DEVELOPMENT OF THE SPOROGONIUM IN THE MOSSES. 285 
Puare XII. 
Fig. 32. Longitudinal optical section through the young growing point of 
sporogonium of P. formosum at stage a, fig. 6. 
Figs. 33 to 43 inclusive from sections cut after imbedding in paraffin 
with Caldwell-Threlfall microtome. 
(A series. Fig. 33, nearest the apex ; fig. 36, furthest off, together with 
fig. 41. 
33. | Transverse sections just below apex of sporogonium at that stage in 
which a theca is going to be formed. 
35.1 O.=octant-walls; Q.=quadrant-walls; er.—exomeristem; end.= 
36. endomeristem ; sk.=sheath ; e.s.=central strand. 
Fig. 33, Atrichum undulatum, after Kienitz-Gerloff. The others from 
Polytrichum formosum. 
37.\ . , 
38. | Transverse sections through the young growing apex of P, juniperinum. 
39, | These with fig. 33 form a series illustrating the development: of the 
40. ^ seta. Letters as in figs. 33 to 36. 
41. | In fig. 39 the small numerals indicate the order in which the walls are 
49. y, formed. 
43. See under fig. 33 above. Section through base of young theca of P. for- 
mosum. Letters as in figs. 33-42. 
44. Diagram to illustrate the primary division into (ero.) exomeristem and 
(end.) endomeristem in a moss sporogonium. Q.=quadrant-walls ; 
O.=octant-walls. ` 
45. Transverse section of young embryo of Frullania dilatata for compa- 
46. 
rison with fig. 44. After Leitgeb (14). 
. Transverse section of young stem of Equisetum for comparison with 
figs. 44 and 45. 
47. Transverse section through the cortex of Polytrichum formosum, x 520. 
(Cut after imbedding in paraffin with Caldwell-Threlfall microtome.) 
ep.=epidermis (this shows the cuticularized outer wall) ; sc/.=cortical 
sclerenchyma ; m./.=middle lamella; ¢.=intercellular spaces. 
48. Vertical section through the wall of the theca of P. commune, to show 
the peculiar pitting of the epidermal cells. 
49. Surface view of epidermis of theca of P. commune. 
