54 HORSFALL 



spread with lightning rapidity over Europe and appeared in Ireland in 1844. 

 We might describe its catastrophic attack on Ireland in the words of an eye 

 witness, Father Matthew, who says, "On July 27th I passed from Cork to 

 Dublin, and the doomed plant bloomed in all the luxuriance of an abundant 

 harvest. Returning on August 3rd, I beheld with sorrow mere wastes of 

 putrefying vegetation." 



In the seven days mentioned by Father Matthew, the stage was set for a 

 famine in which a quarter of a million people actually starved to death from 

 slow malnutrition and a million and a half emigrated, many of them to the 

 United States. Essentially the entire potato crop of Ireland was wiped out. 

 The people who had been dependent upon potatoes to pay the rent and to carry 

 them through the winter suddenly found themselves without any potatoes, 

 and they knew that they faced a dreadful winter. A few feeble efforts at 

 public relief were undertaken, partly by the Church and partly by the State, 

 but they were inadequate and probably could never have been adequate to 

 feed the whole population of Ireland. The best they could do was to stave 

 off the evil day for a few people. The starvation showed first as dull headaches 

 and bloated bellies ; finally, the sufferer came under the spell of hallucinations 

 and died. He did not seem to be in any great pain but died from weakness. 

 Terror and panic were common throughout the land, and the ships sailing 

 westward to the United States were packed to the gunwales with people 

 rushing away from the famine that had encompassed their homeland. 



So much for a couple of plant diseases that altered history. 



WHAT CAUSES DISEASE 



In the fight with the fungi, we had to find out first that it was fungi that 

 we were fighting. We had somehow to discover what it was that caused plant 

 disease. This was not so easy. The ancient man knew some of the causes of 

 food destruction. He could see the locusts that ate his wheat in the field and 

 the rats that ate his wheat in the granary. But he could not see the fungus 

 that was stealing the starch from the grains and causing them to shrivel and 

 shrink. 



We very glibly say these modern days that plant diseases are caused 

 chiefly by fungi, and we all pretty well understand that a fungus is a small, 

 chlorophyll-free thread that we can see quite easily under the microscope. 

 How did we arrive at this simple-sounding conclusion? 



First of all, what is a disease? Is disease a condition? Some people would 

 say that it is. In that case, would you say that fever is a disease? Well, most 

 of us would say that fever is not a disease. Fever is a condition. When our 

 temperature goes up, we have the condition called fever. Is a leaf spot on a 

 plant a disease? No, that is like fever, that is a condition — a symptom of dis- 



