RHIZOCARPEM . ' 31 



Dating megaspores. The roundish megaspoire, which does not nearly 

 11 up the sporange, is completely covered by a very thick warty layer 

 f hardened frothy mucilage, its epispore, which projects far above the 

 pex, and separates, in its upper part, into either three or nine large 

 ear-shaped masses of the same substance, terminating in a tuft of fine 

 ireads. These bodies constitute a, floating apparatus for the megaspore, 

 le fine threads floating on the surface of the water, and suspending 

 eneath them the float-corpuscles, either three in number or more 

 umerous, containing abundance of air-cavities, and the megaspores, to 

 hich the microspores are attached by their glochidiate processes. 



The two genera of Salviniacese, Salvinia and Azolla, each include 

 ut a small number of species, all annual plants, widely distributed over 

 le globe, especially in its warmer regions. Those of Azolla form green 

 r red floating patches of considerable size, with the habit of a Junger- 

 lannia. No economical application is known of either genus* 



Order 2. — Marsileace^e. 



The female prothallium attains here a much smaller degree of 

 evelopment than in the Salviniaceae. It arises within the apical papilla 

 f the megaspore, the protoplasm of which breaks up into several cells, 

 'hich remain for a time unclothed with cellulose, and only subsequently 

 onstitute a tissue containing a small quantity of chlorophyll. Even 

 fter this the prothallium still remains for some time completely enclosed 

 ■ithin the apical papilla of the megaspore, being covered by the epi- 

 ermal layers of the apex of the spore itself, and shut off from the 

 pore-cavity within and below by a diaphragm which is attached to the 

 iternal coat of the spore. By the further growth of the prothallium 

 le epidermal layers of the apical papilla are broken through, and the 

 orsal ridge of the prothallium projects into the funnel formed by the 

 bsence at this spot of the thick outer layers of the epispore. The 

 iaphragm subsequently arches convexly, and the prothallium is pushed 

 irther outwards, but still lies as a hemispherical mass in the funnel- 

 baped opening. 



In those species which have hitherto been examined each prothallium 

 roduces only a single archegone. Even before the prothallium breaks 

 irough the megaspore, the large central cell may be recognised in it, 

 overed only by four cells arranged in a cross, whtch form at the same 

 me the apex of the prothallium. From these are developed the more 

 r less projecting neck and the stigmatic cells of the archegone. As in 

 aiviniacese, a neck-canal-cell is separated from the central cell, which 

 ushes up between the neck-cells, as well as a smaller ventral canal-cell j 



