16 AXXALS NEW YORK ACADEMY OF SCIENCES 



number of chromosomes and when the number is abnormal. The forma- 

 tion of central spindle fibres, of cell plates and of nuclei may also be 

 abnormal in various respects. From one to as many as nine spores may 

 be formed from one pollen mother cell, always, however, with the pres- 

 ence of the phragmaplasts. The number of chromatin elements that 

 enter the microspores varies greatly. Finally, many of the pollen grains 

 are undersized and the poorly developed micro pollen grains regularly 

 contain subnormal numbers of chromosomes. The percentage of via- 

 bility in germination tests is always low. Tests by cross-pollination indi- 

 cate that only a small proportion of the ovules are able to function in the 

 fertilizations that give rise to embryos. There is a very decided abortion 

 of both microspores and macrospores that is persistent and very uniform 

 for all plants of this widely cultivated clon. 



The Chromosome Number for the Eueopa Clon 



Statements as to the number of chromosomes present in the cells of 

 plants of the Europa clon have been made by several investigators. In 

 his paper of 1882 (p. 496) Strasburger states "Die Zahl der Doppel- 

 elemente in der Kernplatte ist annahernd 12." Evidently this statement 

 refers to the number of paired chromosomes and according to this the 

 somatic or diploid number would be 24. But one of his figures (his Fig. 

 62) shows only 6 chromatin masses that are evidently bivalents in the 

 equatorial plate of the first meiotic division. Another figure (his Fig. 61) 

 shows 10 masses in diakinesis, which we may now perhaps interpret as in- 

 eluding 2 bivalents and 8 univalents. He evidently saw cases where the 12 

 univalents were all dividing in the lirst division and considered that this 

 was evidence that the number of paired chromosomes in the reduction 

 divisions is 12. In the material of If. fidva studied for his later paper 

 (1900) Strasburger evidently observed many irregularities in the num- 

 ber of chromatin units, which he seems to attribute largely to poor fixa- 

 tion. Thus in his Fig. 65, which is an equatorial plate of the second 

 division, there are 13 masses which appear to be in the early stages of 

 fragmentation. In his Fig. 66, which is one of the groups of the ana- 

 phase of the second division, there are 1<» splil chromosomes, of which 

 several are X-shaped. 



duel (1897) makes no definite statement regarding the Dumber of 

 chromosomes present in plants of //. fidva. Bui his figures reveal vari- 

 ous oumbers. In the early stages of the first division (his Fig. 2) he 

 shows as many as l<> masses, and in the nielaphase and anaphase of this 



division he presents (his Fig. 6) as many as a total of 24, quite as shown 



