32 A. L. PlERSTORFF 



ovaries to be healthy and the style to be invaded by bacteria. There 

 was a progressive killing of the tissues from the stigma to the ovary. 

 Styles not infected remained healthy until the ovaries were invaded. 

 Infected petals formed a V-shaped light brown area, with the apex 

 at the point of inoculation and the base at the margin of the petal. In 

 many cases the petal became infected but fell before the bacteria could 

 invade the receptacle. 



The results indicate that, under greenhouse conditions, infection of 

 pear and apple blossoms by the fire-blight organism can take place 

 through the petals without wounding the surface, and that infection 

 can result from inoculation of the stigmas. The same conclusion can 

 be drawn for the outdoor conditions, but the percentage of infection 

 resulting from inoculating either the petals or the stigmas is markedly 

 decreased as compared with cut twigs in the greenhouse. 



While the percentage of blighted blossoms was small in some of the 

 experiments, there is no question that infection can take place through 

 both the petals and the stigmas. Isolations were made from the ovaries 

 of the blighted blossoms and a virulent culture was obtained. However, 

 it is not likely that a high percentage of blossoms are inoculated through 

 either the stigmas or the petals under normal conditions. 



In order to determine what tissues are invaded most frequently by 

 the fire-blight bacteria, and to gain further knowledge of blossom 

 infection, apple blossoms were inoculated by atomizing with bouillon 

 culture, and at intervals of twenty-four hours the blossoms were fixed 

 in chrom-acetic acid fixer, embedded in paraffin, sectioned, and stained 

 with Fleming's triple stain. The blossoms were removed from the trees 

 just preceding the fixing. Cheesecloth bags inclosed the blossoms from 

 the time of the early pink stage. 



Progressive killing of the tissue twenty-four, seventy-two, and one 

 hundred and forty-four hours after inoculation is shown in Plate HI, 

 2, 3, and 4. The point most frequently attacked appears to be the 

 nectariferous region (Plate III, 6, A). Gossard and Walton (1922) 

 have shown that the organism can live in nectar. With the nectar 

 as a source of food supply, the bacteria would be able to multiply 

 rapidly and enter the interior of the blossom by means of either 

 enzymic or toxic secretions or both. That the bacteria should attack 

 the base of the style and progress more rapidly toward the center of 

 the receptacle (Plate III, 6, from A toward C) than outward toward 

 the base of the stamens and the petals (Plate III, 6, from A toward 

 B), is logical, since the fire-blight organism thrives best in rapidly 

 growing tissue. No cases were found in which the opposite was true. 

 Killing the tissue of the receptacle from the nectar glands toward 

 the ovaries would soon kill the entire flower. This appears to be the 



