314 



BOTANY 



the shoot is variable. Usually, but not always, a single initial cell 

 can be seen. The cortical tissue is in most species composed of 

 delicate parenchyma, and about the vascular bundles are large air- 

 spaces. In species of dry regions, like S. rupestris, the cortical tissue is 

 largely sclerenchymatous. 



The Leaf 



The general structure of the leaf is like that of Lycopo- 

 diura, but there is always present a peculiar structure, the ligule 

 (Fig. 281, 1). Like the stem, the leaf in most species is traversed by 

 longitudinal air-channels. A marked peculiarity of the green tissue 

 of Selaginella is the presence of but a single chloroplast in each cell. 



A. *-, 



FIG. 281. Selaginella Kraussiana. Section of microsporangium (X 100) ; I, ligule 

 of subtending leaf; t, tapetum. B, wall of young macrosporangium ; t, tapetal 

 cells ( X 600) . C, membrane of young macrospore. 



The Root 



The root, like the shoot, shows a single initial cell. The appar- 

 ently dichotomous branching is stated to be a false dichotomy, simi- 

 lar to that of the stem-apex. The vascular bundle of the root is 

 monarch, and a distinct endoderniis is not developed. 



The Sporangium 



The sporangia (Fig. 281) in the investigated species of Selaginella 

 arise from the axis, just above the origin of the subtending leaf. In 



