34 NUTRITION. 



it is very remarkable in the seed, and is there 

 called the radicle; this principal root, after 

 having sent out branches in all directions, often 

 perishes, and the ramifications frequently take a 

 horizontal course. Besides affording nourish- 

 ment by direct absorption from the soil, the roots 

 are often storehouses of nutritive matter. Such 

 are those of the Dahlia, which abound in starch, 

 the orchis, &c. &c. such roots are generally 

 much swelled or thickened. In their anatomi- 

 cal structure roots principally differ from stems 

 by the absence of stomata, and, in the Exo- 

 genes, by the want of a central pith or medulla 

 (27). 



26. The Stem (caulis). This organ is never 

 really wanting in vascular plants, though in 

 some it is hidden beneath the earth. " The 

 stem is produced by the successive development 

 of leaf buds (35), which lengthen in opposite 

 directions." The stems of Exogenous plants 

 possess the most complicated organization, but 

 as they are much better understood than those 

 of the Endogenous and Cellular tribes, and as 

 the Exogenes comprise all the trees of our own 

 part of the globe, they are more interesting to 

 us. 



Four distinct parts are observed in Exoge- 



