l8 9i.J Anatoinical Characters of N. Am. Graminece. 279 



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thick-walled parenchyma. The stereome shows here but small 

 groups and is often wanting on the inferior face, below the 

 leptome. The uncolored parenchyma consists here of one or 

 two cells on the hadrome side. 



Concerning the distribution of these two forms of mestome- 

 bundles it may only be said, that the smallest ones are 

 prevalent in the whole blade. As indicated above, the stere- 

 ome is rather weakly developed, and forms groups corres- 

 ponding to the mestome-bundles. There are, however, be- 

 sides these groups some isolated ones (plate XXIV, fig. 8) 

 opposite the bulliform cells, and also above the middle of the 

 lacunes on the superior face, besides one at each of the two 

 margins of the blade. The mesophyll is strongest in the 

 middle part of the blade, where it forms one large group on 

 each side of the midrib ; in the lateral parts of the blade it is 

 interrupted by the large lacunes, which extend from the one 

 mestome-bundle to the next one. The uncolored parenchyma 

 is in the mature leaf restricted to small groups, corresponding 

 to the mestome-bundles, as described above. 



Pleuropogon Californiaim (Nees.)— Plate XXIII, fig. 4. a 

 transverse section of the middle part of the blade, shows a re- 

 markable difference from the preceding species. There is a 

 sharp carene on the superior face, a structure undoubtedly 

 very rare in the Gramineai. Otherwise the section reminds 

 one very much of that of P. refractum. 



The epidermis of the superior face consists of rectangular, 

 thin-walled cells with slightly undulated side-walls, especially 

 above the nerves. Wart-shaped expansions are numerous, 

 although wanting- above the large bulliform cells, and there 



are also some lines of thorn-shaped expansions in this species 

 above the nerves. The stomates, which are equally distrib- 

 uted on both faces of the blade, are surrounded, not sur- 

 mounted as in the preceding species, by warts. The epider- 

 mis of the inferior face differs in the presence of dwarf-cells 

 in alternation with longer, rectangular ones, all showing dis- 

 tinctly undulated side-walls. Epidermal expansions are on 

 this face merely warts, which form longitudinal lines below 

 the stereome-bundles or sometimes also between these. 



As to the mestome-bundles, these are also here, representing 

 two degrees, of which the first one may be described from the 

 median (plate XXIII, fig. 5). The parenchyma-sheath 1- un- 

 colored and thin-walled, bordered above and below by one or 



