22 



Experiment 



THE CAUSES OF FLUCTUATIONS IN TURGESCENCE 



V— Two leaves of Kalanchoe with intensely acid sap were taken at 



10-15 



One, 0, weighed 28*7 grammes 



the other, b, 28'58 grammes 



Both 



wer 



then set with the bases of their petioles immersed in water, and a was exposed to dir 



sunshine and b to 

 period, a weighed 



absolute darkness for th 



hou 



and a half 



At the close of this 



27*3 grammes, and the acidity, and especially the permanent 



greatly diminished in intensity; while b weighed 27*87 



On the following morning the 



acidity, of its juice was very 



grammes and yielded fluid of 



acidity of the sap in both cas 



in a moist chamber and exposed for three hours in absolute darkness to a temp 



was 



ely acid reaction. 



alike and intense. The leaf b was now enclosed 



of 88'7 in order to determine whether the effects 



following 



exposure to sunshine 



were m any 



appreciable degree determined 



by heat as distinct from light; but the 



idity of the sap 



ed undiminished at the end of the experim 



In this case the stimulant ultimately leading to a diminution in the acidity of 

 the cell-sap is evidently light, but in other cases heat comes prominently into play in 

 producing similar results. For example, whenever the temperature remains beneath a 

 certain limit the flowers of Ipomcea hederacea, however brilliant the sunlight be, never 

 attain the intense, dusky blue normal to them when in the expanded condition, but 



retain more or less of the red tint proper to the buds — a phenomenon which, as we 

 shall presently see, is due to a relative excess of acid constituents in the cell-sap. Here 

 temperature is the determinant of decrease in acidity, just as in other cases we find that 

 it is the essential determinant of the increase in turgidity of certain masses of tissue 

 on which the expansion of flowers such' as those of Portulaca grandiflora is dependent. 

 The flowers of Portulaca do not unfold in the brightest sunshine until they have 

 attained a temperature of 70' to 80°F. ; and, if only this be provided, expansion takes 

 place in total darkness just in proportion to the rise in temperature. Both heat 

 and light are clearly capable of determining chemical alterations in the nature of the 

 cell-sap and increase in the turgescence of masses of tissue. According to Sachs' 

 theory of the causation of turgescence, in order to account for the phenomena we must 

 assume that in some cases the factors act on the physical properties of the protoplasm, 

 and in others on the chemical nature of the cell-sap; or, in other words, that in some 



cases they affect the structure and in others the function of the protoplasm. But surely 

 it is more reasonable to assume that both chromatic and motor effects are due to 

 stimulation of the latter only. Such stimulation may well give rise to the formation 

 of products differing from one another in different instances, in some characterised 

 by their reaction and in others by their osmotic properties, and accordingly ultimately 

 determining changes of colour in the one case and movements related to altered tumes- 

 cence in the other case. 



In some cases stimulation of functional activity, whether photic or ther 



mic 



) 



leads 



to decrease and in others to increase in the acidity of the cell-sap and to corre- 



sponding changes in the 



tint of colouring matters which 



are dissolved in 



sity of blue and green colours 



being 



the inten- 



related to relative alkalinity and that of red 



ones to relative acidity. That this is the case is shown by the results of the 

 following experiments : — 



Experiment J.— The petals of a flower of Erythrina stricta, which are of a brilliant 



exposed in a chloroform-chamber almost immediately became of a 



scarlet colour 





