XIV] SELAGINELLA 51 



contrasted with Lycopodium, is the presence of a ligule in both 

 foliage leaves and sporophylls. This is a colourless thin lamina 

 attached by a comparatively stout foot to the base of a pit 

 on the upper surface and close to the lower edge of the leaf 

 (fig. 130, 4, Z; fig. 131, E, F, 0. 



In an erect species, such as S. grandis Moore » (fig. 130 and 

 fig. 131, G) from Borneo, the main shoots, which may attain a 

 height of 2 — 3 feet, bear small and inconspicuous leaves of 

 one kind, but the lateral and repeatedly forked shoots are 

 heterophyllous. The passage from the homophyllous to the 

 heterophyllous arrangement is shown in the transition from the 

 erect to the dorsi ventral habit of the lateral shoots (fig. 130, 2). 

 The monopodially or dichotomously branched shoots produce 

 long naked axes at the forks; these grow downwards to the 

 ground where they develop numerous dichotomously forked 

 branches. For certain reasons these naked aerial axes were 

 named rhizophores and have always been styled shoots, the term 

 root being restricted to repeatedly forked branches which the 

 rhizophores produce in the soil. It has, however, been shown by 

 Professor Harvey-Gibson'' that there is no sufficient reason for 

 drawing any morphological distinction between rhizophores and 

 roots, the term root being applicable to both. 



Our knowledge of the anatomy of Selaginella, thanks chiefly 

 to the researches of Harvey-Gibson^, is much more complete 

 than in the case of Lycopodium. The stems, which may be 

 either trailing or erect, are usually dorsiventral, and it is note- 

 worthy that different shoots of the same plant or even the same 

 axis in different regions may exhibit considerable variation in 

 the structure and arrangement of the vascular tissue. In the 

 well-known species, Selaginella Martensii, the stem, which is 

 partly trailing, partly ascending, possesses a single ribbon-shaped 

 stele composed of scalariform tracheids with two marginal 

 protoxylems formed by the fusion of the leaf-traces of the 

 dorsal and ventral leaves respectively. As in Lycopodium the 

 metaxylem tracheae are as a rule scalariform, but reticulate 

 xylem elements are by no means unknown. The tracheal band, 



1 Gard. Chron. (82). '■' Harvey-Gibson (02). ^ jjj^j, (94) (97J (Q2)_ 



