

114 



THE CAUSES OF FLUCTUATIONS IN TUEGESCENCE 



the 



d 



such as 



ppiy 



necessarily to imply increased ii 

 No theory of the communication of impulses givin 



of decreased 

 active protopl 



wa 



contraction in the motor organs will account for these phenomena, because none of them 

 can account for the fact that the propagation of movement should, in the case of young 

 shoots, occur in both directions and in that of old ones in one only, or should, at all 



application, or 



events, not extend beyond the immediate neighbourhood of the site of 



i 



in 



other words, be confined 



to the area in which obstruction can come into 



play in inducing 



decreased supply of water. The theory of active protoplasmic 

 contraction here once more breaks down, whilst the physical theory is able to afford a 

 satisfactory explanation. • 



The phenomena of distribution of movement following the local application of heat 



to some point in th 



of a mature axis of Mimosa pudica may be reproduced 



a 



tably arranged piece of apparatus (Plate I, Fig. 1). This consists of a 



upright 



metal tube closed at the upper extremity, provided with a number of slender, shor 



al branches, and with a 



length that some of the 



fitting stop-cock inserted at such a point in its 



branches lie to 



proximal and others to its distal side 



The 



branches are open at their extremities, and can readily be connected with suitably weight- 

 ed pieces of glass-tubing by flexible joints of rubber-tubing. The majority of the glass 



i out into fine capillary 



tubes 



sealed 



the end, but one or more of them 



draw 



ends and left open, 

 flexion of the rubber 



Their weight ought to be such as to secure a certain amount of 

 oints when the apparatus is filled with water. If the lower end 



of the main tube be connected with a stream of water under a 

 and the stop-cock be left open, fine .jets of water will, of course. 

 the capillary extremities of the open tubes, and the flexion of 

 diminish as 



pressure rises, with 



pondin 



of the 



sufficiently high pressure 



escape continuously from 



all the rubber- joints will 



ass tubes connected with 



But, on sudden closure of the stop-cock, escape of water will continue to occur from 



capillary orifices for some time, and with tl 



tl 



bber 



original state of flexion in all the branches situated to th 



distal 



will recur to their 

 de of the stop-cock 



whilst all those on the proximal side will retain their position of erection unaltered. 

 Here, then, we have a distribution of movement exactly parallel to that occurring- in the 



of mature 



of Mimosa 



The distal discharge of water from the capillary 

 the stream of water entering the lower extremity 



local application of heat at some point in th 



orifices 



presents transpiratory loss, 



supply 



of the main tube represents 

 and the rubber- joints represent portions of tissue, like those present in 



th 



motor organs of the leaves, which are liable to undergo rapid alterations in strength 



connection with alterations in the relat 



between general 



The sudden closure of the stop-cock suddenly obstructs all furth 

 the distal part of the apparatus, and as distal loss continues 



pply and loss of water 



access of water to 



a 



pid fall 



pr 



takes place throughout the whole distal parts of the apparatus, the rubber joints cease to 



by 



turgescent, and the position of the glass tubes comes to be that which is determined 



mere passive structural properties 



But 



conditions of water-supply and loss remain unaltered 



the proximal part of the 



takes pi 



In those cases in which centripetal movements 



if 



appar 



the 



ything, a rise in 



pr 



of heat to mature 

 centripetal 



and hence there is no weakening of the joints or depression of the branches. 



with the application 

 doubt dependent on 



axes of Mimosa pudica, these movements are no 



of the obstructive gaseous expansion, so far as to involve the porti 





