THE ROOT 



37 



-^sS 



48. Every flowering pltiiit, with some rare exceptions, 

 has thus at tiie beginning one or more primary roots de- 

 veloped from tlie tip of the caulicle ; but 



when occasion arises, additional roots are 

 freely produced from other parts of the 

 stem. The Poison Ivy is a woody vine, 

 sometimes assuming a partially erect, 

 shrublike habit. Wherever, in clambering 

 over the rocks, the stem finds shade and 

 moisture, it produces a thick growth of 

 fibrous, clinging rootlets (Fig. 26). The 

 higher shoots, rising Avell above the under 

 shrubbery, and thus exposed to sun and 

 air, are quite devoid of them. In this case 

 the accessory roots ow^e their existence to 

 causes which are in a sense accidental, and 

 they are accordingly said to be adventi- 

 tious. 



49. Any part of the stem may give rise 

 to adventitious roots, but they come most 

 readily from the nodes, as may be seen 

 upon examining almost any creeping plant 

 (see Figs. 34, 45). 



THE FUNCTIONS OF ROOTS 



26. Adveutitious 



50. Roots serve as organs of absorption Poison ivy. 

 and storage, and as holdfasts. 



51. Absorption. — They absorb water and dissolved min- 

 eral matters, and in some cases organic matter left by the 

 decay of former vegetation, or even the juices of living 

 plants. 



52. Water and salts. — If w^e uncover the roots of a tree, 

 we find that they liave a bark impermeable by water. This 

 impermeable covering is thicker or thinner according as it 

 is older or younger, but is never altogether lacking until 

 we reach the young rootlets. Even here the surface is 

 coated with a substance that hinders the free entrance of 



