30 



THALLOPHYTES. 



cells ; they lie either singly or in groups (sometimes as many as twelve) above one another 

 in the filament. In most species each mother -cell of this description (antheridium- 

 cell) divides into two equal special mother-cells, each of which produces a spermato- 

 zoid ; they escape by the splitting of the mother-cell (as in the case of the zoospores) 

 (Fig. 163, D). The androspores from which the dwarf male plants arise are produced 

 from mother-cells similar to those which give birth to the spermatozoids (without 

 formation of special mother-cells). After swarming they fix themselves to a definite 

 part of the female plant, on or near the oogonium, and after germination produce at 

 o«ce the antheridium-cells, and in them the spermatozoids (Fig. 163, A, B, m, m). The 



Fig. 162.— Development of the swarni-spores of 

 CEdogonium (after Pringsheim). A, B their origin 

 from an older filament ; C free swarm-spore in 

 motion ; D commencement of its germination ; 

 E a swarm-spore formed out of the entire con- 

 tents of a germinating plant (X350). 



Fig. 163.—^ CEdogonittm ciliatum (X2S0) middle part of a sexual filament 

 with an antheridium (m) at the upper end, and two fertilised oogonia (og) by 

 the dwarf male plant ?«; R oogonium at the moment of fertilisation; o the 

 oosphere, z the spermatozoid in the act of forcing its way in, m dwarf male 

 plant ; C ripe oospore ; D piece of the male filament of O. ge7nell2pcirzini, 

 z spermatozoids. E branch of a hybernated plant oi Bidbochate intertnedia, 

 with one oogonium still containing a spore, another in the act of allowing it 

 to escape; in the lower part an empty oogonium. F the four swarm-spores 

 resulting from an oospore ; G swarm-spores from an oospore come to rest 

 (after Pringsheim). 



Oogofiium is always developed from the upper daughter-cell of a vegetative cell of the 

 filament which has just divided, and immediately after the division swells up into a 

 spherical or ovoid form. In Bulbochaete the oogonium is always the lowest cell of a 

 fertile branch. This is not opposed to the law of growth above-mentioned, inasmuch as 

 the mother-cell of a branch fulfils at the same time the function of its basal cell ; the 

 oogonium of Bulbochaete is never the first cell of a branch, since this is always developed 

 as a bristle. The oogonium becomes at first more completely filled with contents 

 than the remaining cells ; immediately before fertilisation the protoplasm contracts and 



