898 PHENOMENA OF SEXUAL REPRODUCTION. 



after it is extruded it is set in rotation by the attached antherozoids ; it usually 

 remains enclosed in the mother-cell that produces it (the oogonium of Algae and 

 Fungi, the archegonium of Muscineae, Vascular Cryptogams, and Gymnosperms, 

 and the embryo-sac of Angiosperms), where it awaits fertilisation. While the male 

 cell loses during the union its character as an individual cell, the oosphere is 

 rendered capable of a more complete individual existence, which is first indicated 

 by the invariable formation of a wall of cellulose, even when the oosphere results 

 simply from the contraction of the protoplasm of an oogonium and still remains 

 enclosed in its cell-wall, as in (Edogonium and Vaucheria, In this respect the 

 zygospore of Conjugatae and Mucorini behaves also like a fertilised oosphere 

 or oospore. 



The male cell is more variable in its form and in its behaviour in the process 

 of fertilisation. It always moves to the oosphere which remains at rest ; in the 

 Florideae it is carried passively by the water ; in the Fucaceae, in Vaucheria, (Edogo- 

 nium, and other Algae, in all Characeae, Muscineae, and Vascular Cryptogams, it 

 swims actively. In other cases the male organ becomes attached in its growth to 

 the female organ, as in the antheridial branches (pollinodia) of some Saprolegnieae 

 and of some Ascomycetes, and the pollen-tube of Phanerogams. The great variety of 

 fortn of the male cell becomes especially conspicuous if we compare the roundish 

 swarm-spore-like antherozoids of (Edogonium and Coleochcete with the filiform anther- 

 ozoids of Characeae, Muscineae, and Vascular Cryptogams, and with the rounded 

 non-motile antherozoids of the Florideae which (like the spermatia of Lichens) possess 

 a cell-wall. The form is in each case evidently adapted to produce the right 

 kind of motion in order to convey the fertilising substance to the female organ in 

 a manner in harmony with its structure ; while in the fertilisation of the latter the 

 quality of the substance only is concerned. 



According to the present state of our knowledge it may be assumed that 

 fertilisation essentially consists in a union of protoplasm and nuclear substance 

 derived from the male organ with protoplasm and nuclear substance of the female 

 organ. In conjugation this union is brought about by the coalescence of the two 

 conjugating cells. In the fertilisation of (Edogonium and Vaucheria, the entrance 

 of the antherozoid into the protoplasm of the oosphere and its absorption in it 

 has been observed by Pringsheim. The antherozoids of Muscineae and Ferns 

 were observed by Hofmeister, and those of Marsilia by Hanstein, to enter the 

 archegonium, those of Ferns by Strasburger to penetrate to the oosphere itself. 

 It must therefore be inferred from analogy that in Phanerogams a union ^ takes 

 place of some substance contained in the pollen-tube with the oosphere ; and in 

 certain Ascomycetes of the contents of the poUinodium - with those of the asco- 

 gonium. It would be impossible otherwise to explain how in these cases the 

 mere contact of the often thick-walled pollen-tube with the embryo-sac, or of 

 the pollinodium with the ascogonium, can effect fertilisation, while in the former 

 cases such a complete coalescence of the male and female cells is necessary for 

 this purpose. 



* [See pp. 524 and 584. J 



