IS 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



therefore, lost the great phylogenetic importance which had been 

 attached to it by Treub. Today it is considered to be more of 

 physiological than of phylogenetic significance, although it does 

 have a certain taxonomic value in narrow circles of affinity. 



Double Fertilization. The 

 fate of the second male gam- 

 ete discharged by the pollen 

 tube was not known so far. 

 In a study of Lilium marta- 

 gon and Fritillaria tenella, 

 S. G. Nawaschin (18986) 

 showed that in angiosperms 

 both male gametes are con- 

 cerned in fertilization, one fus- 

 ing with the egg (syngamy) and 

 the other with the two polar 

 nuclei (triple fusion). A few 

 months later L. Guignard 

 (1899) also reported the same 

 phenomenon in Lilium and 

 Fritillaria and presented a se- 

 ries of beautiful drawings to 

 illustrate it (Fig. 19). These 

 discoveries attracted wide- 

 spread attention and were fol- 

 lowed by a series of similar 

 investigations dealing with 

 other species of angiosperms. 

 Double fertilization was soon 

 demonstrated in several plants 

 and within a few years it began 

 to be considered as of universal occurrence in angiosperms. It is 

 interesting to note that a year earlier D. M. Mottier (1897) had seen 

 the second male nucleus in close proximity to one of the polar nuclei, 

 but that he had considered this proximity to be accidental and had 

 failed to realize its true significance. Of considerable interest in this 

 connection is Finn's (1931) report on a preparation of Scilla sibirica 

 ( = S. cernua) made by a Russian botanist, W. Arnoldi, a number of 

 years before Nawaschin's announcement of 1898. Finn found both 



Fig. 16. Casuarina suberosa, l.s. ovule, 

 showing chalazogamy (m = micropyle; 

 p = pollen tube;e = embryo sac). (After 

 Treub, 1891.) 



