ON CROSSES WITH DISSIMILAR HEREDITY. 
249 
ON CROSSES WITH DISSIMILAR HEREDITY. 
By Professor Hugo de Vries. 
[Translated by permission from the Report of the Deutsche Botanische 
Gesellschaft. 1900. Vol. XVIII.] 
(Preliminary Communication.) 
In the previous paper upon the Law of Separation of Characters in 
Crosses,* I have shown that this law, which Mendel had deduced from 
his investigations with regard to Peas, is very generally applicable in the 
vegetable kingdom, and of especial significance in connection with the 
theory of cross-fertilisation. The important and extensive researches of 
Correns, Tschermak, Webber,t and others, which have been subsequently 
published, have confirmed, on the one hand, the correctness of Mendel's 
deductions, and, on the other, the justification of this general application. 
Mendel demonstrated by his crossings of Peas that the results could 
be simply deduced from certain principles. In the first place he found 
that in the vegetative development of the cross-progeny one of each pair 
of characters is dominant and the other recessive. At the formation 
of the sexual organs, however, the two associated antagonistic characters 
in the cross separate from each other in such a way that as regards each 
individual pair of characters the ovules and pollen grains no longer partake 
of the nature of a cross. This separation occurs in equal parts, so that 
50 per cent, of the sexual cells contain the one character of each pair 
and 50 per cent, the other. With respect to this separation, the two 
antagonistic characters are of equal value, independently of the question 
whether they, in the vegetative stage, are dominant or recessive. 
Such an equivalence is, however, by no means essential. The cha- 
racters may, in other cases, become of unequal value at the separation. 
They will then either not separate at all, or in their separation follow 
other rules. Such a case of non-separating crosses Mendel found in 
Hieracium ; these follow other rules than the Peas in so far that the cross 
progeny of the first generation are dissimilar.? The rule of prevalence 
{Prdvalenzregel), as Correns calls the dominance, is here a different one. 
Mendel, however, had not the opportunity to extend his researches further, 
and he therefore did not discover whether one of these two types — 
Hieracium or Peas — would have a more general application in the vege- 
table kingdom. It is for this reason that his results were regarded, until 
recently, as isolated cases without an important principle being involved 
therein, and they consequently lapsed into oblivion. 
Much later, in the year 1894, Millardet discovered, in his pioneer 
* Compare also " Sur la Loi de Disjonction des Hybrides," Comptes Bendus de 
VAcadimie des Sciences, Paris, March 26, 1900. 
f Compare the collection of literature on this subject made by Correns in the 
Botanische Zeitung, Aug. 1, 1900, No. 15, pp. 229-238. Also C. Correns, " Ueber 
Levkoyenbastarde," Botan. Centralblatt, vol. Ixxxiv., 1900 ; and Herbert J. Webber, 
"Xenia, or the Immediate Effects of Pollen in Maize," U.S.A. Department of 
Agriculture, Bull No. 22, 1900. 
X G. Mendel, " Ueber einige aus kilnstlicher Befruchtung gewonnene Hieracium - 
Bastarde," Trans. Naturf.-Verein Briinn, vol. viii. part 1, 1869, pp. 26-31. 
