NORTH AND CENTRAL AMERICAN COMMELINACE^E— HOLM. 177 



THE LEAVES. 



The green leaves are very narrow, with a broad hut shallow groove on the upper face. The 

 cuticle is thin and wrinkled. Epidermis, viewed en face, consists of rectangular cells and has no 

 hairs or stomata on the upper face of the blade. On the lower face of the leaf-blade epidermis 

 shows the same structure outside the collenchyma, hut not where it covers the chlorenchyma. 

 Because we notice here that the cells are more quadratic; besides that stomata and hairs occur in 

 abundance. The stomata have two subsidiary cells parallel with the stoma and are level with 

 epidermis; the air-chamber is shallow, but wide. Hairs of two kinds were observed — short, cla- 

 vate and long, straight, sharply pointed, four-celled; these hairs, (specially the clavate, cover 

 the lower surface of the blade, especially underneath the chlorenchyma. 



A transverse section of the blade shows that the cells of epidermis are much smaller on the 

 dorsal face than on the ventral, besides that the outer cell-walls are moderately thickened. 

 Beneath the entire ventral epidermis is a large water -storage tissue, which only consists of two 

 layers, but of which the cells are very large and thinwalled. Tin 1 ventral face of the blade is 

 thus occupied by a large-celled epidermis and a hypodermal water-storage tissue, which reminds 

 very much of some bulliform cells of certain <• 'nimin, ;<-, Cyperacea?, etc. 



The chlorenchyma represents an almost homogeneous tissue of somewhat oblong or roundish 

 cells (in transverse sections) and with wide intercellular spaces. It is developed as a very open 

 pneumatic tissue underneath the water-storage tissue on the ventral face, but near the margins 

 where this tissue ceases a few palisade cells were observed. On the dorsal face of the blade the 

 chlorenchyma is more compact, and some of the cells show actually the shape of true palisades, 

 vertical on the leaf-surface. Near the mestome-bundles the chlorenchyma shows also here and 

 there some palisades, but we can not say that a typical palisade-tissue was developed in any parts 

 of the leaf-blade. 



The mestome-bundles are arranged in one plane and are supported by a few cells of hypo- 

 dermal collenchyma on the leptome-side. The mestome-strands are thus embedded in the chlo- 

 renchyma. and are surrounded by a colorless, thinwalled parenchyma-sheath. The midvein is 

 larger than the others and is not projecting. There are fourteen mestome-bundles in the blade, 

 seven large and seven much smaller, arranged very regularly in alternation with each other: the 

 leptome is rather small in comparison with the hadrome, which contains about live scalariform 

 vessels and a large lacune with an annular. 



Toward the apex of the blade the margins become involute, forming an almost closed channel 

 on the ventral face. 



THE FORE-LEAVES. 



A fore-leaf of a 3 T oung. vegetative shoot from near the base of a flower-bearing stem is 

 tubular, membranaceous, and hyaline. The cuticle is thin, but wrinkled (PI. VII, tig. -14); epi- 

 dermis is thinwalled and glabrous; it constitutes the only tissue between the two ribs and has 

 but a few stomata. The chlorenchyma is very poorly developed as an open tissue, almost desti- 

 tute of chlorophyll, and is only to be observed around the mestome-strands. which form two 

 prominent keels, one on each side of the tube. The leptome and hadrome are quite well differen- 

 tiated and surrounded by a colorless parenchyma-sheath, but without any support of mechanical 

 tissue such as collenchyma or stereome. The fore-leaf has thus two projecting ribs, of which 

 the one is somewhat more conspicuous than the other, since it contains a small mestome-strand 

 besides the larger one; the leaf is, therefore, actually three-nerved instead of two-nerved, the 

 latter being, however, the most common case among the Monocotyledon.es. 



Tradesccmtia Virginica L. 



The Rhizome. 



The minor structure of the rhizome has been very carefully described and figured by Gravis 

 (1. c). who studied the development of the stem from seedling to matured plant. When culti- 

 vated in gardens our species grows in dense tufts and the rhizome is thus very densely matted. 



