238 On Azolla and Satvinia. 



rather the smallest, presents three connivent valvular lobes. 

 This white body is the incrustation, it is of a thick, appa- 

 rently not organic, crustaceous substance. Its lower two- 

 thirds are occupied by the yellow sac (PL 20. f. 12. 14. 19.) 

 which is with difficulty separable entire; its upper surface, 

 which on drying becomes concave, presents the trifacial line. 

 This sac is filled with a viscid matter, innumerable granules, 

 and irregular globules of oily fluid. A section in the dry 

 state appears solid (PL 20. f. 20.) A few trifacial cells may 

 still often be found between it and the wall of the secondary 

 capsule. 



The mature capsules of both kinds, which are almost 

 similar in appearance, appear to become irregularly ruptur- 

 ed (PL 20. f. 5.) ; they are covered externally with brown 

 rigid hairs, and present at the top a brown striated mark (the 

 original foramen ;) (PL 20. f. 17.) they consist of two layers, 

 an outer, from which the hairs arise, composed of irregular 

 angular cells of a brown colour, and an inner, thinner, 

 colourless one, united to the outer only along certain lines : 

 this is composed of oblong cells, in which a few greenish 

 mobile granules exist. 



Those containing the fewer oblong bodies are the most 

 numerous, and more oblong, they are solitary # and always 

 next the axis ; therefore if only one capsule is developed it will 

 be of this kind, if more than one, it will be the lowest one. 



It will be hence seen that the differences of Salvinia from 

 Azolla consist in the situation of the organs ; in the ab- 

 sence of an indusium or involucrum ; in the nucleus being 

 in all developed into secondary capsules, in the early ap- 

 pearance of the papilla? indicating the future secondary 

 capsules, their unequal size and number, (on which so 

 much depends,) and their being all subsequently deve- 

 loped indiscriminately : in the greater degree of incrusta- 

 tion of the yellow sac, and its three-lobed upper end ; and in 

 the absence of the cellular lobes. The development of the 



