CHAPTER XXII 
PTERIDOPHYTES 
EQUISETALES 
This order was large and prominent in the Carboniferous age, 
but now only a single family, the Equisetaceae, survives. Its only 
genus, Equisetum, contains 24 pieces, 10 of which occur within the 
Gray’s Manual range. Equisetum is often called the “ scouring 
rush,” because the rough stems have been used for scouring kettles. 
The roughness is due to silica. Species, like E. hiemale, which con¬ 
tain much silica, must be treated with hydrofluoric acid before the 
older parts can be cut in paraffin. 
Vegetative Structure. —The roots are very small, but have large 
cells and easily yield good preparations. If a handful of Equisetum 
fluviatile or E. hiemale growing in water be pulled up, scores of root- 
tips may be secured in a few minutes. Fix in chromo-acetic acid 
with a little osmic acid. In case of such small objects it is a good 
plan to add a few drops of eosin to the alcohol during the process of 
dehydrating, in order that the material may be seen more easily. 
The slight staining does no damage, even if more critical stains are 
to be used after the sections are cut. Longitudinal sections of the 
roots may also be obtained by cutting transverse sections of the nodes. 
The growing points of stems may be cut with ease in paraffin. 
E. arvense is particularly favorable on account of the numerous apical 
cells which may be found in a single preparation. 
The “ fertile” stem of Equisetum arvense is so free from silica 
that it can be cut in paraffin without any difficulty. The adult 
vegetative stem of E . arvense , and all stems which contain so much 
silica, must be treated with hydrofluoric acid before imbedding in 
paraffin. However, nearly all of these stems can be cut freehand, 
before fixing, without removing the silica. Fix freehand sections 
in 95 per cent alcohol. Material for paraffin sections should be 
fixed in formalin, alcohol, acetic acid; or in hot alcohol, corrosive 
sublimate acetic. Safranin and anilin blue, with or without a little 
orange, is a good combination. 
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