BRYOPHYTES—HEPATICAE 
235 
sections as free from distortion as were the old celloidin sections. 
But even with well-fixed material great care must be taken not to let 
the paraffin get too hot. Remember that in most paraffin ovens the 
temperature is different in different parts of the oven. Do not let 
the temperature of the paraffin go above 53° C., and, preferably, not 
above 52° C. In Riccia natans it is even more difficult to get median 
longitudinal sections of the sporophyte than of the archegonium. 
Sections perpendicular to the groove, 
whether longitudinal or transverse, 
are almost sure not to give median 
longitudinal sections of the sporo¬ 
phyte, and these are the sections the 
beginner is sure to cut. Examine 
the material and note very exactly 
the orientation of the sporophyte; 
then, for fixing, cut out sections about 
2 mm. thick, taking these sections in 
such a plane that paraffin sections 
parallel to the thick section will give 
the desired median longitudinal sec¬ 
tions of the sporophyte. 
In forms like Pellia and Aneura, 
it is desirable to show the sporophyte 
still inclosed in the calyptra (Fig. 70). 
For such sections, we should recom¬ 
mend fixing in formalin alcohol. 
Aqueous fixing agents are likely to 
cause trouble on account of air bubbles. For cytological studies, 
the calyptra must be removed and a thin slab should be cut 
from opposite sides of the capsule to facilitate fixing and infiltra¬ 
tion. Chromo-acetic acid, with the addition of a little osmic acid, is 
best for fixing. In Pellia and Conocephalus the spores are very large 
and have a rather thin wall. Both these genera show a peculiar intra- 
sporal development of the gametophyte, i.e., the gametophyte 
develops to a considerable extent before it ruptures the spore wall 
and before it is shed from the capsule (Fig. 71). Mitotic figures 
during the first three divisions in these spores are exceptionally beauti¬ 
ful and are very easy to stain with the safranin, gentian-violet, 
orange combination, the chromosomes taking a very brilliant red, 
Fig. 69 .—Riccia natans: young spor¬ 
ophyte inclosed in the archegonium; 
spore mother-cell stage — Delafield’s 
haematoxylin. All the cells of the spor¬ 
ophyte, except a single peripheral layer 
(dotted in the figure), produce spores. 
Celloidin section 30 n in thickness. X104. 
