DESCRIPTIVE INDEX TO THE PLATES. 1 



FIG. 



PLATE 



1. 



I. 



2. 



I. 



3. 



II. 



5. 



III. 



6. 



III. 



Ga. 



III. 



Gb. 



III. 



7. 



IV. 



PAGE 



Cast of one of the Stigmarian trees found at Dixon Fold . . .5 



Cast of a second of the same group of trees . . . .5 



Under surface of a Stigmarian root in the Museum of the Leeds Philosophical 



Society . . . . . . . .5 



II. Under surface of a Stigmarian root in the Museum of the College of Science, 



Leeds . . . . . . . .6 



Side view of a very young Stigmarian root . . . . 



Under surface of Tig. 5 . . . . . .7 



Six of the rootlet-scars from near Fig. 5, a. Nat. size . . .29 



Six similar rootlet-scars from near the point x of Fig. 5. Nat. size . . 29 



Medullary angles of three vascular wedges from a transverse section of the vascular 



cylinder of a Stigmaria. a. Medullary cells, b. Avascular wedges. V . Elongated 



cells of primary medullary rays, b" . Secondary medullary rays. x 90. 



Cabinet, No. 741 . . . . . .10, 14 



8. V. Tangential section from a vascular cylinder, showing transverse sections of the 



primary medullary rays, b' . Vascular rootlet bundles, f. x 5. Cabinet, 

 No. 771 . . . . . . .13, 14 



9. VI. Longitudinal section through a young root of a Stigmaria. Medullary cavity, a. 



Vascular cylinder, b, b. Vessels of the cylinder deflected to form a' rootlet 

 bundle, f, passing out through a primary medullary ray, b'. Secondary 

 medullary rays, b'". Cortex parenchyma, d. Cortex meristem, d'. Base of 

 rootlet, g. Rootlet cushion, h. x 10. Cabinet, No. 776 14, 18, 19, 22, 32 



10. VII. A radial section through the outermost vessels, b, of the vascular cylinder. Cambi- 



form zone, c. Cells belonging to a more external cortical parenchyma, d, d. 

 x 90. Cabinet, No. 779 . . . . . 14, 17, IS 



11. VII. A tangential section through a portion of a vascular cylinder. Xylem laminae, b. 



Secondary medullary rays, b'. Eootlet bundles,/! x 5. Cabinet, No. 771 . 11 



12. IX. Tangential section of part of a xylem cylinder, made close to the medulla, giving a 



transverse section of a primary medullary ray, b, and the vascular rootlet 

 bundle, /, /'. Enlarged secondary medullary rays at the orientation of the 

 younger part of the rootlet bundle, d. X 30. Cabinet, No. 851 . 14, 23 



1 The list of pages appended to each figure shows either where each specimen figured is described, 

 or where some important reference is made to it. 



9 



