STRUCTURE.] SALVINIA. ISOETES. 105 



experiments of Savi of Pisa. This observer introduced into 

 different vessels, 1. the granules; 2. the grains; and, 3., the 

 two intermixed. In the first two nothing germinated; in 

 the third the grains floated to the surface and developed 

 themselves perfectly. The observations have, however, been 

 repeated by Duvernoy without the same result; and it is 

 clear that Mr. Griffith's observations are entirely opposed to 

 the view entertained by Savi, and Adolphe Brongniart, who 

 thus describes the reproductive bodies of Salvinia and Azolla. 

 In these genera he found at the base of the leaves membranous 

 involucres of two sorts, containing different organs. One 

 includes a bunch of cases (sporangia, Martius), 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 : 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. 



Of Isoetes the evidence as to sexuality is equally unsatis- 

 factory. " Delile has published an account of the germination 

 of Isoetes setacea, from which it appears that its sporules 

 sprout upwards and downwards, forming an intermediate 

 solid body, which ultimately becomes the stem, or corm ; 

 but it is not stated whether the points from which the 

 ascending and descending axes take their rise are uniform. 

 In Pilularia, Mr. Valentine finds that germination takes 

 place invariably from a fixed point. Delile points out the 

 great affinity that exists between Isoetes and Lycopodium, 

 particularly in the relative position of the two kinds of repro- 

 ductive matter. In Lycopodium, he says the pulverulent 

 spore-cases occupy the upper ends of the shoots, and the 

 granular spore-cases the lower parts : while, in Isoetes, the 

 former are found in the centre, and the latter at the circum- 

 ference. If this comparison is good, it will afford some 



