2Q THE CAUSES OF FLUCTUATIONS IN TUMESCENCE 



to a ffreat degree coloured the various explanations which have been advanced to account 



for the occurrence of the sudden fluctuations in turgescence on which the movements of 

 masses of vegetable tissues depend. Sachs, for example, affirms that turgescence is essenti- 

 ally due to the great resistance which protoplasm normally presents to the filtrative escape 

 of any liquids which it may have endosmotically acquired, and that any sudden escape 

 of water from a turgescent cell necessarily implies a change in the nature of the proto- 

 plasm whereby it readily permits of filtration.* He practically ascribes everything directly 

 to the protoplasm and nothing to the influence of the products of its activity contained 

 within the cell-sap, and by doing so is constrained to endow the protoplasm with certain 

 special properties in order to account for the phenomena which actually occur. In 

 adopting this view he entirely loses sight of the possibility that turgescence may be due to 

 the osmotic properties of the cell-sap overcoming the filtrative facilities provided by the 

 protoplasm, and that loss of turgescence may arise as the result of diminution in the 

 former and not of any increase in the latter, of these two factors ; and when we come to 

 look for any positive evidence tending to a decision of the question, we find that, whilst 

 we can readily trace the occurrence of chemical changes in the cell-sap which may well 

 cause changes in its osmotic properties coinciding with loss in .turgescence, we are 

 unable to find any proof of alteration in the filtrative power of the protoplasm save the 

 very phenomenon which it is regarded as giving rise to. If we ascribe turgescence 

 directly to the properties of the protoplasm, we are left to assume that any fluctuations 

 in the former must be accompanied by changes in the latter; but if we ascribe it to the 

 properties of the cell-sap, we can at all events show that loss in turgescence is accom- 

 panied by changes in the chemical constitution of the factor. According to the one view, 

 anaesthetics and all the other factors which we have just seen acting as determinants of 

 loss of turgescence must do so simply because they have the common property of increas- 

 ing the filtrative power of the protoplasm; according to the other, the result is due to 

 alterations in the properties of the cell-sap attending depression and abolition of respiratory 

 and assimilative function in the protoplasm, and of the occurrence of which we have 

 in many cases the clearest chemical evidence. 



The conspicuous changes in the colour of common green leaves attending losses in 

 tumescence caused by exposure to injurious media very clearly indicate the occurrence of 

 coincident chemical changes in the contents of the cells ; but much more striking evidence 

 is forthcoming where variously coloured floral tissues form the subjects of experiment. 



I 



In the case of common leaves the changes in colour accompanying depression and 

 abolition of functional activity (unless induced by media, such as ammonia, which secure 

 the addition of extraneous alkaline constituents to the tissues) are such as to indicate a 

 rise in fixed acidity, the yellowing which takes place being precisely of the character 

 presenting itself in neutral solutions of chlorophyll on the addition of acids. This change 

 in certain cases may be partially ascribed to the addition of extraneous acid during the 

 course of the experiment ; but the fact that it manifests itself in cases where chloroform or 

 extremes of temperature are the agents employed shows that no extraneous agency is 

 required to produce it. Fortunately it is not necessary to be satisfied with this chromatic 

 evidence alone, as it is possible to adduce positive proof that depression of functional 

 activity is, in some cases at all events, directly related to an increase in the fixed acidity 





* Vorlesungen, XVI. p. 330, XXXVII. p. 798. 





