102 
F. 0. BOWER. 
division in the root-cap. The section being a thick one, these walls could be 
seen by focussing deeply into the section. 
Fig. 4. — Three-sided apical cell, segments less regular, and the apical cell 
itself is of comparatively small size. The square cell marked (x) may be 
assuming the function of an initial cell. 
Fig. 5. — a. Section through the root-cap. b. Section from the same root 
immediately below a. b shows an irregular arrangement of the meristem, 
with apparently two initial cells (x). 
Fig. 6. — Three initial cells, separated by principal walls, p.p. Sextant 
walls marked s. s. 
Fig. 7. — A similar section immediately below the root-cap. By focussing 
deeply the wall represented by the dotted line appears ; this is a division in 
the root-cap. 
Fig. 8. — A similar section, but less regular. 
Fig. 9. — Quoted from Naegeli and Leitgeb, Taf. xiv, fig. 5. A transverse 
section of the apex of the root of Pteris hastata, s. to., as seen by focus- 
sing below the apical cell. p.p. = the principal walls, s.s. the sextant 
walls, which are in this case homodromous. 
Fig. 10. — Quoted from Naegeli and Leitgeb, Taf. xii, fig. 8. Transverse 
section of the apex of a root of Equisetum hiemale, immediately below 
the apical cell. The sextant walls are here heterodromous. 
Fig. 11. — Median longitudinal section, with pyramidal apical cell. tr. = 
cells developing as tracheides. 
Fig. 12. — A similar section. 
Fig. 13. — An irregular meristem : apparently two pyramidal initial cells of 
very unequal size. 
Fig. 14. — Very irregular meristem, with a pyramidal apical cell (x). Seg- 
ments undergoing repeated periclinal division. Note the curvature of the 
anticlinal or principal walls. 
Fig. 15. — (x 370.) The products of the development of one segment, 
showing how one cell (x) takes the lead ; the arrow shows the direction of the 
organic axis. 
Fig. 16. — Section showing two pyramidal initial cells of equal size. 
Fig. 17. — Two oblong initial cells ; segments are cut off by periclinal walls 
from the lower end of them, as well as from the upper end and sides. 
Fig. 18. — Two similar initial cells with segments. 
Fig. 19.— A group of cells, derived by division from one rhizogenic cell of 
the endodermis. (x) The pyramidal initial cell of this very young lateral 
root. 
Fig. 20. — Apical meristem from a young lateral root, which has extended 
to the outer surface of the cortex of the main root. 
Fig. 21. — Young lateral root, with two oblong initial cells, xy. — the 
xylem of the main root. p. = pericambium. 
Fig. 22. — A similar preparation of a young lateral root. 
