Metaphy ta Selaginella. 137 



not prevent us from comparing its origin with that of the fern 

 sporangium, since the leaf in Selaginella is extremely small, 

 whilst the sporangium is relatively large. Moreover in many 

 allies of the type we are considering the sporangia are borne 

 by the leaf itself. As already stated, the sporangium is, 

 when ripe, a bivalved capsule, although when young the wall 

 of the capsule is complete. On examining the sporangia in 

 more detail, we find that their contents differ from each 

 other and also from the contents of the sporangia of the 

 fern. 



Before discussing the sporangia of Selaginella, it may 

 conduce to clearness if we glance briefly at the sporangia of 

 an allied type, Lycopodium. The sporangia in that type are 

 developed in the axils of the sporophylla, and spring from 

 their bases. The spores are small and rounded in form and 

 all of .the same size. They are comparable to the spores of 

 the fern, and, by one unaccustomed to the microscopic study 

 of plants, might be readily mistaken for them. Each spore 

 is composed of a mass of protoplasm surrounded by firstly 

 an endosporium, and secondly by an exosporium, which (as 

 is usually the case) is raised into spines and prominences. 

 This spore when sown is capable of producing a thallus 

 bearing spermaria and ovaria. An examination of Selaginella 

 at once exhibits to us a great advance in differentiation, for 

 although the sporangia appear all perfectly alike, yet some 

 contain what appear to be numerous small spores, like those 

 of Lycopodium^ whilst others contain a few very large spores, 

 totally different in appearance. These have been known as' 

 microspores and macrospores respectively. These terms are 

 by no means satisfactory, as we shall presently see. A ripe 

 microspore, when artificially clarified and examined under a 

 high power, shows externally a thick exosporium and thinner 

 clear endosporium, but contains, instead of granular pro- 

 toplasm, a considerable number of cells, one of which is 

 segmented off by a distinct cellulose cell-wall. The rest of 

 the cellular mass consists of small naked cells, which are 



