THE ENDOSPERM 261 



an indication that the second sperm fuses with the nucleus in the 

 micropylar chamber." The endosperm formed by the chalazal 

 chamber would therefore be diploid and that formed by the micro- 

 pylar chamber would be triploid. 



While the peculiar behavior reported by Ferguson, Bhaduri, and 

 Buell would easily account for the presence of an endosperm made 

 up of two different genetical constitutions, none of these reports 

 seems to be dependable. Levan (1937) has shown that what Fer- 

 guson believed to be the unopened pollen tube in Petunia was really 

 the fertilized egg. He demonstrated that double fertilization takes 

 place in a perfectly normal fashion, and that all the cells of the endo- 

 sperm, whether micropylar or chalazal, have the normal triploid 

 number of chromosomes. Cooper (1946) has confirmed this, and 

 with this complete refutation of Ferguson's work it seems likely that 

 similar misinterpretations were made by Bhaduri and Buell. 



In conclusion it may be stated that although it is possible that 

 sometimes only one of the polar nuclei is fertilized while the other 

 divides independently, this has not so far been cytologically demon- 

 strated. At the same time Webber's first hypothesis of a series of 

 independent divisions of the second male nucleus also seems im- 

 probable (cf. East, 1913). More likely, endosperm nuclei with 

 deviating chromosome numbers arise because of disturbed mitoses. 

 The most reasonable explanation for mosaic endosperms would, 

 therefore, lie either in an aberrant behavior of the chromosomes or 

 possibly in somatic mutations (cf. Clark and Copeland, 1940). 



References 



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 verwandte Gattungen. Acta Horti Bergiani 8: 123-219. 



Alexandrov, V. G., and Alexandrova, 0. G. 1938. On the endosperm nucleus and 

 its role in the filling and ripening of the grains of cereals. Compt. Rend. 

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Anantaswamy Rau, M. 1950. Endosperm in Cassia tora Linn. Nature (London) 

 165: 157. 



Arber, A. 1934. "The Gramineae." Cambridge University Press. 



Asplund, E. 1920. Studien liber die Entwicklungsgeschichte der Bluten einiger 

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Bacchi, O. 1943. Cytological observations in Citrus. III. Megasporogenesis, 

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Bhaduri, P. N. 1933. A note on the "new type of fertilization" in plants. Cur- 

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Billings, F. H. 1937. Some new features in the reproductive cytology of angio- 

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