ABNORMALITY OF THE NORMAL 



403 



Tetraploids 



Nicotiana Tahacum {4X = 48) 

 Prunus Cerasus {4X = 32) . 

 Primula sinensis {4X = 48) 

 Campanula persicifolia {4X = 32) 

 Triticum durum {4X = 28) . 

 Tulipa stellata {4X — 48) 

 Kniphofia sp. {4X = 24) 



Hexaploids 



Triticum vulgar e, etc. {6x = 42) 



Octoploid 



Bromus erectus, eu-erectus {8x = ^6) 



R. E. Clausen, 1930, 1931. 



D., 1928. 



D., 1931 a. 



Gairdner and D., 1931. 



Thompson and Robertson, 193 1. 



D. and Janaki-Ammal, 1932. 



Moffett, 1932. 



Hollingshead, 1932. 



Kattermann, 1931 {v. Table 31). 



Hh^ '{(^^ 



a 2132033 e i 



Fig. 123. — Side views of two first metaphases in Scilla italica (w = 8), 

 the chromosomes drawn separately. The numbers of chiasmata 

 are given below each bivalent. Right : the two shortest chromo- 

 somes are unpaired, having failed to form one chiasma. An 

 example of lack of adaptation of chiasma frequency to the range 

 of chromosome size as in organisms with new fragments. 

 (After Dark, 1934.) 



Genotypically controlled abnormalities, like those of structural 

 origin, vary in degree from cell to cell and the consequences of their 

 variations can be ascertained. But genotypic abnormalities are 

 particularly important for the analysis of meiosis and of chromosome 

 mechanics in general, because unlike those that are of structural 

 origin they show themselves at different stages. The effects of 

 divergence at each stage on the later stages can therefore be com- 

 pared and the degree to which successive events are independent 

 or otherwise can be determined. Sometimes this is not possible, 

 because either the abnormality of behaviour is spread over a 

 considerable space of time, or it is undefined in its nature (or in the 

 description that is available). In other cases precise conclusions 

 may be drawn. 



