1901] SPORANGIA AND GAMETOPHYTES OF SELAGINELLA 189 
FiG. 30. Section of archegonium in which the egg lies below the ven- 
tral canal cell, and the neck canal cell above it. Two tiers of neck cells are 
FIG. 31. Stage younger than that shown above, before neck cells are 
Fig. 32. Archegonium with egg and ventral canal cell laterally placed. 
No trace of neck canal cell. Neck consists of four tiers of cells, each tier 
comprising an upper (superficial) cover cell, and one neck cell. The cells 
abutting on the venter belong to the prothallium. 
Figs. 33 and 34. Mature archegonia. In fig. 37 a see is lying 
on the receptive spot of the egg. Fig. 74 shows a one-celled em 
PLATE VI, Selaginella apus. Oc. 2, otl immersion y. 
FIG. 35. Section of young megasporangium at earliest stage when mega- 
spore mother cell is distinguishable from sterile cells. For detail see fig. 77. 
Fig. 36. Section of older stage of megasporangium. Megaspore mother 
cell has moved near center of sporangium. 
- 37. Oblique section of megasporangium showing young tetrad, and 
sterile mother cells, floating in slime composed in part of disintegrated sterile 
cells and in part of a secretion poured out by tapetum. 
Fig. 38. Section of somewhat older stage of megasporangium containing 
group of four megaspores (only three are represented). Each spore consists 
limpid fluid and possessing a very small nucleus. e spaces intervening 
between vesicle and median layer and between the latter and the exospore 
are filled with fluid, 
FIGS. 39-41. Successive serial sections of a tetrad, to illustrate the fact 
that the exospore is a continuous envelope common to the group of spores 
and splits as they move apart. 
Fig. 42. Section of group of megaspores but little older than those in 
fig. 38.- Filamentous processes shown between spores. The mother cell 
membrane, beyond whose boundary the radiations do not pass, envelops the 
tetrad. 
43. Section of two megaspores more advanced. The spore at the 
left is cut nearly ir half from apex to base, that at the right is a slice across 
the apex. Protoplasmic vesicle grown but little larger than in fig. 2. 
Spine-like processes upon exospore in connection with radiations. Mother 
cell membrane still evident. 
FiG. 44. Section of the female gametophyte showing the protoplasmic 
vesicle with two nuclei. The radiations extend across the spaces between 
vesicle and median layer, between median layer and exospore, and between 
the latter and the original spore mother cell membrane. 
