THE VASCULAR CRYPTOGAMS 13 



vascular bundle from the stem. The bundle traverses 

 the leaf from end to end, forming the midrib; it has 

 no branches, neither is there any transfusion - tissue, 

 which in Conifers takes the place of the branched veins. 

 The bundle consists of a slender strand of tracheides 

 surrounded by a thin layer of phloem. Around the 

 whole is a bundle-sheath. 



The mesophyll of the leaf is very slightly differentiated, 

 the intercellular spaces being a little larger toward the 

 lower surface. The epidermis, like the mesophyll, con- 

 tains chlorophyll; the chlorophyll bodies in each cell 

 are few and unusually large. 



The stomata, which have the ordinary structure, are 

 usually found on the under-side of the leaf only, and especi- 

 ally in the neighbourhood of the midrib. The membranous 

 ligule at the base of the leaf on its upper surface has already 

 been mentioned (see Figs. 10 and 16, pp. 18 and 29). 



This is the simplest type of leaf that we have yet 

 met with. 



c. The Rhizophores and Roots 



These organs are generally similar to one another in 

 structure; the rhizophores in fact may be regarded as 

 roots which have not yet begun to form a root-cap. The 

 anatomical structure is simple, but unlike that in most 

 other roots. There is a single stele, which contains only 

 one group of xylem and one of phloem. This structure, 

 which may be called monarch, is pretty general in 

 Selaginella and its allies. It is a very ancient character, 

 for the rootlets of the fossil relations of Selaginella, which 

 lived in the Carboniferous epoch, had an almost identical 

 structure. The rhizophore, as distinguished from the root, 

 of S. Kraussiana is peculiar in having central protoxylem. 



