234 
METHODS IN PLANT HISTOLOGY 
development of the oosphere, and the process of fertilization, the 
sections should be from 3 to 6 m in thickness. 
For archegonia containing young embryos, like that shown in D, 
Delafield’s haematoxylin without any counter-stain gives beautiful 
preparations when the staining is well done. It is easier for the 
beginner to get good preparations with the safranin, gentian-violet, 
orange combination. 
In Riccia natans 
{Ricciocarpus natans) 
the direction of the 
axis of the archego- 
nium at every stage 
in the development 
must be known; 
otherwise, there will 
be few good longitu¬ 
dinal sections. 
In forms like 
Porella and Scapania, 
the involucre cover¬ 
ing the archegonia 
is likely to hold a 
bubble of air, which 
will delay or even 
prevent fixing. The 
best plan is to cut 
off the offending leaf 
witn a pair ot slender-pointed scissors. Sometimes the air can be got 
out with an air-pump. 
The Sporophyte.—Sporophytes in early stages of development 
often yield good preparations without very much trouble, but in 
later stages they are frequently difficult to cut on account of the 
secondary thickening of the capsule wall and the stubborn exine of 
the mature spores. Great care must be taken to get Riccia natans 
into paraffin without shrinking, and the same thing may be said of 
other forms which have such loose tissue with large air cavities. 
Formerly, we resorted to celloidin for stages like that shown in 
Figure 69. The gradual processes already described have obviated the 
difficulty, so that the student should be able to get thin paraffin 
Fig. 68. —Marchantia polymorpha: A, three early stages in 
the development of archegonia—Delafield’s haematoxylin; B, 
young archegonium showing two neck canal cells and the central 
cell before the cutting off of the ventral canal cell—fuchsin and 
methyl green; C, mature archegonium immediately before the 
fertilization period—safranin, gentian-violet, orange; D, young 
embryo—Delafield’s haematoxylin. X400. 
