CHAPTER XXI 
PTERID OPHYTES 
This group includes the Lycopodiales, Sphenophyllales, Psilotales, 
Pseudoborniales, Equisetales, and Filicales. The Sphenophyllales 
and Pseudoborniales occur only as fossils and the Psilotales are 
confined to tropical and subtropical regions. The Lycopodiales 
are commonly 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, 
is often treated as an order. Two of its genera, Ophioglossum and 
Botrychium, are widely distributed and well known. Material, except 
in the Psilotales, is abundant and so easily recognized 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 secured 
at a reasonable price from those who make a business of collecting. 
The technic for Sphenophyllales will be found under “ Special 
Methods” (chap. xii). 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 .—Formalin alcohol, with or without the 
addition of acetic acid, is an excellent fixing agent and, quite contrary 
to prevalent notions, the staining capacity of material seems to improve 
with several months’ immersion. We prefer the following formula: 
formalin 10 c.c., acetic acid 5 c.c., 50 per cent alcohol 100 c.c. 
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