MARATTIACEAE 517 
At maturity the more or less indurated superficial layer of cells of 
the sporangial wall is the most conspicuous part, but the thinner-walled 
cells lying. within, though they may shrink, do not entirely disappear. 
The ‘essential parts of the sporangium of <Angzopreris, and especially 
the archesporium, are thus seen to be referable in typical cases to a 
single parent cell: this also is the case typically for all the other genera. 
Beni 
=e 
Fic. 285. 
Marattia fraxinea, Smith. A=section transversely through a sorus : the sporogenous 
cells shaded, the tapetum marked (x, x); the left-hand sporangium is the most usual 
arrangement of sporogenous tissue, the other two less frequent. 8 and C show in similar 
section irregular groupings not referable to a single parent cell. 200. 
But: in Angiopter’s and Marattia, and notably in Danaea, this is not 
always so, and there is much individual divergence of detail. Not only 
is the segmentation conformable to no strict plan, but the size of the 
sporogenous groups varies greatly, while in non-typical cases it is not 
always possible to refer the sporogenous group of one sporangium to a 
single parent cell (Fig. 285). These irregularities are usually associated 
with considerable differences in size of the sporangia. In no genus 
does this irregularity appear more pronounced than in Janaea: an 
almost exact uniformity in size and segmentation of sporangia is so 
