114 



PSEUDO-POLYEMBRYONY 



1. Ovules grown together. 



2. Division of nucellus. 



3. Development of several embryo-sacs in the same nucellus. 

 Probably the oldest record we have is that of Leeuwenhoek, 



who found polj'embryony in orange seeds in 1 7 1 9. It is very con- 

 spicuous in this genus and has been frequently mentioned in the 

 literature. Although the number of seedlings from a single seed 

 is usually only two or three, it may exceed that number and as 

 many as thirteen seedlings from a single seed have been reported. 

 Strasburger * has made a careful study of polyembryony in a 

 number of species and has found that in the orange {Citrus 

 Aiirantiuni) all the embryos except those that developed from the 

 fecundated eggs were produced by cells of the nucellus and to 

 such he gave the name "adventive" embryos. That is to say, 

 these adventive embryos were from the sporophytic tissue of the 

 mother plant, were produced by vegetative multiplication or bud- 

 ding, and therefore derived their character from a single parent. 

 This fact presented a very complicated problem in plant breed- 

 ing, since in hybridization only those embryos which were pro- 

 duced by the fecundated eggs could possess characters derived 

 from double parentage. This was proved by Webber and 

 Swingle (f, t), who collected data for their work on a very large 

 number of Citnis seedlings. They called attention also to the 

 facts that the problem was doubly complicated because the hy- 

 brids frequently resemble the female parent and because the 

 parents are frequently so similar in appearance that it is impossible 

 to tell whether the seedlings are from hybrids or adventive em- 

 bryos. However, they also state that the hybrid seedling is 

 almost invariably more vigorous than the seedlings from adventive 

 embryos, a fact which undoubtedly facilitates the work of the 

 plant-breeder to some extent. 



* Strasburger, E. Ueber Polyembrj'onie. Jenaisch. Zeitsch. Naturwiss. 12: 647— 

 670. 1878. 



t Webber, H. J. Complications in Citrus Hybridizations cau-ed by Polyembryony. 

 Science 11. 11 : 308. 23 F 1900. 



X Webber, H. J., & Swingle, W. T. Yearbook of the Department of Agriculture, 

 1904 : 226, 227. 



