SOME DISEASES OF LETTUCE AND CUCUMBERS. 



During the past winter and spring the writer has been engaged in 

 the study of certain diseases of lettuce and of cucumbers, cultivated 

 under glass. The investigation of some of these is sufficiently 

 advanced to justify the following preliminary announcement. More 

 detailed accounts, with illusti*ations, of the diseases will be given in 

 the next annual report of this Station. 



The Rotting of Lettuce has been a soui'ce of much loss to gardeners 

 who cultivate that plant as a winter crop, but its cause and, there- 

 fore, proper preventive measures have not been known. It usually 

 appears first just al)ove the surface of the soil at the attachment of 

 the lower leaves to the stem and then spreads to the center of the 

 head causing the stem and the bases of the lower leaves, and later 

 the whole of the tender inner leaves, to become decomposed into a 

 slimy mass. The larger leaves being thus cut off from the stem by 

 decay at their bases usually dry up ; and there appears after a time, 

 on the remains of the plant, if left undisturbed, the erect, spore- 

 bearing threads of one of the imperfect fungus forms known by the 

 name Botrytis or Polyaciis. The vegetative threads of this fungus 

 are to be found in the decaying tissues of the host in the early stages 

 of the trouble, and no other fungus has ever been observed in con- 

 nection with it. My observations make it practically certain that 

 the disease is due to the fungus-form mentioned, and this view is 

 supported by the fact that similar forms are known to produce similar 

 diseases in some other plants. The discussion- of its relations to 

 other forms is reserved for our next Report. This fungus appears 

 to be able to develop also a saprophyte on old lettuce leaves and 

 other vegetable refuse and may thus survive a long interval between 

 two crops of lettuce, resuming its parasitic habits when the oppor- 

 tunity is afforded. 



From what has been said, it is evident that careful and thorough 

 treatment is essential to the control of the disease in question ; and 

 the nature of the crop limits this treatment to the removal of all 

 sources of infection. All affected lettuce plants should be at ooce 

 removed tohoHy from the house and destroyed by burning. For this 

 purpose the boiler furnace is conveniently at hand. All dead leaves 

 or other refuse should be often scrupulously cleaned up and burned 

 so that no l)veeding places m:iy be left for the fungus. A house 

 which has been very badly infested by the disease should be thoroughly 

 cleaned, whitewashed or painted, and suiiplied with fresh soil before 

 a new season's operations are begun ; and one may then expect, with 

 the observance of the above described hygienic precautions, to be 

 able to enjoy comparative freedom from loss from this cause. 



