RESULTS, PHYLETIC AND MORPHOLOGICAL 711 



seen living in L. Selago (see frontispiece, also p. 363) : perhaps it may 

 ultimately be found to be even better represented by some others of the 

 thirty-eight less fully known species of the Se/ago-Section of the genus. 

 The undifferentiated "Selago" condition, which is seen in them, is no 

 recent characteristic, for it appears also in certain Palaeozoic Lycopods : from 

 this state the various living forms illustrate the achievement of a more clear 

 segregation of sterile and fertile tracts, initiated by abortion of sporangia 

 in the sterile regions : along with this goes more adequate protection of 

 the sporangia, and their change to a broader form : there is also a greater 

 complexity of the stelar structure, and a greater specialisation of the 

 embryogeny : the essential parallelism of these progressions indicates that 

 they constitute true phyletic lines, the advance having been from the 

 primitive condition of the "Selago" Section to the more specialised state 

 of the rest of the genus. The Ligulate series, which includes the most of 

 the fossil genera and the modern Selaginella and Isoetes, has as a rule 

 more definite heterosporous strobili, though the " Selago " condition is 

 again seen in Isoetes. In this respect the Ligulate Lycopods are more 

 advanced than the Eligulate. The highest type of propagative organs in 

 the whole phylum are the seed-like structures in Lepidocarpon and 

 Miadesmia, which show an advance parallel to that found in the Pterido- 

 sperms. Both the living and the fossil forms are in their simplest types 

 protostelic, but there has been advance to medullation, and finally to 

 disintegration of the xylem of the stele and to secondary thickening in the 

 dendroid forms. Selaginella Spinulosa has been recognised among living 

 species as a relatively primitive Ligulate type, on the ground of its 

 radial construction, its branching, and its anatomy : in these characters, 

 as also in point of the embryogeny, S. Spinulosa resembles L. Selago, 

 notwithstanding its heterosporous state ; this fact has a special interest, and 

 the convergence in many features between the two species confirms the 

 correctness of their recognition as primitive in their respective genera. 



The Lycopodiales stand by themselves in the simplicity of their 

 sporangial arrangement, and constitute a type of extreme antiquity, which 

 has come down practically unaltered to the present day. Their comparative 

 study may be conducted independently of other phyla: for there is no 

 reason to think that they were derived from any other known vascular 

 type. It has been shown that the several lines of comparison converge 

 downwards : the condition actually seen in the "Selago" type may be held as 

 truly primitive, and Lycopodium Selago, with its imperfectly differentiated 

 shoot, is in fact a near approach in a living species to the ideal primitive 

 form which emerges from wide comparative study of the phylum as a whole. 



There are two further characters seen occasionally in the Lycopodiales 

 which call for special remark. In the very early fossil, Lycopodites Stockii 

 (p. 298), the leaves are arranged in whorls, as they are also in certain 

 living species of Lycopodium (p. 291). In others the leaf-arrangement is 

 irregular. Sometimes, however, whorled and spiral arrangements may be 



