1 9 05.] 



Cross-fertilisation of Wheat. 



473 



changed. As far back as 1865 a monk named Gregor Mendel 

 had communicated to the Briinn Society the results of his work 

 on the laws of heredity. Very strangely, this work was lost 

 sight of till 1 90 1, when three observers, working independently 

 — De Vries,Correns, and Tschermak — simultaneously discovered 

 its great importance. So important is it now esteemed that 

 Mendel's laws are being applied to various investigations in 

 both the vegetable and animal worlds. Mendel himself made 

 many of his experiments on peas. 



Mendel pointed out that plants possess some definite charac- 

 teristics to each of which there is an opposite : a pair which may 

 be called a " duality." For instance, wheat may be either beardless 

 or bearded, red or white, the chaff may be felted (rough) or 

 glabrous (smooth). Each " duality " can be handled by the 

 breeder as an entity independent of other " dualities," and 

 capable of forming fresh combinations with other dualities, so 

 that a bearded red crossed on to a beardless white can, among 

 several forms, provide the breeder, if he wants it, with a beard- 

 less red. One characteristic of each duality is what is called 

 4 ' dominant," the other " recessive," and these are reproduced in 

 the progeny in definite ratios, each form occurring in the 

 progeny pure — not as a blend with its opposite. To illustrate 

 this, let us consider what happens as to beardedness or beard- 

 lessness when a bearded wheat is crossed on to a beardless one, 

 or a beardless one on to a bearded. In the first generation, 

 called for convenience F 1, every plant will come beardless ; 

 there will be none bearded, hence the term " dominant " as 

 applied to the member of each duality which comes uppermost 

 in the first generation. In the second generation (F 2) the 

 plants will come beardless and bearded in the ratio of three of 

 the dominant beardless to one of the " recessive " bearded. 

 The bearded forms are fixed as to their beardedness definitely, 

 and will breed true as to that characteristic indefinitely, but 

 the dominant will not. If a hundred plants raised from the 

 F 2 wheat be taken at hazard, we shall get from this third 

 generation (F 3) the twenty-five recessives which were definitely 

 fixed in the second generation, and we shall find that the 

 seventy-five dominants are sub-divided into twenty-five pure 

 dominants which are fixed definitely and will breed true and 



