358 
Proceedings of the Royal Society of Edinburgh. [Sess. 
the greater part of the length of the lamina. The epidermal cells of the 
outer surface of the lower half of the lamina and the vertical outer face of 
the sporophyll-base are large and have thick, lignified walls which show 
curious undulations and infoldings.* The sporangium is attached to the 
upper surface of the sporophyll-base immediately over the vascular bundle 
and close to the commencement of the upward curve of the lamina. It is thus 
in the mature condition removed a considerable distance from the axis, and 
the large sporangium extends between the attachment and the latter, and 
only projects to a relatively slight extent to the distal side of the attachment. 
The stalk is short, and consists of tracheid e-like cells with lignified walls 
and a close, spiral thickening.*)* The basal cells of the sporangial wall have 
the same characters, and this tissue constantly extends for a short distance 
distally as a modification of the epidermal cells of the lower part of the 
lamina. The wall of the sporangium consists of two layers of cells, the 
inner being thin-walled, while those of the epidermal layer have bands of 
thickening on the inner periclinal wall and all the anticlinal walls. While 
these thickenings can be traced all round the sporangium, they are best 
developed and most strongly lignified over the distal convexity ; it is in the 
* Miss Sykes suggests ( loc . tit.', p. 49) that these cells play a part in bending back the 
lamina to allow of spore dispersal. 
t This feature was first recognised by Miss Sykes, and is figured by her for L. cernuum 
{loc. tit., PI. iii., fig. 8). Similar lignified cells in this position are recorded for L. inundatum 
and L. carolinianum , and slight indications of lignification were found in the stalks of some 
other species. The significance of this feature is at present obscure. 
