346 BOTANICAL GAZETTE [MAY 
Fic. 49. The same, showing portion of outer wall. X 490. 
Fic. 50. Portion of an older microsporangium, = differentiation of 
ae ays into trabecule and tapetum (¢). X 4 
G. 51. Portion of trabecula, tapetum (¢), and young spores of a micro- 
sporangium. X 490 
G. 52. Part af outer wall and tapetum (/) of nearly mature microspo- 
rangium. X 490 
Fics. 53-55. Division of mother cells to form microspores; fig. 53 illus- 
trates successive division; fig. 54, simultaneous division; fig. 55, the shape 
of the spores, bilateral in a and 4, tetrahedral in ¢. X 490. 
F1G. 56. Young microspores. X 490. 
Fic. 57. Cross section of megasporangium with young spores and tape- 
tum (¢). x 48. 
Fic. 58. Portion of a trabecula and tapetum (f) of a megasporangium, 
X 490. 
FiG. 59. Tetrahedral arrangement of young megaspores. X 490. 
Fics. 60-61. Successive division of megaspore mother cells, spores 
bilateral. X 490. 
Fic. 62. Median radial longitudinal section of sterile leaf with aborted 
sporangium (shaded). 
Fic. 63. Transverse section of megasporangium first distinguishable as 
such. X 490. 
Fic. 64. Part of transverse section of a megasporangium with a group of 
potential mother cells. X 490. 
Fic. 65. The same with a single mother cell. X 490. 
Fic. 66. Part of a transverse section of a megasporangium ; for explana- 
tion see text. X 490. 
Fig. 67. Diagram of young megasporangium. 
Fic. 68. Diagram of a longitudinal section of the stem. See p. 228. 
Fics. 69, 70. Early stages of the sporangium of a fern. Diagrammatic. 
a, peerage J, fertile sporogenous cell ; s, sterile wall cell. 
. 71, 72. Early stages of a microsporangium of an angiosperm: 
Piepuciease a, archesporium ; ¢, epidermis; s, primary tapetum ; f, pri- 
mary sporogenous cell or cells. 
IGS. 73, 74. Early stages of a megasporangium of an angiosperm: 
Diagrammatic. Letters as in figs. 77, 72. 
