PLANT NUTRITION. 9 
supplied from without, is required before the plant can 
avail itself of these stored-up provisions, but this is not 
always indispensable. Potatoes begin to sprout in their 
cellars or pits, as growers know to their cost, before they 
can have obtained a drop of water from without. In 
this latter case there is water enough already in the tu- 
ber to allow of food being utilized. 
Effect of Temperature.—A certain degree of useful 
heat is, of course, quite indispensable. Practically, no 
plant will feed when its temperature is reduced as low as 
the freezing point, and in most cases the heat requires to 
be considerably greater. Each kind of plant, each indi- 
vidual plant, and indeed each part of a plant, feeds, and 
performs each item of its life-work, best at a certain tem- 
perature, and ceases to work at all when the temperature 
falls below or rises above a certain point. The particu- 
lar degree, whether most or least favorable, varies accord- 
ing to the plant, its age, stage of growth and various ex- 
ternal circumstances, which we need only mention, as 
their effects will be readily understood without the ne- 
cessity of explanation. 
It is clear then that a suitable temperature and access 
of water, either liquid or in the form of vapor, are the 
first essentials in the feeding process in plants. Practi- 
cally, and from force of circumstances, the gardener has 
more control over both temperature and the supply of 
water than the farmer; nevertheless by drainage, by 
choice of aspect, site, by shelter, and other means, even 
the farmer has some power to regulate the temperature 
and the amount or influence of water_to which his crops 
are subjected. 
Water.—Leaving, however, on one side, the temper- 
ature, we have to consider the water which is so essential, 
not only in the feeding processes with which we are now 
‘concerned, but. with every other action of plant life. 
