224 ORGANOGRAPHY. BOOK I. 



which consist of the two genera, Marsilea and Pikilaria, we 

 remark at the base of the leaves certain involucres of a cori- 

 aceous, thick substance, and either indehiscent or opening 

 into several valves, divided internally into cells by mem- 

 branous dissepiments. Each of these cells contains two 

 other cells, inserted on a part of its inner coating : of these 

 one sort is ovaries, or rather grains, composed of an external 

 transparent membrane which swells with humidity, and be- 

 comes a thick layer of gelatinous substance; the other is an 

 internal, hard, and coriaceous membrane, of a yellow colour, 

 and indicating on its surface a particular point, through which 

 the embryo is protruded upon being developed. The other 

 organs are more numerous, and consist of membranous bags, 

 slightly swelling from humidity, opening at the summit, andu 

 enclosing in the middle of a gelatinous mucus many spherical 

 globules, which are much smaller than the grains. Their 

 leaves develope in a gyrate manner, like ferns. 



In the second section of this order, to which the name 

 Salviniese may be given, and which consists of the genera 

 Salvinia and Azolla, we find at the base of the leaves mem- 

 branaceous involucres of two sorts, and containing different 

 organs. One kind includes a bunch of cases {sporangia, 

 Martins), containing only one grain in Salvinia, and from six 

 to nine in Azolla. The integument of these cases is thin, 

 reticulated, brownish, and does not swell in water like that of 

 true Marsileaceas : the pedicel which supports them appears, 

 in Salvinia, to communicate laterally with the case. The 

 other involucres, which are supposed to be male organs, have 

 a very complex structure, and have been well observed by 

 Brown. In Salvinia they contain a great number of spherical 

 granules, attached by long pedicels to a central column : these 

 gi'anules are much smaller than the grains ; their surface is 

 reticulated in like manner, and they do not burst by the 

 action of water. All the species are floaters, and their leaves 

 are not gyrate when developing, but are more like those of 

 Lycopodiaceaj. Thus far Brongniart; see also Martins, Ic. PI. 

 Crj^t. Bras, for many curious additional observations. 



With respect to the nature of these two kinds of grains or 

 granules, it has been thought, as is obvious from the foregoing 



