FOUNDERS OF PEANT BREEDING 
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hundreds or thousands of years, but by sudden leaps and bounds. 
The work of Devries is a most important contribution to the 
study of the origin of species, and is indicative of the fact that 
many factors must be taken into consideration when one attempts 
to analyze the process of organic evolution. One great value of 
his work is that it is based on experiments and that it has given 
a great stimulus to experimental studies. 
NILSSON’S DISCOVERY OF THE ELEMENTARY SPECIES OF 
AGRICULTURAL PLANTS (1890) 
During the last twenty years, experiments in the breeding of 
cereals and other agricultural crops have been conducted on an 
unusually large scale at the Swedish Experiment Station of Svalof 
under the leadership of Dr. Hjalmar Nilsson, Director of the 
Station. Nilsson’s principle for all breeding purposes is to derive 
his strains from single mother plants. Only such strains give 
pure breeds. A second discovery made at Svalof, and equally 
valuable for practice and for science was that of the almost as- 
tonishing richness in elementary species among our agricultural 
crops. Every cultivated species seems to embrace something like 
a hundred of them, and the cereals were found to include even 
several hundred in each of the older species. By carful 
search of the field in almost every case a plant may be found 
which complies with the ideal sought for. From, such a plant a 
pure and constant one may be derived without other means than 
that of isolating and multiplying its progeny. On the basis of 
these facts, Nilsson has founded an elaborate method of selecting 
original plants for his pedigree-cultures and of comparing their 
value for practical purposes. Meanwhile, variation was being 
studied from a new point of view, which we may call biometry. 
Francis Galton (1889) was the founder of biometry but its full 
development has been due chiefly to the valuable work of Karl 
Pearson. The underlying idea in biometry is to apply to the 
study of evolution the precise quantitative method followed in the 
study of physics and chemistry with such signal success. 
Biometry is the statistical study of variation and heredity. 
Biometry is best adapted to deal with continuous variations. Its 
ideal, to make biological investigation more accurate and compre- 
hensive, is wholly commendable. 
JOHANNSEN’S CONCEPTION OF HEREDITY 
The conception that inheritance, as previously noted, is not the 
transmission of external characters from parent to offspring, but 
