GROUP III. PTERIDOPHYTA : LYCOPODIN.E. 389 



development of an embryo from the oospore, but in L. Phleymaria it 

 seems to persist from one season to another. In the latter species the 

 prothallia are multiplied vegetatively by the isolation of branches, as 

 also by small multicellular bulbils. 



Order 2. Psilotaceae. This order consists of the two genera Psilotum 

 and Tmesipteris ; of these the former is widely distributed in the tropics ; 

 the latter is confined to Australia, New Zealand, and Polynesia, and 

 lives epiphytically, and perhaps parasitically, on the trunks of Tree- 

 Ferns. 



THE SPOROPHYTE. The most striking feature in the morphology of 

 these plants is the total absence of roots, the functions of these organs 

 being performed by specially adapted stem-branches bearing minute scale- 

 leaves, and covered with root-hairs. 



The stem. In Psilotum the subterranean shoots have unlimited apical 

 growth : they are much branched, apparently dichotomously, but it 

 seems probable that the branching is really lateral. The subaerial 

 shoots generally arise as lateral branches on the subterranean shoots : 

 they have limited apical growth; they are branched, the mode of branch- 

 ing being probably the same as that of the subterranean shoots ; and they 

 bear small scattered leaves. 



The stem of Tmesipteris appears to agree in all essential morphological 

 points with that of Psilotum ; but with this conspicuous difference, that 

 it is much less branched. 



The leaves. In both genera the leaves of the subaerial shoots are of two 

 kinds. In Psilotum the vegetative leaves are minute scales, whereas in 

 Tmesipteris they are relatively well-developed as foliage-leaves: they 

 are simple and sessile. The sporophylls, on the contrary, are petiolate and 

 bilobed in both genera, a single sporangium being borne on the upper 

 surface of each sporophyll just at the junction of the basis of the two 

 lobes : they are not borne in cones. 



The i>poran<jia are synangia (p. 52) ; that is, they are not unilocular. but 

 multilocular capsules : in Psilotum the synangium is generally trilocular 

 (sometimes 2-4 locular), in Tmesipteris bilocular. Each loculus opens by 

 a longitudinal -slit. The origin of the archesporium has not been fully 

 traced : but it appears probable that it consists primarily of a layer of 

 cells, some of which become the mother-cells of the spores, whilst the lest 

 are sterile and form the tissue of the walls separating the loculi. 



The spores are developed in tetrads from the mother-cells ; bilaterally, 

 as in Tmesipteris 5 or either bilaterally or tetrahedrally, as in Psilotum- 

 They have the typical structure. 



THE GAMETOPHYTE. No observations have as yet been made on the 

 gametophyte of either genus, and consequently the embryogeny of the 

 sporophyte is also unknown. 



SUB-CLASS HETEROSPOREjE. 



Order 3. Selaginellaceae. This order consists of the single genus 

 Selaginella, of which the numerous species are very widely distributed: 

 but only one, S. spinosa (selayinoides), is British. 



