LYCOPSIDA 83 



A Homoeophyllum 



1 Cylindrostachya 



2 Tetragonostachya 



B Heterophyllum 



1 Pleiomacrosporangiatae 



2 Oligomacrosporangiatae 



The Homoeophyllum section is a small one, consisting of 

 fewer than fifty species, all of which are isophyllous and have 

 spirally arranged leaves. The only native British species, 

 Selaginella selaginoides { = S. spinosa, = S. spinulosa) (Fig. 

 14A), is a typical example of this kind of organization and is 

 placed in the subsection CyUndrostachya because the spiral 

 arrangement extends also to the fertile regions. Species 

 belonging to the Tetragonostachya subsection differ in that 

 the sporophylls are arranged in four vertical rows, giving the 

 cone a four-angled appearance. All the members of the 

 Homoeophyllum section are monostelic, but S. selaginoides is 

 pecuhar in that the stele of the creeping region is endarch 

 (Fig. 14I), whereas that of the later-formed axes is exarch 

 (Fig. 14H), as in all other species. According to Bruchmann^ 

 there is a Umited amount of secondary thickening in the so- 

 called hypocotyl region of this species; this is the only 

 record of cambial activity in the whole genus. 



The Heterophyllum section is characterized by a markedly 

 dorsiventral symmetry and by anisophylly, for the leaves are 

 arranged in four rows along the axis, two rows of small leaves 

 attached to the upper side and two of larger ones attached 

 laterally. The fertile regions, however, are isophyllous and 

 the cones are four-angled, which makes them very clearly 

 distinguishable from the vegetative regions (Fig. 14F). The 

 section is divided, somewhat arbitrarily, on the number of 

 megasporophylls in the cone and is further subdivided on the 

 number of steles in the axis. 



Most commonly the axis is monostelic and contains a 

 ribbon-shaped stele, e.g. Selaginella flabellata (Fig. 14K), but 



