S. G. Jones 297 



culture derived directly from diseased material the usual signs of attack 

 and rotting of the blocks took place. 



As above mentioned the farmers who had witnessed the attack in 

 the fields said tiiat the disease had been preceded by a sudden collapse 

 of the foliage. This reported phenomenon at once suggested infection 

 of the leaves by way of the stomata or water-pores. Experiments were 

 carried out on a number of plants in the following way. Uninjured leaves 

 (attached to the plant) of varying ages were plunged into water in a 

 series of petri-dishes to which had been added pure cultures of the 

 organism from bouillon. The leaves were left immersed for an hour. 

 In some plants they were first steriUzed with weak mercuric chloride 

 which afterwards was removed by repeated plunging into sterile water; 

 in others, no surface sterihzation was employed. The leaves of the control 

 plants were also treated in the same way. These experiments failed to 

 show any infection of the foUage. The writer is strongly of opinion that 

 infection is preceded by mechanical injury through some such agency 

 as leaf -cutting insects or slugs and the very earliest signs of tlisease in 

 the very numerous cases seen in the field were the softening and water- 

 soaked appearance of the young fohage. Further inocidation experi- 

 ments were carried out by first .moistening the young foliage at the 

 growing point and then depositing a pure culture from bouillon. The 

 root was then covered over with a bell-jar plugged at the top with 

 cotton-wool. These experiments invariably failed despite the greatest 

 care being taken to keep the inoculated part moist. Accordingly the 

 tender foliage at the growing point was pinched off with a sterile forceps 

 and into the wound thus made a pure culture of the organism was de- 

 posited, the wound being covered over with a piece of steriUzed cotton- 

 wool, and the whole plant again covered over as before. This method 

 of inoculation was always successful but the progress of the disease 

 varied somewhat in different plants. The extent of attack was deter- 

 mined from time to time by probing the cavity with a platinum wire. 

 When a depth of some four inches had been reached the plants were 

 cut open in vertical section. Those in which the pulp was watery showed 

 the characteristic whitish-grey mass accompanied by the marginal brown 

 discoloration. Other roots of a drier spongy texture showed a diseased 

 core of a uniform brown colour. This difference of colour in the diseased 

 parts suggested an idea that it might bear some relation to the water 

 content of the cells and intercellular system or in other words to the 

 extent of aeration of the tissues. During the earlier stages of the investi- 

 gation it was noticed that when the inoculated turnip blocks in the test- 



