or TH 

 UNIVF. 



POLYTRICHUM SEXUAL ORGANS 349 



glycerine : subsequently the sections may be transferred 

 to glycerine jelly. Examine first with a low power, 

 when the usual arrangement of axis and leaves may be 

 observed ; between the youngest leaves an archegonium 

 (or several) may sometimes be detected. If mature, it 

 will be seen to be a flask-shaped organ, seated on a 

 short massive stalk : it consists of 



1. An elongated neck, more or less contorted, com- 

 posed of a single layer of cells arranged in four to six 

 rows : these surround a central canal, which is filled 

 with mucilage at the time of fertilization, but before 

 maturity there may be seen within it a series of 

 canal cells. 



2. A lower, enlarged ventral portion, consisting of 

 two layers of cells, which constitute the wall, and 

 inclose a central space, in which may be seen the 

 naked spherical oosphere or ovum, and above it (up 

 to the period of maturity) the smaller ventral canal 

 cell. 



The process of fertilization cannot readily be observed in 

 Mosses. 



Similar sections, similarly prepared from rather older speci- 

 mens, may show as the first results of fertilization that the neck 

 of the archegonium turns brown and withers, while the wall of 

 the ventral portion and the stalk show considerable increase in 

 bulk, and frequent cell- divisions. Meanwhile growth and cell- 

 division take place also in the fertilised ovum, resulting ulti- 

 mately in the development of the sporogonium : the growth of 

 the wall of the archegonium keeps pace for some time with that 

 of the young sporogonium, completely inclosing it, but as it in- 

 creases towards maturity, the wall of the archegonium is ruptured 

 transversely about half-way up : the apical part is carried up- 

 ward by the growing sporogonium, as the calyptra which covers 



