RHIZOCARPEAl 



29 



;arance, from those of Flowering Plants. Those of Salvinia are re- 

 kably small, and are inserted about halfway up the epidermal cells, 

 ;h are eight or nine times their height. Air-pores occur also in the 

 nerged leaves. The very simple roots of Azolla are of endogenous 

 in. The root-cap originates from a single cell ; in A. Caroliniana 

 ild.) the cap is eventually thrown off, leaving the root-tip naked. 

 The sporanges are enclosed in unilocular sporocarps, formed two 

 ther or in larger numbers ; in Salvinia on the youngest teeth of the 

 nerged leaves, in Azolla on the pendent submerged lobe of the 

 aly bifid leaves, and only on the lowermost leaf of each shoot. The 

 ■segment which is destined to become fertile first of all develops 



a columel or placenta, to which the sporanges are attached. An 

 ular wall, the rudiment of the in- 

 utn, then becomes elevated from 

 base of the columel, eventually 

 •tops its apex, closes up, and 

 ; forms the wall of the sporocarp. 

 ; sporocarp of Salviniacese is 

 efore a metamorphosed portion 



leaf, and corresponds to a sorus 

 he Hymenophyllaceae (Filices), 

 L the difference that in the latter 



envelope remains open in the 

 1 of a cup, while in the former it 

 es completely over the sorus, 

 n Cyathea (Filices). The in- 

 um is much more strongly 

 sloped than that of ferns, and 

 ipletely envelops the sorus ; it 

 jists of two layers of cells, the 



s of which are, in Azolla, strongly lignified in the upper part. Each 

 •ocarp contains one kind of sporange only ; but both kinds always 

 ir on the same individual, and may even spring from the same 

 amorphosed leaf. In Salvinia the megasporanges are considerably 

 er than the microsporanges, and the number of the latter in a sporo- 

 I is greater (see fig. 7). In Azolla the number of microsporanges in 

 orocarp is about forty, while the female sporocarps contain only a 

 le megasporange, and consequently only a single megaspore, en- 

 ped first in the wall of the sporange, and then in the greatly hardened 

 isium. The microsporanges are nearly globular capsules, with long 

 der pedicels, the wall consisting, when mature, of a single layer of 

 i. The megasporanges are pear-shaped, with much shorter and 



Fig. 12. — Fertile shoot oi AzoUa Jiliculotdes 

 Lam., with two female sporocarps, a ( x 27). 

 (After Strasburger.) 



