CYTOLOGICAL INVESTIGATIONS IN PLANT HYBRIDS, 289 
CYTOLOGICAL INVESTIGATIONS IN PLANT HYBRIDS. 
By Prof. O. Rosensera, of the University, Stockholm. 
It is especially through the researches of recent years that the cytologists 
and the students of heredity have come into close relation. 
It has been proved that the principles of Heredity discovered by 
Mendel and others are in accordance with the phenomena of the develop- 
ment of the sexual cells. Especially have the Mendelian principles of 
segregation found their morphological parallel in the conception of the 
Reduction-division among the sexual cells of animals and plants, recently 
promulgated. 
Some years ago, whilst examining a hybrid of Drosera, I found some 
interesting facts concerning the Reduction-division. This hybrid between 
D. longifolia and D. rotundifolia was particularly interesting because the 
cells of the parent plants had an unequal number of chromosomes in their 
nuclei. D. longifolia has forty and D, rotundifolia twenty chromosomes, 
and in the germ-cells twenty and ten respectively. 
It is important to remember that the chromosomes are definite bodies 
in the nucleus, which in all probability are the bearers of hereditary 
characters. It was therefore interesting to follow the behaviour of the 
parental chromosomes in the new hybrid plant formed from the egg-cell 
after conjugation of the two nuclei. 
As I have pointed out in previous papers, all the somatic nuclei of this 
hybrid showed thirty chromosomes, which is the exact average sum of 
those of the parents. At the development of the sexual cells, pollen grains 
and embryo-sacs, I also found some peculiar facts, which agreed very well 
with the new ideas of the Reduction-division and in some points provided 
morphological evidence of their correctness. 
It is considered that the Reduction-process consists in a conjugation 
of parental chromosomes two and two, and that one chromosome (a) of the 
father fuses with one chromosome (a) of the mother. Several facts speak 
in favour of the correctness of this supposition, especially the interesting 
discovery by Sutton and Montgomery of unequal chromosomes. Sutton 
always found in somatic cells two chromosomes of a certain size, while in 
the germ-cells only one of these occurred. 
It is, of course, very difficult to observe this conjugation of parental 
chromosomes, since the chromosomes of a nucleus are generally like one 
. another. 
In the case of Drosera there was a different number of chromosomes in 
each parent, z.e. ten from the father and twenty from the mother. I then 
found that in the conjugation-act of the Reduction-process there occurred 
ten double and ten free single chromosomes round the spindle-figure. From 
this it is clear that ten D. rotundifolia-chromosomes had conjugated 
with ten D. longifolia-chromosomes, and that the remaining longifolia- 
chromosomes, meeting no corresponding rotwndifolia-chromosomes, were 
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