146 CUNNINGHAM ON FLUCTUATIONS IN TUEGESCENCE. 



applied to several axes, but in no instance was the application followed by the occurrence of any 

 appreciable movements, either centrifugally or centrjpetally. 



Experiment XIX— J 



fallen shortly heft 



F. Humidity 94 per cent. The 



Searing of axes 



was 



followed only by very slow, imperfect action confined to the first leaf beyond the point of 



application. 



Now were the effects which, under average conditions of humidity, follow the application of heat to 



axes dependent on the propagation of stimulant fluctuations in pressure conducted along any closed 

 system of tubes containing liquid suoh as Haberlandt's H Reizleitende system/' it is clear that, in place 

 of diminishing and ultimately disappearing with increased humidity, they ought to increase as it 

 increases. They ought to increase with any conditions favouring increased turgidity throughout the 

 syst-m, whereas in fact they follow a precisely opposite course. But such decrease and abolition oft 



i 



movement 



movement is precisely what ought to cccur 

 occurs under ordioiiy circumstances be the outcome of an obstructive gaseous interference with the 

 current of water ascending from the roots. Under ordinary conditions of atmospheric and telluric 

 humidity there is no accumulation of surplus water within the water-conducting system, and the stream 

 traversing the latter only suflices to. maintain full turgescence of the tissues in spite of continuous 

 transpiratory loss. Under such circumstances any obstruction to the continuity of the stream must at 

 once tnd to disturb the pre-existent equilibrium between supply and loss of water in all distally situated 

 ports; and as the diurnal position of the leaves is dependent on maximal turgescence in the tissues of 

 the motor organs, any disturbance of this nature must inevitably tend to cause a departure from it. 

 But where conditions of atmospheric and telluric humidity are maximal, root-supply becomes excessive 

 and transpiratory loss is reduced to a minimum, and with this a surplus stock of water must 



tend to accumulate within the water-conducting system. The latter no longer represents a simple 



system of channels traversed by a stream of water which escapes at the distal extremity in the 

 same bulk as it enters at the proximal one, but a reservoir containing a large store of water from 



very 



~ **** & 



The bulk of water contained w T ithin 



the water-conducting system is greatly in excess of that which is continuously withdrawn from it to 

 maintain full turgesc nee under the conditions of minimal transpiratory loss, and consequently the 

 occurrence of a temporary obstruction of root-supply is of no consequence in respect to the mainten- 

 ance of turgescence. Tee diurnal position of the leaves is determined by the fact that certain masses 



of tissue in 



the motor organs are endowed with excessive assimilatory and osmotic properties under the 

 influence of solar stimulation. But the application of heat to a point in an axis does not affect the 

 ossumlatory and osmohc properties of the motor organs of the leaves in any way, and consequently, 

 bo long as the water-conducting system contains a supply of water from which they can satisfy their 

 orotic caches there is no reason why any fluctuations in their turgescence should attend the appli- 

 cation. *ow a store of surplus water has accumulated within the water-conducting system under the 



:*rvi e zzr d f tent r di . tions of humiditj ' s ° that a ten ™ °"° n to the 



aiiy additional supply 18 of no importance whatever in regard to the maintenance of turges- 



cise i, ™,; i ,1 i , x, . Ettend ltS establi8hm ent. The absence of movements in this 

 case is precisely parallel to the absenoe of movements attend,™ *h« -^. a * i u ^ 



from a nW *»A~ —xe , ___. . , . , movel * ent3 attending the separation of leaves or shoots 



In both cases alike there is an arrest of root- 



access of 



conseq 



plant 



b 

 shoot 



ihoient 



ab 



and couMoueutlv «L l! f . 7 Ca ' 8 '° re ° f water ™ tbi * «'<> *»*»«-*««-- ~— — 



m cousequently any brof, temporary arrest of root-suuolv fa hw—M. „« .-,--,„ 



the 



of the surplus ' w 2r IT T 7 S *" *° "»«»«* °*T after the gradual expenditure 



diate e^tTLte t ^Jf"" f* "•*"«*«*»« **»• *» ■**- «« does auy imm e- 



has occurred 



occur. Wher 



