PTERIDOPHYTES— FILICALES 309 



Xylol and paraffin, saturated at room temperature, 2 days. 

 Xylol and paraffin, saturated on top of oven, 3-4 days. 



6. In the oven until infiltrated, generally about 24 hours. 



7. Imbed. 



8. Soak the paraffin cake in water for a few hours before cutting. 



Such material will cut at 10 ^ or less. Let the sections dry on the 

 slide for at least 24 hours; a month will do no harm. 



Probably most fern rhizomes could be cut by this method. Even 

 the Adiantum pedatum rhizome is not harder than that of Gleichenia. 



The stems of tree ferns require special treatment. With the large 

 leaf bases partly cut away with a sharp razor, transverse sections are 

 easily cut for a considerable distance below the apex. Material fixed in 

 formalin acetic alcohol cuts very well. If fresh material is to be cut, 

 the softer portions should be flooded with alcohol after each section. 

 Farther down, there will be a region where sections can be cut without 

 any flooding, and still farther down, it will be difficult or impossible to 

 cut sections across the whole stem. Sections 1 or 2 cm. thick, cut 

 smooth on the ends, may be kept in 95 per cent alcohol or in glycerin 

 in large glass dishes of the Petri dish pattern. Better still, clear such 

 sections in xylol and preserve in cedar oil. 



The root. — The roots of Filicales develop from a strong apical cell. 

 For mitotic figures and the development of the root from the apical 

 cell, fix in the Chicago chromo-acetic-osmic acid solution. None of the 

 fern roots need any treatment with hydrofluoric acid. If the develop- 

 ment of the root is the principal object, stain in safranin and light 

 green, or in the safranin, gentian violet, orange combination; if mitotic 

 figures are to be studied, stain in iron-haematoxylin with a very light 

 counter-stain in orange. The comparatively large root-tips of Botry- 

 chium are excellent for the apical cell and its segments. Dicksonia 

 pundilobula can also be recommended; but even the very small root- 

 tips of most of our ferns will yield good preparations. 



Roots of tree ferns are sometimes available in greenhouses. In some 

 species the stem is covered by a dense felt of small roots, some of which 

 will be white and soft at the tip. These roots are likely to have about 

 the diameter of onion root-tips, and the beauty of preparations made 

 from them could hardly be excelled. In the tropics, where the plants 

 are often in the spray of cataracts and the lower part of the trunk is 

 often washed by mountain streams, a thousand tips might be secured 

 from a single tree fern. 



