THE ANATOMY AND AFFINITY OF STROM ATOPTERIS MONILIFORMIS, METT. 149 
or divides but once, and supplies only the basal acroscopic portion of the pinna. A 
thick-walled hypoderma is developed towards the upper surface and around the 
revolute margins of the pinna, and tannin-mucilage cells are numerous in the general 
mesophyll and along the margins of the bundles (fig. 66). The latter do not reach 
the margins of the pinnse, and their endings are weak and poor in storage tracheides. 
In form of leaf and leaf-trace, and in pinna-trace origin and venation, Stromatopteris 
is typically Gleicheniaceous, and the anatomical characters of the pinnse are further 
proofs of the xerophytic life conditions of this plant. 
The sorus remains to be considered. It may be stated at once that its position is 
constant towards the base of the upper margin of the pinna (text-fig. 18). The 
massive receptacle varies in form and size. It is typically disc-shaped or reniform, 
and is supplied by the basal acroscopic vein or by its branches, and only occasionally 
are other veins involved in it. The veins either terminate within the receptacle or 
pass beyond it towards the upper margins of the pinna. Many of the pinnse on our 
specimen bear sterile receptacles, but neither size nor form seems a sure guide as to 
sterility and fertility. In only a few cases were sporangia found still attached to the 
receptacle, but it was evident from the points of sporangial insertion that the 
number of sporangia per receptacle is open to considerable variation. The smallest 
number of insertions observed was two, the highest six. Where the number of 
sporangia had been relatively high, the arrangement upon the receptacle was more 
or less rosette ; but where the number had been small, there had been a tendency 
for the sporangia to have developed above a vein. The surface of the receptacle is 
densely covered by a very varied assemblage of irregularly branched hairs and small 
TRANS. ROY. SOC. EDIN., YOL. LII, PART I (NO. 6). 24 
