chap, hi The Morphology of the Flower 103 



Strasburger in 1884. Details of their behaviour in different 

 cases were the subject of numerous memoirs from that 

 date onwards. 



The approach of the pollen tube to the embryo-sac was 

 thought to be uniformly by way of the micropyle till 1891, 

 when the curious process of chalazogamy was discovered 

 by Treub in Casuarina. This discovery excited great 

 attention and was at first held to indicate a new basis 

 of classification of Angiosperms. It was observed again by 

 Nawaschin in Betula, in 1892, by Miss Benson in several 

 families of the Amentiferae in 1894, and by Nawaschin in 

 Juglans in 1895. Further investigations by the last-named 

 writer in 1898 led to the discovery that in two species of 

 Ulmus the mode of entry of the tube into the embryo-sac 

 is varied and irregular, an observation confirmed by 

 Zinger's researches on the Cannabineae ; hence the idea 

 that it is of classificatory value was abandoned. 



Towards the close of the century, in 1898, another discovery 

 of great interest was made by Nawaschin — one which had 

 an important bearing on morphological speculation. This 

 was the fact that in Lilium and Fritillaria both the genera- 

 tive nuclei of the pollen tube are concerned in fertilization, 

 and that while one fuses with the nucleus of the oosphere, 

 the other either unites with the definitive nucleus of the 

 embryo-sac, — the latter being itself the result of the fusion 

 of the polar nuclei, — or it fuses with one of the polar nuclei. 

 This phenomenon has been indifferently spoken of as 

 double fertilization, or triple fusion. It attracted great 

 attention, and many investigations were proceeding as 

 the century closed, with the result that the occurrence 

 was seen to be so wide-spread as to justify the conclusion 

 that it is universal. 



The chief result of the discovery was a re-consideration 

 of the morphology of the so-called endosperm of Angio- 

 sperms. As we have seen, Strasburger included this struc- 



