12 



Until the attacking organism, be it fungus, bacterium, or insect, 

 is tracked down, and its life history studied by a competent biologist, 

 ir, is little more than a waste of time in many cases to guess at the 

 cause of the disease. 



Further still, some of the diseases, such as the apple rust, are due 

 to a fungus which presents two distinct phases in its life history, in 

 one of which it attacks the apple, in the other usually some other 

 plant which need not be the same in all parts of the world, and 

 which has to be sought for in each locality. 



Again, there are various insects like the codlin moth and others 

 which, as you are aware, do much damage to our apple trees when 

 once they gain an entrance into the orchards. In Collinge's "In- 

 jurious Insects" I find he enumerates 29 insects which attack 

 apples in England. 



I was appalled at the list as enumerated in these two works, and 

 I came to the conclusion that I would not touch so big a subject 

 in any particularity. 



"You must remember that," as Prof. Gregory t puts it, "every 

 fly that troubles the agriculturist, every fungus that infests his 

 plants, has to be studied laboriously by biologists specially trained 

 in these particular matters before any accurate knowledge of its life 

 history and its habits can be elucidated, and only then can means of 

 suppression or amelioration be suggested. Whatever is known of 

 the exact relation between cause and effect in all branches of agricul- 

 ture, and whenever fact can be placed against opinion as regards the 

 diseases of plants, the credit is found to belong to the scientific 

 investigator, and not to the actual cultivator of the soil." 



But I will refer to two diseases : "Bitter pit" and "Crown gall." 



In the case of "bitter pit" I would remind you that the Australian 

 Commonwealth Government appointed a well-skilled botanist to 

 investigate the cause of the disease and to suggest a cure and preven- 

 tion. Professor McAlpine, with other botanists, has been at work 

 on this problem for some three or four years, and only now is he 

 prepared to state how the disease arises and to propose remedies. 

 From the reports that have been published from time to time+ by 

 Professor McAlpine, it is clear that this disease presents many com- 

 plications. In the first place he has shown that it is not due to 

 bacterium, nor to fungus, nor to the attacks of any insect or other 

 animal, but that it is what is called a functional disease, and is due 

 to some defect in the physiology of the plant. Many theories have 

 been propounded to account for it, some of them founded on observa- 

 tion ; others merely speculative. But from the later reports it 

 appears to be due to the death of some of the pulp cells immediately 

 below the skin, which is not ruptured, at any rate in early stages of 

 the disease. In order to ascertain the probable cause McAlpine 

 had first to make a more careful study of the anatomy of the apple 

 fruit than had been hitherto done. He found that it is penetrated 



tGregory, R. A., "Discovery: or, The Spirit and Service of Science" (Mac- 

 millan. 



JD. McAlpine. The Cause and Control of Bitter Pit. Government Printer, Melbonrne. 



