224 Howe AND UNDERWOOD: THE GENUS RIELLA 
Ig 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 affint 
Howe & Underw. : 
21. Germ plant, 245. 
22. Same in edgewise view, * 245. 
23. Gametophyte of Rze//a affinis, X II. 
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 vegeta- 
tive point is indicated by «. The elongate form represented in Fig. 36 is common 
when the young plants are well covered with water. 
