230 



piration, oversaturation of the tissues with water being the chief 



danger to be guarded against in this case. Tropophytes are 



plants which at one season of the year are xerophytes and at 



another hygrophytes ; such are many trees in the deciduous 



forests of India which are hygrophilous in the rains and xero- 



philous at other seasons. A plant growing in a soil containing 



abundance of water need not necessarily be a hygrophyte ; the 



water may for instance consist of a concentrated solution of 



salts, in which case the roots can only obtain the necessary 



supply of water and salts slowly and with difficulty. A xero- 



phiious structure is thus necessitated. Such a structure may 



be due to any factor which either favours transpiration or 



interferes with the ready absoiption of water from the soil by 



the roots. 



