§32 CANNON: STUDIES IN PLANT HyBRIDs: 
Mottier * has described processes in the second maturation 
division which should be considered in connection with the earlier 
nuclear divisions as well. In the metaphase of the second division 
the chromosomes are brought into the paired position in the 
nuclear plate by the action of the fibers of the spindle; that is, 
the pairing here is probably due to the activity of the achromatic 
elements. This seems to make unnecessary the conception of the 
preliminary pairing of the chromosomes as a direct preparation 
for heterokinesis, since the spindle can distribute the chromosomes 
at its will, so to speak. It should be considered, however, that 
the rings are bivalent, and are probably formed without the inter- 
vention of the fibers, since the rings antedate the formation of the 
spindle itself. Also, if my observation is correct, the spindle 
fibers are not instrumental in segregating the chromosomes in 
the presynaptic division, because in that case, with possibly one 
exception, the pairing was not observed until the chromosomes 
were at the poles of the spindle and hence probably after the work 
of the fibers of that dividing nucleus was done. So it may well 
be that there is not only a difference in the homologies of the 
chromosome-pairs of the metaphase of the second division and 
those of the presynaptic one, but a difference in their affinities as 
well ; consequently influences, whatever they may be, other than 
those of the spindle, may cause the earlier pairing. 
The foregoing considerations are based upon the idea of the 
individuality of the chromosomes and upon that of their being 
qualitatively unlike.t If these conceptions are valid we should 
* Mottier, D. M. The behavior of the chromosomes in the spore mother-cells of 
higher plants, etc. Bot. Gaz. 35: 250. 1903. 
{The results of Rosenberg’s studies (see bibliography) on the sporogenesis 
of the natural hybrid between Drosera Jongifolia and Drosera rotundifolia seem to 
throw objections in the way of too strict a conception of the individuality of chromo- 
somes in hybrid plants. Rosenberg finds that the reduced number of chromosomes in 
the Drosera hybrid may be to, as in D. rotundifolia, or 20, as in D. longifolia, or 15, 
which is half the somatic number in the hybrid. He also finds some evidence indicat- 
ing that part of the chromosomes may be made up of four portions of chromosomes 
each, and others of two halves of chromosomes each; the former kind are also larger. 
In any case it is difficult to reconcile Rosenberg’s results with the idea that the chro- 
mosomes are distinct morphological entities ; the results point rather to the preserva- 
tion by a portion of the spores of the purity of the chromatin, a fact which may prove 
disconcerting to recent critics in this field (Cook; see bibliography). It should be 
