422 Wilson. — Spermatogenesis in the Bryophyta. 
and Mnium sp. were published by J. and W. Docters van Leeuwen-Reijnvaan 
(40, 41, 4.2). Detailed references to these papers will be given in the 
course of the following description. 
A preliminary note on Mnium hornum has already been published 
(75), and in the present communication a full account of the spermato- 
genesis of this and of other Bryophyta is given. 
Methods. 
The methods employed for preservation and staining were similar in 
each of the Mosses investigated. A small amount of material was fixed in 
the field, but in the majority of cases clumps of the Mosses were brought 
into the laboratory or cool greenhouse, and the male plants were fixed at 
various times in the next few days. In some cases the plants were kept at 
a temperature of 28 ° C. for twelve hours before preservation. 
The following fixing reagents were employed : — - 
Flemming’s strong and weak mixtures, Hermann, Merkel, chrom- 
acetic, acetic alcohol, the sublimate-acetic-formalin mixture recommended 
by J. and W. Docters van Leeuwen-Reijnvaan (42), 70 % alcohol. 
With the exception of acetic alcohol, which was allowed to act from 
10 to 15 minutes, the material was allowed to remain in the fixing fluid for 
a period of 12-24 hours. On the whole, the Mosses are difficult plants to 
fix, and in several cases the preservation was unsatisfactory. Well-preserved 
material was, however, obtained by the use of Flemming’s mixtures, the strong 
formula proving the most satisfactory. The sublimate-acetic-formalin 
mixture gave moderate results as far as the nucleus is concerned, but the 
fixation of the cytoplasm with the reagent leaves much to be desired. 
Acetic alcohol proved unsatisfactory. In all cases air was removed from 
the tissues by means of the air-pump. Concentration was carried out by 
the glycerine method (74) or by the use of successively increasing strengths 
of alcohol. 
Longitudinal sections varying from 3 /x -7 /x in thickness were cut 
through the male receptacle, but in addition to these transverse sections of 
the antheridia were also prepared. 
The following stains were employed : — 
Heidenhain’s haematoxylin in combination with orange G, Congo red 
or safranin, Flemming’s triple stain (safranin, gentian violet, and orange G), 
Breinl’s (70) triple stain (safranin, methylene blue, and orange tannin). 
Mnium hornum. 
Mnium hornum is dioecious, the male plants usually occurring in 
distinct groups, although they are often intermingled with the female 
individuals. The antheridia begin their development about the middle of 
