1905] MOTTIER—HETEROTYPIC CHROMOSOMES 177 
in the foregoing, the spirem contracts and thickens much less before 
its cross segmentation than has been supposed. The greatest con- 
traction occurs after segmentation, and furthermore the two seg- 
ments, or rods, of each chromosome do not represent the parallel 
halves of the longitudinally split spirem, but the approximation of 
serially distinct parts of the spirem as a whole. Each half of the 
chromosome is consequently double, resulting from the early longi- 
tudinal fission of the spirem, and this fission manifests itself during 
the meta- and anaphase. It is, therefore, the original longitudinal 
fission which has been regarded as a second longitudinal splitting. 
The heterotypic chromosomes of Podophyllum, therefore, are biva- 
lent, and the first mitosis in the pollen mother cells is a “reducing” 
division. This seems to me now to be the only proper interpretation 
of the heterotypic chromosomes in Podophyllum. The writer has 
been reluctant to give up the theory that a longitudinal fission 
occurs for each mitosis, and he has done so only after a long and 
careful study of many preparations. 
INDIANA UNIvERsity, BLOOMINGTON. 
LITERATURE CITED. 
ALLEN, C. E., ’o5: Nuclear division in the pollen mother cells of Lilium cana- 
e. Ann. Bot. 19: 191-248. 1905. 
BerGus, J., ’04: Formation des chromosomes hétérotypiques dans la sporo- 
génése végétale. I. Depuis le spir’me jusqu’aux chromosomes mars. La 
Cellule 21: 173-178. 1904. II. Depuis la sporogonie jusqu’au spiréme 
définitif. La Cellule 21: 383-394. 1904. III. La microsporogénése de 
Convallaria maialis. La Cellule 22: 43-49. 1904. 
~——,, ’05: La microsporogénése de Drosera rotundifolia, Narthecium ossi- 
jragum, et Helleborous joetidus. La Cellule 22:141-160. 1905. 
ARMER, J. B. and Moors, J. E. S., ’05: On the maiotic phase (reduction 
divisions) in animals and plants. Quart. Journ. Micr. Sci. 48: 489-557- 1995- 
ARMER, J. B. and SHove, DororHy, ’05: On the structure and development 
of the somatic and heterotype chromosomes of Tradescantia virginica. 
