19 and 20. Spores, outer and inner faces, × 305.
Figures 4, 18–20, are drawn from material collected by Schott in 1855; the others from material collected by Earle and Tracy, April, 1902.
Plate 12
Figs. 21 and 22, Riella Americana Howe & Underw.; Figs. 23–36, Riella affini Howe & Underw.
21. Germ plant, × 245.
22. Same in edgewise view, × 245.
23. Gametophyte of Riella affinis, × 11.
24. Apical portion of another, with involucres and antheridial loculi, × 11.
25 and 26. Involucres, × 16.
27 and 28. Spores, outer and inner faces, respectively, × 330.
29 and 30. Germinating spores, × 55.
31. Germ plant, showing the earlier cell divisions, × 245.
32–36. Various forms assumed by the germ plants, × 55. The principal vegetative point is indicated by c. The elongate form represented in Fig. 36 is common when the young plants are well covered with water.
