FERTILISATION AND PROPAGATION. 



115 



delicate and irritable hairs, situated at one of the extremities of a flattened 

 thread, helicoid in form, which always accompanies this club-shaped vesicle. 

 In most prothalli, however, a process of cell- division goes on in the young 

 antheridium, whereby it is finally made up of a layer of cells surrounding a 

 central cell (see Fig. 4), and, in this central cell, the parent cells are 

 developed, and produce antherozoids. The outer coat, formed by the layer 

 of cells, has to aid in expelling the antherozoids when ripe, and the cells do 

 this by absorbing water rapidly, swelling, and compressing the contents of the 

 central cell till its apex, which is not covered by the layer, is burst (see 

 Fig. 5), the "parent cells" are expelled, and, soon rupturing, set free the 



Fig. 4. Young Antheridium 



(much magnified). 



o, Central Cell, filled with Parent Cells 

 of Antherozoids ; e, e, Epidermis of 

 Prothallus. 



o 



Fig. 5. Ripe Antheridium 



(much magnified), 



From which Antherozoids have been 

 shed by Opening at o. — c, Empty 

 Central Cell ; e, e, Epidermis. 



Fig. 6. immature Archegonium 



(much magnified). 



e, Canal, still Closed above, and Filled 

 by the Canal-cell ; e, e, Epidermis ; 

 n, Neck-cells ; o, Oosphere. 



antherozoids, which have the faculty of moving rapidly in water, or in a drop 

 of dew or rain. 



The " archegonia " (see Fig. 6) are the female organs, in each of which 

 lies the "oosphere"; the latter, fertilised by the " anther ozoa," becomes the 

 " oospore." This oospore develops into the Fern-plant bearing the well-known 

 fronds, on the back of which are visible the groups (sori) of minute, brown 

 spore-cases (sporangia), in which lie numerous spores, like the one with which 

 the cycle began. It will thus be seen that the prothallus and the leafy Fern- 

 plant are two generations in the course of a single cycle. The archegonia, 

 which are developed rather later than the antheridia, are situated in the 

 middle of the lower surface of the prothallus, behind the notch already 

 mentioned (see Fig. 2), and in the vicinity of the antheridia. Each of the 

 archegonia, which are by no means so plentiful as the male organs - most 



