224 
ORGANOGRAPHY. 
BOOK I. 
which consist of the two genera, Marsilea and Pilularia, we 
remark at the base of the leaves certain involucres of a cori- 
aceous, thick substance, and either indeliiscent 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, and 
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 
Salvinieae 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 Marsileaceae : 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 
granules 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 
Lycopodiaceae. Thus far Brongniart; see also Martins, Ic. PI. 
Crypt. 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 
