ORIGIN OF POLYPLOIDY 65 



plants wholly or sectionally tetraploid have developed (cf. Dorsey, 



1936). 



The chief occasion of polyploidy in plants and in many animals is 

 the reunion, or failure of separation, of daughter nuclei in the 

 germinal cells at the last divisions before meiosis. This is known 

 as syndiploidy (i'. Table 7). In some cases multinucleate cells 

 may be formed without fusion [e.g., in Zea). In most cases the 

 fusion takes place after the pachytene stage of meiosis (q.v.), for 

 the nucleus, although tetraploid, does not produce quadrivalent s 

 at metaphase in Datura, Zea, Prunus, Chorthippus, or, as a rule, in 

 Brassica. In Prunus and Chrysanthemum the abnormality is more 

 far-reaching, for small supernumerary nuclei may be formed. This 

 correlation of failure of formation of the cell-wall with failure of 

 aggregation of the chromosomes into single nuclei is characteristic of 

 extreme cases, for both processes depend upon the activity of the 

 spindle. 



The observations on animals and on Brassica and Datura show 

 that the abnormality is often a racial, i.e., a genetic, character. It 

 has been more frequently discovered in hybrids, partly because 

 they have been studied more closely, and partly because it is an 

 undesirable character eliminated in species. 



Table 7 

 Instances of Syndiploidy in Male Germinal Cells 



A, Animals 



Lacertilia, various species, Painter, 192 1. 



Iguanidae, all species. Painter, 192 1. 



Gomphocerus maculatus (Orthoptera), Eisentraut, 1926. , 



Chorthippus elegans D. 1932 d {cf. also Table i6b (p. 145) ). 



B. Plants 



CEnothera .... Geerts, 1909 ; HS,kansson, 1927. 

 Lactuca .... Gates and Rees, 192 1. 



Zea Mays .... McClintock, 1929. 



Beadle, 1930 (asynaptic genotype). 

 Triticum compactum (w) . . Gaines and Aase, 1926. 



Raphanus x Brassica . . Karpechenko, 1927, 



Nicotiana tabacum {n) . . Ruttle, 1928. 



Pyrus Mains .... Kobel, 1927. 



Nebel, 1929. 

 Triticum X ^gilops {^x) . . Kagawa, 1929 a ; Kihara, Lilienfeld, i934- 



R.A. CYTOLOGY. 3 



