SINGLE AND DOUBLE RINGS AT THE REDUCTION 



DIVISION IN UVULARIA. 



JOHN BELLING, 

 CARNEGIE INSTITUTION OF WASHINGTON, DEPARTMENT OF GENETICS. 



It has not, apparently, been yet ascertained in what points 

 the reduction division in flowering plants differs from the corre- 

 sponding division in animals, such as the insects (see Tischler, 

 1922). The absence of a centrosome, indeed, has been noted in 

 many flowering plants; and it has also been presumed that the 

 division of the homologous chromosomes into chromatids is not 

 visible before the early anaphase. But whether the complicated 

 changes described, for instance, by Janssens (1924) as occurring 

 in insect chromosomes and summarized by Wilson (1925), are 

 paralleled in flowering plants, is, it appears, not known (though 

 Chodat, 1925, considers that Allium offers a parallel). The 

 following is a small contribution to the determination of the 

 likenesses and differences of the maturation divisions of flowering 

 plants and those of the best known animals, say, the Orthoptera. 



As compared with most animals, flowering plants may differ 

 in showing a periodicity in the occurrence of the maturation 

 divisions corresponding with the alternations of day and night. 

 Certain stages of Uvularia, for example, apparently usually came 

 late at night and hence were rarely obtained under normal en- 

 vironment in the daytime. However, cold checks or stops the 

 process ; and if preparations are made at intervals after cold has 

 occured in the night, various less common stages can often be 

 procured in the daytime. The first and second metaphases of 

 Uvularia have been readily obtainable under the usual environ- 

 ment; but the stages just previous to the first metaphase, and 

 those showing the separation of the bivalents into their component 

 chromosomes, or chromatids, were not often seen when pre- 

 parations were made at 9 or 10 o'clock in the morning. The 

 preparations were mostly procured after the young buds had 

 been somewhat chilled by the temporary lowering of the night 



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