IN THB MOTOR ORGANS OF LEAVES. 



61 



their action is now expended in producing general rotation of the lamina 



d 



ipondin 



f the flexible vascular axis of the 



P 



Had 



we 



inferior 



d 



pads been disposed inferiorly and superiorl 

 depression, had they been external and internal 

 because they actually are extero 

 the under and upper surfaces of 

 ace and modifying the chara 

 Itimately give lise to. 



pul 



i have had 



e 



elevation and 



convergence and divergence; but 



'Superior 



d 



ted 



half of the lamina 

 of the movements 



nlv 



we have 



respectively to 

 rotation taking 



d tl 



le posit 



whi 



i 



thev 



From the nature of the diurnal and nocturnal p<siti< < of the pinna*, it i> dear 



during the day the intero-superior and durin 





the night the extero-inferi' r pulvi 



they 

 the 



possess 



r 



of strength: and the 



sj)icuou8 differences in col 



liibit rend 



it 



sy to 



prehend why lliis should bo the eas. 



E 



ven 



m 



cursory examination in this case 



cher in chlorophyll than its opponent 



Tl 



th 



a 



d 



is 



h 



pr 



ex( •• ss m 



f 



tional 



ity, and therefore of turgescence, under the intl 



and 



f solar stimulation. 



But increased turgescence implies increased strength and resistance 



which it occurs, and consequently the 



superior pad must 



relative increase in power 



action of its opponent 



duiing 



the dav 



ch 



e 



abl 



it tun) 



IO 



in the tissue in 



ssarily Require a 



• to overcome 



the 



Movements of rotation which are so frequently presi n 



1 



n'gh degree in the case 



of the pinnae and pini 

 of their primary and 

 horizontal 



of nycti tropic leaves are absent 



pic 



in the ease 



ndary peti 



because in them the motor Ippa 



surfaces like those of the laminae to act upon. Where such surfaces are 



pr 



and the opposed masses of tissue 



specially related to them 



» 



of the 



factors which in the case of the petioles give rise to 



convergence and diver- 



gence, elevation and dep 



is partially expended in 



determining 



various 



degrees 



of rotation. In the present instance rotation ad 



so f;ir that the outer half of 





the lamina, and the outer side of the keel of the midrib come to lie directly 



p wards, which of course 



that the basal laminar expansion of the extero- 



ferior pulvinar pad lies to the upper side of the base of the midrib 



It 



is 



ow 



pable of giving rise to any further rotation, 



d its 



power is expend 



ed in producing lateral pressure on the outer, and, for the time being, upper side of 

 the keel of the midrib and proportionate depressive flexion in it. 



The alternation of the diuinal and nocturnal positions is not caused by alt r- 



nating 



diurnal dec 



and 



octurnal increase in the absolute strength of the extero- 



ferior mass of pulvinar tissue, but by 



alternating d 



merea se 



d nocturnal 



dec 



in that of th 



in turgescence of the mass of 



superior one. There is nothing to show that any rise 

 tissue making for the nocturnal position attends removal 



of solar stimul 

 influence 



O 



the contrary 



find the same position appearing under the 



of exposure to excessive transpiratory loss, and in leaves which are detached 



from the axis, and therefore subjected to entire arrest of 



pply. The position 



is thus clearly one 



attending general loss 



d not any localised rise in turgescence. 



O 



th 



removal of solar stimul 



of strength, takes place throughout 

 portions which make for the diuir 



genet al 

 hole pul 



loss of turg 



but the loss is 



position, because they 



and consequently 



in those 

 stronger 



greatest 



physiologically 



d structurally weaker than their opponents 



The result of this is that 



although 



the 





