774 DR R. KIDSTON AND PROF. W. IT. LANG ON OLD RED SANDSTONE PLANTS 



(ep.) from what we interpret as a persistent tapetal layer (taj).). The cells of the 

 latter appear rounded, have thin walls, and vary in size. For the most part the 

 tapetum consists of a single layer with a rather irregular surface towards the cavity 

 of the sporangium, but at places it is two cells thick. 



The tissue intervening between the epidermis and the tapetum was evidently 

 more delicate and is not well preserved in any of our specimens. It is best shown 

 in fig. 68, PI. IX, and consisted of a considerable number of layers of small, thin- 

 walled cells. 



The corresponding layers are recognisable in the sporangial wall when cut 

 longitudinally (fig. 67). The tapetal cells were seen to be longer than broad. 

 In this view the epidermal cells appear almost square. This difference from 

 their appearance in transverse sections (fig. 66) is explained by the actual form of 

 these cells as seen from the outside, being narrowly fusiform, like the epidermis 

 of the stem, though on a smaller scale. 



The thick-walled epidermal layer appears to have been uniformly continuous 

 over the surface of the sporangium. No satisfactory indication of any lines of 

 dehiscence has been detected in any of the sections, though specially looked for. 



The sporangium contained an enormous number of spores. In some cases these 

 were still united in tetrads (PI. X, fig. 70), each spore showing a convex outer wall 

 and a three-sided inner face where it adjoined its sister cells. In other sporangia 

 the spores were separate. They exhibit some variation in form and size but on an 

 average measure about 65 fi in diameter. 



The spores found scattered through the peat (PL X, fig. 7l) resemble those in 

 the sporangia, but had increased slightly in size. Only the cuticularised wall 

 is preserved. One of the spores in fig. 71 shows the triradiate marking on its 

 inner face. 



No stages in the germination of the spore have been seen, nor has the gameto- 

 phyte been found. 



Summary. 



1. The plants grew in a gregarious fashion in a peaty soil practically composed 

 of the decaying remains of the. same species. This land surface was probably in the 

 neighbourhood of water, and liable to periodic inundations. 



2. The plant had no roots and no leaves. It was entirely composed of branched 

 cylindrical stems. 



3. The branched underground rhizomes were attached to the peat by numerous 

 rhizoids, most abundant on large, downwardly directed bulges of the outer cortex. 



4. Some of the branches grew upwards as tapering aerial stems. 



5. The aerial stems bore small lateral projections irregularly scattered over 

 the surface. 



6. Some of the projections, possibly in the lower region, developed rhizoids. 



