THE HIGHER CRYPTOGAMIA. 389 



off the points of the spines. Shortly before the sponta- 

 neous rupture of the macrosporangium the spores adhere 

 rather firmly to its inner wall by means of their spines. 



During the formation of the large spores the macro- 

 sporangium changes its form very considerably. By a 

 vigorous local multiplication and expansion of the cells of 

 the wall, two hemispherical protuberances of the latter are 

 formed in the middle of the two lateral surfaces of the reni- 

 form sporangium which are turned towards the stem and 

 the covering leaf. This occurs even long before any one of 

 the four spores has touched the inner wall of the sporan- 

 gium (PI. LV, fig. 11"). The top of the organ also becomes 

 more steeply arched. At this time the spores still float 

 freely in the watery contents of the macrosporangium, in 

 company with the numerous unchanged sister-cells of the 

 one spherical cell, which, by its division, becomes the mother- 

 cell of the spores. Tour or more of those small delicate- 

 walled cells are often found still loosely adhering to one 

 another, a remnant of the innate connexion which in the 

 earlier stages of development of the sporangium subsisted 

 amongst the mother- cells. The layer of radially-extended, 

 mucilaginous, actively-multiplying cells which clothes the 

 inner wall of the capsule exists up to this time. It disap- 

 pears with the further development of the spores, and the 

 wall of the sporangium when almost ripe consists of only 

 two layers of cells (PL XLI, fig. 16). 



The development of the large spores of many other 

 species, especially of SeJaginella Martensi, helvetica, and 

 spimdosa, differs from that above described, especially in 

 the fact that the special-mother-cells last much longer than 

 in S. hortensis. The spore has therefore (even when fully 

 developed) a somewhat sharply defined tetrahedral form 

 (PI. LV, fig. 13 ; PL LVII, figs. 6, 7), at least its apex ex- 

 hibits three very distinct ridges, meeting at angles of 120, 

 and extending downwards for a considerable distance ; this is 

 the case in S. helvetica. The species in which this occurred 

 are all species in which the macrosporangia and microspo- 

 rangia, differing little if at all in their external form, are 

 intermixed apparently without regularity. In Selaginella 

 Galeotlii even the very young large spores have a regular 

 spherical form. In 8. Martensi a considerable increase in 



