14 ANNAL8 NEW YORK ACADEMY OF SCIENCES 



velopment and there is prompt abscission. In more compatible cross- 

 pollinations the pollen tubes penetrate to the ovules and the ovaries 

 enlarge and develop for some time. Many of these young capsules are 

 entirely empty; some contain only one seed each but these capsules 

 usually shrivel and fall before they are ripe. Occasionally a capsule will 

 mature and yield ripe viable seeds but thus far the greatest number of 

 seeds obtained from a single capsule is 5 (Stout, 1926). The total 

 number of seeds which a mature capsule of the size typical of the Europa 

 clon should be able to yield is perhaps at least 25. As many as 40 seeds 

 have been obtained from a single capsule of other species. It would seem 

 that in the case of the Europa clon only a few ovules of an ovary are 

 able to function and that even with compatible fertilization these do 

 not usually furnish sufficient stimulation to insure development and to 

 check the ready and early abscission of ovaries characteristic of this clon. 

 The inability to produce more than a very few seeds in a capsule is 

 evidence that the proportion of functional ovules is about the same as 

 the proportion of functional pollen grains. 



SUMMARY AND DISCUSSION 



Summary of the Chromosome and Nuclear Behavior in the 



Europa Clon 



The abnormalities that develop during somatic mitosis and during 

 meiosis in plants of the Europa clon are of three main classes: — (1) 

 increase in the number of the chromatin units, (2) unequal and irregu- 

 lar distribution (non-disjunction and non-distribution) of the chromatin 

 units and (3) irregularities in the organization of the nuclei concerned 

 in the processes of meiosis and resulting from them. Due to the abnor- 

 malities that develop during sporogenesis, the abortion of spores is almost 

 complete. 



In the somatic cells of the root tips a nuclear organization of 12 

 chromosomes is maintained in the majority of the cells. But non-dis- 

 tribution of chromosomes frequently occurs giving in the anaphases 

 groups of II and 13, or of 10 and 1 I. A non-distribution as great as 19 

 ami 5 ( PL I, Fig. :!) has been observed. Thus certain nuclei in the root 

 tips receive more than the normal number of L2 chromosomes through 

 non-distribution, and nol merely by fragmentation as reported by Hance 

 (1918) for Oenothera scintillans. When the number of chromatin units 



rises to •.'<; and 30 (PL I. Pig. 5 ) the increase may he brought about by 



non-distribution, or by fragmentation, or by a combination of both. 



