Apr. 19,1924 
Bacterial Leafspot of Delphinium 
263 
to obscure any evidence of the point of entry. Material fixed 24 hours after 
spraying gave no sections suitable for photographic demonstration although the 
spots were water-soaked and scattered bacteria were found under the stomata 
in microtome sections. After 48 hours, however, very good sections were ob¬ 
tained showing bacteria in the intercellular spaces under the stomata chiefly 
lying on the cell walls, singly or in oval masses (PI. 3, A and B). At this stage 
the spot shows as a minute water-soaked point on the lower surface, to be seen 
only under a lens. In microtome sections the bacteria are confined to the loose 
parenchyma. Cells in the vicinity of the invaders often show on their walls what 
appear to be extrusions of cell sap. These are hemispherical bodies which stain 
very deeply (PI. 4, A). Later the palisade tissue is invaded and killed and the 
lesion penetrates to the upper surface as a black spot involving the whole thick¬ 
ness of the leaf. At this stage of infection the bacteria lie on the walls of the 
cells and crowd the intercellular spaces. 
ISOLATIONS 
Poured plates were made in this laboratory in 1903 from spotted leaves from 
New York and Massachusetts and again in 1907 from Massachusetts. In each 
case a white organism was obtained with which successful infections were 
secured on delphiniums. On account of the small amount of cultural work done 
at that time no adequate comparison can be made with isolations of 1920-1923. 
Descriptions and photographs of agar plate colonies agree with those of later 
date but in other cultural characters there is disagreement, not only between 
these early isolations and those of 1920-1923 but also among the several early 
isolations themselves, and it is apparent that some of the early cultural work 
was not fully checked up, since striking inoculations were obtained in 1903 
proceeding from subcultures of single poured-plate colonies of what was undoubt¬ 
edly this organism. 
Isolations have now been made from typical infected plants from all of the States 
mentioned under “ Geographical distribution/* All gave colonies apparently 
of the same white organism. Comparative cultures have shown these to be alike 
in all important points. 
In several cases where material was not in good fresh condition when received 
a yellow organism appeared on the plates in numbers about equaling the white 
colonies and, in one case, only a yellow organism was obtained although three 
separate platings were made from typical spots. This was of a saprophytic 
type frequently appearing on plates poured from many species of plants when 
not in perfectly frefch condition, and it failed to produce any infections when the 
inoculum was either sprayed or rubbed on the lower surface of delphinium leaves. 
INOCULATIONS 
Successful inoculations have been made in the hothouse and out of doors, on 
young and on mature plants, both in cages where moisture could be maintained and 
also without cover. Infections obtained on young plants in the hothouse never 
increased much in size (1 or 2 mm. wide) and few secondary infections were 
found. Reisolations were made from hothouse inoculations of 1920 and used 
for inoculations in the hothouse in 1921 and 1922 with similar results. Outdoor 
inoculations in the summer of 1921 failed, that is only a very few slow-growing 
infections were secured, probably because of the late start made and supervening 
dry, hot weather. 
On May 31, 1922, vigorous young seedling plants of hybrid delphiniums, which 
were set out of doors May 1 and were just beginning to send up blossom stalks, 
were sprayed with subcultures from an isolation of March 29, 1922, from a hot- 
88287— 24f-5 
