474 Bacterial Disease of Pisiim sativum 



carboys, which were kept lying on one side throughout the experiment, 

 great care being taken to keep them as sterile as possible during manipu- 

 lation. Five days after the plants had been placed in the carboys 

 they were inoculated with a pure culture, in sterilized water, of a surface 

 more or less circular opacjue whitish colony isolated from the centre 

 of a diseased cotyledon. A drop of the culture was placed on a young 

 leaf. The leaf turned browny yellow in three days, at the end of ten 

 days the growing point of the stem was practically dead, and laterals 

 had begun to develop. Identical results were obtained from a radiating 

 colony, see Plate VII, fig. 13, from the same original culture, whereas 

 the controls, treated with sterile water only, remained healthy through- 

 out this period. Another carboy was inoculated with a mixture of 

 the two above-mentioned colonies with exactly the same results. The 

 main shoot died back in 10 — 11 days. These results are only conclusive 

 in so far as they show that young tissues can be infected and die back 

 when inoculated on the surface with a pure culture of Ps. seminum. 



Pea plants grown under sterile conditions make poor growth, even 

 when supplied with a complete nutritive solution and, as stated above, 

 succulent growth is necessary for the full development and rapid 

 spread of the organism in the plant. It is also difficult to obtain seed 

 from pea plants grown under moist sterile conditions. Nearly all the 

 flowers in the above experiments shrivelled and dropped off. 



Susceptibility. 



All attempts to find an immune variety of pea have been without 

 success. A number of different varieties of mid-season and late culinary 

 peas were grown to test their resistance to the disease, but all varieties, 

 so far, have been found to be more or less susceptible. The variety 

 which proved to be most resistant was Sutton's Improved Petit Pois, 

 which, sown on infected land, gave from 49 to 50 per cent, healthy 

 plants. Seeds saved from these selected healthy plants and sown 

 again on the same plot the following year also gave approximately 

 50 per cent, healthy plants. 



Duke of Albany and Ne Plus Ultra are very susceptible, the average 

 number of healthy plants of Duke of Albany being 14 to 15 per cent. 

 The growing of the Ne Plus Ultra for Mendelian experiments at this 

 Institution had to be discontinued owing to its extreme susceptibility. 



As mentioned above, the taller varieties of early peas show con- 

 siderably less disease than the later varieties, partly, it is believed, 

 because of their less succulent growth and earlier development, which 



