PLANT NUTRITIOK. 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. 



