PTERIDOPHYTES—FILICALES 
263 
water. Sow the spores on the surface of the pot and cover with a 
bell jar. No further wetting is necessary, except to take care that 
the water in the pan does not dry up. With Pteris longifolia, there 
may be antheridia in 2 weeks; archegonia in 3 or 4 weeks; and in 
5 or 6 weeks, abundant sporophytes in various stages. Prothallia 
grown by Costello’s method are entirely free from soil and, conse¬ 
quently, very convenient for cutting or for mounting a hole. 
While there should always be a study from living material, it is 
worth while to make permanent mounts, even for habit study. For 
such study, the prothallia 
should be mounted whole. 
Fix in the special chromo- 
acetic-osmic-acid solution. 
If the material shows any 
tendency to break up, use 
2 c.c. of acetic acid instead of 
3 c.c. In cities where water is 
treated with copper or other 
substances, the difficulty may 
sometimes be due to the water 
rather than to any excess of 
acetic acid. Formalin-acetic 
acid (10 c.c. formalin, 5 c.c. 
acetic acid to 100 c.c. water) 
is good for material which is 
to be mounted whole. Stain 
some in iron-alum haematoxy- 
lin, and some in Magdala red 
and anilin blue. Mount in 
Venetian turpentine, using 
material from each stain for each mount. Select stages so that 
each preparation will show the filamentous stage, the apical cell stage, 
the group of initials stage, and also antheridia and archegonia. 
For sections, the chromic series is better than formalin or cor¬ 
rosive sublimate. If the gradual processes of dehydrating, clearing, 
and infiltrating have been carefully observed, about 15 or 20 minutes 
in the bath should be sufficient. About 10 /* is a good thickness for 
such views as are shown in Figures 89, 90, 91. Safranin, gentian- 
violet, orange is a good stain. 
prothallia. 
