62 



PRACTICAL COURSE IN BOTANY 



Make a longitudinal section passing through the central 

 portion of the root and extending an inch or two into the 

 lower part of the stem. Do you find any sharp line of divi- 

 sion between them? Notice the hard, woody axis that runs 

 through the center. This is the vascular cylinder and con- 

 tains the conducting vessels, the cut ends of which were 

 shown in cross section in Fig. 76. 



65. Distinctions between root and stem. — Pull off a 

 branch from the stem and one from the root ; which comes 



off the more easily ? Examine the points of 

 I attachment of the two and see why this is so. 



c^^l^^ This mode of branching from the central 

 axis instead of from the external layers, as 

 in the stem, is one marked distinction be- 

 tween the structure of the two organs. In 

 stems, moreover, branches occur normally 

 above the points of leaf insertion at the 

 nodes (46), while in the root they tend to 

 arrange themselves in straight vertical rows. 

 The shoots and cions that often originate 

 from them are not normal root branches, 



but outgrowths from irregular or adventitious buds, that 



may occur on any part of a plant. The root is not divided 



into nodes like the stem, 



and never bears leaves. 



66. The active part of 

 the root. — It is only the 

 newest and most delicate 

 parts of the root that pro- 

 duce hairs and are engaged 

 in the active work of absorp- 

 tion, the older parts acting 

 mainly as carriers. Hence, 

 old roots lose much of their 

 characteristic structure and 



. •■ 1 c i' i^^- ~^- — Root ol a tree on the side of 



take on more and more of a guUey, acting as etem. 



Fig. 77. — Verti- 

 section of branching 

 root, showing the 

 branches, n, n, origi- 

 nating in the central 

 axis, /, and passing 

 through the cortex, 



k 



