PTERIDOPHYTES—FILICALES 255 
pieces about 3 cm. long; but material which is to be imbedded should 
be in pieces not longer than 1 cm. 
Pteris aquilina is a good form to practice with. For freehand 
sections, cut as thin as possible, allow 15 to 30 minutes in 95 per cent 
Fig. 81 .—Dicksonia punctilobula: photomicrograph of transverse section of rhizome. Fixed 
in formalin-acetic alcohol, and stained in safranin and light green. Paraffin section 10 n thick. 
Eastman Commercial Ortho film, Wratten E filter (orange); arc light; J. Swift and Son 1-inch 
lens; exposure, 1 second. Negative by Dr. P. J. Sedgwick. X33. 
alcohol, transfer to 50 per cent alcohol and stain over night in safranin. 
Rinse in 50 per cent alcohol and stain in light green. Paraffin sections 
2 or 3 cm. back of the apex are very instructive, for only the proto- 
xylem will be sufficiently lignified to stain red with safranin, the 
