FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 65 



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

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

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

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

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

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

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

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

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

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

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

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

 D. 29, figs. 7* and 7 ^*'). Passing down the open neck of the amphigonium, now 

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

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

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

 atter becomes fertilized. 



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

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

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

 :dia, another only amphigonia; but in other species antheridia and amphigonia 

 ire 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 

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

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

 ;he oogonium is still barred by the lid-cells of the amphigonium. As in so many 

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

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

 jetween difierent individuals. 



In some Liverworts the antheridia and amphigonia are surrounded by annular 



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



)ther Liverworts separate lobes or branchlets of the thallus are transformed into 



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



liches and compartments on the surface of the shields. Those Muscineas which 



lave their thalli differentiated each into a cauline axis and cellular laminae 



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



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



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



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



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



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



Hosses. The antheridia and amphigonia are here distributed on different individuals. 

 Vol. it. be 



