-.g ANNALS NEW YORK ACADEMY OF SCIENCES 



Thus the numbers reported for the diploid or somatic number of 

 chromosomes in plants of the Europa (don are 24 (Strasburger, 1882; 

 Timm, 1928), 32 (S. Nawaschin per Tischler, 1926), 33 (Belling, 



1925). and 18 (Schiirhoff, 1926). All of these estimates are based on 

 studies of stages in sporogenesis in which, we find, there is frequent multi- 

 plication of chromosomes and of chromatin units, giving numbers much 

 higher than the normal number of 1 ^ present in somatic cells. 



In discussing the reports of different chromosome numbers for //. 

 fulva, Timm suggests that there are different races. It is. however, to be 

 noted that all of the different numbers reported may be found in a single 

 plant and even in a single anther. Our studies involve plants of the 

 Europa (don obtained from Italy, France, Belgium. Holland, Sweden. 

 England and various parts of the United States. All these plants are in- 

 distinguishable ; all have normally 12 chromosomes in the cells of root 

 tips; all have the same types, ranges and degrees of irregularities in 

 sporogenesis. We find, hence, no evidence that there are different races 

 in this particular group of plants. 



It is now fully obvious that the irregular numbers of chromatin units 

 that develop during sporagenesis in plants of the Europa (don make it 

 necessary that a decision as to the number of diploid chromosomes in the 

 tissues of the plant he based on studies of somatic divisions as well as of 

 the early stages of meiotic division. But here also irregular chromosome 

 numbers may occur as our figures show. Possibly this is true of numer- 

 ous other plants now classed as polyploids. 



Increase in the Numbeb ok Chromatin Units 



A feature of special interest in the abnormalities of sporogenesis in 

 plants of the Europa clou is the frequent increase in the number of 

 chromatin units both by irregular segmentation and by splitting. Seg- 

 mentation is seen in diakinesis and in the prophases and metaphases of 

 the lii-st meiosis. In extreme cases it may involve all the chromosomes. 



The splitting of univalents during the firsi meiotic division, such as is 

 aeen in tin- Europa clon, has been observed in various plants. In fact, 

 this behavior seems to he frequent in many hybrids and in many cases 

 of polyploidy. It appears, however, to he the rule that the splitting 

 which occurs in the first division is not followed by another splitting 

 and that the total number of eh roinosoines is. hence, not raised above 

 that which is normal for the total of the second division. Yet in these 

 cases unequal distribution of the units may give greater or less numbers 

 than the normal haploid number to certain of the apores and gametes. 



