No. 4.] Krxnors diskasks. in 



Kx[)rriiiionts h;i\ c .shown tlitit a con criiii:: ol" coarse sand 

 about lettuce plants iiiati'iially reduced rots, .siui[)ly from the 

 fact that sand retains lucMsture nuich less readily than loam, 

 thus oti'ering less favorable opportunities for fungous infec- 

 tion ; and no doubt a circulation of air about the stems 

 would prove beneficial. In the same manner,' sub-irrigation 

 reduces stem rots bv maintainin<r a smaller amount of mois- 

 ture in the top layers of soil. The shutting out of light and 

 air by planting too thickly constitutes a source of danger 

 to disease. A\'atercress and parsley oft'er good examples of 

 the effects of overcrowdiiiir, due to luxuriant irrowth. When 

 these crops are allowed to grow high and become thick they 

 l)roduce weak stems, and become affected with the same 

 fungus that produces "drop" in lettuce, Avhereas when 

 closely cropped there is little loss from this disease. The 

 exclusion of light and air necessarily arising from over- 

 crowding is responsible for this. In most instances the 

 stem rots of the chrysanthenmms have been induced by over- 

 crowding, and undoubtedly the carnation would suffer less 

 if more light and air could reach the stems. 



Yarious stem rots could undoubtedly be eliminated, to a 

 larire extent, bv changing the soil conditions about the 

 plants, such as by the application of coarse sand around the 

 stems. In one case the stem rot in the parsle}'^ was greatly 

 reduced by setting the plants well up above the soil, thus ex- 

 posing the stem and crown to light and air, which resulted 

 in the development of more resistant tissues. The matter 

 of moisture on the foliage plays an important part in infec- 

 tion. The carnation rust has been largely reduced by sub- 

 irrigation methods, and also by applying water absorbents, 

 such as lime, to the foliaije. In short, many funi^ous dis- 

 eases peculiar to foliage can be much lessened, and in many 

 instances prevented, by regulating the moisture conditions 

 of the air. If it were possible to control the moisture con- 

 ditions out of doors, the same would hold true there. For 

 example, a cold, wet spring induces peach leaf curl, while a 

 dry, warm spring is not favorabl(» to the develo})ment of the 

 fungus which causes curl, and many other cases might be 

 cited where infection is due to weather conditions which 



