Osmunda claytoniana , Z., and O. cinnamomea , Z. 91 
Fig. 19. Prothallium of the same, in which cell-division has taken place in 
three planes, x 350. 
Fig. 20. Male prothallium, about four months old, bearing antheridia. x 100. 
Fig. 21. Prothallium of O. claytoniana , two weeks old, showing dichotomous 
branching ; x, x l , apical cells, x 300. 
Fig. 22. Outline of a prothallium of about two months, of O. claytoniana. The 
midrib is indicated by the dotted lines, x 45. 
Fig. 23. Microtome-section of an older prothallium, parallel with the surface, 
showing the single, four-sided apical cell, x. Chromic acid— -Bismarck-brown, 
x 350- 
PLATE IV. 
Fig. 24. Apex of a prothallium of 0 . claytoniana , of about three weeks, x 
350- 
Fig. 25. Vertical section of a full-grown prothallium of 0 . claytoniana . 
Chromic acid — Bismarck-brown, x 300. 
Fig. 26. Prothallium of 0 . cinnamomea , of about six weeks, x 100. 
Fig. 2 7. Microtome-section, parallel to the surface, of an older prothallium of 
the same. Chromic acid — Bismarck-brown ; x, x l , two apical cells (?). x 350. 
Fig. 28. Vertical section through a prothallium of about the same age as 27. 
Chromic acid — Bismarck-brown, x 300. 
Figs. 29, 30. Two male prothallia of 0 . claytoniana , of the filamentous type. 
an , antheridia. x 100. 
Figs. 31, 32. Two cells from the prothallium of 0 . cinnamomea , showing the 
form of the chloroplasts : 31, large abnormal ones ; 32, the ordinary form, x 600. 
Fig. 33. Base of a prothallium (Pr) of 0 . claytoniana , from which is growing 
a secondary prothallium {Pr 1 ) with antheridia {an), x no. 
Figs. 34-38. Successive stages in the development of the antheridium of 0 . 
claytoniana, seen in optical section, m, basal-cell ; n, mother-cell of antheridium. 
The contents of the central cells are shaded, x 600. 
Fig. 39. An older antheridium of 0 . claytoniana. a , upper view of -surface ; 
b, optical section ; c, lower surface ; 0, operculum. x 600. 
Fig. 40. Superficial view of one of about the same age as 39, but turned at 
right angles to it. x 600. 
Fig. 41. Upper surface of a full grown antheridium of 0 . claytoniana ; 0, 
opercular cell, x 600. 
Figs. 42, 43. Transverse optical sections of young antheridia of 0 . claytoniana . 
x 600. 
PLATE V. 
Fig. 44. Vertical microtome-section of a full-grown antheridium of 0 . clay- 
toniana. Chromic acid — alum-cochineal. x 650. 
Fig. 45. Similar section of a younger antheridium of 0 . cinnamomea. Chromic 
acid — alum-cochineal — Bismarck-brown, x 650. 
