Apical Meristems of the Roots of Monocotyledons. 123 
14. The plerome cylinder originates by the division of a single 
initial cell. The pericycle is probably not cut off by the first 
division wall. There is present a central axial row, but this is not 
very clearly marked, and the cells are not longer than the remaining 
pleromic cells. In transverse section it is seen that the cells of the 
plerome are very irregular in shape and arrangement (Fig. 15), 
differing widely from the other genera examined. They are packed 
round the central cell in no particular order. 
A small initial cell gives rise to the periblem and dermatogen, 
the layer forming the dermatogen dividing further away from the 
apex. The root-cap is massive, and the cells outwardly appear to 
lose their tabular form. Van Tieghem considers the outer layers of 
the root-cap to be formed by the divisions of the endodermis of the 
stem. In the material used, the endodermis of the stem, if present, 
could not be determined. 
Limnocharis. Figs. 16 to 19. 
A young stage is shewn at Fig. 16 in longitudinal section. The 
plerome cylinder arises from a single initial. A single initial with 
an undivided segment on either side also gives rise to the dermatogen 
and the periblem. The root-cap is two-layered. 
An older root is shewn at Fig. 17. The central axial row is 
well seen, and the pericycle does not appear to be cut off by the 
first division plane of the single initial cell of the plerome. The 
root-cap is five-layered. 
Limnocharis was the only genus examined in which the embryo- 
genic tissue had become at all differentiated into tissue-elements, at 
any rate as seen in longitudinal section. Figs. 18 and 19 are longi¬ 
tudinal and transverse sections respectively of such a root. In Fig. 19 
the root-cap cells are larger and their staining properties different to 
the other cells of the root. In the plerome cylinder the cells of the 
central axial row elongate further back from the apex, and become 
lignified. Other cells in the pleromic tissue also become lignified 
and shew spiral markings. In the transverse section this is also 
well seen. The xylem cells become lignified, from the pericycle 
inwards. 
General Comparison of Results Obtained from the 
Investigation of Young Adventitious Roots of the 
Genera of Monocotyledons Named. 
I .—The Origin from the Internal Tissues of the Stem. 
Van Teighem (2) says that the root arises entirely from the 
pericycle of the stem, and that the arc of the endodermis external 
