300 ' INTRODUCTION TO CYTOLOGY 



considerably delayed. The chromatin of the two nuclei at the time 

 these unite may be in the reticulate (resting) condition, the male and 

 female chromatins being indistinguishable in the fusion nucleus. This 

 situation was described by most of the earlier workers, including Stras- 

 burger (1900, 1901), Mottier (1904), Nawaschin (1898, 1899), and Ernst 

 (1902). It has also been reported by Sax (1916) in his recent work on 

 Fritillaria. In other cases, as early reported by Guignard (1891), the 

 chromatin has already reached the spireme stage characteristic of the 

 prophase, the male and female elements being distinguishable on the 

 spindle in the ensuing division of the fertilized egg. Such is the condi- 

 tion, for instance, in Calopogon (Pace 1909), Trillium (Nothnagel 1918), 

 and Lilium (Weniger 1918). That the same species may show con- 

 siderable variation in this respect is indicated by the situation in 

 Fritillaria, in which Sax (1916, 1918) finds that fusion, though it usually 

 occurs in the resting stage, sometimes takes place after the spiremes 

 have been developed. Miss Weniger (1918) reports that in Lilium 

 philadelphicum and L. longiflorum the egg nucleus is in the resting con- 

 dition and the male nucleus in the spireme stage at the time of union. 



Chromosome Behavior. — With regard to the behavior of the two par- 

 ental groups of chromosomes, it has been generally held that, whatever 

 their condition at the time of the nuclear union, all of them, both pater- 

 nal and maternal, split longitudinally at the first division of the fer- 

 tilized egg, the daughter chromosomes so formed being distributed to 

 the two resulting nuclei, just as in all the subsequent somatic divisions. 

 Recently, however, Miss Weniger (1918) has reported a condition in 

 Lilium similar to that described by Hutchinson (1915) for Abies: the 

 maternal and paternal chromosomes form pairs and divide transversely 

 into daughter segments which pass to the poles. (See p. 296.) With 

 this conclusion other recent investigations of fertilization in angiosperms 

 are not in agreement. Miss Nothnagel (1918) finds in Trillium no such 

 pairing and cross segmentation as Hutchinson and Miss Weniger de- 

 scribe, and states that each chromosome splits longitudinally as held 

 by Miss Ferguson for Pinus and by cytologists in general. Sax (1918) 

 also shows that each paternal and maternal chromosome in Fritillaria 

 divides longitudinally, the diploid number (24) passing to each pole. 

 In Trillium he reports an essentially similar state of affairs, the diploid 

 number here being about 28. He therefore holds that the first mitosis 

 in the fertilized egg is like any other somatic mitosis, and that no mech- 

 anism for the segregation of factors of inheritance, such as occurs at 

 reduction, exists here. The outcome of this controversy is awaited with 

 much interest because of its great theoretical importance. 



Endosperm Fusion. — The fusion of the second male nucleus with 

 the two polar nuclei of the embryo sac to form the primary endosperm 

 nucleus may be carried out in a variety of ways. The most commonly 



