Disease of the Turnip (Brassica napus). 443 



by degrees the entire rosette of leaves perishes, and the whole root 

 becomes a soft, putrid mass, which eventually collapses, and after a 

 shower of rain almost entirely disappears, exactly the same symptoms 

 appearing as in the case of the plants found decaying in the fields. 

 The most careful microscopic search has failed to detect any trace of 

 hyphae of the higher fungi in the decaying mass, but only a swarming 

 mass of bacteria. The tissues are completely disorganised (see fig. 1), 

 the cells separating from each other along the middle lamella, the cell- 

 walls are soft, swollen, and faintly striated, the protoplasm too has 

 lost its natural colour and become slightly brown and contracted, so 

 that it no longer remains closely in contact with the cell-wall. 



With a view to determine whether the bacteria are the cause of the 

 rottenness, and if so, to isolate the particular organism which produces 

 it, a series of cultures was undertaken. 



In the first instance, a nutrient broth made from turnips was em- 

 ployed. Pieces of turnip finely chopped were steamed in a beaker 

 until soft, sufficient tap-water being added to just cover them ; when 

 soft they were pressed through a cloth and the liquid filtered. To the 

 clear light yellow filtrate thus obtained 5 per cent, of gelatine was 

 added, and the mixture was then steamed, filtered, and drawn into test- 

 tubes, which previously had been plugged with cotton-wool and 

 exposed to a temperature of 140 C. for half an hour. These test 

 tubes, containing about 10 c.c. each of the bouillon, were next steamed 

 for half an hour on three consecutive days, and as a further test of 

 complete sterilisation they were incubated at 20 C. for a few days. 

 No colonies were found to develop. (Whenever mention is made of 

 test-tubes containing nutrient gelatine it must be understood that all 

 have been prepared in this manner, and none have been employed 

 which have not been submitted to these tests.) In some cases the broth 

 was neutralised, in others it was allowed to retain the natural acidity 

 of the cell-sap; but subsequently Koch's bouillon, neutralised with 

 sodium hydrate by the phenolphthalein test, was found to give the 

 most satisfactory results, and hence was always used. 



In separating the various organisms found in the rotten mass a 

 sterile platinum wire was introduced into the turnip (the rotten part 

 practically offering no resistance), and then immersed in a test-tube (A) 

 containing about 10 c.c. of the liquid nutrient gelatine. From this a 

 loop was taken in a similar manner into a second test-tube (B), and so 

 on until a sufficient degree of attenuation was reached. The test-tubes 

 after being well shaken were turned out into petri capsules a, b ... g 

 respectively. These were placed in a cool incubator, and the colonies 

 allowed to develop. In a, and often in b, the entire surface became 

 covered with growing colonies too thickly crowded to be of any use 

 for the purpose of isolation ; but in the others the colonies were less 

 numerous and sufficiently distinct to allow the organisms to be sepa- 



