The Development of the Heterotypic Chromosomes 
in Pollen Mother-cells. 
BY 
DAVID M. MOTTIER, 
Professor of Botany in Indiana University. 
With Plates XXVII and XXVIII. 
I N September, 1905, the writer (Mottier, ’05) published a preliminary 
report on the development of the heterotypic or bivalent chromosomes 
in Podophyllum. The results of observations set forth in that communication 
were as follows : (1) That, in agreement with the conclusion of Farmer and 
Moore (’05) and others, the bivalent chromosome developed in the first or 
heterotypic mitosis is formed by the approximation of two chromosomes 
side by side, or otherwise, which were previously arranged end-to-end in 
the spirem, and not by the approximation of two spirems either before 
or during synapsis, as claimed by Gregoire and his students, Allen, Stras- 
burger, and others. That the separation of these two chromosomes (i. e. the 
two segments, if the bivalent chromosome be considered as one) is a trans- 
verse division, and not a separation along the line of longitudinal fission 
observed in the spirem. (2) That there is no fusion of two distinct spirems 
as the nucleus goes into the first contraction or synapsis. 
In the following communication, the writer hopes to present the 
results of detailed observations substantiating the above conclusions, and 
to show also that, in the plants considered, there is no definite or reliable 
evidence to support the pro-chromosome theory suggested by Rosen- 
berg (’04), and especially emphasized by Overton (’05) for several dicotyle- 
donous plants, and by Miyake (’05) for certain Monocotyledons. The entire 
mitotic history will be traced from the resting nucleus to the complete 
formation of the heterotype chromosomes in the pollen mother-cell of 
Podophyllum peltatum , Lilium Martagon , L. candiditm , and Tradescantia 
virginica , although not in complete detail in the latter. A study of Gal - 
tonia candicans has also been made, and this plant was found to correspond 
in important details with Tradescantia virginica , as will be seen also from 
the results of other observers. 
[Annals of Botany, Vol. XXI. No. LXXXIII. July, 1907.] 
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