132 



OKGANOGRAPHT. 



Contorted or twisted Root. — When the tap-root instead of pro- 

 ceeding in a more or less straight direction, becomes twisted 

 {fig 252), as in the Bistort {Polygonum Bistorta), the above 

 term is applied to it. 



Fig. 2r)3. 



Fig. 252 



Contorted root of Bistort {Pohioonum Bistorta) Fig. 253. Praemorse 



root of the Devil's-bit Scabious {Scabiosa succisa). 



Pra-morse Root. — When the main root ends abrnptlj, so as to 

 give tlie appearance of having been bitten off {fig. 253), it is 

 called an abrupt, truncated, or prcsmorse root. We have a good 

 example of this form of root in the Devil's-bit Scabions {Scabiosa 

 fiuccis(i), which received its common name from a snperstitions 

 opinion connected with this pecnliar 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 expansion of the par- 

 enchyma of the circumference of the stem, or its divisions. In 

 the lowest plants which possess leaves, as in Mosses, tliis is its 

 ordinary stricture; but in all the higher classes, the leaf con- 

 tains in addition to the parenchyma, a framewoi-k or skeleton 

 for its supj)ort, consisting of wood-cells and vessels, which are in 

 direct connexion with similar jiarts of the fibro-vascular system 

 of the stem. We distinguish therefore, in such leaves, as in 

 the stem, both a cellular and a fihro-vascular system, — the 

 former constituting tlic soft ])arts, or the pnrenchifina of the 

 leaf; the latter, the hard parts, which act as a mechanical sup- 



