



no evidence to show that the irritable and contmctible functions 



are 



a moist one. But there is abun- 



stimulated by a dry atmosphere and depressed by 



dant independent evidence to show that conditions of atmospheric humidity directly affect 



turgescence owing to the effects which they produce 



is satisfactory structural evidence that the opposed 

 organs are liable to undergo losses in turgescence 



on transpiratory loss, and there 



masses of tissue within the motor 

 in unlike degree, and at unlike 



"S 



