Forcing-House Miscellanies. 393 



too warm and clamp, and the lettuce becomes flabby, it invades 

 the plant and causes irreparable ruin. There is no remedy, but if 

 the soil is sandy and "sweet" and the house properly managed 

 as to moisture and temperature, and top dressings of manure are 

 avoided, the disease need not be feared. Galloway sj)eaks of it as 

 follows, in the article already quoted : " Wet rot of the lower 

 leaves and rotting of the stems and consequent wilting of the plant 

 are seldom troublesome in this [Boston or sandy] soil if properly 

 handled, because the surface is at all times comparatively dry- 

 Wet I'ot is produced by a fungus which may be found at any time 

 on pieces of sticks and straws scattered through the soil. The 

 fungus does not have the power of breaking down the uninjured 

 tissues of the plant, excepting possibly in very rare cases. When 

 the tissues become water-soaked, however, as they do when in 

 contact with wet soil, the fungus, which is also most active in the 

 presence of moisture, readily gains entrance and soon develops suf- 

 ficient energy to become an active parasite." 



The mildew {Peronospora gmigliformis) is the staple lettuce 

 disease of the books, but we have never had experience with it. 

 No doubt much of the trouble ascribed to mildew is really the rot. 



Leaf-bum is a dying of the tips of the leaves when the plant is 

 nearly or quite mature. It is particularly troublesome on the 

 heading varieties, in which the slightest blemish upon the leaves 

 detracts greatly from the selling qualities of the lettuce. This 

 difficulty, according to Galloway, is attributable largely to the soil : 

 " Top burn, one of the worst troubles of the lettuce grower, does 

 comparatively little injury on this Boston soil, providing the pro- 

 per attention is given to ventilation and the management of the 

 water and heat. Burn is the direct result of the collapse and death 

 of the cells composing the edges of the leaves. It is most likely 

 to occur just as the plant begins to head and may be induced by 

 a number of causes. The trouble is most likely to result on a 

 bright day following several days of cloudy, wet weather. During 

 cloudy weather in winter the air in a greenhouse is practically 

 saturated, and in consequence there is comparatively little trans- 

 piration on the part of the leaves. The calls, therefore, become 

 excessively turgid and are probably weakened by the presence of 

 organic acids. When the sun suddenly appears, as it often does 

 after a cloudy spell in winter, there is an immediate, rapid rise in 

 temperature and a diminution of the amount of moisture in the 



