SYSTEMATIC BOTANY. 103 



the family Filices, is surrounded by an elastic ring (annulus). 

 This contracts and ruptures the sporangium, thus setting the 

 spores free at maturity. The stems are mostly short or creep- 

 ing (rhizomes), but in the Tropics they are often of consider- 

 able thickness and height. They contain flat fibro-vascular 

 bundles, usually arranged in a circle. When the stems be- 

 come thick with increase of growth, a network of anastomosing 

 bundles is formed in place of the central bundle. Ferns ap- 

 peared in the Devonian Age, represented by twelve genera, 

 belonging to extinct families. In the Carboniferous Age they 

 were much more numerous, but have decreased up to the 

 present time. These plants are very ornamental, but other- 

 wise of comparatively little economic value. The largest and 

 commonest genera are Asplenium, Dryopteris, Botrychium, 

 Cystopteris, etc. 



Collect specimens of the diiferent species of Ferns showing various forms 

 of fruit, which may be found in late spring and summer. Make an outline 

 sketch of a small portion of the frond (leaf). The figure should be large 

 enough to show plainly the venation and the fruit. Both vary much in dif- 

 ferent genera and serve to characterize the latter. Specimens of the small 

 prothallia with young fern-plants developing may often be found on the soil 

 of pots in green-houses. For making herbarium specimens, follow the direc- 

 tions given on p. 105 for collecting and preserving flowering plants. 



19. The Horsetails or Scouring Rushes have hollow, 

 jointed grooved stems, in the epidermis of which there is a 

 large amount of silica. The leaves are borne at each node in 

 the form of a sheath. The branches are verticillate. The 

 spores are produced in sporangia forming a cone-like spike 

 at the end of the stems. The stems of the Club-mosses are 

 solid, leafy, and mostly erect. The leaves are simple, small, 

 sessile, imbricated, and resemble those of the Mosses. The 

 spores are produced in sporangia, situated in the axils, and 

 are appendages of the leaves. In some of the genera (Lyco- 

 podium, etc.) the spores are all alike ; in others (Selaginella, 

 etc.) there are two kinds — large spores (macrospores) and small 

 spores (microspores). The plants of this class, now generally 

 terrestrial, and only a few inches high, were numerous in the 



