ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 909 
a tangential section of the strobilus, was square, probably somewhat. lobed, with 
depressions between the insertions of the sporangia (Plate 81, fig. 32). 
The sporangia were attached to the edge of the peltate head, at its four corners, 
and on its lower side. Each sporangium is connected with the sporangiophore by a 
narrow neck of tissue only, through which the vascular bundle passes, to end at the 
base of the sporangium itself (see Plate 81, fig. 29).* The palisade-layer extends 
over the short stalk of the sporangium on its outer side, its cells becoming shorter 
here, and appears to have been continuous with the sporangium-wall. 
C. The Sporangia. 
Each sporangium has the form of a somewhat elongated sac; its long axis is 
parallel to the pedicel of the sporangiophore, and is therefore radial to the axis of 
the strobilus. As seen in tangential section the sporangia are approximately square. 
In most instances, the sporangium, as preserved in our specimens, has a wall which 
is one-cell only in thickness. Remains of tissue lining the inside of this persistent 
layer are frequent, but only show structure in exceptional cases, to be considered 
presently. 
The cells of the sporangial wall are lozenge-shaped, as seen in surface view, their 
long axes being parallel to the major axis of the sporangium (Plate 81, fig. 31, A). 
Their lateral walls are thin, but are stiffened by vertical plates, which project, like 
buttresses, from the cell-wall, and correspond to one another in adjacent cells. These 
buttresses are broadest at the base, 7.¢., where they abut on the inner cell-wall, next 
the cavity of the sporangium (fig. 31, Aand B). Ina tangential section of the whole 
strobilus, which gives a transverse section of the sporangium, the cells of the wall are 
cut across, so that we see the buttresses on either side of each vertical septum (fig. 31, 
B). In transverse or radial sections of the strobilus, however, which give longitudinal 
sections of the sporangia, the cells of the wall are cut lengthwise. In this case the 
narrow edges of the buttresses are seen, so that the vertical septa appear to be much 
more numerous than they really are (fig. 31, C). The actual cell-wails are seldom 
seen well in this view, no doubt because they are usualiy cut obliquely. The mode of 
thickening of the cell-membranes of the sporangial wall bears a considerable resemblance 
to that of the “ fibrous layer” of some anthers, and may very probably have discharged 
the same function, that of effecting dehiscence. 
In certain cases a layer of thin-walled tissue, two or three cells in thickness, is found 
lining the whole or part of the sporangial wall (Plate 82, fig. 35). One is tempted at 
first to regard this layer as a persistent tapetwm, but the inconstancy of its occurrence, 
even in the most perfectly preserved specimens, and its very variable thickness when 
present, are scarcely consistent with such a view. In other instances the entire 
* See also Wittramson, “ Organization,” Part XI., Plate 54, fig. 23 (C.N. 1017). 
