LIST OF ILLUSTRATIONS AND EXPLANATION OF PLATES. 51 
EXPLANATION OF PLATES.* 
Key to index-letters on figures (except figs. 47-51). 
a, initial cell. ip, inner pericycle, r, root. 
e, cortex, iph, inner phloem. rh, root-hair, 
cj, conjunctive parenchyma, is, Inner sclerenchyima, rt, rootlet. 
e, epidermis. ist, inner starchy tissue. s, sclerenchyma, 
J, fundamental tissue. mn, endodermis. sa, air-space. 
h, hypodermis. Pp, pericycle. sp, Spiral tracheid. 
i, rhizogenous cell. pa, parenchyma, si, Starchy tissue. 
ic, inner fundamental tissue, ph, phloem, t trachbeid. 
icj, inner conjunctive paren- pl, plerome, v, sieve-tube. 
chyma, : pph, protophloem, x, xylem. 
in, inner endodermis. px, protoxylem. 
Letters used variously: b, d, m, 0, u, 7, 1, 2, 8, ete, 
PLATE 1: 
1, Habitat of D. punctilobula; Massachusetts. Photo by C. E. Waters, Ph.D. 
2. Leaves as they grow. From Waters, 1903, by courtesy of the author and publishers 
PLATE 2: 
3. Rhizome, natural size, showing fork, leaf bases, and leaf-shoots. 
4. Leaf-bud with two unequal leaf-shoots, natural size. 3 and 4 from photo by 
C. E. Waters, Ph.D. 
5. Portion of pinna showing pinnules, lobes, crenations, sori, and hairs. XX about 
10, From Waters, 1903, by courtesy of the author and publishers. 
PLATE 3: 
6-8. Diagrams showing distances between rootlets, natural size. 
g. Diagrammatic projection of a piece of stem 5 cm. long, including apex, with 
figures to indicate the number. of roots attached to each eighth of the 
circumference. 
10-13. Diagrams of divisions of rovt-cap segment as seen from distal side. 
14. Diagrammatic longitudinal section of root-tip, showing the origin of the various 
tissues. Walls numbered in order of formation. 
15-22. Diagrams of division in segments of root-initial. Walls numbered in order 
of formation, 
PLATE 4: 
20-22. See above. 
23. Root-tip in longitudinal section. x 210. 
24. Longitudinal section of an anomalous root-cap, showing two layers from one 
segment at point marked *, X 210. 
25-32. Successive transverse sections of a root-tip. 25, 26 in cap; 27-32 in root; J 
indicates root-cap. Initial and second set of segments dotted. Allin 
the same relative position. X 210. 
PLATE 5: 
28-32. See above. 
33. Transverse section of same root, 0.1 mm. farther up than 32; J, root-cap. X 210. 
34. Rhizogenous cell, undivided, in transverse section of root. X 210. 
35. Rhizogenous cell, second division, in similar section. X 210. 
PLATE 6: 
36. Rhizogenous cell, third division. X 210. 
37. First division in rhizogenous cell; longitudinal radial section of root. X 210. 
38. Endodermis with rhizogenous cells, tangential view. Reconstruction from 
serial longitudinal sections of root. X 210. 
39. Ditto: another root. X 210. 
40. Oblique tangential view of rhizogenous cell, showing its first three divisions. 
X 210. 
41. Rootlet initial from longitudinal tangential section of root. X 210. 
42. Rootlet initial in transverse section of root; one cap-layer. Cells within the 
chain of arrows have arisen by proliferation of cortex. X 210. 
43. Ditto; two cap-layers, 4, and digestive layer of cortex, 0. X 210. 
44. Part of transverse section of nearly mature root. X 210. 
45. Transverse section of stele of fully mature root. X 210. 
46, Part of transverse section of old root with outer layers shedding off. X 100. 
*All figures ure of Dennsetdtia punctilobula unless otherwise stated in the description. 
