HISTORICAL SKETCH 



19 



syngamy and triple fusion to be so clear in one of the sections on 

 this slide (Fig. 20) that it is surprising that the process could have been 

 missed at all. As it was, however, Arnoldi mistook the male gam- 

 etes for displaced nuclei (of the nucellus?) which had in some way 

 entered into the embryo sac during the process of sectioning, and 

 he therefore ignored them altogether. 



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J22L £^ 





Fig. 17. 



Sergius Nawaschin. (Photograph ob- 

 tained through the courtesy of Dr. A. W. 

 Haupt.) 



Fig. 18. 

 Leon Guignard. 



One of the results of Nawaschin 's discovery was that it gave a 

 plausible explanation of "xenia." This term had been coined by 

 Focke (1881) to denote those cases in which the pollen produced a 

 visible influence on the hereditary characters of those parts of the 

 ovule which surround the embryo. It now became clear that just 

 as the fertilized egg gives rise to an embryo combining the charac- 

 ters of the two parents, so does the triple fusion nucleus give rise to 

 a tissue containing the potentialities of both the parents. 



A controversy soon started, however, on the morphological nature 

 of the endosperm, which is neither n nor 2n but Sn. Some claimed 

 that it was a continuation of the old gametophytic tissue, while 

 others (Sargant, 1900) thought it to be a second embryo which took 



