262 
Journal of Agricultural Research 
Vol. XXVIII, No. 3 
returned from a trip and find that the delphinium all the way from Ridgefield, 
Conn, out to Chicago, Ill., is badly affected by the ‘black disease.' ” A delphi¬ 
nium grower and breeder in California reported in 1923 that the “Black disease” 
which gives so much trouble in the East had not as yet appeared or seemed not 
to be known on the West Coast. 
Leaves from Castine, Me., received early in July, 1922, were 23 cm. across 
and came from plants 3 meters high. They were thickly covered with the 
largest spots observed, i. e., 1 to 2 cm. in diameter (PI. 1, B). Probably the cool, 
moist climate in this location which was a large factor in the vigor of these plants 
also increased the virulence of the disease. On less vigorous plants the spots 
are usually smaller (PI. 1, A). No specimens have been received from farther 
south than Pennsylvania, and inoculations in Washington, D. C., where the cli¬ 
mate does not favor this plant, while giving numerous typical infections, have 
never produced spots more than a few mm. wide (PI. 1, C). During the heated 
summer term it has been found impossible to produce artificial infections in 
Washington, D. C., except in the event of a cool, rainy spell. 
APPEARANCE OF DISEASED PLANTS 
The leafspots are very striking in appearance. On the upper surface they 
form tarry black areas of irregular shape and size that may reach a diameter of 
2 cm. on large vigorous leaves (PI. 1, B). On the lower surface they are brown 
and the smaller ones do not yet show through to the upper side. Old spots lack 
the water-soaked edges that so frequently accompany other bacterial spots, al¬ 
though in very young stages water-soaking is present and is the first indication 
of infection observable under a hand lens. Although the lower surface of spots 
may appear sunken, the upper surface usually appears to be raised slightly and, 
in many spots, there is a tendency to concentric rings strongly suggesting fungus 
infection (PI. 2, D and E). Such spots were repeatedly sectioned to make 
sure that no mistake was being made, but in every case bacteria oozed out in 
v|ist quantities, while no fungus was observed and cultures of Bacterium del - 
phinii were obtained when poured plates were made. Spots resulting from pure 
culture inoculations also often showed this zoning, which has since been noted 
in bacterial spots on other plants, notably tobacco. 
Spots may occur .on any part of the leaf blade, the result of stomatal infec¬ 
tion, and are also common on the leaf tips where they make their entrance 
through the large water-pores (PI. 2, A, B, and C). When infection takes place 
on young leaves, and especially in the deep sinuses, distortion usually results 
from the failure of the diseased areas to keep pace with the growing healthy 
tissue. Flower buds are also occasionally attacked, becoming black-spotted and 
distorted, but this should not be confused with the common distortion of buds 
and young leaves caused by mite infestation where a blackening of the very 
young tissues often occurs in severe cases. This is a continuous blackening in¬ 
stead of a spotting and no bacteria are present. The bacterial spot occurs also 
on petioles and stems. In later stages of the disease the spots may coalesce, 
forming large black areas, involving in some cases almost the entire blade of the 
leaf. 
HISTOLOGY OF DISEASED LEAVES 
The bacteria enter the leaf through the stomata of the lower epidermis or 
through the water pores at the tips of the serratures. As the spongy parenchyma 
just beneath this epidermis is very loose, it is difficult to demonstrate stomatal 
infection in its earliest stages, since the baeteria scatter so readily on entering. 
Also, unless sections are made early enough the infection spreads so rapidly as 
