LYCOPOD TALES 



319 



below for Ferns. It consists of sharply circumscribed stelar tracts, 

 with tracheides but no vessels, and no secondary thickening. 



But the greatest interest lies not in the structure of the plant so 

 much as in its sporangia, and the germination of its spores : for these 

 give lines of comparison with the Seed-Plants. The strobilus or cone 

 that bears them is distal on a vegetative branch, and even in the 

 flattened species it has the primitive radial form, all the sporophylls 

 being of equal size (Fig. 259, A). A longitudinal section shows that a 

 short-stalked sporangium is borne in the axil of each. These sporangia 



FIG. 260. FIG. 261. 



Microsporangium of Selaginella apus, in Megasporangium of Selaginella apus, in median 



median vertical section, containing numerous vertical section, showing three of the four mega- 



microspores. The ligule is seen in Figs. 260, spores. ( x 21.) (After Miss Lyon.) 

 261, as a small tongue-like body, at the base 

 of the leaf. ( x 55.) (After Miss Lyon.) 



are of two sorts, which are associated in the same strobilus, but dis- 

 posed in various ways in different species. In S. inaequalifolia those on 

 the right side of the section shown in Fig. 259, B, are all megasporangia, 

 with four large spores in each ; those on the left-hand side are micro - 

 sporangia, containing many small microspores. In form the sporangia 

 are alike ; they differ in the number and size of their contents. A 

 mature microsporangium, with its subtending sporophyll and ligule, 

 is shown in median section in Fig. 260. The line of dehiscence is 

 distal, where the cells of the wall are smallest, and the structure of 

 the cells of the wall is such as to lead to its valves being everted as 

 they dry on ripening, so that the spores are shed. The mature 

 megasporangium behaves in a similar way, but the spores are ejected 



