156 



SYSTEMATIC BOTANY. 



branches from the upper bundles unite to form the bundle 

 in the lower internode. The class Equisetinese has but a 

 single living genus, Equisetum, which contains about 

 twenty-five species, most of them being small plants. In 

 the Devonian and Carboniferous Ages there were many 

 genera, forming an order Calamariece, which became extinct 

 in the Permian Period. 



2. Filicinae. The plants (non- 

 sexual generation) of this class 

 (Ferns) have a solid stem, with 

 roots and broadly expanded leaves. 

 They are mostly terrestrial, and 

 all richly supplied with chloro- 

 phyll. The spores are developed 

 in sporangia on the surface or 

 margins of the ordinary or modi- 

 fied leaves. The leaves, called 

 fronds, are circinate (Fig. 35) in 

 their unfolding, and often divided 

 and several times compound. On 

 their under surface are the clusters 

 of sporangia, or sori (Fig. 268, sr). 

 The sorus may be naked, or covered by a membrane, 

 called the indusium (Fig. 268, iri), which is of various 

 shapes, and has various modes of attachment in the dif- 

 ferent genera. The sporangia are generally roundish and 

 pedicelled bodies. Each (in the Order Filiees) is sur- 

 rounded by an elastic ring (annuhis), which contracts, 

 and sets the spores free when ripe. The stems are mostly 

 short, or creeping, but in the Tropics they are often of 



Fig. 268. A Fern {Camptosarus rhizophyolllts)\/rtiTGT\A\ jor, Sop; in, indu- 

 sium ; sptlf sporangium ; spo, spore. 



