THE BOOT 



48. Every liuwering phuit, \\'\i\\ some rare exceptions, 

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

 veloped from tlie tip of tlie caulicle ; but 

 wlien occasion arises, aihlitional roots are 

 freely produced from otlier parts of the 

 stem. The Poison Ivy is a woody vine, 

 sometimes assuming a partially erect, 

 shrublilce liabit. Wlierever, in clambering 

 o\-er the rocks, tlie stem jiuds sliade and 

 moisture, it produces a lliiclc growtli of 

 librous, clinging rootlets (Fig. 26). The 

 higher shoots, rising well aliovc the under 

 shrubbery, and thus exposed to sun and 

 air, are quite devoid of them. In tlds case 

 the accessory rcxjts owe tlicir existence to 

 causes which are in a sense accidental, and 

 they are accordingly said to be adventi- 

 tious. 



49. Any part of the stem inay give rise 

 to adventitious roots, but they come inost 

 readily from the nodes, as nuiy be seen 

 upon examining almost any creeping plant 

 (see Figs. 34, 46). 



; 



THE FUNCTIONS OF ROOTS 



20. Adventitious 

 roots of the 

 Poison Ivy. 



50. Roots serve ^s organs of absorption 

 and storage, and as holdfasts. 



51. Absorption. — They al)sorb 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 

 [) hints. 



52. Water and salts. — If we uncover the roots of a tree, 

 we find that they have 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 



