THE EMBRYO 211 



In 1898 Juel 53, 66 reported parthenogenesis in Antennaria 

 alpina, and two years later published a very full account of 

 this species and also of A. dioica, in the latter of which fertili- 

 zation occurs regularly. In the parthenogenetic A. alpina usu- 

 ally only pistillate plants are found, and in the staminate plants 

 that do occur the pollen is either lacking or feebly developed. 

 Juel was able to show conclusively that the embryo develops 

 from the unfertilized egg. lie was also able to satisfy himself 

 that the number of chromosomes (about fifty) remains un- 

 changed throughout the entire life history, no reduction taking- 

 place in the formation or germination of the megaspore. The 

 first division of the nucleus of the megaspore mother-cell is like 

 the divisions in vegetative cells, and neither in the form of 

 chromosomes nor in the character of the spindle does it resemble 

 the heterotypic division that is so constantly associated with the 

 reduction of chromosomes. The mother-cell gives rise to only 

 one megaspore, not forming a tetrad. In A. dioica, in which 

 fertilization regularly occurs, the megaspore mother-cell gives 

 rise to a tetrad, the first division being accompanied by a reduc- 

 tion in the number of chromosomes ( from about twenty- four to 

 about twelve). While the number of chromosomes was not de- 

 termined with absolute accuracy for either species, the numer- 

 ous countings prove the principal point, namely, that in .1. 

 dioica a reduction occurs at the beginning of the gametophyte 

 generation, but in the parthenogenetic A. alpina the number 

 remains unchanged throughout the life history. In the latter 

 also the polar nuclei do not fuse to form a primary endosperm 

 nucleus, but each divides independently and forms a mass of 

 endosperm, showing, like the egg, an ability to divide without 

 previous fusion. 



In 1901 Murbeck 76 discovered that parthenogenesis is more 

 or less constant in all the species of AlchemiUa belonging to 

 Eualchemilla ; but he succeeded in finding a species (A. ar- 

 vensis) in which fertilization regularly occurs. In the struc- 

 ture of the nucellus AlchemiUa differs decidedly from Anten- 

 naria, there being a large number of megaspore mother-cells, 

 many of which form tetrads ; and it is not uncommon for sev- 

 eral of the resulting megaspores to germinate. The general 

 appearance of the embryo-sac is normal, and the polar nuclei 

 usually fuse to form a primary endosperm nucleus. Since this 



