No. 554] SHORTER ARTICLES AND DISCUSSION 119 



and in the F 2 generation there was likewise a splitting of the 

 culture into forms of biennis and cruciata. One of the biennis- 

 like forms presented a more vigorous habit and a larger size 

 of buds, flowers and leaves, suggesting the differences between 

 Lamarckiana and its derivative gigas. The style was longer 

 than in biennis and self-pollination, characteristic of biennis, 

 was impossible. This plant proved to be almost sterile. 



A count of the chromosomes as shown by mitotic figures in 

 meristematic tissue of young buds determined them to he 21 in 

 number. This important fact placed the plant in that group 

 intermediate between the usual types of (Enothera with 14 

 chromosomes and that very rare variant from Lamarckiana, 

 called gigas, which has 28 chromosomes. It has recently been 

 shown that certain plants that have been mistaken for gigas have 

 21 chromosomes and for these the name soni-gigas has been pro- 

 posed. Consequently Stomps calls the plant from the cross 

 cruciata X biennis with 21 chromosomes biennis semi-gigas. 



The observation of this remarkable plant and the determina- 

 tion of its chromosome count is a matter of great interest. The 

 fact that the number of the chromosomes (21) is not twice the 

 number of the parent types (14) shows that the germinal varia- 

 tion did not take place after a normal fertilization, for a doub- 

 ling of the number of chromosomes in the fertilized egg or 

 embryo would give a plant with 28 chromosomes. It indicates 

 that a gamete produced by one of the plants in the F t generation 

 had 14 chromosomes and that this element combining with a 

 normal gamete (7 chromosomes) produced this exceptional plant 

 with 21 chromosomes. 



I have suggested 2 a way in which gametes of an (Enothera 

 might be formed with 14 chromosomes in place of the normal 

 number. The presence of 28 chromosomes instead of the normal 

 number 14, during a heterotypic mitosis in an (Enothera might 

 come about from a somewhat earlier appearance of that prema- 

 ture division of the chromosomes which normally takes place as 

 early as anaphase of this mitosis. Thus a pushing forward of this 

 premature fission of the chromosomes from the anaphase to the 

 metaphase of the heterotypic mitosis would result in the distribu- 

 tion of 14 chromosomes to each pole of the spindle. Another fis- 

 sion introduced before the metaphase of the homotypic mitosis 

 would make possible a group of 4 nuclei at the end of the reduc- 



* Annals of Botany, Vol. XXV, p. 959, 1911. 



