ESSENTIAL ELEMENT IN THE PROCESS OF SEXUAL REPRODUCTION. 803 



least where any internal differentiation is exhibited (as in the formation of chloro- 

 phyll and the granular contents in OEdogonium and other Algse), the phenomenon 

 is a secondary one in the process of fertilisation. The germ-cell (or its equivalent 

 the ascogonium) is never actively motile, even when, as in the Fucacece, it is expelled 

 and set in rotation by the attached spermatozoids ; it usually remains enclosed in 

 the mother-cell that produces it (the oogonium of Algae and Fungi, the central cell 

 of the archegonium of IVIuscineae and Vascular Cryptogams, the corpusculum of 

 Gymnosperms, and the embryo-sac of Angiosperms), where it awaits fertihsation 

 by the male cell. While the latter loses during the union its character as an indi- 

 vidual cell, the germ-cell is rendered capable of a more complete individual exist- 

 ence, which is first indicated by the invariable formation of a wall of cellulose, even 

 when the germ-cell results simply from the contraction of the protoplasm of an 

 oogonium and still remains enclosed in its cell-wall, as in CEdogonium and Vaucheria. 

 In this respect the zygospore of Conjugatae and Mucorini behaves also Hke a fertilised 

 germ-cell 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 germ-cell which remains at rest ; in the 

 Floridece it is carried passively by the water ; in the Fucacese, in Vaucheria, CEdogo- 

 nium, and other Algae, in some Saprolegnieae, and in all Characeae, Muscineae, and 

 Vascular Cryptogams, it swims actively ; in other cases it becomes attached in its 

 growth to the female cell, as in the antheridial branches of some Saprolegnieae and 

 the antheridium of Ascomycetes, or it is carried passively to the female organ, as 

 the pollen-grain of Phanerogams and the spermatozoid of Florideae. The great 

 variety of form of the male cell becomes especially conspicuous if we compare 

 the roundish swarm-spore-like spermatozoids of CEdogonium and Coleochcete with 

 the filiform anlherozoids of Characeae, Muscineae, and Vascular Cryptogams, 

 and with the pollen-tube of Phanerogams. The form is in each case evidently 

 adapted to produce the right kind of motion in order to convey the fertilising sub- 

 stance to the female cell in a manner in harmony with its structure; while in the 

 fertihsation 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 always 

 consists in a union of the fertilising substance of the male cell with the protop' ; m 

 of the female cell. In conjugation this union is brought about by the coalescence of 

 the two cells. In the fertilisation of CEdogonium and Vaucheria, the entrance of 

 the spermatozoid into the protoplasm of the oosphere and its absorption in it has 

 been observed by Pringsheim. The antherozoids of Muscineae and Ferns were ob- 

 served by Hofmeister, and those of Marsilea 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 by diffusion takes place of 

 some substance contained in the pollen-tube wuth the germ-cell ; and in Ascomy- 

 cetes of the contents of the antheridium with those of the ascogonium. It would 

 be impossible otherwise to explain how the mere contact of the often [thick-walled 

 pollen-tube with the embryo-sac, or of the antheridium with the ascogonium, can 

 fertilise the latter, while in the former cases such a complete coalescence of the male 

 and female cells is necessary for this purpose. 



The product resulting from the sexual process is usually a new individual, which 



