I] 



ANTHERIDIA AND ARCHEGONIA 



17 



The archegonium also originates from a single superficial cell, and grows 

 out so as to project from the downward surface of the thallus. It consists 

 when mature of a peripheral wall of cells constituting the projecting neck, 

 and a central group arranged serially. The deepest-seated of these is the 

 large ovum, which is sunk in the tissue of the cushion ; above this is a small 

 ventral-ca7ial-cell, and a longer canal-cell {¥\g. 21, A). If prothalli be grown 

 in moist air, and only watered by absorption from below, the archegonia 



Fig. 20. I, an attenuated male prolhallus of Dryopteris Filix-rnas. 

 2-5, stages of development of the antheridium. 6, 7, ruptured 

 antheridia. 8, a spermatozoid highly magnified. (After Kny. ) 



will have no access to fluid water, and they will remain closed. Fertilisation 

 is then impossible. But if they are watered from above, as they would be 

 by rain in the ordinary course of nature, the external fluid water will bathe 

 them, and rupture will result. This may be observed in living archegonia 

 which have been kept relatively dry and then mounted in water. The neck 

 bursts at the distal end, owing to internal mucilaginous swelling, and its 

 cells diverge widely. The canal-cell and ventral-canal-cell are extruded, and 

 the ovum remains as a deeply seated spherical protoplast, while access to it 

 B. 2 



