Manchester Memoirs, Vol. li. (1907), No. 8. 13 



not sufficiently good to allow this to be definitely deter- 

 mined. A consideration of Fig. 2 of the Plate leads one to 

 suppose that if replaced into its normal position adjoining 

 the parichnos strand (par.), it would not come up to the 

 surface of the leaf base, but terminate in a slight depres- 

 sion, and from the appearance of longitudinal sections I 

 conclude that it was covered in by an epidermal layer, 

 provided with numerous stomata, as seems to be the case 

 with the epidermal layer overlying the parichnos strands 

 of LepidopJdoios. In Lepidophloios, where I have also 

 found aerenchyma in connection with the parichnos 

 strand, the reflexed and imbricating leaf-bases offer some 

 protection against undue evaporation from the parichnos 

 strands, while in Lepidodendron the aerenchyma com- 

 municates with the exterior through stomata, set in a 

 depression, and thus also preventing undue transpiration, 

 while giving every facility for the aeration of the plant. 



That such pit-like depressions which can only be 

 inferred from the transverse sections actually exist, 

 becomes evident from an examination of a series of 

 tangential sections taken through the leaf-cushions of a 

 Lepidodendron (see Fig. 3 of Plate). Examining a series 

 of these, one sees that they are lozenge-shaped and 

 vertically elongate. Those cut close to the axis show the 

 leaf-trace and a single parichnos strand. A little nearer 

 the outside the parichnos strand divides into two, and 

 almost at the same time one notices traces of the ligular 

 pit showing that this organ must have been very deeply 

 set. A little further from the stem, two cavities lined 

 with dark epidermal cells make their appearance (l.p. in 

 Fig- 3 (i-) oi Plate), and these on sections cut a little 

 further from the base open out on either side of the 

 median ridge {Fig. 3 (ii.) of Plate), thus showing that they 

 were the inner terminations of pit-like depressions, which 



