150 CANNON: STUDIES IN PLANT HyBRIDS 
Another peculiarity in the mitosis was the frequent inequality in 
the division of the chromosomes, in some instances only about 
one fourth of a chromosome going to one pole.’’ At page 248 
he concludes that ‘‘these peculiarities in chromosome formation 
may point perhaps to a tendency in the chromatin of each parent 
species to retain its individuality. If such is the case, then in 
those cells with two spindles each bearing eight chromosomes, 
it is evident that after division, some of the new cells will have 
chromatin from only one of the original parent species, and some 
from the other. Some of the spermatozoa, therefore, will bear 
chromatin from only one of these species. It is a well-known 
fact that the offspring of hybrids are extremely variable, a portion 
of these variations being usually in the form of reversions to one 
or the other of the parent species. The possibility presents itself 
then, that this reversion may be due to the persistence of the 
chromatin of only one species in one or both of the germ cells. 
Carrying the conception still further, the other variations in the 
offspring of hybrids may be due, perhaps, to the varying propor- 
tions of the chromatin of each species in the mature germ cells.” 
And, finally, Metcalf * has studied the spermatogenesis of 
hybrid Gladiolus. He finds a condition analogous to the two- 
spindle nuclei of hybrid pigeons in all of the pollen-mother-cells 
of the hybrid, and he also concludes from this that the two groups 
of chromosomes represent maternal and paternal derivatives re- 
spectively. It is not stated whether the hybrid is a fertile one. 
In addition to the cytological studies as above outlined, some 
work on the structure of hybrids has also been done. This may 
be summarized in the following paragraphs. 
Macfarlane { conducted an extensive series of investigations on 
the minute anatomy of several hybrids, his main result being that 
all of the hybrids which he studied were intermediate in structure, 
* Metcalf, Certain Problems Relating to the Individuality of Chromosomes. Proc. 
Neb. Acad, Sci. 7: 109. N Igo1 (read before the Academy, N 1900). 
+ Metcalf in a private letter assures me that the hybrid G/adio/us is fertile. 
{ Macfarlane, The Microscopic Structure of Hybrids. Gard, Chron. III. 7: 543. 
1890; A Comparison of the minute Structure of Plant Hybrids with that of their Parents, 
and its bearing on biological problems. Trans. Roy. Soc. Edinb. 371: 203. 18923 
Observations on Pitchered Insectivorous Plants. Ann. Bot. 7: 445. 1893; Observa- 
tions on some Hybrids between Drosera filiformis and D. intermedia. Contr. Bot. Lab. 
Univ. Penn. 2: 87. 1898. 
