Red Spider. 235 



to a weak, drawn shoot of the pelargonium ; and it is the same with most 

 insects : come they do, and whatever they attack is checked in growth, 

 and more or less reduced in health, vigor, and fertility. In whatever state 

 a plant may be attacked, whether weak or strong, the effects are the same : 

 it becomes impaiied in strength and vigor; and, when freed from insects, it 

 regains both. Surely this does not show that constitutional ill health and 

 impaired vigor are essentials to insect attacks I believe that they are not 

 induced so much by any peculiar condition of the plant as by the atmos- 

 phere being favorable to the development and increase of the insects. 

 Make a plant as unhealthy as we may, it will not be attacked by the insect 

 peculiar to it until we also produce an atmosphere favorable to that insect. 

 Tliat the red spider delights in and is encouraged by a dry atmosphere, 

 none having experience of it will doubt ; and it is most abundant where the 

 heat in houses is artificially derived from flues or hot-water pipes. I can 

 also affirm, from many years' daily observations, that where there is a 

 plentiful supply of atmospheric moisture, a temperature from fire or natural 

 heat no more than the plant requires, and thorough ventilation, that the 

 attacks of red spider are not grievous. Any one having experience in 

 forcing vines, melons, &c., knows how much more liable to the attacks of 

 red spider are the crops obtained by employing great artificial heat than 

 those to which less artificial heat and more air are given ; nor can those 

 who wash or syringe their peach-trees have failed to find how free of red 

 spider such trees are, while others not syringed are literally eaten up if dry 

 weather prevail. A dry atmosphere, too high a temperature, especially at 

 night, and insufficient ventilation, are the conditions under which red 

 spider presents itself; but there are cases in which it will appear when 

 none of the conditions favorable to its existence are present. Still the fact 

 of the insect's existing may be taken as evidence that the air is too dr)', 

 too hot, or imperfectly ventilated. 



(To be continued) 



