INTRODUCTION. 



etc., they live parasitically on living or dead organisms, 

 thereby obtaining the required albuminous substance 

 requisite to sustain life. 



Pungi living on dead or decaying organic matter are 

 termed saprophytes ; others infesting living plants, caus- 

 ing more or less serious disease in the host, are termed 

 parasites. 



According to Dr. Sieber {Journal fur Praktische 

 Cliemie [2], 23, p. 412) certain common mildews have the 

 following compositions : — 



The analyses show that mildews contain a considerable 

 percentage of albumin, derived in the first instance from 

 the host-plant upon which the parasites live. The host- 

 plant thereby becomes diseased, and its vitality is greatly 

 impa,ired. The vitality of the spores of most fungi is very 

 considerable ; and the spores are capable of being dried 

 up in the dust of the atmosphere for months, and it may 

 be years, -without losing their vitality. 



So far, we have spoken in a general way of the struc- 

 ture, etc., of the vegetable foes which are injurious to 

 farm crops. We now offer a few remarks concerning 

 those members of the animal kingdom which are un- 

 doubtedly the foes of the farm. 



