CHAPTER XXIII 



PTERIDOPHYTES 



This group includes the Lycopodiales, Sphenophyllales, Psilotales, 

 Pseudoborniales, Equisetales, and Fihcales. The Sphenophyllales 

 and Pseudoborniales occur only as fossils and the Psilotales are con- 

 fined to tropical and subtropical regions. The Lycopodiales are com- 

 monly called club mosses or ground pines, the Equisetales are called 

 horsetail rushes or scouring rushes, and the Filicales are the common 

 ferns. The Ophioglossaceae, a family of the Filicales, are often treated 

 as an order. Two of its genera, Ophioglossum and Botrychium, are 

 widely distributed and well known. Material of the living forms, ex- 

 cept in the Psilotales, is abundant and so easily recognized that any- 

 one 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 secured at 

 a reasonable price from those who make a business of collecting. 



The technique for Sphenophyllales will be found in chapter xiii. 

 Nothing but impressions has yet been found in Pseudoborniales. 

 Gametophytes of Psilotales have been found only recently. Their 

 young sporangia cut easily, but older stages are very refractory and 

 should receive extreme 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. — For stems and roots we recommend formalin 

 10 c.c, acetic acid 5 c.c, and 70 per cent alcohol 85 c.c, as a successful 

 fixing agent. 



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

 some stems, like those of Lycopodium lucidulum and L. inundatum, 

 cut well even after the metaxylem has become lignified. Cut at 5 or 



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