12 



4. Sudden and extreme changes in the temperature when the 

 plants have been growing inpjdly and are soft and tender. 



0. The same temperature both day and night. 



1. In our experience the best results have been obtained where 

 tlie temperature runs as low as 35° and 40° at night, and not higher 

 than 65° to 70° during the day, and where but little outside air is 

 admitted lo the house, unless the out-door temperature is as high as 40°. 



On the nights of Feb. 4th, 5th and 7th, the temperature ranged 

 from 4(S'^ to 52°, and our records show that the mildew developed 

 rapidly during that time, while on the nights of Feb. 19th, 20th and 

 21st the temperature stood below 40*, and during this time there was 

 no perceptible increase. 



2. All the elements of plant food must be supplied in abundance 

 and especially, in a quickly soluble form. In an experiment made 

 with Sulphate of Potash, Muriate of Potash, Nitrate of Soda, Nitrate 

 of Potash, Sulphate of Ammonia, Bone Black, Dried Blood, and 

 seven other mixed fertilizers, it was found that the Nitrates of Soda 

 and Potash, applied to a soil liberally supplied with stable manure, 

 produced a vigor of leaf that was much less injured than where the 

 other elements were used. 



Of two soils, one made of rotted sods and old compost taken fi'om 

 a hot bed, and the other of the sods and freshly-composted stable 

 manure, it was found that the first gave by far the best results. 

 Equal quantities of each material were used as nearly as could be 

 determined in both cases. 



3. While lettuce cannot be grown under glass without an abund- 

 ance of water, it has been found best to apply it only in the morning. 

 It is a settled fact that the lettuce mildew, like most plants of its 

 kind, can only grow under conditions of a close moist atmosphere 

 and a high temperature, and if the watering is done in the morning, 

 and especially on sunny days, the moisture gets dried from the leaves 

 before night and the mildew is less liable to grow. 



4. As with the rose mildew, a sudden chill, wheu the lettuce plants 

 are growing rapidly, will check their growth and so weaken them that 

 the cells develope food in the proper condition for the rapid growth 

 of such parasitic plants. That a plant in a vigorous, healthy condi- 

 tion will resist the attack of the mildew longer than a sickly one, is 

 shown by the fact that the weakest plants are always first injured 

 by it. 



Under proper conditions of soil, temperature and moisture, the 

 lettuce crop can be successfully grown, but if the plants become 



