318 



BOTANY OF THE LIVING PLANT 



upon a short succulent stock, which is fixed by dichotomous roots in 

 the mud at the bottom. Others are the Club Mosses (Lyco podium), 

 of which some five species grow on heaths and moors, chiefly in hilly 

 districts ; while nearly IOO other species are widely spread through 

 the tropics and temperate zones. They also are low-growing plants, 



and some are epiphytes. These 

 inconspicuous plants are the meagre 

 present-day representatives of a 

 type which grew to tree-like size in 

 the Coal Period, and contributed 

 largely to the organic remains pre- 

 served as Coal. 



The Lycopodiales are divided into 

 two Series, the Ligulatae, which include 

 Selaginella and Isoetes, and most of the 

 early fossil types. They are character- 

 ised by a minute scale, or ligule, 

 borne on the upper surface of each 

 leaf near its base (Figs. 260, 261) The 

 Eligulatae have no ligule. They include 

 the Club-Mosses (Lycopodium) , and 

 some of the early fossils. 



SELAGINELLA. 



The primitive type of Selaginella 

 had upright radial axes, with leaves 

 of equal size all round it ; and this 

 is the case in 5. spinulosa. But 

 most of the species have a much- 

 branched, dorsiventral shoot of ar 

 " espalier " type, sometimes simu- 

 lating highly compound leaves (Fig. 

 258). On these shoots the actuz 

 leaves are disposed in four longi- 

 tudinal rows, those on the lower flanks being larger, those on 

 upper smaller. Such shoots are commonly propped up by root- 

 like organs (rhizophores), borne at the forkings of the shoot, am 

 themselves showing very regular dichotomy. They are not actually 

 roots, but on reaching the ground they give rise to roots endogenously : 

 hence their name. Structurally Selaginella is relatively simple. The 

 vascular system is essentially of the same type as that to be describee 



FIG. 259. 



Selaginella inaequalifolia. A, fertile branch, 

 half natural size. B, its tip in longitudinal 

 section, with microsporangia to the left, and 

 megasporangia to the right. (After Sachs.) 



