A TEXT-BOOK OF BOTANY 



and work of roots. One of the most obvious contrasts 

 with the stem in external appearance is that roots bear no 

 leaves or scales, and are not made up of nodes and inter- 

 nodes. 



The root that comes from the seed, including all of its 

 subsequent branches, is the primary root. In some cases 

 the primary root develops a single prominent vertically 

 descending axis, called the tap-root, which gives off small 

 branches, as in the dandelion (Fig. 68, A); in other cases 

 the primary root breaks up at once into a cluster of branches, 

 as in many grasses (Fig. 68, B). In many cases the tap- 

 root becomes conspicuously thickened for food storage, as 



illustrated by such common 

 vegetables as radish (Fig. 69, 

 A), turnip, and parsnip. In 

 some cases where there is no 



FIG. 



). Fleshy roots: A, radish with fleshy tap-root; B, dahlia with cluster of 

 fleshy roots 



tap-root, the branches become thickened, forming such 

 clusters of thickened roots as those of the dahlia (Fig. 69, 

 B} and of the sweet potato. Roots that arise from the 

 stem or the leaves are secondary roots. For example, a 

 subterranean stem or a creeping stem strikes root from the 



