1900 | SPOROPHYLLS AND SPORANGIA OF ISOETES 345 
Figs. 16, 18, First division of terminal cell of ligule sectioned in plane 
a—a of fig. 15. X 490. 
Fig. 17. The same sectioned in plane 6—4 of fig. 75. X 490. 
Fig. 19. Tangential section of older ligule. x 490. 
Fig. 20. Transverse section of ligule of same age as that of fig. 79. 
X 490. 
Fac. 21. Transverse section of still older ligule. x 300. 
Fig. 22. Median radial longitudinal section of base of half-grown ligule; 
5, the sheath, g, the glossopodium, v, the velum. X 490. 
Fig. 23. Radial longitudinal section of base of mature ligule at the posi- 
tion indicated by a—é of fig. 25, showing the thickened cells of the velum 
and leaf adjacent to the ligule. x 48. 
Fig. 24. The same in /. Engelmanni. 
FIG. 25. Transverse section of ligule and lant at the position indicated by 
a—é of fig. 23. X 30. 
Fic. 26. Median radial longitudinal section of young sporophyll, showing 
rudiment of the Ssporangium. X 490 
Figs. 27-28. The same more evened: X 490 
Fig. 29. Transve tion of young sporophyll ‘ik sporangium. X 490. 
FG. 30. Transverse section of sporangium more advanced. X 490. 
FIG. 31. Tangential section of young sporangium. X 490. 
Figs. 32-38. Radial longitudinal sections of young sporophyll ; fig. 37 is 
a section through the side of the sporangium of which fig. 76 is a median sec- 
tion; v, the velum, g, the glossopodium, s, the sheath. X 490. 
he, 39. Transverse section of sporangium more advanced. X 4 
Fie. 40, Transverse section of leaf with sporangium of same age as that 
of fig. 39. X 490. 
Fig. 41. Median radial See section of a sporangium of about the 
Same age as the last. x 4 
1G, 42, ts dina section of side of sporangium. X 4 
FIG. 43. Transverse section of a sporangium still older Me in which the 
trabecule are not yet recognizable. X 490. 
1G. 44. Transverse section of young leaves and of microsporangium at 
the time of the first differentiation of fertile and sterile regions ; the shaded 
Portion represents the fertile region; v, the velum, J, the ligule, f, the vas- 
cular bundle, x 48. 
Fic. 45, Oblique nearly tangential section of microsporangium. X 48. 
Fig. 46, Tangential section of microsporangium. O. 
Fig. 47. Cross section of sporophyll and microsporangium, showing the 
trabeculze, aie ¢, and a few microspores; v, the velum (semidiagram- 
Matic). x 
6. 48. Os of microsporangium at the time of the first differentiation 
Fig 
of fertile and sterile regions. x 490. 
