CHAP. I. 



THE TRUNK. 45 



down roots at regular intervals, as in the case of 

 common Creeping Cinquefoil, or of Ground-ivy. 

 Another familiar exception is that of the climbing 

 stem, which attaches itself by means of roots, or 

 other peculiar organs, to other plants or other 

 bodies for support, not being of itself sufficiently 

 strong to assume or maintain the upright position. 

 Such are the stems of the Vine and Ivy. But the 

 most elegant as well as most singular exception is 

 that of the twining stem of botanists, which being Twining 

 too slender to support itself, ascends by twisting 

 itself spirally around some other plant or prop. 

 And what is most to be remarked, in the economy 

 of such stems, is that the spiral twining is never 

 effected at random, but always in a determinate 

 manner in the same species ; some stems twisting 

 themselves round their prop in a direction from left 

 to right (PL I. Fig. 9.), or according to the ap- 

 parent motion of the sun, and never otherwise, as 

 in the Honey-suckle and Black Briony (PL I. 

 Fig. 10.); and others twisting themselves from right 

 to left, or contrary to the apparent motion of the sun, 

 and never otherwise, as in Con-volvulus sepium or 

 Great Bindweed. 



SUBSECTION II. 



The Culm. The culm or straw (PL I. Fig. 11.) 

 is the trunk of the grasses, rushes, and several other 

 plants nearly allied to them. In their figure such Figure, 

 trunks are generally cylindrical, as in wheat and oats; 



0^ T H 



TV 



