CHAPTER XXV 



PTERIDOPHYTES 



FILICALES 



This order includes the common ferns and also the Ophioglossaceae, 

 which was treated as an order, co-ordinate with Filicales, until Chrys- 

 ler showed that it was only a family under the Filicales. Some of the 

 ferns are sure to be available in almost any locality, and all stages in 

 the Hfe-history are easily secured, except early stages in the Ophio- 

 glossaceae. 



Vegetative structure. — From a technical standpoint, the vegetative 

 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 ramen- 

 tum, either remove the covering entirely or, in case of rather fleshy 

 ramentum, remove only the scales which are beginning to turn brown- 

 ish. The white scales will fix and cut. Use chromo-acetic acid (1 g. 

 chromic acid and 3 c.c. acetic acid to 100 c.c. water). Unless mitotic 

 figures are 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 jjl 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. 96). 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 laboratory. Then, if they 

 are to be cut without imbedding, cut into pieces about 3 cm. long; but 



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