232 THE FRUIT GROWER'S GUIDE. 



greater or less malignity. The fungus, Nectria ditissima, pushes its mycelial liyphce 

 (spawn threads) through the live portions of the cortex (bark), cambium (formative 

 fluid found between the bark and wood), and alburnous tissues (younger outer layers 

 of wood), causing their destruction. This occasions a considerable swelling of the 

 surrounding tissues, the bark dies sooner or later, becomes fissured and scaly, forming 

 an unsightly excrescence. No exudation occurs. The extension of the mycelium is 

 intermittent, quiet in winter, and active in spring and summer. Then the fungus 

 strives to enlarge the wound. This the tree resists, and a struggle for the mastery 

 ensues. By throwing out an excessive callus around the circumference of the wound 

 the tree endeavours to cover over the wood, and thus expel the fungus and safeguard 

 itself against further inroads. This battle may last many years in the larger branches 

 without causing their death, but in the smaller it is more rapidly fatal, the small twigs 

 and shoots succumbing in the year of attack. 



Aiding trees to repel disease forms no insignificant part of intelligent culture, and 

 a knowledge of the enemy to be combated is an immense advantage ; therefore the illus- 

 tration (Fig. 61) will be suggestive. 



Steps to combat canker are 1, preventive ; 2, remedial. Preventives are those 

 promoting the tree's health, in which all its functions are perfectly performed. A tree 

 growing in too rich soil does not digest and secrete its juices healthily ; hence its tissues 

 arc large and weak, the wood soft and pithy, and the bark tender, therefore highly 

 susceptible of injury from hailstones, severe frost, bruises, and abrasions in performing 

 cultural operations. This condition, fatal alike to health and fruitfulness, must be 

 prevented by timely lifting and root-pruning, additions of less rich soil or incorporation 

 of counteracting substances, such as old mortar rubbish. This, with the soil firmed, 

 and, perhaps, shallower planting, will induce sturdier and shorter-jointed growth, 

 stouter-textured leaves, assuring solidity to the wood, and a denser, harder (yet elastic) 

 cuticle to the bark. 



On the other hand, a tree growing in thin, poor or unsuitable soil, or otherwise 

 enfeebled, must be stimulated, by judicious manurial applications and thinning the 

 branches, to imbibe by its roots and elaborate through its leaves the nourishment 

 essential to its health and vigour. Cleansing the bark enables it to swell. Stunted 

 trees are liable to rend the old bark under a generous regimen. Cleanliness imparts 

 the essential elasticity to the bark, ensuring its enlargement over the new layers of 

 wood without splitting. 



