

IN THE MOTOR OKGANS OF LEAVES. 



M 



ure 



coatained in Appendix E. The effects of exposure to the influence of saturated soil 



diminishing 



capacity for movement are constantly presenting them- 



various ways. Whilst working at the subj. . 



and atmosphere in 



selves in the most conspicuous fashion in 



I have had constant occasion to take specimens of Mimosa pudica from the parden 



in which they are grown to my laboratory which is situated at a distance <-f about a 



mile from it. When the transfer is effected during periods when atmospherie humidity tl 



relatively low, even slight displacement of pot plants is followed by extensive mov.-im i.t 



of the leaves, and the agitation to which they are exposed during the drive over tl,. 



rough road^ which intervenes between the two localities certainly leads to maximal 



movements in the pinnules and primary petioles, and to considerable convergence of 



the secondary rachises. But with increased h 

 of movement deer 



timidity the tendency to the ocenrrem< 



the plants undergo 



eases; and when humidity of soil and atmosphere are at a maximum 



» 



all the agitation to which the transfer 



exposes them either with- 



out exhibiting any movements at all, or movements of only the most limited and 

 partial kind. Parallel phenomena make their appearance under the influence of artificial 

 elevation or depression of atmospheric humidity. If two plants luted into can fall;. 

 stoppered and waxed pots be exposed side by side in two hermetically s< ak I chambers 

 one containing a vessel of water and the other a vessel of pure sulphuric acid, their 

 leaves are of course coincidently exposed respectively to a saturated and to a very dry 

 atmosphere. As the result, transpiratory loss is arrested in the one but rises to a high 

 level in the other, and corresponding differences in their so-called irritability also make 

 their appearance. The leaves in the saturated atmosphere become highly ■ ievated and 

 extremely expanded, and after an hour or two of exposure they fail to respond even ' 

 the violent agitation produced by shaking the chamber within which they are endow I. 

 The leaves in the sulphuric acid-chamber, on the other hand, also show extreme 

 expansion and elevation, but are very 



susceptible to agitation, even slight shaking of 



the chamber being 



followed by depression of the primary p< tioles and complete 

 assumption of the nocturnal position by the pinnules. So, again, when a leaf or a 



portion of a 



shoot bearing several leaves 



is separated from a plant at a time 



when 



air 



and soil are alike relatively dry, the separation is followed 



by 



1111- 



)V 



mediate, rapid and complete movements in the pinnules and primary petioles, and 1 

 considerable convergence of the secondary rachises; whilst when atmospheric aud telluric 

 moisture is excessive, no movements whatever manifest themselves for some ti , and 

 the movements which ultimately do occur are very slowly, imperfectly, and gradually con- 

 ducted. Under conditions of maximal moisture, the primary absence of any movement 

 whatever, and the delayed and imperfect character of those which ultimately occur, 

 become wonderfully conspicuous. Under such circumstances, shoots will frerpiently stan 

 exposure to all the disturbing influences of separation from the axis, and of considerable 

 and relatively prolonged agitation without showing any appreciable movements. I have 

 accordingly been able to separate shoots and transfer them from the site in which they 

 were grown to my laboratory without their showing any more evidences of movement 



than rooted plants do un 



Under similar circumstances exposure to conditions which determine the artificial 



der conditions of high soil and atmospheric moisture. 



regards movement. 



W h en 



escape of liquid from the tissues produce minimal effects as 

 the air and soil are both moderately dry, amputation of the tip of a distal pinnule is 

 normally followed by immediate and rapid action in the injured pinnule and simultane- 

 ous, or practically simultaneous, action in the opposite one, rapid spreading centripetal 



Ann. Roy. Bot. Gar». Calcutta Vol. VI. 



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