36 THE STORY OF PLANT LIFE 



The water and nutrient salts are enabled to enter 

 by a special process, termed osmosis. By this means 

 water can permeate a cellulose wall owing to its 

 density being less than that of the solution on the 

 inner side of the wall. By this means the cells 

 become distended or filled, and are turgid. There 

 is a continual passage of the water and nutrient salts 

 inwards and a permanent state of turgescence within. 

 This process is akin to diffusion, and in this special 

 form is called osmosis. A similar process is recog- 

 nised in the formation of crystals in the case of 

 minerals. 



The fluids tend to pass from a less dense condition 

 to a denser by the affinity of the watery solution for 

 the special conditions that are presented in the cells 

 and tissues, where they undergo further elaboration. 

 The dividing membranes play a part in increasing 

 the concentration of the solution until it is sufficiently 

 formative and capable of further elaboration. 



External conditions assist the absorption of water 

 and nutrient salts, such as temperature, absorption 

 being rapid in a warm soil, slow in a cold soil. 

 Above a certain degree (5 per cent.) solutions cannot, 

 however, enter the plant, hence the reduction in 

 osmosis in saline soil and in peat soil, where also 

 the root-hairs are reduced in number. 



Epiphytes get their water from rain and nutrient 

 salts from whatever soil or humus accumulates in 

 their aerial habitat. Desert plants also absorb water 

 through hairs on the leaves. 



