30 
FOURTEENTH REPORT. 
ing it forward with great persistence and success. It remained for 
Dr. Hjalman Nilsson, head of the Swedish Experiment Station at 
Svalof, to rediscover the method of Sheriff and Le Contour, realize its 
scientific importance and place it on a firm, practical basis. This method, 
established at his station since 1893, has placed him at the head of grain 
breeders and made Svalof the model for experiment stations the world 
over. We thus have agricultural practice in accord with biological 
theory. 
The method of isolation of a single plant is probably of wide appli- 
cation. Many species of plants both wild and cultivated are now known 
to be made up of a number of subspecies freely crossed among 
themselves. These elementary species or biotypes are of very great 
significance. They breed true and in self- fertilizing plants can be isolated 
as pure lines when their real nature is shown. Once the pure line is 
established we have a very definite unit which holds its characters from 
generation to generation, and defies all powers of selection, for the 
iluctuating variations exhibited by individuals of the biotype are not 
inherited. Thus we have revived the fixity, not of species, but of bio- 
types, or rather of the genes which give its character to the biotype. 
What have the plant breeders been doing? Brilliant as is their suc- 
cess it has been founded on a misunderstanding of the facts. The basis 
of artificial and also of natural selection was the variations which all 
individuals of a species showed, and which were supposed to be trans- 
mitted from parent to offspring. The only subject of dispute was 
whether characters acquired during life were inherited, a question which 
seemingly must be answered in the negative. Now it seems that this 
variation is a mingling of two contrasting kinds, the fluctuations, which 
arc not inherited, and the changed unit-characters forming mutations 
or new biotypes and that pass, not from, but rather thru generation 
to generation unaltered. A species may, therefore, consist of a large 
number of biotypes, promiscuously crossed and their dividing lines 
further blurred by fluctuating variation. The selector instead of chang- 
ing the position of a norm has really been sifting out fixed biotypes 
and been changing the average numbers of the constituents. 
The breeder does not always desire to produce a pure line, even if 
he could. It is probable the particular combination of characters that 
make his ideal is only to be found in a “blend” or “cross,” as he would 
term a heterozygous genotypic constitution. Here also comes in the 
well known fact that crosses often exhibit a greater vigor and better 
growth than either of the parents. It is certain that the best results 
in some instances, as with corn, can only be attained by the maintenance 
of heterozygous forms and this presents a problem to the breeder of 
great complexity, as under these circumstances simple selection would 
tend to make the strain “run out” as we say, and so defeat its own 
ends. The history of corn breeding is worthy of a detailed notice im- 
possible to give here. The success of the old continuous selection method 
as exemplified by the Illinois work already alluded to, the improved 
ear-to-row centgener method, the recent fine work of East and Shull 
designed to identify the genotypes and then maintain a heterozygous 
strain, all this shows the growth of the scientific method and the triumph- 
ant application of biologic theory to matters of our common life. And 
let us note with pride that the earliest work done in corn improvement 
