602 
Journal of Agricultural Research 
Vol. XI, No. it 
heterozygous. Then, a certain amount of segregation would be expected 
when the plants are subjected to these conditions. Segregation would 
likewise be expected to take place in the first-generation offspring from 
crosses of these plants with plants of the susceptible strain, provided 
the plants are grown in the abnormal environment. Differences of the 
individual plants of the susceptible strain with regard to the resistant 
character might account for considerable variation in the amount of 
segregation in the first generation from such crosses. A difference of 
this kind has been the basis for the selection of resistant strains. It is 
possible that some of these plants have one or more of the factors for 
resistance, which may be either homozygous or heterozygous, but do 
not have a sufficient number of them to cause the plant to resist where 
the disease develops normally. In crossing susceptible plants of this 
kind with plants of the resistant strain various factor combinations 
would be obtained, some of which would produce resistance in the first 
generation under the severe conditions while others would not. Results 
obtained in these experiments could easily be correlated with a theory 
of this kind. 
The perfecting of methods rather than the development of any defi¬ 
nite proof of laws governing the inheritance of wilt resistance in flax 
has been the main accomplishment in this work. Therefore a few help¬ 
ful suggestions might be offered by way of conclusion of this chapter. 
(i) The resistant plant should be tested under severe disease con¬ 
ditions before making the cross. (2) Reciprocal crosses should be 
made in each case, and selfed seed should be obtained from both parent 
plants, this to be planted along with the crossed seed. (3) First-gen¬ 
eration plants should be grown in disease-free soil to obtain seed for a 
second generation. (4) First and second-generation plants which are 
to be tested should be grown under similar conditions with selfed seed 
from the parents planted as controls. (5) The experiments should be 
conducted under uniform environmental conditions in order to obtain 
conclusive results. 
CONCLUSIONS 
(1) The flax plant is most suitable for a study of the nature and in¬ 
heritance of wilt resistance, since it grows very well in the greenhouse, 
has a short growing season, is easily crossed, resistant and susceptible 
strains are available, and conditions for infection can be produced 
with certainty. 
(2) Fusarium lini penetrates the flax plant through root hairs, young 
epidermal cells, stomata of seedlings, and perhaps through wounds. 
(3) Fusarium conglutinans is able to penetrate the root hairs of 
young cabbage seedlings when the seedlings are grown in tube cultures. 
(4) F. lini invades the various tissues of the susceptible flax plant 
causing the disease known as flaxwilt. No considerable clogging of 
