2l6 



FERTILIZATION OF THE OVUM 



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

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

 nuclei — 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. 

 Many early observers from the time of Pringsheim ('55) onward 

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

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

 flowering plants by Strasburger in 1877-78, and carefully described 

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



Fig. 105. — Fertilization in Pilularia. [Campbell.] 

 A. B. Early stages in the 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 spermatozoids of ferns and of Marsilia, Fig. 71). D. Archegonium during fertilization. In 

 the centre the ovum containing the apposed germ-nuclei (cf, ?). 



conjugating cells of Spirogyra in 1879, and made similar observations 

 on other algae in 1884. Among other forms in which the same 

 phenomenon has been described may be mentioned GLdigonium 

 (Klebahn, '92), Vaiichcria (Oltmanns, '95), Cystoptis (Wager, '96), 

 Sphcerotheca and iT/jj-////^ (Harper, '96), /v/r//.? ( Farmer and Williams, 

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

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

 and Liliuni (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 



1 For unicellular forms see pp. 228, 280. 



