PLANT-BREEDING METHODS 425 
The Svalof System.—At the Swedish Institute for the Improvement of 
Field Crops, Nilsson has worked out a very complete and efficient system 
of plant breeding. Gradually, as increased appropriations of funds have 
permitted expansion, a corps of experts has been employed, each in- 
vestigator concentrating on one or two species, and thereby training 
himself to distinguish all the different forms so as to judge of the relative 
value of different combinations of characters. Furthermore a definite 
course of procedure has been developed as a result of many years of 
experience during which time marked success has been achieved in the 
inprovement of Swedish field crops. To begin with the work consisted 
mainly of variety testing and extensive effort at improvement through 
mass selection. These methods still find a place in the routine work, but 
they are of insignificant value as compared with the codrdination of 
intensive methods which makes the Institute’s system a model which 
institutions engaged in similar work may profitably follow. From 
Nilsson’s description we find that the Svaléf system may be briefly out- 
lined under three heads, viz., genotype selection, strain tests and hybridiza- 
tion. In all this work the methods of pedigree culture are followed so 
that the original source and performance record of each form grown at 
the station or distributed for trial can be accurately stated. Genotype 
selection in all plants except the self-sterile species is accomplished by 
the pedigree method of testing the progeny of single individuals. In 
wheat, barley, oats, peas and vetches, which were the first crops chosen 
for improvement at Svaléf, this means of course the isolation of pure 
lines from the beginning, and the more recent work with rye, clover, 
forage grasses, beets, etc., has determined that allogamous species are 
composed of biotypes which are analogous to the pure lines of autogamous 
species and which can be segregated from one another by continued 
inbreeding, exactly as inbreeding in maize has been found to isolate 
biotypes. Although inbreeding must be continued for several years 
before these biotypes or strains acquire a satisfactory degree of purity 
and stability, yet it has been shown already according to Nilsson that 
this method can be used to bring about the same practical results as have 
been secured in wheat and other autogamous plants. In connection 
with this preliminary selection of promising forms the intensive study of 
the specialists at Svaléf has made each member skilful in detecting 
different forms in the species with which he is working and in judging 
the relative value of the characters displayed. Having separated from 
the population some of the biotypes of which the “variety” is composed, 
it next becomes necessary to subject all these strains to comparative 
tests in order that the few superior forms may be discovered and pro- 
pagated more extensively. This requires long years of careful work and 
the overcoming of certain difficulties which will be discussed later. The 
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