APOMIXIS 



321 



plate and undergo the usual longitudinal splitting, followed by a 

 separation of the daughter chromosomes (Fig. 182H-L). 



Generative apospory. Holmgren (1919) has made a very detailed 

 study of the embryology of several species of the genus Ewpatorium. 

 Some species are entirely normal and reproduce sexually, but E. 



Fig. 183. Development of embryo sac in Eupatorium glandulosum. A-C, mega- 

 spore mother cell. D, nucleus of megaspore mother cell in division. E,F, two- 

 nucleate embryo sacs. G, four-nucleate embryo sac. H, eight-nucleate embryo 

 sac. (After Holmgren, 1919.) 



glandulosum, which is a triploid, is apomictic (Fig. 183). Here the 

 division of the megaspore mother cell differs little from a somatic 

 mitosis except in the fact that the cell elongates considerably, de- 

 molishing the nucellar epidermis and becoming vacuolate even before 

 it is ready to divide. There is no synapsis or pairing of chromo- 

 somes. Three nuclear divisions take place, to give rise to an eight- 

 nucleate embryo sac with two or three antipodal cells which may 



