SPOROPHYTE. 15 



evil (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 rhizog'enous 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 Cyatheacea.- all 

 of the cells in the same vertical line with the rhizogenous cell are said to be 

 of the same width as the latter (c. g., Cibolhii/i regale; cf. Sadebeck 1898, 

 p. 63). Dennst&dtia, therefore, agrees with Polypodiaceae 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 

 rootlet, excepting epidermis and outer cortex (including hypodermis), are 

 respectively continuous. Certain inner cortical cells of the main root bend 

 out into the branch, but eiidodermis 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 



