sSo 



A TEXTBOOK OF THEORETICAL BOTANY 



forms a ring round the xylem. It is similar in structure to that of the Ferns 

 and contains a small amount of phloem parenchyma. Surrounding the 

 phloem is the single-layered pericycle. The xylem elements are all tracheids 

 in the present species, but in S. riipicola and one or two other species true 

 vessels are formed. 



The stele is separated from the cortex by a well-marked annular space, 

 like that around the spore layer in a Moss capsule. As in the latter case the 

 space is bridged by a number of trabeculae, which are at first unicellular, 

 but later become divided into slender rows of cells by which the steles are 

 supported. They are generally regarded as the endodermis, and they may 

 show a cutinized belt around the first cell in the early stage. The cortex is 



Meristeit 

 Endodermal cavity 



Fig. 589. — Selaginella kranssiana. Transverse section 

 of the stem showing two steles surrounded by 

 endodermal cavities. Trabeculae are not shown in 

 this section. 



composed of thin-walled parenchyma cells without air spaces. The cells 

 contain chloroplasts united in chains and obviously derived from a single 

 original plastid, of which a rudiment occurs in the meristem cells. On the 

 outside is the epidermis, which consists of elongated, pointed cells, without 

 stomata. The steles run parallel to each other, but they unite below each 

 branch and separate again above it (Fig. 590). The space between them 

 has been interpreted as a branch gap, corresponding to the leaf gaps in the 

 Ferns. The leaf traces in Selaginella make no gaps in the stele. 



Anatomy of the Leaf 



The leaf is entire, small and simple in structure. Stomata are confined 

 to the lower surface. The epidermal cells and the assimilatory cells of the 

 mesophyll have each only a single, very large chloroplast, sometimes more 

 or less divided into two, recalling the condition in Anthoceros. The mesophyll 



