CHAPTER XXIII 
PTERIDOPHYTES 
FILICALES 
This order includes the common ferns and also the Ophioglossaceae, 
which, in the previous edition of this book, was treated as an order, 
Ophioglossales, co-ordinate with Filicales. Some of the ferns are 
sure to be available in almost any locality, and all stages in the life- 
history are easily secured, except early stages in the Ophioglossaceae. 
Vegetative Structure.—From a technical standpoint, the vegeta¬ 
tive structures of Filicales present a wide range of conditions, some 
being so soft that the greatest care must be taken to get them into 
paraffin, while others are so hard that it is almost impossible to cut 
them at all. 
The stem .—Growing points, even of the largest ferns, can be cut 
in paraffin. If the growing point is covered with dense hairs or 
ramentum, either remove the covering entirely or, in case of rather 
fleshy ramentum, remove only the scales which are beginning to turn 
brownish. The white scales will fix and cut. Use chromo-acetic 
acid (1 g. chromic acid and 1 c.c. acetic acid to 100 c.c. water). 
Unless mitotic figures are particularly desirable, it is just as well not 
to add any osmic acid. For illustrating the development of the stem 
from the apical cell, sections 10, 15, or even 20 /* are not too thick. 
Older portions of the stem, or rhizome, in most ferns are easily 
cut while fresh, the sections being transferred to 95 per cent alcohol 
after cutting. But even fairly well-developed rhizomes, after the 
xylem has become lignified sufficiently to stain sharply in safranin, 
can be cut in paraffin, and much finer sections can be obtained than by 
cutting without imbedding (Fig. 81). In digging up rhizomes, do not 
merely dig down until the rhizome can be grasped and then pull it 
up, for such material is sure to show the pericycle of the bundles 
torn away from the parenchyma. Dig carefully around the rhizome 
and then with a very sharp knife cut off pieces which are perfectly 
free. The pieces can be wrapped in wet paper and taken to the labo¬ 
ratory. Then, if they are to be cut without imbedding, cut into 
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