2l6 



FERTIUZATIOX OF THE OVUM 



uur knowledge of it is rather incomplete. It is, however, sufficient 

 to show that the essential fact is everywhere a union of two germ- 

 j^^jclci — a process agreeing fundamentally with that observed in 

 animals. On the other hand, almost nothing is known regarding the 

 centrosome and the archoplasmic or kinoplasmic structures; and 

 most recent observations point to the conclusion that in the lowering 

 plants and pteridophytes no centrosomes are concerned in fertilization. 

 Manv earl v observers from the time of Pringsheim ('55) onward 

 described a conjugation of cells in the lower plants, but the union of 

 germ-Huclci, as far as I can find, was first clearly made out in the 

 Howering plants by Strasburger in xZ'j'j-'j'^, and carefully described 

 by him in 1884. Schmitz observed a union of the nuclei of the 



B 



Fig. 105. — I-'ertilization in Pilularia. [Cami'HELL.] 



A. /?. Early stages in tlie formation of the spermatozoid. C. The mature spermatozoid ; the 



nucleus lies above in the spiral turns; below is a cytoplasmic mass containing starch-grains {cf. 



the spermatozoJds of ferns and of Marsilia, Fig. 71). D. Archegonium during fertilization. In 

 the centre the ovum containing the apposed germ-nuclei (d", 9 ). 



conjugating cells of Spirogyra in 1879, and made similar observations 

 on other algx in 1S84, Among other forms in which the same 

 phenomenon has been described may be mentioned Gidigoniuin 

 (Klebahn, '92), Vauchcria (Oltmanns, '95), Cystopus (Wager, '96), 

 Splurrothcca and /:";;;'.v////r (Harper, '96), /v/^/m' ( Farmer and Williams, 

 '96, Strasburger, '97), Inisidioboliis (Fairchild, '97), Pilularia (Fig. 

 105, Campbell, '88), Onoclca (Shaw, '98, 2), Zamia (Webber, '97, 2), 

 and Lilitim (Guignard, '91, Mottier, '97), Ginkgo (Hirase, '97).^ In 

 all of these forms and many others fertilization is effected by the 

 union of a single paternal and a single maternal uninucleated cell, 

 such as occurs throughout the animal kingdom. There are, however, 

 some apparently well-determined exceptions to this rule occurring 

 in the "compound" multinucleate oospheres of some of the lower 



^ For unicellular forms see pp. 228, 280. 



