168 THE’ ORCHID REVIEW. [Nov.-DEc., 1919. 
supposed to unite with a corresponding unit from the reproductive cell of 
the other parent on fertilisation. Mendel denoted these supposed units by 
the letters of the alphabet. The results of the union is not identical in all 
cases. Sometimes an intermediate condition results—as, indeed, would be 
expected—but in the case of peas, one unit seems to overpower the other, 
hence it is termed dominant, and denoted by a capital letter (say A), while 
the one that is eclipsed is called recessive, and denoted by the corresponding 
small letter (a). Additional units would be denoted, B b, Cc, &c. 
As to the number of alternating characters present in each reproductive 
cell, the answer is that it depends entirely on circumstances. A cross 
between two closely allied species would show a small number of such 
characters, while in a wide cross they would be far more numerous, the 
reason being that in the former case more of the characters are identical, 
and thus fail to alternate. Mendel himself remarked of the reproductive 
cells, ‘In the formation of these cells all existing elements participate in 
an entirely free and equal arrangement, by which it is only the differentiating 
ones which mutually separate themselves. In this way the production 
would be rendered possible of as many egg and pollen cells as there are 
combinations possible among the formative elements.” Everything 
depends upon the antiquity of the character, a matter, so far as we can see, 
unaccounted for in the Mendelian philosophy. To give anexample, a cross 
between two green-leaved Cypripediums would give a green-leaved hybrid, 
greenness in this case being homozygous. But now cross one of the same 
green-leaved species.with one of the set having tessellated leaves, and the 
hybrid is at once heterozygous for the same ‘character. The tessellated- 
leaved character is an adaptation of some antiquity, for the group has now 
broken up into quite a number of distinct species. Such illustrations could 
be given ad infinitum. 3 
The same example illustrates one particularly weak point in the 
Mendelian philosophy. Neither greenness nor tessellation are dominant, 
in fact dominance is quite an exceptional character among hybrids 
generally, and it shows how unfortunate it was that Mendel should have 
selected such an exceptional group on which to found a theory of heredity, 
a fact which he himself realised when he came to compare his results with 
those obtained by Gartner, | Wichura, and others, in numerous different 
groups of plants. Mendelism is aterm for what Mendel is supposed to 
have discovered. Mendel made experiments, discovered certain phenomena 
of hybridisation that were already known, and based upon them an 
elaborate mathematical theory, which is only applicable to an exceptional 
class of results. His discovery might better be defined as “ Incompatibility.” 
Ae ee = 
