THE FIGHT WITH THE FUNGI 55 



ease. We see that it is not the disease but it is a symptom of a diseased plant, 

 the same as fever is a symptom of a diseased human. 



A characteristic of disease is that it is continuous. If we cut our finger, 

 we don't say that it is diseased — it's abnormal but it's not diseased, because 

 we know that it is a transient and temporary thing, and so we distinguish an 

 injury like that from a disease. Similarly a lawn mower does not produce 

 disease in the grass; it cuts the grass off, producing some injury, but we don't 

 say the grass is diseased. We can, therefore, help to distinguish disease from 

 injury by saying that disease is a continuously acting process, not a transient, 

 temporary one such as the bite of a dog or the cut of a lawn mower in the 

 grass. So, in simple language, we can say that disease is an abnormal and 

 deleterious process caused by something which acts more or less continuously. 



The crux of this matter of plant disease lies in that term caused by. Cause 

 is not a very difficult concept. We have seen that reckless driving causes acci- 

 dents, and we say that eating a green apple causes a stomach-ache. But what 

 causes plant diseases? 



The cause of plant disease remained enigmatic for a long time because for 

 many centuries we could not see the fungus involved. 



We could not see it or feel it or otherwise experience it with one or more 

 of our five senses. 



The Israelites were told (Deuteronomy 28:22) that God was responsible 

 for wheat rust, that the Lord would smite them with blasting and mildew if 

 they didn't obey the commandments of Jehovah. There must have been some 

 doubters about this point, however, because four or five hundred years later 

 the prophet, Haggai, says, 'T smote you with blasting and mildew and with 

 hail and yet ye turned not to me, saith the Lord." It is not recorded in the 

 Bible what the people thought caused wheat rust, but they must have doubted 

 that the Lord did or Haggai would never have said that in spite of the blast 

 and mildew they still did not obey the Lord. 



The writer of Genesis (41:23), however, must have been somewhat more of 

 a naturalist than the writer of Deuteronomy because he referred to the east 

 wind as the cause of the blasting. This, however, undoubtedly meant the 

 drying east wind coming off the desert which would blast the blossoms if it 

 hit them at the proper time. 



There is, however, some element of truth in this east wind business even for 

 rust. In the United States, at least, many of our storms come in on the east 

 wind which brings water with it. Of course, moisture itself does not bring on 

 wheat rust. The wheat rust fungus is the true cause; but the fungus likes 

 moisture, grows best in moisture, grows more prolifically in moisture. Hence, 

 we can say that moisture encourages wheat rust and to that degree is a cause 

 of the disease. 



Wheat rust swept on down through the ages, and nobody learned what 



