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 
