IN THE MOTOR ORGANS OF LEAVES. 



4 



» 



of active contraction of the protoplasts of the motor organs, we find abundant evidence 

 that they are due to an essentially similar causation. The movements in these cases 

 being determined not by individual cells, but by masses of tissue, are often of very 

 considerable magnitude and are thus more readily appreciable than the stomatic move- 

 ments are; but, like the latter, they are determined either by fluctuations in the retentive 

 power of the cell-sap or by variations in the supply of fluid available for retention. 

 Accordingly we find them manifesting themselves either as tho result of alt (rations in 

 stimulation of assimilatory activity of the protoplasts of tho motor organs, of variations 

 in the relation of root-supply to transpiratory loss, or of variations in conditions a i I'm ting 



filtration. 



The periodic assumpt 



of the nocturnal and diurnal positions 



yctitropic 



leaves is a phe 



of precisely the same nature as the coincident opening and 



closure of the stomata and the changes in col 



of the fronds of ticlag 



9crpcn8) m 



being essentially due to alterations in the osmotic properties of tho cell-sap, but 



action of these is affected by their 



cid 



with certain general relations of 



PPty 



and loss of fluid. Consequently, just as in Selag 

 whiteness in the fronds occurring in the first part of t 



wo find the maximum of 



night, 



tho 



of nycti 



tropic leaves we find the 



nal position attaining its maximum at tho same 



The attainment of the maximum of the 



dition at or shortly 



set 



and the occurrence of a reversion 



part of the 



ght 



are characteristic 



feat 



ur 



nal coi 

 da the diurnal one 



nyctitropic ph 



during 



m 



after sun- 



the latter 

 generally. 



The maximum is attained at the time 



it is 



j 



b 



then the cessation of solar 



stimulation of assimilatory 



ty and the 



quent losg in osmotic property of 



the cell- sap 



de with unaltered, or inappreciably altered, relations bet 



general 



loss and supply of water. Dep 



of turgescence reaches its 



al 



maximum 



> 



w 



hilst abs 



of solar stim 



and 



ed transpiration are acting coincidently 



to give rise to loss of fluid from the tissues; and 



wh 



one of the factors ceases 



to act, a rise in turg 

 so far as almost to 



naturally follows, and in certain cases may even go 

 establish the diurnal condition under normal circumstances. 



During the day we have to deal with two opposing factors, increased protop 

 „±; — lo^on on the one hand, and increased transpiratory loss on the other 



At 



we 



tw 



stimulat 



sunset 



evaporat m 



been reached, there is a continued absence of solar stimulation ; but this is no longer 



have 

 acting 



factors, decreased protoplasmic stimulation and continued 

 itaneously to diminish turgescence. After the dew-point lias 



associated with tra 

 is left at liberty 1 

 from the addition 

 influence of solar stimulation 



ipiratory loss, and, the root-supply continuing as before, the cell-sap 

 satisfy any osmotic capacities which it continues to have apart 



it by the protoplasm under the 



of special assimilatory products to it 



The absence of solar stimu 



d 



not cause a com 



plete cessation of protoplasmic activity or a total 



death of the 



does in th 



on 



unstable compounds; it only giv 

 stimulation does not give rise to an 



loss of osmotic property in the cell -sap, 

 which the osmotic property is dependent 

 rise to depression in them. Absence of solar- 



cases m 



abolition of functional activity 



merely 



withdrawal of one special stimulus to its exercise. Even in tl 



total absence of solar 



stimulation, 



general suj 

 turgescence 



therefore, a great degree of turgescence persists under 

 ply and loss of fluid; and, where supply 



mal 



f 



ay 



ly attain the degree which it 



and loss 

 Jly has v 



arrested, the 



? 



1 



the tissues 



posed to coincident 



stimulat 



and normal 



piratory loss, and may exceed 



