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TEXTBOOK OF PLANT PHYSIOLOGY 



All these adaptations serve for the absorption of water in liquid 

 form. Indications that plants are able to absorb water vapor are 

 based on erroneous observations and are nowadays refuted by 

 the majority of investigators. 



48. Absorption of Substances Found in the Soil Solution. — 

 The root hairs, and from these all other parts of the plant, absorb 

 the substances present in the soil solution along with water. It 

 would be erroneous, however, to think that a plant, like a simple 



Fig. 6.3. — Absorption scale of a bromeliaceous plant: A, in swollen condition 



B, during drought {after Nathansohn). 



wick, passively absorbs all substances dissolved in the soil solution. 

 Before entering the vessels of the plant, the soil solution has to 

 pass through a series of living cells. These, being endowed with 

 selective permeability, produce considerable changes in the so- 

 lution. 



Experimental evidence based on the composition of plants, and 

 consequently the amount of soil minerals accumulated by it have 

 shown that absorption of soil nutrients depends to a higher degree 

 on the specific properties of the plant itself than on the compo- 

 sition of the soil solution. Thus, the potato will always accumu- 

 late potash salts; the pigweed and nettle, potassium nitrate; and 

 cereals, silica. The composition of the nutritive solution used in 



