102 BKITISH FERNS. 



ence on the temperature of the interior of the case ; and an 

 extreme degree of confined heat would be anything but fa- 

 vourable to these plants. 



The appearance of the case would, no doubt, be improved 

 by covering the soil entirely with living Sphagnum moss, 

 which, if neatly packed on the surface with the tops of its 

 stems uppermost, would continue to grow. Most of the 

 species of Club-moss would prefer to grow amongst the 

 Sphagnum, which, to prevent its being drawn up and smo- 

 thering the plants, should be neatly clipped down occasion- 

 ally with a pair of scissors. 



The interest of such a collection, so far as their appearance 

 is concerned, would depend of course upon the taste with 

 which the rockwork was designed and executed, and the 

 plants distributed about it; but whatever the result as a 

 matter of taste, the study of the living plant might be pro- 

 secuted without inconvenience, and which could never 

 happen in their wild localities all the species might be 

 brought under the eye at one time, for the purpose of con- 

 trasting them, and studying their differences. 



CHAPTER XXIV. 



THE BRITISH PEPPERWORTS. 



THE group of plants to which the name of Pepperworts has 

 been given, is technically called Marsileacece, and contains 

 but a few genera, these being of very curious structure. It 

 has only two representatives in tlie British flora. These two 

 plants belong to different genera, and are both submerged 

 aquatic plants of small size, agreeing in having grassy or 

 quill-like foliage, but differing materially in habit, the one 

 being a creeping grower and the other tufted. 



Isoetes is sometimes classed with the Club-mosses instead 

 of the Pepperworts. It takes its scientific name from the 

 Greek word isos, equal, and etos, the year, from its retaining 

 its fronds throughout the year; and is commonly called 

 Quillwort. The genus differs from Pilularia, its nearest 

 ally, in having its spore-cases enveloped by the dilated bases 

 of its hollow leaves; some of the spore-cases containing 

 large and some much smaller pollen-like spores. It may 

 also be known, when examined in a fresh state, by its hollow 

 ^rvyes being composed of four rows of elongated cells, which 



