11 



Caution. It is well kuowu that burning sulphur is quickly destruc- 

 tive to all plant growth, and every precaution should be taken that it 

 is not heated so hot as to take fire, or that the kettle does not get 

 upset. The lamp or stove should have a broad base or the kettle be 

 placed on a tripod with feet well spread. It should be placed under 

 the bench where it can be readily seen, but where the clothes of a 

 person passing by may not catch upon it and upset it. 



ROSE MILDEW. 



Erysiphe {Sphaerotheca) pannosa. 



Another very common difficulty we have had to contend with in 

 our greenhouses, which are not properly constructed for successful 

 rose culture, is the rose mildew. 



Careful observations lead us to the conclusions : (l)That this dis- 

 ease may be brought on by the exposure of the plants to draughts of 

 extremely cold air when they are growing rapidly, (2) by high tem- 

 perature running the same both night and day, (3) by watering or 

 syringing just before night, (4) by too little water, (5) by extreme 

 dryness, (6) by poor drainage, and (7) by a deficiency in plant food. 

 In fact anything that may in any way weaken the plant. 



REMEDIES. 



Since the use of evaporated sulphur was begun in the house it has 

 l)een almost impossible to find enough mildew on the plants to afford 

 specimens for examination in the laboratory. 



LETTUCE MILDEW. 



( Peronospora gangliformis.) 



Perhaps the greatest obstacle to the growth of good lettuce under 

 glass, and which causes the greatest loss to our market gardeners, 

 is that of the lettuce mildew. 



By observations made in the growth of lettuce in our greenhouses 

 for the past ten years, we conclude that this disease may be brought 

 on by the following conditions : 



1. A temperature ranging from 45° to 50° at night, especially if 

 following a cloudy day, when it has not been above 55°. In sunny 

 days, if the temperature runs up to 66° or 70°, the night temperature 

 may run up to 45°, and perhaps higher, without injury, if the house 

 and beds are not very moist. 



2. Want of proper plant food in the soil. 



3. Too much moisture in the soil. 



