466 Bacterial Disease of Pisum sativum 



Fusarium or injury by soil insects. How the organism passes into 

 the interior of the seed is not known. The bacilK have never actually 

 been seen passing up tke micropyle, but they occur in the thin-walled 

 layer of cells lining the pod, immediately inside the sclerenchymatous 

 layer of supportive tissue. The infection of the young seed probably 

 occurs earlier, as all the seeds in a pod are diseased to an equal extent. 

 It is more probable that infection takes place through the parenchyma 

 and phloem of the vascular bundle which passes up the funicle, and 

 which is connected with the vascular strands running along the midrib 

 of the pod. Cultures of the organism, however, have been obtained 

 from the cells of the thin-walled innermost lining of the pod, which 

 cells, under moist conditions, sometimes grow out into unicellular hairs. 

 The interior of a very young pea is filled with sap, and it was thought 

 that the organism might be present in this sap, but smears made of 

 this sap and stained with bacterial stains failed to reveal the organism 

 in the rod stage. 



Morphology of the Organism. 



Ps. seminum is a large motile rod, with a single polar flagellum, 

 attached rather to one side of the pole. The length of the rod varies 

 considerably according to the age of the colony, and the medium used. 

 On solid media, taken from a young colony the length is from ifx to 

 bfi X IjjL, but in liquid media the rods can attain a length of from 9/x 

 to 10/x before division. Chains of four to five rods reaching in length 

 from 30 fx to 4()/x are not infrequently met with in young broth cultures. 

 On solid media the organism soon passes into the beaded state. This 

 consists of oval bodies, either separate or occurring in chains. They 

 are formed inside the rods and are approximately as broad as the rods. 

 They are highly refractive when alive, and might easily be mistaken 

 for spores. When stained with ordinary bacterial stains such as Gram, 

 Gentian Violet, Carbol Fuchsin, Methylene Blue, etc., these oval bodies 

 take the stains very lightly. The margin is stained rather more than 

 the interior, which remains almost colourless. As repeated efforts to 

 stain them with spore stains failed, it was thought that the cultures 

 were impure, and that there were two organisms present. In order 

 to separate the two organisms numbers of sub-cultures were made in 

 various liquid media including sterile water only, and then replated on 

 to solid media, but without success. The oval and rod stages occurred 

 persistently. Moreover, the colonies varied considerably in size and 

 shape, all, however, giving the same characteristic reaction to litmus 



