118 Botanisches Centralblatt. — Beiheft 2. 



A midrib is plainly visible and is supported by a larger group 

 of stereome than the others. Bulliform cells are well-developed 

 between the ribs and are located only on the upper face of the 

 blade in the furrows, but there are none above the midrib. In 

 M. glomerata the midrib exhibits a large mass of colorless tissue 

 on the Upper face, which is separated from the epidermis by a 

 few layers of stereome, covering the entire surface of the relatively 

 broad midrib. No such colorless tissue was observed in any of 

 the other species of this particular type either above the midrib or 

 between the mestome-bundles of the lateral parts of the blade. 

 Stomata occur on either face of the leaf and are always level 

 with the epidermis. The stereome is quite thick-walled, but occurs 

 mostly in small groups on the leptome-side of the mestome-bundles, 

 and on the hadrome-side of the larger bundles; besides there is 

 an isolated group of stereome on the margin. — The mesophyll 

 is quite dense and consists of palisades, most of which are 

 arranged radially around the mestome-bundles, where they border 

 on a thin-walled green and large-celled parenchyma-sheath. A 

 mestome sheath is also present and shoAvs the usual thickening of the 

 inner cell-walls, at least in the larger nevves, besides that a more 

 or less thick-walled layer of mestome -parenchyma was observed 

 between the leptome and hadrome. A cross - section of the 

 mestome-bundles shows most of these, even the larger, to be 

 orbicular. 



Comparing this structure with that of the species from drier 

 ground, mountain-slopes or hill-sides, the following differences are 

 notable. The leaves are thicker, much narrower and mostly 

 conduplicate ; both faces, but especially the upper, are distinctly 

 furrowed, the furrows offen deep and narrow. Epidermal pro- 

 jections abound on the upper face as pointed papillae or as long 

 hairs {M. gracilis and gracülima), while the bulliform cells are 

 much better developed in these species and border on layers of 

 colorless tissue, located in the spaces between the ribs. The outer 

 cell-walls of epidermis are heavily thickened on the dorsal face, 

 and the stomata, which are level with the epidermis, are located 

 on the sides of the furrows, surrounded by the epidermal projections. 

 Groups of thick-walled stereome are to be seen above and below 

 the mestome-bundles, and this tissue is especially well-developed 

 in M. gracilis and graciUima, where it Covers almost the entire 

 dorsal face of the blade. — The mesophyll is very compact and 

 consists of palisades, which radiate towards the center of the 

 mestome-bundles. These are surrounded by a closed, large-celled 

 and green parenchyma-sheath, the cells of which are quite thick- 

 walled on the leptome- and hadrome-side, where the sheath is in 

 contact with the stereome. A mestome-sheath is also developed*) 

 as in the species, mentioned above, besides that we find layers 



*) In describinfc the leaf-structure of Muhlenbergia filipes Curtis from 

 the dand-strand of Ocracoke Island, M. capillaris (Michx.) Kunth from dry 

 Sandy or rocky soil and M. trichopodes (Ell.) Cliapm. from low pine-barrens, 



