THE BBYOPHYTA 



123 



walls, so that the division is complete. We must not, 

 however, suppose that this peculiar form of mother-cell 

 is general in all Liverworts, though it is very common 

 among them. 



The venter of the archegonium enlarges very rapidly 

 to keep pace with the growth of the fruit inside, which 

 it completely envelops for a long time ; in Pellia, how- 

 ever, this envelope (called the calyptra) is not entirely 

 formed from the venter of the archegonium, but the 

 neighbouring thallus-tissue also takes part in the growth, 



FIG. 56. Elaters and spore mother-cells of Pellia. sp.^ and sp. , 

 spore mother-cells about to divide ; el, el, young elaters with 

 indications of spiral thickenings. Magnified 360. (R. S.) 



so that we see abortive, unfertilised archegonia carried 

 up on the sides of the calyptra (see Fig. 55, ar), while at 

 the top, the neck of the fertilised archegonium itself can 

 still be recognised (Fig. 55, ri). The cells of the thallus 

 surrounding the foot become especially crowded with 

 starch, and thus provide food for the developing 

 fruit. The whole structure of the fruit is already com- 

 plete while the seta still remains quite short. Its 

 elongation, as we have seen, is a comparatively sudden 

 process, and is due to the great stretching of cells which 



