CONFIGURATIONS OF BIVALENTS OF HYACINTHUS 

 WITH REGARD TO SEGMENTAL INTERCHANGE. 



JOHN BELLING, 



CARNEGIE INSTITUTION OF WASHINGTON, DEPARTMENT OF GENETICS, 

 COLD SPRING HARBOR, N. Y. 



INTRODUCTION. 



In the majority of the flowering plants examined by the 

 writer, and apparently also in most of those investigated in this 

 respect by others, the homologous chromosomes, which form 

 bivalents at the reduction metaphase, are joined only at the 

 extreme ends. As examples, Canna and Datura may serve, in 

 which this rule holds in the triploids as well as in the diploids. 

 In the largest bivalent of Uvularia, however (Belling, 1926), 

 there are additional points of junction (nodes) not at the ends. 

 The short and medium chromosomes of Uvularia seem usually 

 to be connected at or near the constriction, and the same is 

 the case with the short and medium chromosomes of Hyacinthus 

 (Belling, 1925). These will not be further considered here. 



FIG. i. Camera drawing of the eight bivalents of the diploid hyacinth, squeezed 

 from a pollen-mother-cell. The four large bivalents are alone considered here. 

 They are described in the text. 



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