296 CONSERVATIVE ORGANS. [LECT. VII. 



diameter of the stem appears divided by two seem- 

 ingly solid cords, into three nearly equal compart- 

 ments. Mirbel, in treating 1 of this description 

 of steins, says, " their pith, instead of being en- 

 " closed in a canal, in the centre of the stem, ex- 

 " tends almost to the circumference * ;" but there 

 are exceptions to this remark, as, for instance, in 

 the Rush, Juncus, which has a perfect pith, sur- 

 rounded, however, by a cellular tube, in the sub- 

 stance of which the vascular cords characteristic 

 of the monocotyledonous stems are perfectly ap- 

 parent, arranged in beautiful order; and dis- 

 tinguish it from an herbaceous dicotyledonous 

 stem, the vessels of which, as I shall afterwards 

 demonstrate to you, are arranged in a very dif- 

 ferent manner. 



Such are the appearances which, to the naked 

 eye, or to the eye aided by a common lens, the 

 solid monocotyledonous stems present. Under 

 the microscope, we perceive that each ligneous 

 cord is composed of very narrow oblong cells, 

 and of vessels which are either spiral, or annular, 

 or porous, those in the centre being always spiral ; 

 that, in the cellular substance of the more solid 

 stems, the cells are chiefly oblong, whilst in that 



v " Et leur moelle, au lieu d'etre resseree dans un canal, 

 " au centre de la tige, s'etend presque jusqu'a la circonference. 1 ' 

 Element de Phys. veg. Partie 1. p. 117. 



