296 PLANTS 



and the turnip have tap roots. Often the roots are divided into many 

 branches, as in grass and corn. The roots that come from creeping 

 stems, such as those formed at the nodes of the strawberry plant, arc 

 secondary roots. 



The root has a growing tip, protected by layers of cells. Near the 

 tip the root develops root hairs. These have delicate walls, and bring 

 the root into very close connection with the soil particles, so that it can 

 absorb water and nutriment (cf. 298) . 



317. Underground Storage of Food. We have seen 

 (cf. 307) that many plants store away in the embryo food 

 for the next generation. Plants may die after one season 

 (annuals), or they may need two seasons to produce seed 

 and may then die (biennials), or they may last year 

 after year (perennials). Many plants store away food, 

 not in seeds, but in other plant structures. The plant 

 draws upon this supply in the following spring, when 

 rapid growth begins. Man has developed some of these 

 plants, so that they store away food for him. Often 

 the plant has an underground stem on which under- 

 ground leaves are developed for the purpose of stor- 

 age. The inner leaves become much thickened, and 

 the outer leaves take the form of tough, dry scales 

 that cover the inner leaves. Thus we get bulbs. The 

 onion and the lily are bulb-forming plants. An under- 

 ground stem is called a rootstock. The common ferns, 

 the wild ginger, the iris, and the bloodroot have root- 

 stocks. 



When the underground stem becomes much enlarged, 

 it produces tubers, such as the potato. The surface of 

 the potato has little scales, which are imperfect leaves. 

 In the axils of these scales (cf. 312) are the "eyes" 



