9 o PLANT-BREEDING 



now in a period of stability, as is the case with the larger 

 number of our wild species. 



Summing up the main features of f his short description 

 of the method of selection developed by Nilsson and his staff 

 at the Swedish agricultural experiment station, we may point 

 out the following propositions: Ordinary varieties of cereals 

 are built up of hundreds of elementary forms which, with few 

 exceptions, have hitherto escaped observation. They may 

 be distinguished in the fields by distinct marks derived from 

 their botanical characters, and will afterward prove to possess 

 corresponding differences in their industrial qualities. They 

 have to be selected but once and afterward will be quite uni- 

 form and constant, with the exception of accidental hybrids 

 which, however, will also yield constant andjDure races after 

 repeated selection. The purity of the races is such as to be 

 practically absolute, but this does not exclude the occurrence 

 of stray mutations by which new and valuable improvements 

 may be secured. The high variability which is commonly 

 attributed to our ordinary varieties of cereals consists only in 

 the differences among these constituents of the mixtures. 

 But these differences have been found to be so great as to 

 afford material for all desirable selections and to yield new 

 races for all the climates and soils of Sweden, for all the di- 

 vergent needs and demands of its various industries and even, 

 to a large extent, for exportation into other countries. 



D. A CRITICISM OF THE PRINCIPLE OF CONTINUOUS 

 SELECTION. 



In the biological sciences the name of Darwin is chiefly 

 attached to two great principles, the theory of descent and the 

 hypothesis of natural selection. 



The theory of descent was founded by Lamarck, but 

 it owes its present form to the work of Darwin. -By means 

 of immeasurable groups of facts, brought together from the 



