372 



VASCULAR CRFPTOGAMS. 



The Sporangia of Equisetaceae are outgrowths of peculiar!}' metamorphosed 

 leaves, and are generally formed in numerous whorls at the summit of ordinary 

 shoots or of those specially destined for this purpose. Above the last sterile leaf- 

 sheath of the fertile axis an imperfectly developed leaf-sheath is first of all produced 

 (Fig. 279, a), a structure corresponding in some degree to the bracts of Phanerogams. 

 The development of this structure is sometimes more sometimes less leaf-like ; foliar 

 girdles are formed above it in acropetal succession beneath the growing end of 



the shoot, projecting however but slightly, 

 as in the ordinary formation of leaves of 

 Equisetum. A larger number of protuber- 

 ances project from each of these girdles, 

 corresponding to the teeth of the ordinary 

 leaf-sheaths ; and thus several whorls of 

 hemispherical projecdons are formed lying 

 closely one over another, which, increasing 

 more rapidly in size at their outer part, 

 press against one another, and thus become 

 hexagonal, the successive whorls alternat- 

 ing; while the basal (inner) portion of each 

 protuberance remains slender, and forms the 

 pedicel of the hexagonal peltate scale. The 

 outer surface of these scales is tangential to 

 the axis of the spike ; on its inner side, facing 

 the axis, arise the sporangia, five or ten in 

 number on each scale. In the early stages 

 of development each single sporangium has 

 the appearance of a small blunt multicellular 

 wart, the internal tissue of which ^ produces 

 the spore-mother-cells which become isolated, 

 while of the three exterior cell-layers which 

 at first envelope it only the outermost finally 

 remains as the wall of the sporangium or 

 spore-sac. The mother-cells of the spores, 

 connected together in groups of fours or 

 eights, float freely in a fluid which fills the 

 sporangium and is interspersed with granules. 

 The processes that take place in the mother- 

 cells up to the time of the formation of the 

 spores have already been described in detail 

 in Chap. I (see Fig. 10, p. 14). It was there shown how the division into four of 

 the mother-cells is preceded by a bipartition which is at least indicated in Equi- 

 setum, in a manner analogous to the corresponding process in Ferns. The ripe 

 sporangium opens by a longitudinal slit on the side which faces the pedicel of the 



Fig. 279. — EgJtisetum Tehnateia ; A upper part of 

 a fertile stem with the lower half of the spike (natural 

 size), b leaf-sheath, a the annular 'bract,' x the pedi- 

 cels of peltate scales which have been cut off, y 

 transverse section of the rachis of the spike ; B 

 peltate scales in various positions (slightly magni- 

 fied) ; st the pedicel, s the peltate scale, s^ the spo- 

 rangia. 



' The formation of the spore-mother-cells from a single original central cell which occurs in 

 Ferns and Rhizocarps, has been contrasted by Russow with that of Equisetum (compare p. 358). 



