13 



weakened from any cause, they are likely to be attacked when the 

 temperature is allowed to go above 40^ at uight. 



5. In order to have perfect assimilation and growth in plants 

 under glass, that temperature must be provided under which they 

 grow most vigorously out of doors. In the garden we find the night 

 temperature averaging from 15° to 25° lower than that of the day. 

 In the summer when the temperature is high and ranges about the 

 same, night and day, mildew, blight, rust, smuts, and all manner of 

 parasitic plants grow rapidly. Now, if in our greenhouses we venti- 

 late during the daytime, and at night start up the fires so that the 

 temperature is as high at night as during the day, we have just the 

 conditions under which mildews develope outside, and if a record of 

 the temperature were kept I am confident that in those houses most 

 afflicted with mildew this condition of things would be found. 



PREVENTIVES. 



Before looking for remedies we should take advantage first of such 

 preventive measures as are effective, and experience has shown that: 



1. Lettuce must be grown at a low temperature, ranging from 35° 

 to 40*^ at night to 50° to 70° during the day to escape the mildew. 



2. An abundance of plant food must be supplied at all times. 



3. Nitrate of Soda and Potash are valuable in developing a vigor 

 of leaf that will tend to resist the attack of the mildew. 



4. An abundance of water must be used, but the drainage should 

 be good and the watering done in the morning and on bright days only. 



5. Sudden extreme changes of temperature must be avoided. 



REMEDIES. 



Evaporated Sulphur. To test the value of this remedy for lettuce 

 mildew, the tem[)erature of the house on the nights of March 12th, 

 13th, 14th, and 15th was allowed to run up to 50°, 56°, 47°, and 51° 

 respectively. Most of the crop had been cut for market, but what 

 remained was badly mildewed. Two kettles of sulphur were kept 

 running from 6 to 9 o'clock in each evening, the vapor being very 

 abundant. Except where the vapor could not penetrate among the 

 leaves the mildew was certainly very much checked and no new growth 

 appeared on the exposed surface of the leaves. 



From this trial and the continued use of it for several weeks pre- 

 vious, although not as thoroughly made, we feel convinced that 

 evaporated sulphur will largely prevent the development of mildew, 

 but when it has once become established it will not entirely destroy 

 it. 



