CHAPTER XXXVIII, 



CONCLUSION. 



WE have now rapidly passed in review some of the most 

 familiar forms of disease as seen in our field and garden 

 crops, and not a few of our readers may possibly think 

 the details as described both complicated and difficult. 

 Yet on careful study it will be found that the courses of 

 all diseases more or less follow one or two simple general 

 plans. The details may vary and the colours may be 

 changed, but the chief outlines are not essentially different 

 from each other. 



It is only in the knowledge obtained after completely 

 mastering the life history of each disease that any pre- 

 ventive remedy against disease can be hoped for. With 

 a full knowledge of the character and habit of an enemy, 

 it can be fought under favourable circumstances, as in a 

 bright light. Without the proper knowledge it is like 

 fighting against a powerful, unknown, and merciless foe 

 in the dark. 



One point that must impress every reader is the 

 extreme, almost inconceivable, smallness and attenuation 

 of the parts of some of the most destructive of our field 

 and garden fungi. To give an idea of this smallness, we 

 have in Fig. 142 engraved the foot of a common house- 

 fly, with its hairs and claws, enlarged 100 diameters. At 

 AA are seen six of the spores or conidia of the potato 

 fungus, Peronospora infestans, Mont. Each of these spores 

 contains within itself, on an average, eight other little 

 spores or zoospores, illustrated as free from the investing 

 spore or conidium at B, and each of these smaller spores 



