Manchester Memoirs, Vol. li. (1907), No. 8- II 



The leaf cushions, as can be seen both from transverse 

 and tangential longitudinal sections, were diamond shaped, 

 their long axis coinciding with that of the stem, so that 

 they were of the Lepidodendron rather than the Lepi- 

 dophloios type. In transverse sections the parichnos 

 strands can be seen running almost horizontally in the 

 leaf base, often showing very clearly the bifurcation (see 

 Fig. 1 of Plate), which takes place in the leaf base and not 

 in the outer cortex as has sometimes been stated. In 

 some instances the parichnos strand can be followed to 

 quite near the edge of the cushion, and it will be seen to 

 join two patches of specialised cells close below the leaf 

 scar, on either side of the median ridge of the leaf cushion. 

 That is the case in Fig. 1, where the left-hand branch of 

 the parichnos is not yet in touch with the exterior, while 

 the right-hand branch (the section being slightly oblique), 

 which is cut a little higher up, joins a pit-like depression 

 partially filled with a group of cells which will be 

 described in more detail a little further on. That these 

 cells lie a little below the leaf scar is indicated by the 

 presence of a median ridge which disappears on the leaf 

 scar itself. 



At the point where the parichnos strand stops, there 

 is a gap probably due to the delicate nature of the cells 

 which join the parichnos to the group of specialised cells, 

 which in the sections have slipped somewhat out of their 

 position. An examination of the cells on either side of 

 this gap shows that the tissue in which the split has taken 

 place consisted of exceedingly small stellate cells (st.c. in 

 Fig. 2 of Plate), much smaller than the cells of the 

 parichnos strand, or of any of the neighbouring tissues. 



These stellate cells were, by their shape, separated 

 from each other by wide intercellular spaces, and formed 

 consequently an admirable "aerenchyma" similar to that 



