STRUCTURE.] EHIZOME VINE PSEUDOBULB. 183 



mother plant, as in Sempervivum. It differs very little from 

 the runner. 



The Rootstock, fig. 29. (rhizoma), is a prostrate thickened 

 rooting stem, which yearly produces young branches or plants. 

 It is chiefly found in Irids and epiphytal Orchids, and is often 

 called caudex repens. The old botanists named it cervix, 

 a term now forgotten. 



The Vine, fig. 32. (viticula, Fuchs.), is a stem which trails 

 along the ground without rooting, or entangles itself with 

 other plants, to which it adheres by means of its tendrils, as 

 the Cucumber and the Vine. This term is now rarely em- 

 ployed. De Candolle refers it to the runner or sarmentum ; 

 but it is essentially distinct from that form of stem, because 

 it does not root. 



The Pseudobulb is an enlarged aerial stem, resembling a 

 tuber, from which it scarcely differs, except in its being formed 

 above ground, in having an epidermis that is often extremely 

 hard, and in retaining upon its surface the scars of leaves 

 which it once bore. This is only known in Orchidaceous 

 plants, among which it is very common. 



The term stem (caulis) is generally applied to the ascending 

 caudex of herbaceous plants" or shrubs, and not to trees, in 

 which the word trunk is employed to indicate their main stem; 

 sometimes, however, this is called caulis arboreus. From the 

 caulis, Linnaeus, following the older botanists, distinguished 

 the culmus or straw, which is the stem of Grasses ; and De 

 Candolle has further adopted the name Calamus for all fistular 

 simple stems without articulations, as those of Rushes ; but 

 neither of these differ in any material degree from common 

 stems, and the employment of either term is superfluous. 

 This has already been remarked with respect to culmus 

 by Link, who very justly inquires (Linnsea, ii. 235.) "cur 

 Graminibus caulem denegares et culmum diceres ?" 



If a plant is apparently destitute of an aerial stem, it is 

 technically called stemless (acaulis), a term which must not 

 however be understood to be exact, because it is, from the 

 nature of things, impossible that any plant can exist without 

 a stem in a greater or less degree of development. All that 

 the term acaulis really means, is that the stem is very short. 



