THEORETICAL CONCLUSIONS 425 



garded triple fusion as an act of true fertilization, and this view 

 was strongly supported by Sargant (1900). She compared it to a 

 sexual union in that the fusion involved one normal male element 

 (twin structure to the male gamete fertilizing the egg cell) and one 

 normal female element (the upper polar nucleus, which is sister to 

 the egg cell). However, there entered into the process a third 

 nucleus from the chalazal end which "with its redundant chromo- 

 somes" upset the whole balance and brought about the degeneracy 

 of the resulting tissue. The second embryo was thus "maimed" 

 from the beginning and converted into a formless mass of tissue 

 or "monster," enabling the survival of the first without a struggle. 



Strasburger (1900) gave a different analysis and suggested that 

 triple fusion is not true fertilization but only a growth stimulus. 

 He emphasized the extremely reduced nature of the female gameto- 

 phyte of angiosperms, with little or no reserves of food material. 

 Triple fusion served as a stimulus toward its growth, he thought, 

 and the endosperm was therefore to be regarded as belated gameto- 

 phytic tissue. This postponement of endosperm formation was 

 considered by him to be an advantage, for it avoided the waste of 

 material which would occur if this massive tissue were lost by the 

 plant with every unfertilized ovule. 



The views presented above were based on the assumption that 

 the endosperm is always a product of triple fusion. Detailed stud- 

 ies during the present century have revealed, however, that there 

 is no such uniformity in its origin. In the entire family Onagraceae 

 the embryo sacs are 4-nucleate, comprising only an egg apparatus 

 and an upper polar nucleus. Here the primary endosperm nucleus 

 arises from the fusion of the male gamete and single polar nucleus 

 and is therefore diploid (Fig. 216 A). The same is true of some 

 reduced embryo sacs like those of Butomopsis, in which there is an 

 egg apparatus, a single polar nucleus, and one degenerating antip- 

 odal nucleus (Fig. 2165), and of some members of the Balanophora- 

 ceae in which the upper polar nucleus alone is fertilized and the 

 lower fuses with the 3 antipodal nuclei to form a degenerat- 

 ing structure which does not take part in further development. In 

 Ditepalanthus (Fagerlind, 1938), on the other hand, the primary 

 endosperm nucleus is tetraploid, being derived from a fusion of 3 

 polar nuclei and a male gamete. In Fritillaria and Plumbagella, it 

 is formed from a fusion of the haploid upper polar nucleus, the 



