ABSORPTION. ' 87 



contribute' to the extension of the subterranean branches 

 by the food which they absorb from the soil, exactly as the 

 leaves induce a growth of the branches in the atmosphere 

 by exercising the same function. A fibre and a leaf are 

 wonderfully different in form and color, yet both are ab- 

 sorbents, beautifully adapted to the media in which they 

 develop. 



The plant is nourished by inorganic substances, Oxygen, 

 Hydrogen, Carbon, Nitrogen, and some mineral salts. 

 Analysis shows us these elementary substances in plants, 

 which combining among themselves, form all their various 

 and diversified products. These elementary substances 

 exist only in the earth and atmosphere, the two grand 

 sources of all vegetable nutrition. Sometimes they exist 

 there |_in an isolated state, or they make part of other 

 combinations, which the plant has the power to destroy 

 in order to appropriate them to itself. 



Water is necessarily the vehicle of the alimentary sub- 

 stances of plants. It enters the plant from the earth, ac- 

 cording to the common laws of endosmosis and capillarity, 

 by the delicate hair-like fibres of the roots. The leaves 

 favor this absorption by the evaporation which is continu- 

 ally taking place from their surface, which renders addi- 

 tionally thick and mucilaginous the fluid in the leaf-cells, 

 and throughout the organism of the plant. The leaves 

 also absorb water from the atmosphere, which always exists 

 there more or less in a state of vapor, but principally car- 

 bonic acid, which enters largely into Ihe composition of the 

 vegetable framework. 



So long as the roots can absorb as much water as the 

 leaves -evaporate, the plant will appear fresh and green, but 

 the foliage droops (as is often seen on a hot summer's day 

 towards noon,) when the evaporation from the leaves ex- 



