_ 
CANNON: StupiEs in PLant Hysrips 155 
type rings of the normal mitoses in pure races of animals are not 
only of double origin, but they are so organized that the halves 
of any chromatin loop are of diverse origin, that is, one half is 
derived from the one and the other half from the other parent. 
So that in pure races of animals if the chromatin is of pure descent, 
and, further, ¢f the maternal and paternal chromatin is segregated 
as a result of the maturation mitoses, the ultimate sex-cells are also 
of pure descent, two of any group containing chromatin lineally 
derived from one parent and two chromatin from the other. I 
therefore have suggested * that the same organization of the 
chromatin occurs in fertile hybrids, and that it forms the mor- 
phological basis for variation in accord with the Mendelian con- 
ception.t 
The organization of heterotype rings by the conjugation two and 
two of previously distinct chromosomes appears thus to be fairly 
well founded, but the purity of the chromosomes as regards 
descent is, I take it, not so well established, and here may per- 
haps be sought a cause for variations outside of the Piswm-type. 
But there is also considerable evidence to show that the chro- 
mosomes preserve their individuality during the ontogeny, or if 
the chromosomes do not retain their individualty, at any rate that 
the chromatin may retain its purity. Wilson (/. c. 204) says: 
‘Observations have given the strongest reason to believe that, as 
far as the chromatin is concerned, a true fusion of the nuclei never 
takes place during fertilization, and that the paternal and mater- 
nal chromatin may remain separate and distinct in the later stages 
of development—possibly throughout life.’’ On page 299 this 
*Cannon, A Cytological Basis for the Mendelian Laws, Bull. Torrey Club, 2g : 
657. D 1902. 
if as was also independently formed by W. S. sation + On the Mor- 
phology of the Chromosome Group in Brachystola magna. Biol. Bull. 4: 24, 2 
1902, Guyer has recently advanced a similar conclusion : Hybridism and the Germ- 
cell. Univ. Cincinnati Bull. No. 21. N 1902. ie ‘aoe 
The hypothesis above given to account for the variation of the hybrid race after the 
type of Mendel’s pea hybrids applies of course to those whose pure parents are a 
tated-by one character only, that is, to monohybrids, and does not clearly to polyhy- 
brids, or to those whose pure parents are distinguished by more than one poses 
If, however, we find that the two-spindle condition obtains in the spore-mother-cel s : 
fertile hybrids to a considerable degree it seems to me that in the combined results o 
such abnormal with the normal mitoses we may find a structural basis for the essen- 
tials of the variations in the more complex types of hybrids. 
