NORTH AND CENTRAL AMERICAN COMMELINACEiE— HOLM. 17.") 



endodermis. It borders on a closed ring of thinwalled stereome, which surrounds the peripheral 

 mestome-bundles completely and separates the cortex from the pith. The peripheral mestome- 

 strands are thus supported by stereome on all sides; they are collateral and have many very wide 

 vessels, which cover the sides of the Ieptome in the shape of the letter V. The thinwalled pith 

 contains no starch or raphides. but is traversed by a few mestome-bundles, with a little stereome 

 on the leptome-side. 



THE LEAVES. 



The stomata show the same structure as those of the stem, and they occur only on the dorsal 

 face of the blade. No hairs were observed, but along the margins the epidermis is extended into 

 roundish warts, which are quite thickwalled. The chlorenchyma contained many cells with 

 raphides, but we were unable to ascertain whether a palisade-tissue was developed, since our 

 material had been dried and pressed. The midrib is slightly thicker than the other veins on 

 account of the presence of a group of collenchyma and water-storage tissue on the leptome-side. 



Tradescantia rosea Vent. 



The Rhizome. 



This species possesses a horizontally creeping rhizome with stretched internodes partly 

 covered with membranaceous, scale-like leaves and provided with fleshy roots. The ramification 

 is, as may be seen from our figure (PI. II, fig. 12), monopodial, until the partly subterranean 

 stem becomes terminated by an inflorescence (I 6 ). The internodes I 1 to I' are all horizontal, while 

 the long internode P is vertical and constitutes the base of an aerial, flowerbearing shoot. Four 

 axillary, flower-bearing shoots (S'-S 1 ) are developed in this specimen, and the basal internodes 

 of these have partly fused together with the respective main axes the internodes I 3 to P; these 

 axillary shoots are, of course, aerial and ascending, hut in order to facilitate the view of the 

 complete rhizome we have drawn all the axes, the main and the lateral, in one plane. Thick and 

 fleshy roots develop at the nodes of the main rhizome, while some more slender ones are to he 

 observed at the nodes of the axillary shoots. 



The Ramification of the Shoot. 



If we examine one of the axillary shoots, for instance, S ! . we notice the following structure 

 (tig. 13): / signifies the scale-like leaf, from the axil of which the shoot has developed: P is the 

 internode above this leaf. As normally in monocotyledonous plants the first leaf of the lateral 

 shoot is an addorsed fore-leaf (P 1 ), succeeded by a green leaf (L 1 ), while an inflorescence (S 3 ) 

 terminates the shoot. In the axil of L', however, another shoot is visible, which also commences 

 with an addorsed fore-leaf (P'~), succeeded by two alternating green leaves L 2 and L 3 . which sur- 

 round a minute inflorescence of third order; this inflorescence stays dormant until the following 

 season. If we compare now the diagram of Tradescantia (tig. 13) with those of Commelina (tigs. 

 9 and 11), we notice at once that all the leaves, the fore-leaves and the green ones, alternate with 

 each other in Tradescantia, while in Commelina the green leaves are turned 90 to the side of 

 the fore-leaf. 



The Internal Structure of the Vegetative Organs. 



the roots. 



A thick, secondary root, examined near the apex, shows the following structure: The thin- 

 walled epidermis is exceedingly hairy, and covers an exodermis, which consists of a single layer 

 and of which the cellwalls are folded and very slightly thickened. The cortex is represented by 

 about eight strata with narrow intercellular spaces and with large deposits of starch. The 

 endodermis is moderately thickened and surrounds a thinwalled pericambium, which is continu- 

 ous in some of these secondary roots, but interrupted in others. When such interruptions were 



