28 The: Colorado Experiment Station 
plants inoculated with pure cultures of Ps. medicaginis, n. sp.; 
second, that cultures of this organism produce identically the same 
symptoms irrespective of their origin, i. e., whether they were ori¬ 
ginally isolated from stem, leaf or exudate; third, that it has been 
possible to produce the disease by introducing the germs through 
needle pricks and by smearing them upon scarified areas, as well 
as by spreading them upon the unbroken epidermis; however, in¬ 
oculations by the last method develop more slowly and are not as 
typical of field lesions; fourth, that after cultivation upon nutrient 
agar for five months, Ps. medicaginis, n. sp. seems to have re¬ 
tained its initial virulence practically undiminished; fifth, that 
neither of the other two cultures which have been found associated 
with the trouble are able to produce the disease; sixth, that the in¬ 
fection is not communicated to the plants through the roots. 
FIELD EXPERIMENTS. 
Inasmuch as the disease seems to be directly tracable to soil 
infection, and consequently may be considered a soil trouble, the 
only practical method of controling it is by the introduction of 
resistant varieties. To this end we have planted twenty-six varie¬ 
ties of alfalfa on sick land with the hope of obtaining one or more 
blight resistant strains. The seed for this work was procured from 
the United States Department of Agriculture through Mr. W. T. 
Brand, and planted April 16 and 17, 1907. The ground upon which 
the plats are located is owned by Hon. J. L. Chatfield, and had been 
in alfalfa a number of years, was plowed in the spring of 1905 and 
planted to oats and potatoes; in 1906 again planted to oats and 
produced 100 bushels per acre. The rows of the plot are about fif¬ 
teen rods long and run from east to west. Two rows of each 
variety were planted through the plot, then the series was repeated 
in the same order but only one row of a kind was used. The variety 
designated as Gypsum No. 1 was grown from cuttings which were 
taken from land that had been in alfalfa, and was plowed up be¬ 
cause of the prevalence of the disease, and planted in oats. These 
plants were very vigorous at the time the cuttings were made. This 
part of the work was begun by Professor Paddock over two years 
ago. 
The following is a list of the varieties which we have used in 
our field tests. 
No. 9451, Sairam. 
No. 1 127 5, first quality commercial. 
No. 12398, from Colorado. 
No. 1 2409, Utah, non-irrigated. 
No. 12671, from Kansas. 
No. 1 2702, from Sherman, Texas. 
No. 1 2747, from Billings, Mont. 
No. 1 2748, from Germany. 
No. 12784, Utah, irrigated. 
