﻿1903] BEHAVIOR OF THE CHROMOSOMES 251 



phase, the first appearance of the reduced number of the chro- 

 mosomes, and the double longitudinal splitting of the latter. 



It is chiefly upon the behavior of the chromosomes during 

 these divisions that the great diversity of opinion rests, and this 

 is not surprising when one realizes the complexity of the prob- 

 lem and the difficulties attending its investigation. However, 

 in certain plants the double character of the daughter segments 

 during the anaphase of the first nuclear division in the pollen 

 mother-cell is so evident that one is surprised that it has been 

 overlooked for so long a time and by so many observers. In all 

 probability, this phenomenon may have been observed by earlier 

 investigators, but as its significance was not understood the 

 double nature of the daughter chromosomes ma}^ have been con- 

 sidered more apparent than real. 



Heuser ('84) seems to have been the first to call attention to 

 the double character of the daughter chromosomes in the diaster 

 stage of Tradescantia virginica^ but he interpreted the separa- 

 tion of the daughter segments during metakinesls of the first 

 \ mitosis as a transverse division. 



r 



* In 1895 Strasburger, basing his conclusions largely upon a 



* study of Larix, properly explained the V-shaped daughter chro- 

 I niosomes, which so frequently appear during the anaphase of 



the first division in the spore mother-cell, as the result of a 

 I second longitudinal splitting taking place at right angles to the 



first. Each V-shaped element, therefore, represents two grand- 

 daughter chromosomes which remain attached at the ends to 

 which the spindle fibers are fastened, while the opposite ends 

 <iiverge, forming the V. 



Two years later, Strasbursrer tosfether with the writer aban- 

 . doned the doctrine of the double longitudinal splitting, and the 

 V- and U-shaped elements were explained as the result of a fold- 

 ing together of the chromosomes, or as a bending during 

 metakinesis or previously, a view which had been held by other 

 observers. Our conclusions were based largely upon the ring- 

 or loop-shaped chromosomes which often occur in other plants, 

 such as Podophyllum and Tradescantia, and upon phenomena 

 observed in the second mitosis of the embryo-sac of Lilium 





