S8 !'I:SCIIIPTIVB BOTANY. PART ?. 



organs the root, stem, and leaf, which are more es- 

 pecially considered to be the " fundamental organs" of 

 nutrition. The presence of neither of these can be 

 dispensed with without injuring vegetation, and ulti- 

 mately involving the destruction of the individual ; unless 

 where some means have been provided (as we shall see. 

 in the case of parasitic plants) to supply their deficiency, 

 or where (as in the lowest tribes of cryptogamic plants) 

 they are probably so blended and confounded together 

 that we are not able to distinguish them. 



(3<).) Root. The most common position for the 

 roots of plants, is at the base of the stern, from whence 

 they descend into the ground, gradually tapering to a 

 point, and giving off filamentous branches on all sides, 

 in an irregular and indeterminate manner. Thrsi 

 branches of the roots are termed " fibrils," and are 

 composed of ducts and cellular tissue, and covered by an 

 epidermis, except at their extremities where the cellular 

 tissue is exposed. It is here that the true absorbents of 

 the root exist, termed its " spongioles." The structure of 

 the main trunk, " caudex," or " tap" of the root (when 

 well developed) is strikingly analogous to that of the 

 stem, except that in dicotyledonous plants there is no 

 pith, and in all cases the epidermis is without stomata. 

 The medullary rays, however, are present ; and the 

 bark generally bears a much larger proportion to the 

 whole mass, than in the stem. This latter circumstance 

 is owing to its being kept moist by its underground 

 position, which renders it more capable of disten- 

 tion. In the carrot, this is well exhibited by a differ- 

 ence in the colours of these parts. The concentric woody 

 layers are not distinguishable, and it very seldom hap- 

 pens that tracheae are found in roots. They are very 

 rarely of a green colour, excepting some of those which 

 are developed above ground ; and even then it is seldom 

 more than the spongioles which are thus partially 

 tinted. Where the root has no descending caudex, 

 which in some plants soon dies away, the fibrils are 

 given off from below the neck, or from a flattened disc 



