Plant-breeding; comments on the experiments of Nilsson and Burbank . result. The German breeders assumed,as a rule, that they produced their races at will and by aprocess of slow variability and repeated selection. It ismainly upon this conviction that Darwin has based his con-ception of an analogous slow improvement of species innature. This (ierman method has, however, been STib-mitted to a severe criticism by Dr. Xilsson, the director ofthe Swedish agricultural experiment station at pedigree-cultures have shown that the idea of a slowaccumulation of characters by repeated selecti
Plant-breeding; comments on the experiments of Nilsson and Burbank . result. The German breeders assumed,as a rule, that they produced their races at will and by aprocess of slow variability and repeated selection. It ismainly upon this conviction that Darwin has based his con-ception of an analogous slow improvement of species innature. This (ierman method has, however, been STib-mitted to a severe criticism by Dr. Xilsson, the director ofthe Swedish agricultural experiment station at pedigree-cultures have shown that the idea of a slowaccumulation of characters by repeated selection is due toincorrect observations and to the use of untrustv/orthvmethods. According to his experiments, changes occur inagricultural plants as suddenly as in horticultural species;there is no essential difference between them in this these discoveries the main support of the theory of slowand gradual evolution is broken down, and the analogvbetween artificial and natural production of species comesto plead wholly for the theory of mutation. These new. i6 PLANT-BREEDING facts will be dealt with in our next chapter, and it may besufhcient, here, merely to have indicated them. The principle of mutation is conducive to the assump-tion of distinct units in the characters of plants and as chemistry has reached its present high develop-ment chiellv through the assumption of atoms and mole-cules as definite units, the ([ualities of which would be meas-urable and could be expressed in figures, in the same waysystematic botany and the allied comparative studies arein need of a basis for measurement and calculations. Thedetermination of the degree of affinity now largely de])endsupon vague estimates and personal views; while, on thebasis of the theory of mutations, the relationship is meas-ured by the numlx-r of the mutations which have made theforms under consideration different from their commonancestors. The mutations themselves have evidently oc-curred in ])r
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