640 PRACTICAL PROBLEMS 



4. The greater likelihood of mutations arising from mere 

 point of numbers, if from no other cause, and the greater ease 

 with which these may be detected if they do arise. 



5. The greater chance of preserving mutations, owing to 

 rapid powers of reproduction. 



6. The possibility of reproducing asexually by budding, cut- 

 ting, etc., which overcomes to a large extent the disasters of 

 sterility and avoids the operation of Mendel's law in the propa- 

 gation of hybrids. 



The plant breeder, therefore, not only enjoys superior advan- 

 tages in selection, but he is free to make full use of mutations 

 and the principle of crossing, two forms of improvement all but 

 closed to the animal breeder. Naturally, therefore, his operations 

 assume one of three well-defined forms or systems of breeding : 



1. " Straight selection," or breeding from the best, the pur- 

 pose being the improvement of existing varieties rather than the 

 production of new strains. 



2. Maintaining extensive plantings in the hope of detecting 

 spontaneous mutants, the object being the production of new 

 varieties. 



3. Crossing, or hybridizing, with the purpose of producing 

 new strains. 



New strains produced by either the second or the third method 

 are of course variable and capable of improvement by straight 

 selection. Each system of breeding requires its own methods, 

 suited to the material in hand and the character of the improve- 

 ment sought. Some species do best with one system, others 

 with another, and only experience can decide which is most 

 prolific of results in a particular case. The first, straight selec- 

 tion, is the safest, and is always certain of results ; but most 

 specie:: respond well to the second and the third, which, with 

 suitable material, are capable of the richest results known to all 

 breeding, and are the systems par excellence for the production 

 of new strains. 



Crossing has latterly fallen into some disrepute because of 

 the emphasis laid on Mendel's law, and the principle of mutation 

 is but recently recognized ; but the prediction is ventured that 

 the former w:ll be restored to favor in plant breeding, and that 



