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A Rhizoctonia Disease of Lettuce. 



We are somewhat at a loss for a popular name to characterize this 

 hitherto undescribed lettuce disease. Those few growers who recog- 

 nize it use the name "Mildew," which covers other things as well 

 and is not at all distinctive. This is not a common disease, and we 

 have never seen it doing any great damage except in our own house, 

 where crop after crop of lettuce has been grown in the same soil and 

 diseases of all kinds encouraged to develop as much as possible. 

 We have often seen a little of this disease, however, on a plant here 

 and there in various houses, and our own experience shows that it 

 can most effectually ruin a crop when well started. The trouble 

 appears first on the lower leaves where they lie on the ground. A 

 moist, brown rot sets in here which spreads through the leaf in a very 

 characteristic manner. The green blade rapidly rots away and dis- 

 appears, so that the stalk and mid-rib remain clean and sound as 

 though the blade had been carefully cut away or eaten by insects. 

 (See Fig. 8.) This distinguishes the trouble at once from the 

 Drop and Botrytis, in each of which the leaf stalk and mid-rib rot 

 first, leaving the blade to dry up. One leaf infects another at 

 points where they touch, so that the rotting ofteYi reaches the centre 

 of the head while the outer leaves are only affected in small spots, 

 one corresponding to another on the next leaf, by which the track 

 of the fungus can be traced. Delicate 

 threads of the fungus can be seen on 

 and amongst the leaves and to some 

 extent on the soil. It does not, how- 

 ever, make the profuse growth of 

 Botrytis or Sclerotinia. In the centre 

 of the head the rotting becomes general 

 and the tender, inner leaves resolve into 

 a slimy, black mass. In many cases the 

 rotting does not reach this point, but the 

 outer leaves keep drying off one after 

 the other. This has an effect similar to 

 that of the Black Root ; but even more 



marked. No head is formed, but F'fi- 9- Filaments of Rhizoctonia. 



the inner leaves remain straight and 



slender, forming a loose rosette. (See Fig. lo.) This is quite 



