184 PRACTICAL BOTANY 



upon it, but which bears antheridia : these will be situated at the 

 apices of the shorter axes : many of the longer axes will appear 

 to be terminated by ordinary vegetative leaves, and it is on 

 these axes that the archegonia may be found. 



From such buds, after hardening in alcohol, cut median 

 longitudinal sections : if not transparent enough treat with dilute 

 potash solution, and mount in weak 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, composed 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 the smaller ventral canal cell. 



Sporophyte Generation. 



The Sporogonium. 



X. Having noted the external characters of the sporogonium 

 of Polytrichum, as above described, cut transverse sections of 

 the mature seta : mount in glycerine or glycerine jelly. Being 

 a cylindrical organ the transverse section is circular. Note 



i. The superficial layer of cells with a definite cuticle and thick 

 yellow walls. 



spring and early summer, it will be convenient in most cases to use the former in 

 examining the archegonia. In either case, however, it is a matter of some experience 

 and expenditure of time to get a good series of preparations illustrating the develop- 

 ment and structure of the archegonium, and the early stages of the production of the 

 sporogonium. Various other Mosses might be used for the purpose of this work, 

 especially such as grow in tufts, and produce their sporogonia almost simultaneously. 



