316 PRACTICAL BOTANY 



diately 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 prothallus, and incloses the cells (a) and (&) of 

 the central series, while (c), the ovum, is embedded in, 

 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 it will be seen to consist essentially of 

 an outer wall, one layer of cells in thickness, which 

 incloses a central mass of cells, the contents of which 

 may be seen to be rounded off, and to have assumed 

 the form of a closely coiled spiral : these are the 

 spermatocytes or mother-cells of the spermatozoids. 



By comparing carefully-prepared and well-cut sections, the 

 development of the antheridia and archegonia may be traced, 

 and in both cases it may be seen that they originate from single 

 superficial cells. In the case of the antheridia young stages of 

 development are to be found on sections through the lateral and 

 posterior parts of the prothallus, while young stages of develop- 

 ment of the archegonia lie near to the organic apex : these 

 preparations may be cleared with "eau de javelle." Young 

 archegonia should also be observed from above in young prothalli 

 mounted with the lower surface uppermost. If drawings be 

 made of archegonia from both points of view, and of various 

 ages, a comparison of them will give a clear idea of the processes 

 of development. 



