LUTHER BURBANK 
they are JJ; for shipping qualities they are SS; 
for resistance to disease RR; for hardiness HH; 
and for productivity PP. That is to say, they are 
pure dominants for each of these qualities. 
Their germ plasm requires only an infusion of 
the dominant factor for bigness and their progeny 
will prove that breeding does tell. 
There is a tradition that passes current among 
dog breeders which I do not vouch for but which 
suggests a condition so comparable to that of our 
cherry that I cite it by way of illustration. It is 
said that the greyhound had been bred so exclu- 
sively for speed that it developed all the desired 
speed qualities of a hunting dog, able to overtake 
any quarry, but lacked the courage to seize the 
quarry once it had been overhauled. To over- 
come this defect, so the story goes, some one 
crossed the greyhound with the bulldog, thus 
breeding in a strain of courage; and in subsequent 
generations eliminated all the bulldog traits ex- 
cept courage by selective breeding; and so gave 
us a race of greyhounds in which the one missing 
quality had been supplied. 
This greyhound legend seems much more 
plausible to-day, now that attention has been so 
generally called to the segregation of unit charac- 
ters, than it formerly seemed. But whatever its 
truth, the case of the hypothetical greyhound 
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