THE DEVELOPMENT OF THE HETEROTYPIC CHRO- 
MOSOMES IN POLLEN MOTHER CELLS. 
D. M. MOTTIER. 
(PRELIMINARY COMMUNICATION) 
THE theory of a reduction division in the spore mother cells of 
higher plants has gained considerable ground in the past two or 
three years; so that at present probably the majority of observers, 
who have devoted themselves almost constantly to the problems of 
the chromosomes, seem firmly convinced that one of the two mitoses 
in the formation of the tetrad is a “reducing” division. There is 
still, on the other hand, some diversity of opinion, and several years 
may elapse before cytologists will be strictly in accord upon this the 
most difficult of cell problems. 
One of the most important facts brought out by recent investiga- 
tions is the shifting of the point in the tetrad formation, at which the 
qualitative separation of the chromosomes is held to occur, from the 
second, or homotypic mitosis, to the first or heterotypic division. 
Since it has been shown by FLEMMING and Meves for the animal cell, 
and by GuIGNARD, STRASBURGER, and the writer, for the higher 
plants, that the daughter chromosomes of the heterotypic mitosis are 
split lengthwise as they separate in the metaphase, a more critical 
study has been devoted to the prophase of this division, and much 
light has been thrown upon certain obscure steps that have not as 
yet been satisfactorily explained. This double nature of the retreat- 
ing chromosomes was regarded as a second longitudinal fission, since 
It could be seen that the spirem was double in a very early prophase. 
This apparent second longitudinal division seemed to have proved 
beyond any shadow of a doubt that the second mitosis is not a reduc- 
ing division, as has been so insistently maintained by many zoolo- 
gists. Now that it has been shown that the homotypic mitosis in the 
spore mother cells of plants is not a reduction division, the question 
to be answered is whether in the heterotypic division the chromo- 
somes are bivalent, or whether the segments of each pair separate 
along the line of longitudinal fission. 
1905] 171 
