Structure of the Leaves of Catamites. 183 



there will be little difficulty in making out the following 

 histological details : — 



(i). The epidermis is a single layer of cells, uniform in 

 size, whose outer walls are thickened. Some of the walls 

 seem to be thickened all round, but others are not so, and 

 there are no definite traces of stomata. A comparison of 

 the epidermal cells of this specimen with those of longitu- 

 dinal sections in other preparations brings out the fact that 

 the cells were elongated in the longitudinal direction, a 

 detail which is vaguely shown in Fig I. 



(ii.) Beneath the epidermis is a layer of assimilating 

 tissue, which is continuous round the whole section, and 

 widens out laterally to form two obtuse opposite wings. This 

 tissue is composed of thin-walled cylindrical cells, resem- 

 bling the palisade cells of existing plants, in some of which 

 the contents appear to be granular. In the middle of the 

 upper and lower surfaces of the leaf the cells stand with 

 their long axes at right angles to the epidermis, and in a 

 single row, but in the lateral wings they become oblique, 

 and the number of rows is increased. The lateral connec- 

 tions of the assimilating cells, inter se, are very slight, 

 comparatively large intercellular spaces often separating 

 them entirely, except at the extremities, where the dilated 

 ends are in contact with one another. These intercellular 

 spaces are specially developed in the lateral wings, where 

 the cells of successive rows unite end to end, and form fila- 

 ments, which are separated from one another by the spaces 

 in question for considerable parts of their length. 



(iii.) Within the assimilating tissue lies the central 

 portion of the leaf, which has a circular outline. Externally 

 it carries a layer of " melasmatic " tissue, for the most part 

 one cell thick, which, as we have already seen, is continuous 

 with the same tissue of the stem. At the middle point of 

 the upper side this tissue is interrupted by the intercalation 

 of an element of a different kind, which is the outermost of 



