268 
METHODS IN PLANT HISTOLOGY 
at least 10 minutes, clear in clove oil, and mount in balsam. Such 
a preparation will often show a score of sperms in the gelatinous 
funnel leading down to the neck of the archegonium. 
Azolla is not difficult to obtain, and it is easy to get a series of 
stages in the development of the micro- and megasporangia; but 
it is not at all easy to find the gametophytes, since the spores ger¬ 
minate only after they have been set free by the decay of the plant. 
Azolla does not fix well in any of the chromic-acid series, because it 
catches so much air that it will not sink. Alcohol-formalin-acetic, 
or hot alcoholic corrosive sublimate-acetic acid, formalin (4 g. 
corrosive sublimate, 5 c.c. formalin; 5 c.c. acetic acid, 100 c.c. of 
50 per cent alcohol) can be recommended for both Azolla and Salvinia. 
Both of these forms grow well in the greenhouse, floating on the water 
in tanks or aquaria; but Azolla seldom fruits under such conditions. 
Salvinia sometimes produces microsporangia in the greenhouse, but 
megasporangia are comparatively rare. 
