PLATE IV. 



Fig. 7. — Medullary angles of three vascular wedges from a transverse section 

 of the vascular cylinder of a Stigmaria. a. Medullary cells, b. Vascular wedges. 

 b'. Elongated cells of primary medullary rays. b". Secondary medullary rays. 

 X 90. Cabinet, No. 744. (Pages 10, 14.) 



Fig. 17. — Part of a transverse section of a vascular cylinder, including a 

 longitudinal section of a secondary medullary ray containing barred Tracheids. 

 Two radial lines of vessels of the cylinder, b, b. Barred Tracheids, b". X 80. 

 Cabinet, No. 767. (Page 15.) 



Fig. 19. — Peripheral portion of the transverse section of the vascular cylinder, 

 Fig. 14, PI. VII, in which a new zone is being added exogenously. Older vessels 

 of the cylinder, b. Imperfectly developed vessels, &c, of the newer zone, b'. X 39. 

 (Pages 17, 24, 32.) 



Fig. 20. — Periphery of a transverse section of a vascular cylinder with an 

 investing cellular layer, which appears to be a cambium. Peripheral vessels of 

 the vascular cylinder, b. Procambial cells, c. X 75. Cabinet, No. 744. (Page 

 17.) 



Fig. 25. — Transverse section of a fragment of Stigmaria with a considerable 

 development of the prosenchymatous zone, e, of figs. 22 and 23, Plate VIII. X 3. 

 Cabinet, No. 795. (Page 20.) 



Figs. 28, 29, 30, 31, 32, 33. — Transverse sections of six rootlet bundles after 

 they have escaped from the peripheral ends of the primary medullary rays, but 

 before they have penetrated the cortex. In each of these, /' indicates the proto- 

 xylem of the wedge-shaped bundle and the broad opposite base of the wedge, 

 including the small vessels, /, its latest additions. X 80. Cabinet, No. 744. 

 (Pages 23, 24, 26, 31.) 



Fig. 53. — Small portion of the longitudinal section of a young rootlet bundle. 

 Vascular bundle,/. Cells of the bundle sheath,/,/". X 100. (Page 28.) 



