464 Bacterial Disease of Pisum sativum 



cells, in proximity to other cortical cells filled with bacteria. If the 

 disease is developing rapidly the younger portions of the plant show 

 discoloration and fail to develop properly. Except in bad cases the 

 plants can grow to full height, can flower and set a fair crop of seed, 

 but on examination the cotyledons of the seed show the typical brown 

 discoloured area in the centre of each cotyledon, which may be limited 

 to a mere spot, or, on the other hand, nearly the whole cotyledon may 

 be involved. The young embryo, especially the plumule, can also 

 become infected. In bad cases there is frequently a cavity in the 

 centre of each cotyledon. Sections of young green diseased cotyledons 

 show large numbers of bacilli in various stages of development, both 

 in the cells and in the intercellular spaces. If one pea is diseased all 

 the other peas in the same pod are diseased to an equal extent. Healthy 

 and diseased seeds have never been found in one and the same pod. 



A large number of plants have been examined and the pods and 

 seeds recorded in the order of development from below upwards, and 

 it is a general rule that the first set pods show less discoloration of 

 the internal tissues of the cotyledons than those developed later. Fre- 

 quently the first set pod is free from infection. I venture to suggest 

 in explanation of this, that the external temperature was too low for 

 the rapid development of the organism, and the pods were able to mature 

 sufficiently to resist infection before the organism could get the upper 

 hand. The organism can only penetrate uninjured tissues when they 

 are very young. 



In some respects the symptoms resemble those of the formidable 

 "Streak" disease of the Sweet Pea {Lathyrus odoratus) and in my prelimi- 

 nary note I suggested that Sweet Pea Streak was due to bacteria and not 

 to Thielavia hasicola as previously held (•'>,10). Early in the following year, 

 1913, a paper was read before the American Phytopathological Society, 

 Cleveland, by J. J. Taubenhaus(9), and a short extract published in 

 the Gardeners' Chronicle, showing that Streak in Sweet Peas was a 

 bacterial disease due to Bacillus lathyri. This bacillus was found by 

 the authors to occur on a wide range of other host plants, including 

 Forage Lathyrus, Red Clover, Alsike Clover, Soy Bean, Wax Bean, 

 Lima Bean, and Cowpea. 



I have been unable to obtain further details than those published 

 in this abstract, as to the biochemical characteristics of the organism, 

 but a yellow organism isolated from a Sweet Pea suffering from Streak, 

 which I took to be the same organism as that obtained by the above 

 author, proved not to be Ps. seminum. Cross inoculations were 



