NORTH AND CENTRAL AMERICAN COMMELINACEiE— HOLM. 169 



branches begin with an addorsed foreleaf. Dormant buds occur in the leafaxils. The length of 

 the complete rhizome is very variable, and we have noticed as many as nine internodes between 

 two flower-bearing shoots, representing the growth of one season. 



THE RAMIFICATION OF THE AERIAL SHOOT. 



The species is more robust and taller than the others, but the stem is less branched. Vege- 

 tative shoots may develop near the base, but seldom at the upper part, and a few inflorescences 

 are to be observed at the apex. The stem-leaves are ample and provided with large sheaths; 

 they are on the lateral shoots preceded by a small tubular foreleaf, which is bicarinate. and slit 

 on the frontal face. (PI. I, figs. 6 and 7.) 



By examining the position of the leaves, foreleaves. and spathes in a lateral shoot we notice 

 that the green leaves are turned 90 degrees to the side of the foreleaf, as in the species described 

 above. As many as three green leaves may be observed on a single, flowering, lateral shoot, 

 alternating with each other and supporting lateral inflorescences, each of which begins with an 

 addorsed foreleaf and where the spathe is turned 90 degrees to the side of this. 



The Internal Structure of the Vegetative Organs. 



the ROOTS. 



As mentioned in the preceding the roots of this species are somewhat fleshy, but not tuber- 

 ous; they may be designated as "nutritive" and at the same time "contractile." but not as 

 -forage roots. 



The thinwalled epidermis shows a profuse development of hairs. An exodermis of a single 

 layer of, in transverse sections, polygonal thinwalled cells separate epidermis from the cortex; 

 viewed in longitudinal sections the cell-walls of the exodermis show numerous foldings. (PI. V, 

 fig. 29.) The cortical parenchyma constitutes a homogeneous thinwalled tissue, which fre- 

 quently collapses tangentially; or the peripheral strata of the cortex may consist of thickwalled 

 cells, stereoinatic, with the lumen quite narrow; these cells are, however, relatively short and 

 the cross-walls horizontal instead of oblique as in typical stereome. 



Endodermis is mostly thinwalled, but we observed, also, cases where the inner and radial 

 cell-walls were moderately thickened. The pericambium consists of a single layer and we noticed 

 no instances in the secondary roots where it was interrupted by the proto-hadrome vessels. (PI. 

 VI, fig. 34.) The leptome occurs as broad groups as in the other species examined, and the 

 hadrome constitutes a very variable number of rays from four to eight, but five being the most 

 frequent; the rays are very short, and the innermost vessels, which are reticulated, are the 

 widest. One of these may occupy the center of the root, but very seldom. The proto-hadrome 

 vessels (PII in tig. 34) are very narrow and either single or two together. The conjunctive tis- 

 sue is often more or less thickwalled, and extends to the center of the root. 



If we now examine the much thinner lateral roots, we notice only a few layers of thinwalled 

 cortical parenchyma which do not collapse. The number of hadromatic rays may lie reduced to 

 only two, of which the proto-hadrome vessels border directly on endodermis; when four or five 

 rays were developed, these vessels were located inside the pericambium as in the mother-root. 

 But otherwise the structure of the lateral roots appeared to be very uniform with epidermis, 

 exodermis, endodermis. and the conjunctive tissue thinwalled throughout. 



It would thus appear as if the pericambium is continuous in the secondary roots, judging 

 from the large number of roots that have been studied and at different places, but sometimes 

 interrupted in the lateral. Finally may be mentioned that " thyllen" were observed in the reticu- 

 lated vessels of some of these roots. 



THE RHIZOME. 



The horizontal internodes show the following structure: A thin, smooth cuticle covers 

 epidermis, from which numerous clavate hairs are developed. The cortex is differentiated into 

 a hypodermal collenchyma of about three strata, and a cortex proper of about twenty layer-: 



