LUTHER BURBANK 



For example, our first cross, say in the case 

 of a prune, may be made between two varieties 

 that both show a fair quality of fruit. Careful 

 attention to the result will guide us in the 

 matter of the next experimental crossing. We 

 soon discover which qualities are prepotent, and 

 which tend to remain latent, and by selecting only 

 individuals that show a tendency to vary in the 

 desired direction, we introduce an element of 

 direction into the experiment. 



I am accustomed to speak of this as "momen- 

 tum of variation." We do not always know why 

 a certain plant tends to vary in a given direction, 

 but we may observe the fact, and the wise experi- 

 menter is always on the lookout for this tendency, 

 and ready to avail himself of the advantages it 

 offers. Technical workers sometimes give the 

 name "orthogenesis" to this tendency to vary in 

 a certain direction, which I speak of as the plant's 

 "momentum." 



Whatever aid we may gain in this way, how- 

 ever, the manner of our advance is often devious. 



In fact, it is very likely to be somewhat 

 comparable to the progress of a sailing ship which 

 tacks this way and that, and which at times may 

 seem to be progressing in the wrong direction, yet 

 which in the end forges ahead. 



Take by way of illustration the case of our 



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