SPOROPHYTE. 15 
cell (figs. 32, 33, 34). On one side it lies in a major sextant, on the other 
side in a minor; but both of these sextants remain much narrower than 
the other four (figs. 32, 33), as if to accommodate this undivided cell. 
As the root elongates in this region, transverse divisions take place in 
the rhizogenous cell. The more distal member in each case retains its 
identity, while the others sooner or later divide radially and become like 
ordinary endodermal cells (figs. 38-40). If the radial walls are slow 
to appear, we may have a row of three or four equally broad cells (figs. 
38-40), of which only the most distal is rhizogenous. In Cyatheacee all 
of the cells in the same vertical line with the rhizogenous cell are said to be 
of the same width as the latter (e. g¢., Cibotium regale; of. Sadebeck 1898, 
p. 63).  Dennstedtia, therefore, agrees with Polypodiacee in this respect. 
After elongation of the root is complete, the definitive rhizogenous cell 
swells out into a lens-shaped body (fig. 34). On its proximal side it is 
cut once more by a transverse wall, but this wall passes obliquely inward 
(fig. 37). Two obliquely longitudinal walls follow (figs. 35, 36, 40, 41) hew- 
ing out a tetrahedral cell with one face against the cortex, one side toward 
the stem, and the apex toward the subjacent pericycle. This is the rootlet 
initial (figs. 36, 40, 41), and the three cells which bound its sides are the 
first segments of the rootlets. This initial and all of its segments proceed 
to develop as in the case of the parent root (figs. 41-43). The rootlet 
being smaller than the root (fig. 54), its segments undergo fewer divisions 
in the cortical region. The xylem of the rootlet stands transversely to 
that of the root. Therefore the protoxylems are to the right and left if the 
root is held in a vertical position, and the xylem band of the rootlet will 
lie horizontally. The xylems of the rootlet arise in the second and third 
(and overlying) segments formed from the rootlet-initial, and in their. 
proximal sextants. 
Meanwhile divisions have also occurred (as shown by mitotic figures) 
in the neighboring endodermal and cortical cells. In the former no regu- 
larity was observed. The cortex, however, develops a mass of small pro- 
toplasmic cells directly over the rootlet (figs. 34, 42, 43) and undergoes 
no induration here. The cells immediately adjacent to the root-cap are 
finally organized into a special layer (fig. 43) which advances through the 
remaining cortex, etc., apparently causing the disintegration and absorp- 
tion of these tissues. In the mature stage all of the tissues of root and 
rdotlet, excepting epidermis and outer cortex (including hypodermis), are 
respectively continuous. Certain inner cortical cells of the main root bend 
out into the branch, but endodermis and pericycle (fig. 55) connect by the 
intervention of a number of cubical cells. The xylem tracheids of the 
branch terminate abruptly against the side of those of the main root and 
at right angles to them (figs. 56, 57). The phloems connect in a manner 
similar to the xylems. The mature rootlet repeats the structure of an 
ordinary root on a smaller scale (fig. 54). In a slender rootlet there may 
