April 24, 1889.] 



Garden and Forest 



199 



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used, Init tlie draina.t^e sliould be good and the waterinij done 

 in tlie morning and on l)right days only ; tliat sudden extreme 

 changes of temperature must be avoided. 



The reasons for these precautions are tliat in oriler to liave 

 perfect assimilation and growth in plants inider glass, that 

 temperature must be provided under wiiich they grow most 

 vigorously out-of-doors. In the garden we find thenight tem- 

 jierature averaging from fifteen to tv\'enty-fi\-e degrees lowei" 

 than that of the day. In the summer when the temperature is 

 high and ranges about tlie same, night and day, mildew, 

 blight, rust, smuts and all manner of parasitic jtlants gi-ow 

 rapidly. Now, if in our green-houses we \-entilate during the 

 day-tmie, and at night start up the fires so that the temperature 



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

 tions under which mildews develop outside, and if a record of 

 the temperature were kept in those houses most afflicted with 

 nn'Idew this condition of things would, no doubt, be foimd. 



As with the Rose mildew, a sudden chill, when the Lettuce 

 plants are growing rajjidly, will check their growth and so 

 weaken them that the cellsdevelop food in the proper condi- 

 tion for the rapid growth of such parasitic plants. That a 

 ])lant in a vigorous, healthy contlition will resist the attack of 

 the mildew longer than a sickly one is shown bv the fact that 

 the weakest plants are always tb-st injured by it. It is to guard 

 against such weakness that. all the elements of ))lant-food 

 must be supjilied in abumlance, and especially in a quickly 



