GENERAL MORPHOLOGY 



291 



straggling or creeping forms these may arise adventitiously at points far 

 up along the axis. It is by comparison as regards the differences which 

 occur in this otherwise uniform family that some knowledge of the course 

 of development of the Lycopod-type may be derived. 



The Lycopodiales are divided, according to the presence or absence 

 of a ligule, into two divisions; the Eligulatae, which include the Lycopo- 

 diaceae, that is the living genera Lycopodium and P/iylloglossinn, with which 

 are also to be associated certain early fossils designated Lycopodites ; and 



E 



FIG. 141. 



Shoots of several species of Lycopodium to show the form and arrangement of the 

 leaves. A=L. rufcscens, Hook. X 2. B = L. niandioccatium, Raddi. Natural size. 

 C = L. refli:\'it>u, Lam. X2. D=-L. castiariiioidcs. Spring. : part of a terminal branch of 

 an old plant. X4- E=L. cernniiiii, L. X2. F=L. voliibilc, Forst, seen from above. 

 X 2. (From Engler and Prantl.) 



the Ligulatae, which include the Selaginellaceae and Isoetaceae of living 

 forms, together with the fossil Lepidodendraceae and Sigillariaceae. These 

 will be severally considered as illustrating variants on the simple strobiloid 

 type of the whole phylum. 



A. ELIGULATAE. 



The genus Lycopodium. which includes about a hundred living species, 

 was arranged by Spring according to the degree of differentiation of the 

 several species. 1 He distinguished two main sections of the genus, the 

 first including those with sporangia scattered over the length of the shoot : 

 the second including those with the sporangia associated in definite cones. 

 The former section was again sub-divided according as the leaves were 

 all alike, or as a distinction appeared between sterile and fertile leaves : 

 the latter section according as the shoot was developed radially or 

 dorsiventrally. The details of Spring's scheme have since been modified, 

 but the principle remains the same in the classifications of the present 

 day : it is to arrange the genus along lines which clearly indicate a 

 progressive differentiation and specialisation of sterile and fertile tracts. Such 

 an arrangement naturally harmonises with evolutionary theory. The species 



^ Monographic des Lycopodiactes, 1841. 



