36 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. X, NO. 2. 



It may, therefore, be advisable to treat of some of these species by themselves, beginning with 

 C. Chamissonis. The stem bears many pairs of opposite leaves, which are held in an almost 

 vertical position, and their structure is as follows: The cuticle is distinct, wrinkled near the 

 margins of the blade, but is otherwise smooth. The outer cell-walls of epidermis are moderately 

 thickened, and the radial are more or less undulate, especially on the upper, the ventral face of 

 the blade. Stomata abound on both faces; they are raised a little, and possess two subsidiary 

 cells, which are parallel with the stoma, and the air chamber is wide and deep. No trichomes of 

 any kind were observed, but small, stiff hairs were, nevertheless, observed upon the earliest 

 leaves, succeeding the cotyledons. The chlorenchyma is differentiated into a typical palisade 

 tissue on the ventral part of the blade, and as an open pneumatic tissue on the dorsal. No 

 mechanical tissue, neither as stereome or collenchyma was observed, and the mestome-bundles are 

 only surrounded by a thin-walled parenchyma sheath, and deeply imbedded in the chlorenchyma. 



In the bulb-scales of this same species the thin-walled epidermis lacks, of course, stomata, 

 and the mesophyll is merely represented as a homogenous tissue of closely packed roundish 

 cells tilled with starch. The mestome-bundles are very small and only three in number. 



In C. Virginica the stomata are most abundant on the dorsal face of the blade, and they 

 have often two pairs of parallel subsidiary cells instead of but one; moreover, the cells of the 

 ventral epidermis are usually somewhat larger than those of the dorsal. In regard to the 

 chlorenchyma, this shows the differentiation as in the former species, but the pneumatic tissue 

 is still more open, on account of the very irregular shape of the cells, leaving very wide inter- 

 cellular spaces. The mestome-bundles are also small in this species and are not supported by 

 any kind of mechanical tissue. The basal leaves have very long and slender petioles, in which 

 there is a chlorophyll-bearing cortex with very wide intercellular spaces, besides lacunes. There 

 is one crescent-shaped central mestome-bundle and two small lateral, which are orbicular in 

 transverse sections; each of these is surrounded by a special thin-walled endodermis. 



If we now examine the overwintering leaf of G. megarrhiza, we notice in this a very thick 

 and smooth cuticle, covering an epidermis, with the outer cell-walls prominently thickened, but 

 perfectly glabrous. The stomata (PI. 2, fig. 9 ) are somewhat- raised, and possess mostly two 

 pairs of subsidiary cells, more or less parallel with the stoma. They appear to be equally 

 distributed on both faces of the blade. A thick homogenous parenchymatic tissue represents 

 the chlorenchyma, the individual cells of which are shaped like, palisades, vertical on the leaf 

 blade and filled with chlorophyll. The mestome-bundles are small and deeply imbedded in this 

 tissue. No support of mechanical tissue was observed. 



Although the leaves of C. sanm ittoxii are green during the winter, thick and fleshy like 

 those of C. megarrhiza, they nevertheless show a very different structure. The stomata are 

 almost exclusively confined to the dorsal face, and the cuticle is very thin. In this species the 

 chlorenchyma is plainly differentiated into a ventral palisade tissue and a dorsal pneumatic, which 

 consists of -irregularly branched cells, like those observed in < '. Virginica. Otherwise the struc- 

 ture of the mestome-bundles, etc., is like that of the previously described species. 



The isolateral leaf-structure exhibited by ('. megarrhiza is a character that has been observed 

 in several other alpine species, pertaining to remote genera; the prominent development of the 

 chlorenchyma into a palisade tissue seems to confirm the general supposition that in alpine 

 plants the assimilation governs the structure of the chlorenchyma. On the other hand, the 

 plainly dorsiventral structure, with the very open pneumatic tissue, as represented by C. sar- 

 mentosa, is a good illustration of a plant adapted to an atmosphere charged with excessive mois- 

 ture. In this case the transpiration seems to be a more important factor than the assimilation, as 

 far as concerns the differentiation of the chlorenchyma into both a palisade and a pneumatic 

 tissue. 



It is somewhat surprising to observe a very open pneumatic tissue in the leaf of C. Virgin- 

 ica, which is not an inhabitant of wet localities or is in any way exposed to a damp atmosphere. 

 Nevertheless, the leaf-structure of this species is more open than that of C. Chamissonis, a plant 

 that grows exclusively in very wet places — in beaver swamps or along creeks in the aspen zone 



