STOUT AND SUSA, CHROMOSOME IRREGULARITIES 5 



An extended search has been made in somatic tissues prepared by the 

 paraffin method in the effort to determine for plants of the Europa clon 

 the frequency of nuclei having increased numbers of chromosomes and 

 the range of these numbers. The counts are most easily made in the 

 late stages of the anaphase of mitosis. In some root tips only the normal 

 numbers of 12 and 12 were found. In other root tips of the same plant, 

 cells with increased numbers of chromosomes were observed intermingled 

 with cells that had the normal number. Division figures, such as are 

 shown in PI. I, Figs. 2 and 4, were noted side by side in a single root tip, 

 but in most cases the large majority of the cells possessed the normal 

 number. The highest number of chromosomes recorded thus far for the 

 division of any somatic cell is 56 (PL I, Fig. 5). 



Arber (1920) has reported that the somatic cells in certain portions 

 of the flowering axis of plants of IT. fulva are commonly binucleated 

 or even multinucleated. Such cells have not been observed by us either 

 in the somatic tissues, where mitosis has been especially studied, or in 

 the pollen mother cells, although they have been noted among the tapetal 

 cells. 



CHROMOSOME AND NUCLEAR BEHAVIOR DURING 

 SPOROGENESIS 



Synapsis 



The stages of synapsis have been very carefully studied for various 

 plants of the Europa clon obtained from different localities in Europe 

 and America. In every plant the synapsis of pollen mother cells was 

 very uniformly normal. Disintegration such as is described by Timm 

 (1928, Abb. 1) was not found to a noticeable degree in the nuclei of 

 spore mother cells. Also, in no case were two resting nuclei or two 

 synaptic knots noted in a single spore mother cell. Special study was 

 made of this point, for it is important to know whether the presence 

 of two nuclei in pollen mother cells is a factor in the increase in the 

 number of chromosomes observed in later stages, as is reported to be the 

 case by Karpechenko (1927) for certain hybrids between Raphanus 

 sativus and Brassica oleracea. 



The Normal Number of Chromosomes in Diakinesis 



During diakinesis the total number of individual chromosomes in many 

 of the nuclei is apparently 12, which is in agreement with the normal 

 diploid number in the somatic cells. These may occasionally be arranged 



