io8 Morphology BOOK i 



in that both the cells resulting from the first division 

 of the zygote take part in the formation of the true 

 embryo. 



The first satisfactory account of the development of the 

 embryo in the Coniferae was given by Strasburger in 1872 

 and 1879. In the other groups of the Gymnosperms its 

 development had not been traced before the end of the 

 century. 



Polyembryony, or the occurrence of more than one embryo 

 in the embryo-sac in Angiosperms has already been spoken 

 of as arising from fertilization of the synergidae. This is not, 

 however, the only cause of its origination. Strasburger, in 

 1878, observed the formation of embryos by budding from 

 various cells of the nucellus, some of them situated some 

 little way from the embryo-sac. The young bud-like body 

 pushed its way into the embryo-sac and developed into 

 an embryo. The plants in which this occurred were 

 Funkia ovata, Coelebogyne ilicijolia, Nothoscordon fragrans 

 and Citrus Aurantiiim. In 1897 Hegelmaier observed 

 a similar formation mAllium odorum, from the inner integu- 

 ment. Ganong, in 1898, found polyembryony caused in 

 the same way in Opuntia. These cases were called ' sporo- 

 phytic budding '. 



Apogamy or oophy tic budding, the development of an em- 

 bryo from a vegetative cell of the prothallus, was observed 

 in 1895, by Tretjakow in the same species of Allium, the 

 antipodal cells being those concerned. Hegelmaier made 

 a similar observation two years later. These cases can 

 only be explained as occurrences of apogamy, comparable 

 to what we have noted in the Cryptogams, or as giving 

 evidence that the antipodals like the synergidae are poten- 

 tial sexual cells. In this case, on that hypothesis the 

 embryo developed parthenogenetically. 



Another abnormal case of embryo formation was noticed 

 in 1895 by Jeffrey in Erythronium. The embryo arises 



