Bryophytes Hepaticae 



209 



where the various organs are not raised above the thallus. In forms 

 like Marchantia, where the antheridia, archegonia, and sporophytes 

 are borne upon stalked receptacles, it is better to make separate 

 preparations to show the structure of the mature thallus. Sections 

 intended to show the structure of the mature thallus should be 15 n 

 to 25 n in thickness, but sections to show the growing point and 

 development of the thallus should not be thicker than 10 p. The 

 apical region of the J ungermanniaceae (Figs. 60, 61) affords an 



FIG. 61. Pellia epiphylla: photomicrograph of apex of gametophyte, showing 

 apical cell and segments; safranin, gentian- violet, orange. The negative was made by 

 Dr. Kohler at the Zeiss factory in Jena, Germany. 



excellent opportunity for studying the development of the plant 

 body from a single apical cell. If mixtures containing osmic acid 

 are used for fixing, there may be difficulty in the staining, even 

 after using peroxide of hydrogen. 



Chromo-acetic mixtures, without osmic acid, are better for the 

 apical region. Chromo-acetic acid, followed by Delafield's haema- 

 toxylin, is good for the apical cells and developing regions, but a 

 light counter-stain with erythrosin improves preparations of the 

 mature thallus. In forms like Pellia, where even the apical cells 

 are more or less vacuolated, a sharp stain in safranin and gentian- 

 violet is quite satisfactory, bringing out not only the cell walls, but 



