NORTH AND CENTRAL AMERICAN COMMELINACEiE— HOLM. 163 



repeated, as described above, with the only difference that the upper portion of the shoot may 

 show a turning of somewhat less than ninety degrees from the axis. 



It has been mentioned above that accessory buds occur, and these are to be found within the 

 fore-leaves of first or second order, though not in the axils of these; they are usually collateral, 

 when considered in connection with the other shoots, and begin, like these, with a fore-leaf pre- 

 ceding a green leaf and sometimes a rudimentary inflorescence. 



The Internal Structure of the Vecetative Orcans. 

 the roots. 



All the roots of O. mid/flora are nutritive. As shown in our figure 2, there are several 

 secondary roots developed at the basal nodes of the stem, and these bear lateral ramifications in 

 some distance from the surface of the soil. Of these the secondary are naturally the strongest 

 developed and are quite thick. The epidermis (Ep. in fig. 17, PI. Ill) is thinwalled and hairy: 

 it surrounds a thinwalled exodermis (Ex. in fig. 17). the cells of which arc much larger than those 

 of epidermis. Between the exodermis and the cortex arc usually two layers of stereomatic cells 

 with the cross- walls distinctly oblique. The cortical parenchyma consists of about ten strata of 

 very thinwalled cells which decrease in size toward endodermis; the cortex is quite solid, the 

 intercellular spaces being very narrow. The endodermis (End. in figs. 16 and 18) shows a more 

 or less prominent thickening of the radial and inner cell walls, but contains no starch. In regard 

 to the pericambium the structure was observed to be somewhat variable in a number of roots. 

 It was either thinwalled throughout or thickwalled outside the hadromatic rays; moreover it was 

 found to be continuous in some roots, hut interrupted by the proto-hadrome in others, while in 

 some roots it was continuous near the apex, but interrupted at the base. It would therefore 

 appear as if 'he pericambium shows no constant structure in our plant, even if we did observe 

 that it was continuous in most of the roots that were examined. Similar irregularities in the 

 structure of the pericambium we have observed in other plants, for instance. Eriocaulon, a various 

 Carices, b Graminese," etc. The leptome, when viewed in transverse sections, forms large and 

 broad groups, with the proto-leptome cells plainly visible. The hadrome consists mostly of five 

 rays, but six or seven were also occasionally observed; the peripheral scalariform vessels are 

 either single or two arranged side by side; the innermost vessels are very wide and reticulated, 

 and one of these may sometimes occupy the center of the root. The conjunctive tissue is thin- 

 walled in some roots, hut more or less thickened in others. 



If we compare now the structure of these secondary roots with that of their lateral ramifica- 

 tions, we notice only a very few deviations. These consist, in the absence of stereomatic tissue. 

 in the more delicate structure of the endodermis; besides in the smaller number of vessels. But 

 in respect to the pericambium we noticed exactly the same variations as in the secondary roots. 



THE STEM. 



The basal internodeof a flowering specimen (I 1 in tig. 2, PI. I) shows the following structure: 

 A thin and smooth cuticle covers the epidermis, of which the outer cell-walls are slightly 

 thickened; then follows a collenchymatic tissue of two or three layers bordering on a thinwalled 

 cortex of about six strata, with small, but distinct, intercellular spaces. 



An endodermis (End. in fig. 2(> on PI. IV) with heavily thickened inner and radial walls 

 surrounds the central cylinder, which is furthermore strengthened by a closed ring of stereome 

 bordering directly on endodermis, and which consists of a single layer outside the leptome 

 of the four peripheral mestoine-bundles, but of several between these. There are only four 

 mestome- bundles in which the hadrome of wide reticulated and narrower scalariform vessels 



a Botanical Gazette, vol. 31, 1901, p. 17. 

 b Am. Journ. Sc, vol. 10. 1900. p. 278. 

 'Bot Gaz., vol. 39, 1905, p. 131. 



