78 VEGETABLE FORCING 



264 plants, was treated similarly, with about the same 

 results." 



The 1902 report of the Hatch station says also : "There 

 are other effects of drying on the soil which prove very 

 destructive to the development of lettuce plants, although 

 we have not observed this effect on other species. On 

 lettuce we have observed this repeatedly, and the char- 

 acteristic results of such drying are manifested in a 

 stunted growth and an abnormally colored and worthless 

 crop. The crop scarcely ever attains more than one- 

 third of its size. The texture of the plant is poor, being 

 thick and tough, and inclined to crinkle. That this is 

 caused by desiccation alone is shown by the fact that 

 wherever any drip fell from the roof upon the soil during 

 the summer rains, the plants growing in such places 

 were always normal. Distinctly sharp lines can be ob- 

 served in a lettuce crop grown under such conditions, 

 owing to the difference in development brought out by 

 desiccation and the presence of a small amount of water 

 due to dripping. Instances have come to our notice 

 where large houses devoted to lettuce have been allowed 

 to become too dry in summer. If such drying occurs, the 

 soil can be entirely renovated by applying hot water or 

 steam to it." 



The drying of greenhouse soils not only increases the 

 difficulty from disease, but it is decidedly harmful to the 

 silt and clay types, which, after thorough desiccation, 

 break up lumpy in the course of preparation for planting. 



Summer mulching. The Ohio station has been con- 

 ducting a series of experiments with mulches used during 

 the summer period of non-cropping. Horse manure has 

 been the most effective. For seven years practically no 

 disease has appeared upon any of the standard vegetables 

 grown in the experimental houses. It should be noted 

 that not only was the soil kept moist, as advocated by 

 the Massachusetts station, but plant food and humus 



