CURRENT LITERATURE 



NOTES FOR STUDENTS 



Mitosis in Vicia. — Sakamura 1 has studied the somatic and maturation 

 mitoses in Vicia Cracca L. In the somatic cells of the young flower organs 

 he has made the following observations. At anaphase the 12 chromosomes, 

 which vary in size, pass to the poles without splitting. After being tightly 

 pressed together, they separate and become vacuolate chiefly along the center, 

 which results in the appearance several writers have erroneously interpreted 

 as a telophasic split. Contrary to the opinion of Fraser and Snell, the anas- 

 tomoses are thought to play no important part in the transformation of the 

 chromosomes. The chromosomes can be distinguished as alveolar bands very 

 late, but are no longer visible when the resting stage is fully reached. The 

 resting reticulum is finely uniform, with neither prochromosomes nor other 

 conspicuous chromatic aggregations. In prophase the reticulum gives rise to 

 chromatic bands which have the same arrangement as those in the preceding 

 telophase. This persistence of polarity is believed to favor the theory of 

 the individuality of the chromosomes. There are no chromomeres, no tetrad 

 structure such as Miss Merriman has described, and no continuous spirem 

 either at telophase or at prophase. The split occurs in the very early prophases 

 and remains until the metaphase. 



In the pollen mother cells the reticulum is somewhat looser than in the 

 somatic cells. The chromatic granules appear to be more numerous, but there 

 are no prochromosomes. As synizesis approaches, the granules form many 

 small clumps along the linin threads and the w r hole network contracts into 

 a tight ball. Although a parallel arrangement of threads was not seen before 

 or during the contraction, the author believes such a side-by-side conjugation 

 occurs, since double threads are seen projecting from the knot and in the 

 immediately following stages. As the spirem loosens up, the two halves are 

 distinguishable only in places, but later become very distinct. When the 

 "hollow spirem" is formed they fuse, but soon split apart again. A second 

 contraction occurs, during which the 6 bivalent chromosomes are formed by 

 the simple cross segmentation of the double spirem. 



At diakinesis the gemini, 2 of them larger than the other 4, sometimes show 

 a secondary split, thus forming " Langstetraden " such as other authors have 

 described. At metaphase of the first maturation mitosis, the members of each 

 pair appear to be wholly fused. As they separate during the anaphase, the 

 split which is to take effect in the second mitosis appears. At telophase there 



Sakamura, T. 7 Uber die Kernteilung bei Vicia Cracca L. Bot. Mag. Tokyo 



28:131-147. pi. 2. 1914. 



372 



