NORTH AND CENTRAL AMERICAN COMMELINACE^E— HOLM. 187 



stomata, but no hairs, were observed. Cortex consists of ten strata of thinwalled cells, with narrow 

 intercellular spaces; no starch, but raphides and very little chlorophyll, was observed. The 

 cortex is not separated from the broad central mass of parenchyma by any sheath of stereome or 

 by any stratum that might be distinguished as an endodermis. Nevertheless we did notice one 

 or sometimes two layers of cells that were more closelj- connected with each other than those 

 of the cortex, and these bordered on the leptome-side of the peripheral mestome-bundles. 

 Examined in longitudinal sections these cells did not differ from those of the adjoining paren- 

 chyma, nor did they resist concentrated sulphuric acid any better. 



The peripheral mestome-bundles (twenty-five) are arranged in a circle. They are relatively 

 small and almost orbicular in transverse sections; they are collateral and contain only a few 

 vessels and a small group of leptome. Resides these regularly arranged peripheral mestome- 

 strands we find in the central portion of the pith about forty others, which are apparently 

 scattered and not arranged in any order. These mestome-bundles are larger, since they posses 

 more leptome and much wider vessels, but they are all collateral like the others. The pith is 

 thinwalled, quite solid, and contains many raphides, but no deposits of starch. 



Characteristic of the stem of Weldenia is the absence of collenchyma and stereome. We 

 must remember, however, that the stem is subterranean and of relatively short duration. 



THE GKEEN LEAVES. 



The lanceolate blades are quite thick and smooth. Viewed en face the ventral epidermis 

 consists of very regular hexagonal cells, some of which are developed into four-celled hairs with 

 the apical cell very long and obtuse. (PI. VIII, fig. 52.) On the dorsal face the cells show the 

 same shape, but are much shorter in the stomatiferous strata than between these. The stomata 

 (PI. VIII, fig. 53) are arranged in longitudinal rows parallel with the longitudinal axis of the 

 blade; the}' have one pair of subsidiary cells and are slightly raised above the surrounding 

 epidermal cells: the air-chamber is broad and deep. Between the stomatiferous strata are longi- 

 tudinal rows of hairs of the same type as described above, but these are very numerous on this 

 face of the blade, the dorsal, and they are often developed in small tufts of four or five together. 

 These hairs occur, furthermore, along the margins of the blade. Viewed in transverse 

 sections the epidermis-cells are thinwalled and rather small on both faces; the cuticle is thin and 

 smooth. Underneath the ventral epidermis is a large tissue of colorless, thinwalled cells in about 

 live strata above the middle portion of the blade, but of only one near the margins. This tissue, 

 composed of large cells, represents a water-storage-tissue and is distributed over the entire ventral 

 face of the blade, but decreases in thickness toward the apex and the margins. A much narrower 

 portion of the leaf-blade is occupied by the chlorenchyrna. This consists of two layers of short 

 palisades which border on the water-storage tissue and of a pneumatic tissue of star-shaped cells 

 with broad intercellular spaces. The latter tissue is thus located near the dorsal epidermis, from 

 which it is separated by groups of collenchyma which support the larger veins, while it borders 

 directly on the epidermis between these. The collenchyma is very thickwalled and is confined 

 to the leptome side of the mestome bundles. No stereome was observed. Cells with raphides 

 abound in the chlorenchyrna. 



There are ten almost parallel veins which traverse the chlorenchyrna from the base of the 

 blade to the apex; they are connected with each other by numerous fine anastomoses. The larger 

 veins are collateral, with the leptome and hadrome well developed and surrounded by a thinwalled, 

 colorless parenchyma-sheath, but they have no mestome-sheath and no thickwalled niestome- 

 parenchyma. Tin' anastomoses are much smaller and orbicular in transverse sections. 



If we examine the small leaves that surround the inflorescence, we find the same structure as 

 described in the preceding, but the blade is thinner on account of the lesser development of the 

 water-storage tissue. 



89369°— vol in— n 13 



