26 POPULAR FRUIT GROWING. 



the store of food accumulated the year before. After this rapid 

 growth has passed comes a period of slower growth in which the 

 wood is said to ripen. That is, it becomes hard by reason of its 

 cells becoming filled with starch or other plant food which 

 is used to start growth in the spring. When this is completed 

 active growth stops, but plant food is probably being stored 

 up as long as the leaves still remain green. When we have 

 warm, moist weather late in autumn, active growth sometimes 

 starts again and some of this plant food is changed to unstable 

 compounds which may result in winter killing. Some varieties 

 are much more liable to start in this way than others. No 

 characteristic of hardiness in plants is more certain than ear- 

 ly maturity of wood. 



Assimilation. Plants are made up of various tissues and 

 these are composed of numerous cells. The material of which 

 the cells are composed is largely carbon. This carbon is de- 

 rived from the carbon dioxide of the air which enters the 

 leaves, and, under the action of light, air and water is decom- 

 posed; the oxygen is given off and the carbon is retained and, 

 combining with water obtained from the roots, forms starch, 

 sugar, gum and other plant foods. This process of food mak- 

 ing is called assimilation and can be carried on only in the green 

 parts of the plant and in these, only when exposed to light and 

 air. Hence foliage, air and light are essential elements for 

 plant growth, and the greater the quantity and better the de- 

 velopment of foliage and the more light this foliage has at 

 its disposal for its work the more vigorously will the tree grow. 



In general, therefore, the growth of the fruit and wood may 

 be reduced -either by the removal of foliage, which reduces 

 the working surface, or by shading, which somewhat checks 

 the activity of the foliage by hindering light action. 



Transpiration. The flow of sap in trees is not well un- 

 derstood. In a general way it may be said that the sapwood 

 transmits the water from the roots to the leaves, where a part 

 enters into the assimilated sap and goes to build up the plant, 

 and the remainder, which is by far the greater part, passes off 

 as vapor. The amount thus transpired varies greatly with the 

 species, age of the tree, amount of foliage at work, amount of 



