1901] SPORANG/A AND GAMETOPHYTES OF SELAGINELLA 193 
eggs and spermatozoids. The necks of the archegonia have been sliced off 
somewhat obliquely 
PLATE 1X. Selaginella rupestris. 
G. - Apex of a strobilus in radial section. A single archesporial 
cell hee at the base of a sporophyll. The cell with black nucleus is the 
initial cell of the next younger sporophyll of the same ra 
1G. 102. First division of archesporial cell into a ibid and a 
superficial cell. 
FIG. 103. The superficial cell of the first division has divided into three 
wall cells, and the hypodermal cell into two sporogenous cells, forming a 
wedge-shaped mass. ; 
FIG. 104. Radial section of portion of strobilus. The largest sporophyll 
has ceased to grow at the apex which is converted into a branched spine 
The initial cells of the ligule at the base of the sporophyll are represented 
with black nuclei. The tissue is rupturing to form air chambers in the basal 
region. The sporangium has been outstripped in growth by the sporophyll 
next above it. The two shaded cells in the upper part of the figure represent 
the same stage of sporangium as seen in fig. 702 
FIG. 105. Section of sporangium. The wall is nearly completed and the 
tapetum is becoming differentiated from the sporogenous complex of cells. 
The limits of the latter in the basal region not so clearly defined as repre 
sented in the figure. 
Fig. 106. Detail showing two megaspores and several sterile mother 
FiGs. 107-117. Phases undergone by megaspore mother cells preceding 
divisions into spores. 
Fic. 118. First division of megaspore mother cells into two spores. 
FIG. 119. Section through sister megaspores. A portion of the sculptured 
€xospore is removed from the upper surface of each, showing the proto- 
plasmic vesicle with a small nucleus floating in liquid. The spore mother 
cell membrane envelops the two spores. 
Fig. 120. Section showing incomplete division of the protoplasm of two 
megaspores. The nucleus of the spore mother cell has not divided. 
Fig. 121. Section through a single megaspore whose contour and large 
nucleus suggest that it is the direct product of a spore mother cell which has 
failed to divide. 
Figs. 122, 123. Older stages of megaspor 
Fig. 124. Median vertical section of tip s pails showing relation of 
Sporangia to sporophylls and vascular system. The meristematic regions at 
the bases of the sporangium pedicels grow upward slightly by causing the 
Megasporangia to appear sunken in the hollows thus formed. There were 
only megasporangia in this strobilus. 
