ROOTS 45 



are now to consider the structure and principal functions of 

 those organs called roots, stems, and leaves. (See Figure j.) 



E. Protection. The great functions of living things are 

 sometimes spoken of as nutrition, reproduction, and protec- 

 tion. Thus, for example, your skin, and what may be 

 called the skin of plants, are organs whose function is 

 largely to protect the more delicate organs which lie be- 

 neath. The teeth and claws of animals are organs which 

 they often use to protect themselves and their young as 

 well as to procure food. However, since nutrition and re- 

 production are properly used to refer to the whole mainte- 

 nance of life, as well as to mere nourishment and the 

 production of offspring, these words include protection. 

 Protection is thus a subdivision of both nutrition and 

 reproduction. 



15. Roots. By roots we generally mean that part of 

 the plant which is related to the soil. Roots branch 

 freely and penetrate the soil in all directions. 



Roots of the same kind of plant are much alike if they 

 are growing in soil of the same nature, but if they are 

 growing in soils of different nature, they may be quite 

 different. Thus they tend to extend farther in poor soil 

 than they do in rich soil ; they grow deeper in dry soil 

 than they do in moist soil ; they seem to be seeking for 

 what they need. They appear to be modified to suit their 

 surroundings. Such modifications are called responses. 

 The modified organ appears to have responded to the con- 

 ditions which surround it. 



The roots nearest the stem may be large and strong, 

 but the last branches are always soft and slender. These 

 soft and slender branches are usually very numerous. The 



