198 CALIFORNIA ACADP:MY OF SCIENCES. 



The opening of the archegonium is brought about by 

 the swelling of the neck cells combined with the pressure 

 exerted by the swollen mass produced by the disintegra- 

 tion of the canal cells, which are forced out more or less 

 completely as the archegonium opens, and thus a channel 

 is formed down to the egg. 



Owing to the small amount of chromatin in the egg 

 nucleus, and the strong staining of the cytoplasm, it was 

 found impracticable to attempt a careful study of the 

 fertilization. 



The mucilage about the spore often forms a sort of 

 funnel-shaped cavity above the archegonium, and in this 

 and the surrounding mucilage the spermatozoids assemble 

 in immense number, and as soon as the archegonium 

 opens they collect in such numbers about it that its open- 

 ing is often completely choked up. Several of the first 

 comers usually succeed in penetrating to the central cell, 

 but probably as in other cases where this has been care- 

 fully studied, only one enters the egg. Here it soon 

 unites with the egg-nucleus, which has in the meantime 

 increased in size and moved towards the receptive spot. 



As soon as fertilization is effected the egg secretes a 

 membrane about itself, which effectually prevents the 

 entrance of other spermatozoids. At the same time the 

 inner membranes of the neck cells assume a dark brown 

 color. With the first division in the fertilized egg, a 

 division begins in the cells of the prothallium, which 

 changes the single layer of cells enveloping the egg into 

 a double layer, except in the basal cells which undergo 

 no further division (pi. iv, figs. 15 and 16). The lower 

 may divide further so that here the prothallium may be- 

 come several cells thick, and the surface cells may grow 

 out later into root-hairs. 



