232 
METHODS IN PLANT HISTOLOGY 
Antheridia.—It is not difficult to get good preparations showing 
the development of antheridia. In forms like Conocephalus, Asterella, 
Pellia , etc., cut out small portions of the thallus bearing the anther¬ 
idia. The piece should not be more than 1 cm. long and 5 mm. 
wide, preferably smaller. For the development of the antheridia of 
Marchantia, select young antheridiophores which still lie close to the 
thallus. With the antheridiophore, cut out a small piece of the 
thallus, about 5 mm. in length. For general development, cut 10 p, 
but for details of spermatogenesis, sections should not be thicker 
Fig. 66. —Pellia epiphylla: photomicrograph of apex of gametophyte showing apical cell 
and segments; fixed in chromo-acetic-osmic acid and stained in safranin, gentian-violet, orange. 
The negative was made by Dr. Kohler at the Zeiss factory in Jena, Germany. 
than 5 p (Fig. 67). Sections should be stained in iron-alum haema- 
toxylin. The cells are very small and the contents very dense; 
consequently, the staining must be very critical to show the blepharo- 
plasts and chromosomes or, in later stages, the transformation of 
spermatids into sperms. If the material is perfectly infiltrated and 
imbedded, a constant cooling with ice should make it possible to 
secure smooth sections as thin as 3 p, or even 2 p. 
If sperms are found escaping, transfer them to a small drop of 
water on a clean slide, invert the drop over a 1 per cent solution 
of osmic acid for 2 or 3 minutes, allow the drop to dry up, pass the 
slide through the flame 2 or 3 times, as in mounting bacteria, and 
