214 VEGETABLE PHYSIOLOGY 



irregular duration are caused by differences in these respects, 

 even during an ordinary day, and still more by the alterna- 

 tion of day and night ; in the case of perennial plants yet 

 greater disturbances are caused by the succession of the 

 seasons of the year, and the alterations these produce in 

 the amount of foliage which the plant preserves ; weather 

 and its vicissitudes form a series of disturbing influences. 

 We have thus the certainty of failure to survive in the 

 struggle for existence unless the initial absorptive and 

 constructive processes are supplemented by others, which 

 in some way shall make the organism indifferent to these 

 changes and intermissions of supply, and capable of carry- 

 ing out true nutritive work, when the initial stages of 

 such work are checked or suspended. In other words, 

 suitable conditions for the construction of food being 

 intermittent, the plant must accumulate a reserve store on 

 which it can subsist during the periods, short or prolonged, 

 when no such manufacture is possible. 



We may view the matter from a slightly different stand- 

 point, and yet come to the same conclusion. The processes 

 of absorption in a plant depend, as we have seen, almost 

 entirely upon physical conditions. Given a certain amount 

 of carbon dioxide in the air, and a certain amount of water 

 in the plant to which that air has access, the carbon dioxide 

 will be dissolved according to the power of the water to 

 dissolve it, or putting it more technically according to its 

 coefficient of solubility. In the presence of the chlorophyll 

 apparatus, with the access of sunlight, the other subsequent 

 changes, which we have discussed, lead to the continuation 

 of the absorption of the gas. This is the case again with the 

 root and its relations to the soil. The process of absorption 

 of water with its dissolved substances will proceed as long 

 as certain physical conditions obtain. Thus the plant is, 

 on the whole, rather passive than active in the initial stages 

 of its own feeding, exercising no inhibitory power, such 

 as that which in an animal is attendant upon a failure or 

 cessation of appetite. 





