98 VEGETABLE PARASITES AND EPIPHYTES 



the increase being only in this case from I to 1 cwt. per 

 acre per year. 



The table given below shows the cost of canker 

 excision and burning of diseased tissues at the Experi- 

 ment Station, Peradeniya, Ceylon, during the year 1907 

 (Annual Report, Botanical Department, Ceylon, 1907). 



From the above-mentioned figures it is seen that the 

 total cost per year of excising and burning diseased 

 tissues on a cocoa estate affected with canker only 

 amounted to 3 rupees 9 cents (4s. 1^.) per acre. 



This expenditure cannot be considered excessive when 

 the gradual depletion of the crop is at stake. It should, 

 however, be pointed out that the excising of cankered 

 tissues commenced on the plantation in 1902, at which 

 time nearly every tree was affected by the disease. The 

 first year's operations are reported to have cost 17 rupees 

 (£1 2s. 8d.) per acre, and that of the several following 

 years cost from 8 to 12 rupees (10s. M. to 16s.) per acre. 

 During this period diseased trees were reduced from 96 

 to 6 per cent. 



Canker in the West Indies. — ^The principal fungus 

 parasites responsible for cankered cocoa trees in the West 

 Indies are Nectria Theobromce, Massee, and Calonectria 

 flavida, Massee. Both of these parasites are sometimes 

 found in the same diseased area, and at other times they 

 occur alone. 



The symptoms of the West Indian canker diseases 

 differ slightly from those of Ceylon canker. In the 

 former, the bark of diseased areas presents a peculiar 



