THE ARCHEGONIAT^E 203 



the Green Algae. They may properly be considered as homologous 

 with zoospores. In other cases the gemmae are developed super- 

 ficially, and break off from the thallus. In Marchantia (Fig. 169) 

 and Lunularia these are produced in special receptacles. 



The Archegonium. The sexual organs may be borne upon the 

 same plant, or the plants may be unisexual. 



The development of the archegonium (Fig. 165) is remarkably 

 uniform throughout the Hepaticae. It arises from a superficial cell 

 which usually, but not always, divides by a transverse wall into a 

 stalk-cell and an upper cell. The latter divides by three intersecting 

 vertical walls, with a central cell and three peripheral ones. These 

 peripheral cells undergo later another longitudinal division, so that 

 the central cell becomes surrounded by six peripheral ones. In the 

 Jungermanniales, this longitudinal division is usually suppressed in 

 the case of the smallest primary peripheral cell, so that there are but 

 five of these formed. 



The next division is transverse and divides the young archegonium 

 into two tiers, the upper giving rise to the neck, the lower one to the 

 venter. From the axial cell of the neck a cover-cell is cut off, which 

 now divides by intersecting walls into four, placed crosswise. Re- 

 peated transverse divisions take place in all the neck-cells, so that 

 the neck rapidly increases in length. The axial row of cells con- 

 stitute the neck-canal cells. The axial cell of the venter divides 

 once transversely, and of the two resulting cells, the lower becomes 

 the egg, the upper the ventral canal-cell. 



At maturity the transverse walls of the neck-canal cells become 

 mucilaginous, and dissolve when the ripe archegonium absorbs water. 

 The protoplasm of the egg-cell contracts and assumes a globular 

 form. The cytoplasm is usually densely granular, except at the top, 

 where a more or less evident clear " receptive spot " can usually be 

 made out. 



The neck-cells become strongly distended by the water absorbed, 

 and the pressure exerted by the swelling mucilaginous mass formed 

 from the disorganized canal-cells finally becomes so great, that the 

 apex of the neck is ruptured, and the contents of the canal are forced 

 out, leaving an open channel through the neck, down to the central 

 cavity of the venter in which the egg lies. 



The Antheridium. The antheridium (Fig. 166) shows much more 

 variation than the archegonium. With the exception of the Antho- 

 cerotales, it is developed from a single superficial cell, which gener- 

 ally divides into a basal and a terminal cell. The latter develops a 

 mass of central sperm-cells, surrounded by a layer of larger sterile 

 cells, which often contain chlorophyll. The nucleus of the sperm- 

 cell is relatively large, and assumes a spiral form as the spermatozoid 

 develops. The two long cilia always found in the spermatozoids of 



