176 - PRACTICAL BOTANY 



also be made from fresh material, but the results will not be 

 nearly so good as if one of the above methods of fixing and 

 hardening be adopted. 



Hold a prothallus thus prepared between pieces of pith, or 

 embed as directed on p. 173 : then cut sections perpendicularly 

 to the surface of the prothallus, so as to pass through the cushion, 

 following the organic axis from base to apex. Mount in 

 glycerine, and examine first with a low power. 



The lower surface may easily be recognized by the presence 

 of root-hairs : on this lower side, chiefly near to the apical end 

 of the section, which is characterized by its small cells with 

 thin walls, will be found archegonia: these may be recognized 

 by the multicellular neck, which projects beyond the surface of 

 the section. In some cases the canal of the neck may appear 

 of a deep brown colour : this is the case in old archegonia 

 which have not been fertilized, and they should be disregarded. 

 Select one archegonium of full size and healthy appearance, and 

 examine it under a high power. 



Observe that it consists of 



A. The central series of three cells, which may be distin- 

 guished as 



a. The canal-cell ; this is oblong in form, and its walls are 

 subject to mucilaginous degeneration : it occupies the channel 

 of the neck, and has been above alluded to as being visible 

 when the neck of the archegonium is seen from above. 



b. The small ventral canal-cell, which lies immediately 

 below the oblong canal-cell, and is of rounded form. 



c. The oosphere, or ovum, which is of relatively large size, 

 and roughly spherical form : it is embedded in the tissue of the 

 cushion, and consists of a dense mass of granular protoplasm. 



B. The neck, which is composed of cells arranged in four 

 rows, constituting together a cylinder or tube, one layer of 

 cells in thickness : this projects from the surface of the pro- 

 thallus, and incloses the cells (a) and (b} of the central series, 

 while (<r), the ovum, is embedded ih, and surrounded by, cells 

 of the cushion. 



At the end of the section more remote from the apex 

 may be found antheridia. Select one fully developed, and 



