A Stem Blight oe Field and Garden Peas 
19 
chloride, i-iooo, after which a section to be plated was removed 
with a sterile scalpel. It was next transferred to alcoholic mercuric 
chloride (i-iooo) for 15 seconds, then washed in three changes of 
sterile, distilled water. From the distilled water it was transferred 
to a tube of nutrient broth where it was crushed, and dilution 
plates were made from the suspension thus obtained. 
The second set of plates was made directly from the watery 
petiole without any previous sterilization. 
Pure cultures of the original organism were obtained from 
both sets of plates in the second and third dilutions; the colonies in 
the first dilution were sO' numerous, that it was impossible to tell 
anything about their purity. 
Three colonies were picked up from the first set of plates and 
six from the second, making nine pure cultures in all, of presum¬ 
ably the same organism. 
On December 17, these were all inoculated into pea plants, as 
described before on page 13 with positive results. 
DESCRIPTION OF THE CAUSAL ORGANISM 
I 
Pseudomonas pisi, n. sp. 
History .—The microorganism herein described as the cause of 
a bacterial stem blight of field and garden peas, and to which the 
writer has given the name Pseudomonas pisi, n. sp., was isolated 
June 4, 1915, from the watery portion of a diseased leaf blade. It 
was grown upon +10 nutrient agar until November 25, 1915, when 
it was inoculated into a pea plant, where it produced all of the symp¬ 
toms characteristic of the disease. On December 7, 1915, a reisola¬ 
tion of the organism was accomplished, and after replating to in¬ 
sure purity, it was again inoculated into peas on December 17, 1915, 
January 6, 1916, February 19, 1916, March 9, 1916, and March 
23, 1916. In every case, positive results have been obtained. The 
culture which has been used in the following species description 
came from the same stock as that used in the plant inoculations of 
December 17. 
I. MORPHOLOGY 
I. vegetative cells. —As the organism occurs both on cul¬ 
ture media and in the plant, it is a short rod with rounded ends, 
mostly single and in pairs (Plate I, Fig. i), but occasionally in 
fours and 'sixes; filaments have been obtained from very young 
agar cultures 10 to 97 in length. (Plate I, Fig. 2.) The indi¬ 
vidual rods nleasure i.ii to 3.28 long and .58 to .82 /x wide. 
The length of the majority is 2.26 and the width, .68 ft. 
