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 io the continuation 
of the absorption of the gas. This is the case again with the 
root and its relations to the soil. he 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. 
