26 



THE CAUSES OF FLUCTUATIONS IN TUKGESCENCE 



of 



sap. 

 sap 



7 



In the case of blue Ci 

 but this alkalinity is 



the tint is certainly related 



g 



part due to the pr 



of 



alkalinity 

 i- fugitive, 



fixed materials. In many yellow flo 



the other hand 



persistence of the colour 



after death of the tissues depends on much of the colouring matter being insoluble in 



sap 



In the African marigold, for example, the g 



bul 



of the pigment of the 



corolla is not in solution, but is deposited 



the form of resinous gr 



hich are 



d therefore any changes in the reaction of the cell-sap do 



that 



quite insoluble in water, ai 



appreciably affect their colour. The fact, therefor 



loss in turgescence in the tissues to be accompanied by any conspicuous 



colour, cannot be taken as any evidence that chemical changes in the nature of the cell 



chan 



do not find 

 3 in their 



o 



sap hav 



ed 



the constancy with 



presence of such changes, in cases where indices 

 supports the belief in the normal coincidence of 



rhich we encounter evidences of the 

 their occurrence are present, strongly 

 orations in turgescence, which depend 



on fluctuations in functional activity of the protoplasts, and chemical changes in the 



cell-sap. 



The chromatic change accompanying depression or abolition of function in vegetable 



tissues is not, of course, an absolute proof of coincident alterations in their osmotic 



properties, but merely of alterations in the composition of 



their 



cell-sap. 



It 



is 



j 



however, highly probable that the processes 



leading 



to the latter may affect the 



former also, and there are certain phenomena which to a certain extent appear to 

 indicate that they actually do so; for in cases in which depression and abolition 

 of functional activity is accompanied by very marked chromatic changes, we find 

 the coincident loss in turgidity excessive, whilst in cases where chromatic changes 

 are inconspicuous, the loss in turgidity is not nearly so great. For example, when 

 the flowers of blue Clitoria are killed by continued exposure to the vapour of chloro- 



form, hardly any 



change 



manifests itself in their colour, whilst in the case of flowers 



A 



corre- 



of scarlet Hibiscus under similar circumstances the change is very great, 

 sponding difference occurs in relation to the coincident loss in turgidity, for, although 

 there is a considerable loss in Clitoria, it is limited in degree as compared with that 

 occurring in Hibiscus, in which the great change in colour is accompanied by absolute 

 flaccidity of texture. The absence of conspicuous change in colour, and the limitation 

 in loss of turgescence, in Clitoria are at all events both ascribable to the presence of 

 certain stable constituents in the cell-sap which serve to maintain conditions in it 

 subsequent to the death of the tissues which can only be maintained in Hibiscus as 

 the result of the continued exercise of functional activity. 



The experimental data which have been given above afford sufficient evidence that 

 alterations in turgescence following exposure to influences of the most diverse nature, and 

 which can hardly be supposed to produce any common effect on the nature of the proto- 

 plasts of the tissues beyond depressing and ultimately abolishing their functional activi- 

 ties, are accompanied by conspicuous alterations in the chemical constitution of the 

 cell-sap. This in itself is sufficient to suggest that it is to the properties of the latter, 

 and not to those of the protoplasts, that turgescence is immediately related; but we are 

 not obliged to remain content with any ambiguous evidence, as it is not hard to find 

 examples in which turgescence persists even in a very high degree quite apart from 

 the presence of any living protoplasts in the tissue. The tissue of the mesocarp of 

 a ripe orange is one of the most striking of these. Here we certainly have a highly 

 turgid mass of tissue in which turgescence is maintained in spite of the absence of 



