2 SCIENCE AND FRUIT GROWING 



ROOT. Roots are specially adapted for anchoring the plant 

 in the ground, and preventing it from being blown over by strong 

 winds, or washed out of the soil by heavy rains ; in addition to 

 this, they form the channels through which all the water and 

 the raw food-material, necessary for the various functions of the 

 plant, are absorbed. 



The structure of the root differs from that of the stem in some 

 particulars. If a transverse section be made (Fig. i) of a fairly 

 young root it is seen to consist of - 



(1) An outer layer of rather thin-walled cells, called the pili- 

 ferous layer, from which root-hairs are formed. 



(2) A broad band of cells forming the cortex, bounded on the 

 inner side by the endodermis with thickened walls. The cortex 

 of the root does not contain any green colouring matter. 



(3) A stele, or central cylinder, of which the outer layer is 

 called the peri cycle. Within this, groups of xylem, or wood, 

 (water-conducting tissue,) and of phloem, or bast, (conveying 

 elaborated food throughout the plant,) are arranged alternately, 

 the xylem being nearer the centre than the phloem. Within 

 these, again, there is a certain amount of pith, made up of thin- 

 walled cells. 



As the root gets older, a cambium, or reproductive layer, forms 

 between the groups of xylem and phloem, and by the division of 

 its cells gives rise to more wood and bast, the volume of the 

 wood being greater than that of the bast. In course of time the 

 pith often becomes crushed and unrecognisable. While the root 

 is thus growing in thickness, the friction of the earth rubs off the 

 root-hairs and the piliferous layer, and gradually abrades the 

 cortex. The particles thus rubbed off from the root materially 

 increase the supply of organic matter in the soil. A very old 

 root consists of little but the strong vascular cylinder and shreds 

 of cortex, and becomes a mere conduction channel. 



The continuance of the function of absorption is provided for 

 in a very remarkable way. Towards the end of a root is the 

 growing point, consisting of tissues which are constantly dividing, 

 and adding to the length of the root. This root-tip, or growing 

 point, is covered with a thick layer of cells, called the root-cap, 

 which protects the tender tip from injury as it forces its way 

 through the soil. Just behind the root-tip, constant supplies of 

 new root-hairs are formed to replace those higher up, which have 

 finished their work and have been rubbed off. 



A healthy growing root puts out large numbers of lateral 

 rootlets, originating from the central cylinder, and making their 



