FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 65 



The antheridia arise in the same manner as the fruit-rudiments. A superficial 

 cell of the thallus is enlarged into a papilla, and, by the repeated partition in all 

 directions of its first segments, a body of tissue is produced, which includes a delicate 

 stalk and a thickened upper portion, either clavate or spherical in shape. The 

 latter part consists of a multicellular sac-like envelope and a parenchymatous 

 filling-tissue inclosed within the envelope. In each cell of the internal tissue the 

 protoplasm fashions itself into a spirally-bent spermatozoid, and shortly afterwards 

 the entire filling-in tissue is resolved into its separate cells. The antheridium now 

 opens at the top, and the loose cells with the mucilage in which they are embedded 

 are ejected into the surrounding aqueous medium composed of rain or dew-drops. 

 The spermatozoids then escape from their delicate cell-membranes, and swim about 

 the water by the help of the two long cilia wherewith each is furnished (see vol. i. 

 p. 29, figs. 7® and 7 ^°). Passing down the open neck of the amphigonium, now 

 filled with mucilage only, they succeed in reaching the oogonium in the enlarged 

 base of the fruit-rudiment and apply themselves closely to its surface; a constituent 

 portion of the spermatoplasm is absorbed into the ooplasm with the result that the 

 latter becomes fertilized. 



Usually several antheridia are situated close together. In Mosses they are 

 mingled with paraphyses, structures resembling hairs, the significance of which 

 has not yet been explained. In many species one individual develops only anther- 

 idia, another only amphigonia; but in other species antheridia and amphigonia 

 are developed side by side on the same Moss-plant. Where the latter is the case 

 either the oogonium exhibits an earlier development than the antheridium, or the 

 reverse is the case. Either the passage leading to the oogonium through the neck 

 of the amphigonium is opened whilst the adjacent antheridia are still closed, or 

 else the spermatozoids are set free from the antheridia at a time when access to 

 the oogonium is still barred by the lid-cells of the amphigonium. As in so man}^ 

 cases of a similar kind this contrivance prevents a union between the ooplasm and 

 the spermatoplasm produced by the same individual, and favours cross-fertilization 

 Ijetween different individuals. 



In some Liverworts the antheridia and amphigonia are surrounded by annular 

 walls, and these organs then appear to be sunk in depressions of the thallus. In 

 other Liverworts separate lobes or branchlets of the thallus are transformed into 

 stalked shields or discs, and the antheridia and amphigonia are formed in special 

 niches and compartments on the surface of the shields. Those Muscinese which 

 have their thalli differentiated each into a cauline axis and cellular laminaj 

 resembling leaflets, develop antheridia in the axils of the leaflets, or else in pitcher- 

 shaped cavities at the tops of the stems. In Mosses the principal or secondary 

 axes terminate in groups of antheridia or amphigonia, and specialized leaflets act 

 as envelopes or roofs and constitute the " perichsetium ". Sometimes these leaflets 

 have the appearance of floral leaves, as, for instance, in the Hair-Mosses (Poly- 

 trichum), several species of which may be included amongst the commonest of our 



Mosses. The antheridia and amphigonia are here distributed on diflferent individuals. 

 Vol. II. 65 



