CHAPTER XXIII 



PTERIDOPHYTES 

 FILICALES 



This order includes the ferns. Some members are sure to be 

 available in almost any locality and all stages in the life history are 

 easily secured. 



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. 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 /JL 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. It is really better to cut freehand the stems of Pteris 

 aquilina and forms of similar consistency (Fig. 77). 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 cut off with a very sharp knife pieces 

 about two inches in length. Put the fresh rhizome into the micro- 

 tome and cut sections as thin as possible. Keep the knife wet with 

 water and put the sections into alcohol as soon as they are cut. 

 Stain in safranin and anilin blue, safranin and light green, or safranin 



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