STEM AND BUANCIIES. 



9 



of other pknts, tlioir roofs ponotriitin<? tlio bark and siirkinpf \ip the juiccii 

 nh'oady tliiboriitid for their ikhmIs. To this class belong' tlio bi'ich-(h'oj)s 

 [I'Jliiphrijns I'i I'lji iiiunu liiirUm), i)av[iHii'n: upon the roots of the beech, and 

 American niistletoo {I'l'.urailtnidroii Jlavescnin Nuttall), a woody ijarasito 

 iipon the branches of forest trees, common in tlio Southern States. 



Still other plants arc mainly nourished by roots which lianj* in the air. 

 These, called air-plants, arc almost exclusively inhabitants of warm, moist 



regions. 



Another important oflico of some roots is to servo as storehouses of 

 nourishment for the future needs of the plant. The great mass of plants 

 are annuals, living at a single season, during which they germinate from 

 the seed, attaii: th( n full development, flower, produce fruit, and die. 

 These hive no n:'(>l for a reserv-e store of nourishment, iieiice their roots 

 are iibrous and not thickened. 



]iut many plants, termed biennials, gorminate from the seed in 

 spring, i)ro;luco a cluster of radical leaves, and develop a very large t;.^)- 

 root during the lirst season. The next spring, drawing upon the store of 

 nourishme.'.t laid up in the root, they send up vigorous llowei'-stems, pro- 

 duce seed, and die. ^^fany such roots, as the beet, carrot, and turnip, are 

 of great importimeo as articles of food. 



Plants which endure for several years, termed perennials, not un- 

 frequently have roots of the same character. These thickened njots in 

 many instances contain the active medicinal principles of the plants. 



THE STEJI AND BRANCHES. 



We have seen that the stem is the ascending axis of a plant ; that it 

 grows upward toward the light at the same time that the root is develo^v 

 ing in an opposite direction. Wo have now to consider more particularly 

 its mode of growth md some of its more common forms. 



In the case of the bean it was observed that riitcr ih.o seed-leaves came 

 a pair of green leaves (Fig. 5) ; jjfter these another pair, and so on. The 

 points where these leaves appear are termed nodes or joints, and the 

 spaces between them internodes. Now,* duiing the earlier stages of 

 growth the internodes increase both longitudinally and in diameter also 

 by cell-proliferation, so that though two nodes of a growing shoot may, 

 when their leaves first unfold, be quite close together, in the end avc find 

 them separated by an interval of i^erhaps several inches. In this particular, 

 as stated above, the gi'owth of the stem ditTers greatly from tliat of the 

 root. 



Again, it w ..^ noted that in the axils of the leaves were buds which nor- 

 mally developed into branches subject to the same laws of growth as the 

 main stem. We have now only to suppose that these axillary buds keep 

 pace with the development of the main stem, and every oi^posite-leaved 



