NUTRITION: THE WORK AND THE MATERIALS. 3 



entered on the creditor side as a receipt. The plant will 

 indeed feed upon itself for a time, or rather it will feed 

 upon what its predecessor left it as an inheritance for this 

 very purpose, or upon the stores accumulated in the plant 

 itself during the preceding season ; thus, when a seed, or 

 rather the young plant within the seed, begins to grow, it is 

 at first unable to forage for itself, but it depends for its 

 sustenance on the materials laid up for its use during the 

 preceding season by the parent plant. So the bud of a tree 

 awakening into life, and beginning its career as a shoot 

 which is to bear leaves and flowers, derives its first meals 

 from the reserves accumulated the autumn previously in the 

 parent branch. Very generally a little water, supplied from 

 without, is required before the plant can avail itself of 

 these stored-up provisions, but this is not always indispens- 

 able. 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 tuber to allow of food being 

 utilised. 



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 individual 

 plant, and indeed each part of a plant, feeds, and performs 

 each item of its life-work, best at a certain temperature, 

 and ceases to work at all when the temperature falls below 

 or rises above a certain point. The particular degree, 

 whether most or least favourable, varies according to th<? 

 plant, its age, stage of growth and various external cir- 



B 2 



