4 TEXTBOOK OF BOTANY 



shape and not so large as the leaves formed later. The plu- 

 mule, which has already begun to grow, now grows more 

 rapidly ; the two secondary leaves which it bears, and which 

 were already formed within the seed, spread out and become 

 large and green ; they are shaped much like the later leaves 

 of the plant. By the further growth of the plumule into a 

 long stem and by the production of more leaves upon the 

 stem, the above-ground portion of the seedling develops into 

 that of the mature plant at the same time that the root and its 

 branches are growing and pushing into the soil. 



4. The Mature Cucumber Plant : Roots. — The primary 

 root is developed from the lower end of the radicle, which 

 continues to grow farther and farther into the soil. After 

 a time, however, the primary root grows more slowly, and 

 some of the branch roots grow fast enough so that they come 

 to be fully as long as the primary root. These branch roots 

 occasionally branch also, so that the root system of an older 

 plant is made up of a great many slender roots. It is by 

 means of this system of roots that the plant is firmly an- 

 chored in the soil. The roots also take up ■ from the soil 

 large amounts of water as well as some other substances that 

 the plant needs, and these are carried through the roots to 

 the stem and thence to all parts of the plant above ground. 

 The water and other materials are not taken in from the soil 

 by all parts of the roots, but only through very short, slender 

 root hairs (see Fig. 2). These root hairs are borne in large 

 numbers, but only on the youngest parts of the root system — 

 that is, close to the growing ends of the primary root and of 

 each branch root. 



5. The Stem. — We have seen that the plumule grows into 

 the stem of the mature plant. The stem branches, like the 

 primary root, though less frequently, and each branch of the 

 stem may branch again. The stem and its branches, like 

 the primary root and its branches, may continue to grow in 

 length as long as the plant lives. The stem at first grows 



