126 



ORGANOGRAPHY. 



called roots of the Eadish, the Turnip, the Cyclamen, and 

 probably some others, are really enlarged stems. We have, how- 

 ever, placed them here, in accordance with the commonly accepted 

 views of their nature, and on account of their importance in 

 practical botany. The two next described forms of roots are also 

 more properly rhizomes, but it is convenient to notice them 

 here, and so long as their nature is indicated no confusion can 

 arise. 



Contorted or twisted Boot. — When a tap-root, instead of pro- 

 ceeding in a more or less straight direction, becomes twisted, as 

 in the Bistort {Polygonimi Bistorta), {fig. 245), the root is said 

 to be contorted or twisted. 



Fremorse Boot. — When the main root ends abruptly, so as to 



Fig. 245. 



Fig. 246. 



Fig. 245. Contorted root of Bistort (Polygonum Bistorta). Fig. 246. 



Prsemorse root of the Devil's-bit Scabious iScabiosa succisa). 



present the appearance of having been bitten off, it is called 

 an abrupt, tnmcated, or frmmorse root {fig. 246). We have 

 a good example of this form of root in the Devil's-bit Scabious 

 [Scabiosa succisa), which received its common name from a 

 superstitious opinion connected with this peculiar bitten-off 

 appearance of the root. 



Section 3. The Leaf. 



1. GENERAL DESCRIPTION AND PARTS OF THE LEAF. 



The leaf may be defined as a lateral development of the par- 

 enchyma of the circumference of the stem or branch. In the lowest 

 leaf-bearing plants, as Mosses, this is its ordinary structure ; but in 



