372 MARSILEACE^E. PART 11. 



turity into four equal valves. Each cell has a sort of 

 placenta to which the sporangium and antheridia are 

 attached ; and its upper half is lined with three minute, 

 sessile, obovate, yellowish bodies, which are the anthe- 

 ridia ; the other half is occupied by a larger, roundish, 

 or oblong sessile sporangium, containing one spore, 

 which has a firm outer coat, tapering to a point, and 

 leaving a cavity at the top of the nucleus. According 

 to Hofmeister, this cavity becomes filled with cellular 

 tissue, constituting a conical prothallus confluent with 

 the nucleus. A single archegonium is formed in the 

 centre, the orifice of which corresponds with the apex 

 of the prothallus. The antheridia contain numerous 

 granules, from which long spiral delicate spermatozoids 

 are ultimately developed. 3 The embryos of the young 

 plants push forth their radicle in one direction to fix 

 them to the soil, and a frond or leaf in the opposite 

 direction. Thus these minute plants, approaching so 

 nearly to a monocotyledon, exhibit a high organization, 

 only inferior to that of the Lycopods. 



The group contains the genera Marsilea, which has 

 leaves made up of cuneiform lobes, and resembling those 

 of some leguminous plant ; and Salvinia and Azolla, both 

 of which consist of small floating plants, which mostly 

 occur in tropical or subtropical countries. 



8 Berkeley's ' Cryptogamic Botany.' 



