No. 46o.] STUDIES ON PLANT CELL.~V. 257 



(Corydalis, Strasburger, '80 ; Tischler, : 00 ; Canna, Humphrey, 

 '96). Such nuclei are known to unite two or more and some- 

 times several together within the cells, forming fusion nuclei 

 with a large and variable number of chromosomes. In Peperomia 

 and Gunnera the endosperm nucleus results from the fusion of 

 several free nuclei and a number of instances are recorded in 

 which no fusion of the polar nuclei takes place, but the endo- 

 sperm is derived from the division of one or both. Such irregu- 

 larities, which will probably be greatly increased in number as 

 investigations proceed, indicate that the double and triple 

 fusions preceding the differentiation of the endosperm nucleus 

 are not of phylogenetic importance but are more likely to be 

 special developments in relation to peculiarities of seed forma- 

 tion among the angiosperms rather than of a sexual nature. 



However, the triple fusions, when a sperm enters into the 

 composition of the endosperm nucleus, seem to furnish a 

 cytological explanation of the phenomenon of xenia and thus 

 come into very close physiological relations to sexual processes. 

 In xenia we find the effects of hybridization expressed immedi- 

 ately outside of the embryo in the endosperm of the seeds. If 

 paternal chromatin has entered into the composition of the endo- 

 sperm nucleus or should the sperm nucleus by itself give rise to 

 a series of endosperm nuclei the appearance of paternal char- 

 acters would be expected. This explanation of xenia was worked 

 out independently by DeVries, Correns, and Webber, the last 

 author having published a particularly clear and full account of 

 the phenomenon (Webber, : 00). Even though the relation of 

 xenia to hybridization is apparent, it is nevertheless clear that 

 we are dealing with an exceptional process only possible because 

 of the unusual conditions within the embryo sac which allow a 

 second sperm nucleus to enter into the activities of seed forma- 

 tion and it is certainly not established that these activities have 

 any phylogenetic relations to past sexual processes. 



Some interesting studies of Nemec (: 02-: 03 ; : 04) upon 

 asexual nuclear' fusions may open the way for explanations of 

 some of the examples which we have considered as asexual in 

 the latter portion of this paper. Nemec found that mitosis in 

 the root tip of Pisum sativum could be checked during anaphase 



