302 CONSERVATIVE ORGANS. |~LECT. VII. 



lar border ; as is beautifully demonstrated in the 

 culm of Wheat * : but in some plants, as, for in- 

 stance, the Common Rush, these apertures are 

 perceptible in the furrows only between the striae, 

 the elevations being apparently free from any 

 exhaling pores-f~. In some of the herbaceous dico- 

 tyledons, silex is found deposited in, or rather 

 immediately undeiv the epidermis. 



Monocotyledonous stems, those even of the 

 largest diameter, display no medullary rays, such, 

 as I shall soon have occasion to demonstrate, as 

 characterize the dicotyledonous ; nor do such ap- 

 pear to be necessary, owing to the extensive dis- 

 tribution of the cellular matter throughout the 

 substance of these stems. The woody bundles, 

 however, become indurated by age, and the more 

 external being enlarged by the deposition of new 

 ligneous matter, they at length occasionally touch 

 each other, and form a circle of continuous wood ; 

 but the interior bundles never attain this state, 

 and are always sufficient to distinguish the stem 

 as a monocotyledon. 



Monocotyledonous stems increase in length 

 or height ; but, with very few exceptions, not in 

 diameter. As I have had no opportunity of tracing 

 the manner in which this is effected, in the ligneous 



* Vide Plate 5, fig. 12. 



t Vide Plate 5, fig. 13. a. the appearance of the cuticle over 

 the ridges ; b. its cribriform appearance in the furrows. 



