280 The Botanical Gazette. [October, 



two similar uncolored cells. There is a distinct mestome- 

 sheath, the walls of which are especially thickened inwards. 

 The leptome and hadrome are separated from each other by 

 two strata of thick-walled parenchymatic cells. These large 

 bundles are supported by groups of stereome above and be- 

 low, which are separated from the parenchyma-sheath by a 

 few uncolored cells, excepting in the median one, where the 

 mesophyll forms an uninterrupted group above the entire 

 bundle. The mestome bundles of second degree differ in 

 size from those of first degree ; besides which the mestome- 

 sheath shows merely thin-walled cells, and the leptome is in 

 immediate contact with the hadrome. 



The stereome agrees very well with that of P. refractum, 

 but the number of isolated groups is larger here, there being 

 three groups opposite the bulliform cells, one below and about 

 three above the lacunes. The mesophyll and the uncol- 

 ored parenchyma correspond in most details with those of the 

 preceding species. 



Plcuropogon Sabinei R. Brown. — Epidermis of the superior 



face consists of thin-walled, rectangular cells with nearly 



straight side walls, and there are numerous conical warts. 



The stomates are restricted to this face and are surmounted 



by conical .expansions of the surrounding epidermis cells. 



The inferior face of the blade is entirely smooth ; the cells 



show strongly undulated side-walls and are nearly equal in 

 size. 



A transverse section of half of the blade shows about the 

 same structure as in P. Californicum with the sharp keel on 

 the superior face. The mestome-bundles are also nearly the 

 same, but it must be remarked, that in this species the mes- 

 tome-sheath is merely thin-walled in both forms of bundles; 

 besides which the leptome and hadrome are but imperfectly 

 separated in the largest ones by a few not very thick-walled 

 parenchymatic cells. 



The stereome shows in this species a still smaller develop- 

 ment than has been observed in the two other species, and 

 forms here merely two isolated groups in the mar-ins of the 

 blade I he mesophyll and the uncolored parenchyma agree 



in all the detads with the corresponding tissues of P. Cali- 

 tornicum. 



Considering now these three species of Plcuropogon to- 

 gether, it .s evident that they are, in spite of their great sim- 



