ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 43 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 including' Cell-Contents. 



Chromosomes in Oenothera.* — R. II. Hates has crossed (Enofhera 

 lata with (E. gigas and finds 21 chromosomes in the somatic cells, 7 of 

 which are of maternal origin and the remainder of paternal origin. At 

 the time of reduction the chromosomes segregate, half the germ-cells 

 receiving 10 chromosomes and the other half 11 chromosomes, but 

 sometimes the distribution is irregular, and this irregularity accounts 

 for a variation in the number of chromosomes in the individuals of a 

 race. The segregation of chromosomes in the germ-cells of the hybrid 

 proves that there is no pairing and separation of homologous chromo- 

 somes, but separation into numerically equal groups. It seems that 

 there are two general methods of reduction in plants, viz. a side-by-side 

 pairing of chromatin threads to form a double spirem, and an end-to-end 

 arrangement to form one single spirem which afterwards splits longi- 

 tudinally. The behaviour of the chromosomes in (Enothera favours the 

 view of their continuity from generation to generation. If it can be 

 proved that the chromosomes of (Enothera are " of unequal hereditary 

 value," the author believes that it would be possible to account for the 

 mutations in (E. Lamar xlciana. 



Mitosis in Synchytrium.t — In previous papers R. F. Griggs showed 

 that the nuclei of Synchytrium were derived very largely by amitosis ; 

 the present paper describes the mitoses which follow and their correla- 

 tion with the amitoses. As in ccenocytes generally he found that all the 

 nuclei in a cyst pass into mitosis simultaneously. In the resting nuclei 

 the chromatin is concentrated in a globular mass, the karyosome ; the 

 spirem is formed from the compact karyosome and differs in several 

 respects from the amitotic spirem, though often they are indistinguish- 

 able ; the spindle seems to be differentiated from a spirem strand ; some 

 of them show nucleoli lying in the nuclear cavity beside the spindle, in 

 others no nucleolus is present ; there are no centrosomes ; asters are 

 formed at the poles and form the nuclear membrane. There are con- 

 stantly four chromosomes, and the author discusses at great length the 

 nature of these ; he concludes that there is no morphological continuity 

 in the chromosomes, and that the nucleus rather than the chromosome 

 is the morphological unit. 



* Eot. Gaz., xlviii. (1909) pp. 179-99 (3 pis.). 

 t Tom. cit., pp. 339-58 (3 pis.). 



