LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 419 



three distinct kinds, t as I have represented them 

 (Fig. 5, plate 8), viz. the annular, the punctuated 

 spiral, and the ringed membranous. 



Such is the general structure of those her- 

 baceous dicotyledonous stems, which approximate 

 in some of their characters to monocotyledonous 

 stems, particularly in the arrangement of the vas- 

 cular fasciculi through the parenchyma. But, in 

 regarding the Bryony as a good specimen of the 

 structure of this our first division of herbaceous 

 dicotyledonous stems, we must bear in mind that 

 the division admits of many modifications. In all, 

 however, the fasciculi are distinct, as in the stems 

 of monocotyledons ; the chief feature that distin- 

 guishes them from monocotyledonous stems, being 

 the presence of a decided cortex, more or less ap- 

 proaching the characters of that which is always 

 present in ligneous dicotyledons; while the stem of 

 the monocotyledon is a fascis of vascular fasciculi, 

 interspersed with cellular matter and covered only 

 by a simple cuticle, 



b. The structure of the entire herbaceous stem, 

 in which the arrangement of the parts approaches 

 to that in trees and shrubs, is well illustrated in 

 the Madder, Rubia tinctorum. In a transverse slice 

 of the stem of this plant, which is hexangular, 

 we find the following parts: 1. a cortex a. (Plate 

 8, fig. 6) easily separable from the parts beneath 

 it; 2. a vascular layer, b. resembling in its con- 



EE2 



