THE 



CAUSES 



OF 



FLUCTUATIONS 



IN 



TURGESCENCE 



IN THE 



MOTOR ORGANS 



OF 



L E A VE S. 



♦ 



CHAPTER 



%kt essential nature of iurgtsctnce in begetable tissms, the causes 



flibinj rise 



fluctuations in 



anb the harious effects 



tohich the latter mag proimre. 



As all the massive movements occurring in the higher plants, and which are 

 ordinarily ascribed to their irritable properties, are directly dependent on variations in 

 turgidity, it seems to be desirable at the outset briefly to consider certain points regarding 

 the nature and causes of the latter condition. 



Turgidity is a condition in vegetable tissues in which they contain a greater amount 

 of liquid than that sufficing for their simple saturation. In other words, turgid tissues 

 contain more liquid than they are capable of accommodating as the result of then- 

 passive physical capacity. The excess of liquid content is the result of the presence of 

 osmotic materials within the tissue elements, and its retention must necessarily give 

 rise to certain effects in these, to an increase in size, to elevation of conditions of 

 pressure, or to both of these combined in various proportions. In the case of free proto- 

 plasts simple increase in size will occur, and in most tissues increased intracellular 

 pressure will arise in those cases where the cell walls are rigid either intrinsically or 

 from their relations to neighbouring parts, and varying combinations of increased size 

 and increased intracellular pressure where the cell-walls are extensible and elastic. 



of cases turgidity in vegetable tissues is essentially dependent 

 their continued vitality; but at the same time the occurrence of cases in which we 



In the great majority 



on 



find it existing in 



the highest degree 



after the death or even entire removal of the 

 protoplasm show that it cannot be directly caused by the latter. There is no direct 

 relation between turgidity and the presence of living protoplasm in the turgid elements; 



as it 



but yet living protoplasm is necessary in order to the development of turgidity, 

 is due to the presence of products of protoplastic activities that the latter arises. The 

 condition which holds a direct causal relation to turgidity is the presence of osmotic 

 materials within the protoplasm or cell-sap, and these materials are the products of the 

 functional activities of the protoplasm. Whether the actual presence of living proto- 



plasm is necessary or unnecessary to the maintenance of turgidity in a tissue is determined 



Ann. Kot. Bot. Gaed. Calcutta Yol. VI 





