CHAP. II. 



STEM. 63 



such plants when they are not caulescent. It is composed of 

 cellular tissue, traversed by bundles of vessels and woody 

 fibre, and has the form of a flattened disk. The fleshy root 

 of the Arum, that of the Crocus and the Colchicum, are all 

 different forms of die Cormus. It has been called hulbo-tuher 

 by Ker, and hulbus solidus by many others ; the last is a con- 

 tradiction in terms. [See Bulb.) 



The stems of Palms have by some wTiters been considered 

 as an extended cormus, and not a true stem, but this seems an 

 extravagant application of the term ; or rather an application 

 which reduces the signification of the term to nothing. A 

 cormus is a depressed subterranean stem of a particular kind ; 

 the trunk of a Palm is, as far as its external character is con- 

 cerned, as much a stem as that of an Oak. De Candolle ap- 

 plies the name cormus only to the stems of Cryptogamous 

 plants, and refers to it the Anabices of Necker. 



The Tuber, fig. 24. {Tuberculum if very small), is an 

 annual thickened subterranean stem, provided at the sides 

 with latent buds, from which new plants are produced the 

 succeedins year, as in the Potato and Arrow-root. A tuber 

 is, in reality, a part of a subterranean stem, excessively en- 

 larged by the developement to an unusual degree of cellular 

 tissue. The usual consequences attendant upon such a state 

 take place ; the regular and symmetrical arrangement of the 

 buds is disturbed ; the buds themselves are sunk beneath the 

 surface, or half obliterated, and the whole becomes a shapeless 

 mass. Such is not, however, always the case; the enlarge- 

 ment sometimes occurs without being accompanied by much 

 distortion, and the true nature of the tuber stands revealed ; 

 this is remarkably the case in the Asparagus Potato. In most, 

 perhaps all tubers, a great quantity of amylaceous matter 

 is deposited, on which account they are frequently found to 

 possess highly nutritive properties. 



Tlie Creeping stem, fig. 25. (soboles), is a slender stem, which 

 creeps along horizontally below the surface of the earth, emit- 

 ting roots and new plants at intervals, as in the Triticum 

 repens. It differs in nothing whatever from the rhizoma, ex- 

 cept in being subterranean. This is what many botanists call 



