176 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. X, NO. 6. 



noticed, it was generally only a few of the proto-hadrome vessels that had broken through the 

 pericambium— for instance, two rays in pentarchic roots. The hadromatic rays are short, con- 

 sisting only of one wide, central, reticulated, and a few much narrower scalariform vessels. 

 Theleptome is well developed and the proto-leptome cell plainly visible. By examining this same 

 root near the base we noticed that the cortex and endodermis had become considerably thick- 

 walled and porous. (PI. VII, fig. 42. ) The somewhat thinner lateral roots show the same 

 structure as the secondary, described above, with the only exception that the cortical paren- 

 chyma is less developed, and consists of only two or three strata; moreover, the pericambium is 

 mostly interrupted by all the proto-hadrome- vessels. These interruptions of the pericambium 

 appear, however, as being very .irregular, and we noticed, for instance, that in one root this 

 tissue was continuous in some places, but interrupted in others, besides that it was either inter- 

 rupted by all the proto-hadrome vessels or only by two or three of these in tetrarchic roots. 



The roots, especially the secondary, of Tradescantia rosea arc thus contractile, and at the 

 same time storage-roots. 



THE KHIZOME. 



The structure of the horizontal internodes is identical and may be described as follows: The 

 internodes are cylindric and smooth, covered by a thick, wrinkled cuticle. The outer cell-walls 

 of epidermis are moderately thickened, and stomata with the guard-cells raised (PI. VII, tig. 45) 

 occur on the upper face of the rhizome, where also chlorophyll was observed. There is no col- 

 lenchyma. and the cortex borders thus directly on epidermis. The cortical tissue is slightly thick- 

 walled and quite compact; it contains starch and raphides. The mestome-strands are arranged 

 in two concentric bands, sixteen peripheral and live near the center. Of these the peripheral are- 

 supported by one or sometimes two layers of thickwalled cells, which resemble stereome; the lep- 

 tome is mostly covered by the hadrome on the sides. In regard to the inner band of mestome- 

 bundles these show the same structure, bat their mechanical support is much weaker and each 

 contains a wide lacune with an annular vessel. The pith is thinwalled and contains no starch. 



The sixth internode (I 11 in tig. 12) is almost above ground and differs from the others, 

 the horizontal, by being hemic ylindric and densely hairy. The cuticle is thick and prominently 

 wrinkled. Epidermis is quite thickwalled and the outer cell-walls show several and very 

 distinct longitudinal ridges; stomata and clavate hairs were observed. Two to three layers of 

 collenchyma in isolated groups are located beneath the epidermis. The cortical parenchyma is 

 thinwalled and very open from wide intercellular spaces; ii contains a little chlorophyll and 

 passes gradually over into the central pith, the cells of which are much larger. Two concentric 

 bands of mestome-bundles traverse this internode, there being eighteen peripheral and about five 

 near the center. The peripheral are located in the cortex in the same radius as the groups of 

 collenchyma. though separated from these by the cortex, and several of these are almost lepto- 

 centric, since the leptome is more or less surrounded by the vessels; no stereome was observed. 

 The innermost mestome-strands are all collateral and somewhat larger than the peripheral; they 

 are located in the pith, which is thinwalled and which contains no deposits of starch. 



THE STEM ABOVE GROUND. 



The basal internodes show exactly the same structure as the sixth internode of the rhizome, 

 described above. If we, on the other hand, examine the upper portion of the stem near the 

 inflorescence we notice some slight modification in structure, which principally depends upon 

 the number of the mestome-bundles. These are present in a smaller number, only nine periph- 

 eral and seven near the center; they constitute two bands, which are not quite concentric, but 

 the mestome shows the same position as described above, the leptome being almost surrounded 

 by the hadrome in the peripheral as well as in the central strands. The upper internodes are 

 cylindric, glabrous, and smooth, but exhibit otherwise the same structure as the basal in regard 

 to cuticle, epidermis, collenchyma, cortex, and pith. No stereome was observed, and the cortical 

 parenchyma did not show the innermost stratum differentiated as an endodermis. 



