CHAPTER XX 

 PTERIDOPHYTES 



This group includes the Lycopodiales, Sphenophyllales, Psilotales, 

 Equisetales, Ophioglossales, and Filicales. The Sphenophyllales 

 occur only as fossils and the Psilotales are confined to tropical and 

 subtropical regions. The rest are cosmopolitan. The Lycopodiales 

 are commonly called club mosses or ground pines, the Equisetales 

 are called horsetail rushes or scouring rushes, the two common 

 genera of the Ophioglossales are known as the adder's tongue 

 (Ophioglossum) and the grape fern (Botrychium) , and the Filicales 

 are the common ferns. Material is abundant, and so easily recog- 

 nized that anyone who pays a little attention to collecting can, in a 

 single season, get a fine supply for a study of the group. Some 

 desirable forms may not be present in all localities, but these will be 

 few, and can be obtained at a reasonable price from those who make a 

 business of collecting. 



The technic for Sphenophyllales will be found under " Special 

 Methods" (chap. xi). The gametophytes of Psilotales are unknown. 

 The young sporangia cut easily, but the older stages should receive 

 great care in dehydrating, clearing, and infiltration. No further 

 directions will be given for these rather inaccessible orders. 



LYCOPODIALES 



Lycopodium. The genus is evergreen, and consequently some 

 stage in development can be secured at any season. In general, the 

 tropical species are easier to cut than the temperate. Without any 

 regard to taxonomic sequence, we shall consider the vegetative 

 structure, the strobili, and the prothallia. 



Vegetative structure. Formalin alcohol is an excellent fixing 

 agent, and, quite contrary to prevalent notions, the staining capacity 

 of material seems to improve with several months' immersion. 



The growing points of stems and roots cut easily in paraffin, and 

 when the material becomes too hard to cut in paraffin it can be cut 



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