AI.TKUXATIOX (IK ( ;i:N KU ATIONS. 



177 



in cones of closely-fitting scales, each of which bears a sporangium. The spores in 

 Lycopodiurn an- all alike, ami on germination form prothallia, which bear antheridia 

 ami arehegonia. It is interesting- to note in passing that we haw only become 

 acquainted with these prothallia in recent years, and for the most part in exotic 

 species. The prothallia of a limited number of European species, however, have 

 been seen. Included in the Lycopodime is the genus Selngi iuil<t (<■/. tig. 1 I 1 ', 

 vol. i. p. 421), resembling Lycopodiwm in its moss-like habit, bui differing from it 

 in that two sorts of spores are produced. These spores, known as macrospores and 



Fig. 350. — Alternation of Generations in Mosses. 



> A spore germinating. 2 a moss-protonema. 3 Protonema giving rise to a bud from which will arise a leafy moss-shoot 

 4 Longitudinal sectiun of tip uf a male shoot of a moss-plant; antheridia are present between the scales. 5 Tip of a female 

 »hoot with archegouia; two of them have much enlarged due to the swelling of the young sporogoniums within. 6 Leafy- 

 female shoot of a moss-plant with fully developed sporogonium at its tip. Spores arise asexually iu the terminal capsule. 

 ". s. ' x 350-400 ; * x 15 ; ' x 80 ; « x 6. 



microspores, arise in different sporangia in the same cone, in many cases. The 

 macrospores are relatively large, and are contained four in a sporangium: the 

 microspores are small, and a large number of them is present in a sporangium. 

 The prothallia resulting from their germination are of two kinds; the macrospore 

 gives rise to a female prothallium which bears archegonia; the microspore to a 

 much reduced male prothallium bearing a single antheridium. The sexual genera- 

 tion — which in the Fern consists of one structure, the prothallium — here consists of 

 two structures, the male and female prothallia. After fertilization the archegonium 

 gives rise to a new, asexual SelagineUa plant. 



This differentiation amongst the spores in Selaginella (in consequence of which 

 the plant is termed l><terosporous, in contradistinction to Ferns, and Lycopodiurn, 



