Bryophytes -Musci 



217 



and sometimes in summer; besides, it is easily kept in the green- 

 house, where it may fruit at any time. Bryum has a still larger 

 cluster of antheridia, which may be seen at a distance of several yards. 

 Polytrichum also has a large cluster of antheridia surrounded by 

 reddish leaves, so that the whole is sometimes called the moss 

 "flower." In making preparations of Polytrichum these colored 

 leaves should be carefully removed after the material has been got 

 into 70 per cent alcohol. A single antheridial plant of Polytrichum 

 often furnishes a fairly complete series of stages in the development 

 of antheridia. Transverse sections 

 show not only the antheridia, but 

 also good views of the peculiar leaf 

 of this genus. In all cases the stem 

 should be cut off close up to the 

 antheridia, for many of the moss 

 stems cut like wire. 



Sections to show the develop- 

 ment of the antheridium should be 

 5 to 10 JLI in thickness. The safranin, 

 gentian-violet, orange is a good combi- 

 nation (Fig. 68). For details of sper- 

 matogenesis, sections should not be 

 thicker than 3 /z. Iron-haematoxylin 

 is a better stain for the chromatin 

 and blepharoplasts. 



Although sections 20 to 50 ju in 



thickness can be cut to show topography, it is far better to study 

 such stages in the fresh material. When a particularly fine view is 

 secured in this way, a permanent preparation may be made by 

 putting the piece into 10 per cent glycerin, without any fixing or 

 staining, and allowing the glycerin to concentrate. Then mount in 

 glycerin jelly. 



Archegonia. Since the necks of the archegonia are usually 

 long and more or less curved, it is necessary, for habit work, to cut 

 sections as thick as 20 or 30 JJL in order to get a view of an arche- 

 gonium in a single section (Fig. 68, A). Mayer's albumen fixative is 



B 



FIG. 68. A, archegonia of Webera 

 candicans; celloidin section 20 n thick; 

 X104; B, young antheridia of Poly- 

 trichum commune; X420. 



