634 
Journal of Agricultural Research 
Vol. XXXI, No. 7 
on each disk. It soon became evident that the number of seedlings 
surviving the salt solution increased somewhat in proportion to the 
length of the radicles. In the effort to determine the limit of age or 
size influence on resistance, tests were made with seedlings which 
had been allowed to develop primary roots 100 to 125 mm. long 
before subjecting them to the solutions. After finding increased 
resistance, even at this advanced stage, it became necessary to resort 
to some other method of classification according to size in order to 
work with still older seedlings, since at this stage many secondary sem¬ 
inal roots had developed and difficulty was encountered in handling 
and measuring the roots. It was found that the stage of development 
of the plumule afforded a very satisfactory means of classing the 
seedlings at this age, and no measurements were necessary. After 
May 22 all classification was based on the plumule development, and 
the radicle length was disregarded. 
In the preparation of the seedlings for testing in groups according 
to stage of plumule development, they were sorted ana transferred 
to culture pans containing tap water as soon as the radicles of the 
youngest group were of sufficient length to balance the seeds well on 
the perforated disks. It was usually possible at this time to sort 
fairly accurately; however, when the desired stage of development 
was reached they were again classified according to the extent of 
plumule development and then placed in a salt solution of the desired 
concentration. 
During a greater part of the investigation the seedlings were 
allowed to remain in the salt solution for 72 hours, but it became 
evident when working with seedlings in the plumule stage, and espe¬ 
cially during warm weather, that this period frequently was too short 
to bring to the death point more than 50 per cent of the individuals, 
even in the high concentrations used, ana the period was increased 
to 96 hours. 
After subjecting the seedlings to the solutions for the 96-hour 
period, the number of individuals which apparently had survived in 
each pan was recorded and the live plants were transferred in groups 
to other pans containing tap water. Another count was made 72 
hours later, and plants which had failed to resume growth of roots 
or plumule in the water were classed as dead. The extent of the 
green coloring in the basal portion of the coleoptyle afforded an easy 
means of distinguishing those seedlings which were likely to over¬ 
come their injuries when removed to tap water, and it was seldom 
that more than 4 or 5 per cent of seedlings of the first selection were 
later eliminated. 
After working with varied concentrations for several months the 
writers became convinced that the stage of growth of the seedlings 
was a greater factor in determining the toxic limits of the plants than 
small differences in the amount of salt in solution. It was therefore 
decided to investigate this phase of the problem, and a concentration 
of 22,000 parts per million of sodium chloride was adopted as a 
standard for further study. 
In view of the methods employed in this experiment it isobvious 
that the results are not comparable with those obtained bymost of 
the previous investigators, some of whom have sought to fix the 
maximum tolerance or toxic limits of various plants for alkali salts. 
In previous investigations effort apparently has been made to deter- 
