Black Dry Rot in Swedes. 



29 



of Agriculture (Vol. VI., No. 4). I was unfortunately unable 

 to visit the field from which the diseased specimens were 

 taken, and Professor Middleton kindly sent me further 

 •samples, this time specially selected by himself. These 

 swedes presented a very different appearance. The rind was 

 #Tean, and curiously rough and furrowed, but bayond this 

 there was nothing to indicate a diseased condition, and it 

 was not until the roots were cut open that the actual state of 

 things, and extent of the damage, was revealed. 



A typical illustration of the attack in a well advanced 

 stage is shown in the figure. As evidenced by its size, the 

 plant had been attacked when fully grown. The centre pre- 

 sented a blackish mass of disorganised tissue, in which were 

 numerous cracks and cavities, caused by the decay and 

 separation of the cells from each other. This was sur- 

 rounded by a brown area spreading outwards to the sides. 

 The rind was firm, and retained the original shape of the root. 

 In specimens in a more advanced stage, the cavities had 

 coalesced and formed a large hollow, the whole of the 

 internal tissues being destroyed, and the root reduced to a 

 mere shell. The initial stages of the attack were indicated 

 by dark spots and lines occurring in the central part of the 

 " bulb " on the otherwise quite healthy flesh, and no sign of 

 its commencement could be detected externally. 



One somewhat striking feature of this disease is the fairly 

 dry condition of the "bulb," which, even in the most 

 advanced stages, does not become converted into the soft 

 pulpy mass so characteristic of the " White Rot " ( Pseudo- 

 monas destructans). The decay also, in this case, does not 

 extend very rapidly; " bulbs" in which the disease was just 

 commencing still remained partially sound after being kept 

 three months in the laboratory. 



The infestation appears to have originated in the root fibres ; 

 as these became destroyed the supply of water from the soil 

 would be diminished and gradually cut off, while the leaves 

 would continue to evaporate water, and to this I am' inclined 

 to attribute the unusual dryness of the tissues. In the 

 "White Rot " the conditions are very different, the attack 

 commences at the crown, or at some part of the "bulb 



