PRACTICAL ASPECTS IN IIKKEDITY. o ■ 



many years, if the investigations go on at the present rate, before the breeder 

 will be in a position not so very different from that in which the chemist is : — 

 when he will be able to do what he wants to do, instead of merely what 

 happens to turn up. Hitherto I think it is not too much to say that the 

 results of hybridization had given a hopeless entanglement of contradictory 

 results. We did not know what to expect. We crossed two things ; we 

 saw the incomprehensible diversity that comes in the second generation; we 

 did not know how to reason about it, how to appreciate it, or what it meant. 

 We got contradictory results, and the thing looked hopeless. But with the 

 discovery of the purity of the germ cells we have the first step, which, I think, 

 is bound in a very short time to become a path through many of those won- 

 derful mazes of heredity. 



To the practical man, I take it, the importance of this discovery comes 

 in, first, somewhat as follows : Seeing that the gametes are pure with respect 

 to their characters, it follows that an individual which is produced as the 

 offspring of a cross will be composed, in respect to any one pair of these 

 characters, either of two similar gametes or of two dissimilar gametes. Take 

 the case of the pea. Any one pea descended from an original cross between 

 yellow and green will either be composed of two similar green gametes, or of 

 two similar yellow gametes, or of a yellow and a green. Now, as it happens 

 in the case of the pea, and in a great number of other cases, unfortunately for 

 the breeder, there is no means of distinguishing outwardly by any test that we 

 can apply whether the organism is a hybrid or pure to the dominant character. 

 There is no way of distinguishing in the cases where yellow meets green 

 whether the organism is a hybrid that is composed of yellow and green, or 

 whether it is pure to the yellow character and is composed of two yellow 

 gametes. There is no possibility of distinguishing, because the yellow is, as 

 Mendel calls it, dominant, and the green is hidden, or, as he calls it, recessive. 

 We have, therefore, in such a case as that, two classes of organisms, pure and 

 hybrid, each showing the dominant character, and it is owing to the fact that 

 the pure dominant cannot be distinguished from the dominant hybrid con- 

 taining both dominant and recessive characters that an immense number of 

 the contradictions which the practical breeder experiences have come about. 

 For example, a breeder or seedsman introduces some strain of a new variety 

 of his seed — peas, or whatever it may be. He finds a number of rogues which 

 are not true to the character which he desires to put on the market — rogues 

 which he is unable to eliminate. Formerly we said it was only a question of 

 lime; he must hoe out the rogues and go on, and he will gradually fix his 

 type. But now we begin to see what the facts really mean. He hoes out the 

 rogues, and again they come — in diminishing number, no doubt, but they 

 are still there. We now suspect the nature of such rogues in a considerable 

 number of examples. For example, the bearded wheats occurring among 

 wheats which are intended to be beardless. Every year they grow, and every 

 year the seedsman hoes them out, and again they come back. Those bearded 

 wheats may come from the fact that the beardless wheats had a bearded 

 ancestor, and some of them contain bearded germs. If you cross a bearded 

 wheat with a beardless wheat, the first cross will be a beardless wheat. You 

 allow it to fertilize itself, and you sow your crop; you begin to get beards and 



