30 Walter H. Burkholder 



manner it is introduced into the field in the following year. There may 

 be other methods by which the pathogene may survive the winter, but 

 they are probably not important in its life history. The production of 

 diseased plants from slightly infected seeds can be demonstrated easily, 

 and infected seeds are sometimes frequent in seed beans. On the other 

 hand, no work has been done to determine whether or not the bacteria can 

 overwinter in the soil or in refuse. In a dry condition in the seed, and 

 even in the leaves, of its host plants, the organism is extremely resistant. 

 It has been isolated from dried leaves kept in the herbarium for five years, 

 and from seed stored in the laboratory for a similar period of time. This 

 duration of time is possibly not the limit of its viability period, but further 

 tests have not been made. Infected seed treated at a temperature of 

 100° C. in a hot-air oven for an hour still yield pathogenic cultures. 



The activities of Phyt. flaccamfaciens in relation to its host are as follows: 

 When an infected seed germinates in the soil, the bacteria become active 

 and pass from the cotyledons into the stem. Here they may be found in 

 great numbers in the tissue of the xylem vessels, for which they show a 

 decided preference. This organism, as well as Phyt. phaseoli, passes 

 through an entire plant in the vascular system. Other tissue besides the 

 xylem seldom is infected, and the organism appears to lack the ability to 

 invade such tissue. In spreading from one bean plant to another, however, 

 there is some difficulty. The bacteria can produce an infection only 

 through mechanical injury, as Miss Hedges (1926) has shown. Conse- 

 quently, rain splashing the bacteria from plant to plant would be of no 

 importance unless some injury had already occurred in the plant that was 

 spattered. In many bean fields, insects of both the leaf-chewing and the 

 sucking types are found commonly, and probably are an important factor 

 in the spread of the pathogene. Experimental evidence on this point, 

 however, is lacking. 



In completing their life history, the bacteria must again infect the seed. 

 They do this, in a large majority of cases, by passing into the seed through 

 the vascular system. The entrance of Phyt. flaccumfaciens through the 

 side of the pod and the ultimate invasion of the seed, as is a common 

 occurrence with Phyt. phaseoli, rarely happens. Phyt. flaccumfaciens, 

 when introduced into the fleshy tissue on the side of the pod, does not 

 cause infection, or, at the most, produces only a very slight lesion (Plate III, 

 A). When the injury extends into the pod cavity, however, the bacteria 

 may multiply there, although they cause scarcely any discoloration of the 

 pod tissue. Under such conditions, bacteria have been observed to grow 

 on the surface of a seed while the seed matured normally. If the seeds 

 are injured during inoculation, they become infected and rot. Seeds 

 infested with the bacteria on their surface may give rise to diseased seedlings. 



When Phyt. flaccumfaciens enters the pod through the vascular system 

 of the pedicel, a suture lesion usually is produced (Plate IV). Since 

 otherwise this pod tissue does not become infected, the suture lesion appears 

 to be the result of an overflowing of the bacteria from the xylem vessels. 



