, „ i y ] DUPLER— T. I X US 3 ° 5 



EXPLANATION OF PLATES XXIV-XXVI. 



All drawings were made with a camera lucida; text figs, i-io and 13-22 

 are drawn to the same scale, with a magnification in reproduction of approxi- 

 mately 36; text figs, n-12 and all plate figs, are drawn to the same scale, 

 reduced one-half in reproduction, having a magnification of approximately 475. 



PLATE XXIV 



Fig. 23. — Young sporophyll primordium, showing 2 archesporial initials 

 in hypodermal layer of rounded primordium. 



Fig. 24. — Archesporial initial in hypoderm; division of epidermal cell. 



Fig. 25. — Archesporial initial in tangential section. 



Fig. 26. — Archesporium of 2 cells. 



Fig. 27. — Metaphase in division of archesporial initial. 



Fig. 28. — Late stage in division of archesporial initial. 



Fig. 29.— Primary wall cell (outer cell) and primary sporogenous cell 

 (inner cell), resulting from division of initial. 



Fig. 30.— Primary wall cell and division of primary sporogenous cell. 



Fig. 31. — Primary wall cell has formed 2 tiers of wall cells, in one of 

 which division is taking place; primary sporogenous cell has divided anti- 

 clinally, forming 2 sporogenous cells. 



Fig. 32.— Lobe of young sporophyll, showing small mass of sporogenous 

 tissue, 2-layered sporangium wall formed on outer side, and meristematic basal 

 portion of epidermis differentiated from remainder of epidermis. 



Fig. ^^- — Somewhat older stage than fig. 32. 



Fig. 34. — Sporangium wall complete, entirely surrounding sporogenous 

 mass; latter part of July. 



Fig. 35. — Older sporangium, showing differentiation of tapetum from 

 sporogenous tissue. 



Fig. 36. — Portion of sporophyll, showing epidermis, 2-layered sporangium 

 wall with narrow flat cells, tapetum (1 cell binucleate), and microspores; 

 winter condition. 



PLATE xxv 



Fig. 37. — Transverse section of portion of lower scale, showing stoma on 

 inner surface and heavily cutinized epidermal walls, especially on outer surface. 



Fig. 38. — Transverse section of portion of upper scale, showing vascular 

 bundle and inner epidermis of scale; in vascular bundle note centripetal xylem 

 and 2 transfusion cells, 1 dorsal, 1 lateral to xylem. 



Fig. 39. — Transverse section of bundle a of fig. J3, showing phloem char- 

 acter of bundle; no xylem present. 



Fig. 40. — Bundle a at level of fig. 15. showing mesarch character. 



Fig. 41. — Bundle e of fig. 15; single xylem cell surrounded by phloem. 



