GROUP III. PTERIDOPHYTA : LYCOPODIN.E. 



391 



the archesporium probably consists of a single row of cells, and is entirely 

 sporogenous. 



There are two kinds of sporangia, macrosporangia and microsporangia, 

 distinguished by the kind of spores which they produce, and by their size. 

 The macrosporangia each give rise to generally four (sometimes 2 or 8), 

 relatively large macrospores ; the microsporangia each give rise to a con- 

 siderable number of microspores. 



The relative distribution of the two kinds of sporangia presents some 

 variation. As a rule both kinds of sporangia are present in the same cone, 

 so that, like the flower of most Angiosperms, it contains both microsporo- 

 phylls and macrosporophylls ; in this case there may be several macro- 

 sporophylls at the 

 lower part of the 

 cone, or only a 

 single one. 



The spores are de- 

 veloped in fours 

 from the mother- 

 cells resulting from 

 the growth and 

 multiplication of 

 the archesporial 

 cells. They are 

 developed tetra- 

 hedrally: but in the 

 macrospora n g i u m 

 usually only one 

 of the mother-cells 

 undergoes division 

 to form spores. 

 The structure of 

 the spores is normal. 

 The roots are all 

 adventitious- and 

 endogenous. In 

 some species (e.g. S. 

 cuspidata and Wil- 

 de nodi) they spring 

 directly from the 

 lower surface of the 

 stem at the points where branching takes place. In other (e.y. S. 

 Marleiisii and Kraussiana) cases they spring from near the apex of the 

 rhizophores after the rhizophores have reached and entered the soil. The 

 roots branch monopodially. 



FIG. 233. Prothallium and embryo of Selaginella Martensii 

 (x 65: after Pfeffer) s coat of macrospore ; p prothallium ; 

 o archegouiam ; d-d diaphragm ; end so-called endosperm : B 

 an embryo (there is a smaller one to the right) : * snspensor ; 

 c c developing cotyledons ; ( stem ; r origin of the root ; / o- 

 ca'.led foot. 



General Histology. The stem is, in some species (S. spinulosa and denticu- 

 lata), monostelic, but in most species it is polystelic (two or three). The 

 epidermal and the ground-tissues of the stem are prosenchymatous, with- 



