174 FllUIl CULTURE. 



According to Goethe, a German authority, and strongly 

 supported by Mr. Fraser, of Kew, the malady itself is 

 caused by a fungus, Nectria Ditissima (Fig. 51). Goathe 

 has succeeded in cultivating the parasite on the apple, 

 pear, and some forest trees. The fungus lives beneath the 

 bark, destroying it, and causing the decorticated rings, 

 patches, and shrivelled appearance of the shoots and 

 branches so well known to cultivators, as shown in the 

 accompanying illustration. 



Although this fungus may be present in all canker 

 wounds, yet it is probably only an accompanying effect, 

 and not the cause of the disease. 



Mr. Douglas, of Ilford, is however probably nearer the 

 mark when he attributes the cause to " want of prepara- 

 tion of the soil, and subsequent neglect of the special 

 requirement of each class of trees." 



We find Mr. Tonks, of Birmingham, practically suppor- 

 ting the same theory, and he gave in a paper read at the 

 Apple and Pear Conference at Chiswick, in 1888, the 

 result of his investigations and experiments in this di- 

 rection. He says in his paper : 



" Yefc these, and most of the other writers on the sub- 

 ject, according to my idea, indirectly indicate both the 

 cause and the remedy for the disease ; the cause being 

 mal-iiutrition, the consequence of an imperfect provision 

 in the soil of the food required by the plant ; the remedy, 

 the supply of the food which is deficient." 



He tried the experiment upon badly cankered trees of 

 supplying them with the deficiencies of plant food in. the 

 soil. This was followed by the complete arrest of the 

 disease ; and he says : 



" I can only conclude that the arrest of the disease is 

 due to the supply of elements of food required by the trees, 



