398 F. M. Rolfs 



and after twelve days water-soaked spots appeared abundantly. The 

 inoculated tissue on the twigs assumed a water-soaked appearance in 

 most cases by the seventh day. The typical black-spot and black-tip 

 condition of the twig did not develop until after the twenty-fifth day. 

 Poured plate cultui'es from the young leaf spots and the black spots on 

 the twigs yielded colonies of the organism abundantly. Pure cultures 

 of the organism from the twigs of the four kinds of trees were grown 

 side by side on various culture media for six weeks, and in all cultural 

 characters the strains were the same. All check wounds on the twigs 

 soon healed, and the check leaves remained free from spots. 



In 1912, at Ithaca, cross inoculations with strains of the organism 

 from twigs of the four hosts were made on three-j^ears-old Alexander 

 apricot, Early Violet nectarine, Elberta peach, and Burbank plum trees 

 (Figs. 59, 65, and 66). One hundred leaves and from twelve to twenty 

 twigs were used in each case. The organism from young-slant Hiss- 

 glucose cultures was scraped into sterile water. The fingers were then 

 dipped into the water, and the material was applied to the lower surface 

 of the leaf by gently rubbing the leaf between thumb and fingers. Each 

 twig was inoculated at from three to five points with a hypodermic syringe 

 (Fig. 61). Spots on the leaves appeared in from five to seven days, 

 and water-soaked spots became numerous after the eighth day. The 

 inoculated tissue on the twigs took on a water-soaked appearance in about 

 seven days, but did not become dark brown until after the twenty-fifth 

 day. Both leaf and twig spots yielded the characteristic yellow colonies 

 on poured plate cultures. All check wounds on the twigs soon healed, 

 and the check leaves remained free from spots. 



Morphology 



Vegetative cells. — The organism is a rather short rod, with rounded ends. 

 It is found singly, in pairs, and, in liquid media, often in short chains. 

 Individuals from a forty-eight-hours-slant Hiss-glucose culture are from 

 0.8 to 0.9 /x in length and from 0.3 to 0.5 /x in width. Bacteria taken 

 directly from the twig cankers and stained with gentian violet measure 

 from 1.6 to 1.8 Ai in length and from 0.4 to 0.6 fx in width. 



Endospores. — No endospores have been observed. 



Flagella. — The organism is motile by means of one or several polar 

 flagella. Both Bitfield's and Moore's flagella stains were used with 



