280 PEACTICAL FLOEICULTUKE. 



CHAPTEE LV. 

 MILDEW. 



Opinions as to the cause of mildew are varied and 

 somewhat contradictory. My view is, that mildew being 

 a fungus growth, its seeds or spores are ever present in 

 the atmosphere; and when a relaxed condition of the plant 

 ensues, the minute germs find a suitable place for their 

 development in the enfeebled leaf. Therefore I believe 

 that anything that impedes the flow of the sap, places 

 the plant in the condition fitted to develop mildew. 

 Thus we often see our Roses without a taint of mildew 

 during all the winter and early spring months, until the 

 hot, dry weather of the middle or end of May dries the 

 soil in the pots to such a degree that the plant wilts 

 the sap is impeded, and mildew follows. Or a door may be 

 left open and the frosty air fastens on the stems and 

 leaves, congeals the sap, enfeebles the plant, and though 

 from an entirely opposite cause, the result is the same. 



I once had a most marked example of this kind. Early 

 in April we had an old-fashioned lean-to green-house 

 filled with Roses in full leaf, in the very highest state of 

 vigor. The house was some sixty feet in length and was 

 ventilated by sliding down every alternate sash at the 

 top. In ventilating on one occasion, the sashes had been 

 neglected to be closed until so late in the evening that 

 the Roses exposed to the air had become chilled by frost 

 so that the young shoots hung down as if wilted; as the 

 greenhouse got heated up they recovered, and to all ap- 

 pearance next morning looked none the worse for being 

 frozen; but in a week after, mildew appeared in a clear- 

 ly defined square space of about 3x3 feet, following al- 

 most exactly in the line where the plants had been frost- 

 bitten. It would here seem that the leaves thus enfeebled 



