NORTH AND CENTRAL AMERICAN COMMELINACEjE— HOLM. 167 



where it is developed as a collenchymatic tissue of four to live hypodermal strata, and the cortex 

 proper contains much chlorophyll, besides raphides in long tubular cells. Inside the cortex is 

 a closed sheath of thickwalled cells which reminds of an endodermis. but they did not resist the 

 effect of concentrated sulphuric acid. This sheath surrounds several strata of typical stereome, 

 which forms a massive closed ring around the mestome-bundles. Some of these about twenty 

 five, are arranged in a peripheral band bordering directly on the stereome. while the others, 

 about twenty, are scattered very irregularly in the pith. Of these the peripheral possess a very 

 large group of leptome. two wide pitted ducts, and one annular vessel located between two 

 scalariform. No parenchyma- or mestoine-sheath was observed. 



The innermost mestome-bundles have only one. but very wide, pitted duct and sometimes an 

 annular and a scalariform vessel, but they lack the support of stereome. 



A pith of large roundish cells occupies the center of the stem; it contained very much starch, 

 and tubes with raphides were also observed. 



THE STEM-LEAVES. 



The blade is held in a horizontal position and is very hairy. Epidermis of the ventral face. 

 when viewed en face, consists of penta- or hexagonal cells (PI. VI, tig. 37) with many pointed 

 hairs of only two cells, but with very few stomata. The dorsal face, on the contrary, is almost 

 glabrous, but amply provided with stomata of the same structure as those of the stern. (PI. VII, 

 fig. 40.) A cross-section of the leaf -blade shows a thin and smooth cuticle on both faces. The 

 outer cell-wall of epidermis is moderately thickened, and the lumen of the cells, which is rather 

 narrow above and below the midrib, increases in size from there toward the margins of the 

 blade: the stomata are seen now to be somewdiat projecting, and their air-chamber is deep and 

 quite wide. A single stratum of collenchyma is noticeable above and below the midrib, which is 

 prominent only on the lower face of the blade. This collenchyma passes gradually over into a 

 layer of colorless cells on the ventral face of the midvein. while on the dorsal there is a mass of 

 similar colorless tissue, the function of which is evidently to store water. This colorless tissue, 

 together with the collenchyma, is thus confined to the two faces of the midvein alone. 



The chlorenchyma consists of a dense palisade tissue of one layer and of a very open pneu- 

 matic tissue of very irregular cells in several strata. Cells with raphides are scattered on the 

 ventral face beneath the epidermis. 



The stereome is weakly developed and occurs as small strands on the leptome-side of the 

 mestome-bundles except the midvein; no stereome was observed on the hadrome-side or in the 

 margins of the blade. 



The mestome-bundles are almost orbicular in cross-section; they an 1 surrounded by a thin- 

 walled, colorless, parenchyma-sheath. No mestome-sheath is developed, but the leptome is, 

 nevertheless, covered and protected by a layer of thickwalled mestome-parenchyma. The leptome 

 is well developed, and the hadrome has. at least in the largest veins, two very wide pitted ducts, 

 one annular and two or three scalariform vessels. 



The leaf-sheath is tubular and densely covered by long, hooked hairs. (PI. VII, tig. 39.) The 

 collenchyma is here only developed on the dorsal face of the midvein, and the chlorenchyma is 

 traversed by broad lacunes beneath the ventral epidermis. No palisades are developed, and the 

 mestome-bundles are somewhat weaker than in the leaf-blade. 



Commelina erecta L. 



Having been unable to detect any points by which this species may be distinguished from 

 C. Virginica L.. as far as concerns the ramification of rhizome and aerial shoots, we will confine 

 ourselves to describe the internal structure alone. 



