Dec. 1895.] 



INJURIOUS INSECTS AND FUNGI. 



319 



useless for fruit bearing. Very large boughs are often found 

 ruined in this way, and occasionally young trees have large 

 canker centres in their main stems which must materially affect 

 their powers of fruit production and their full development. 



Young boughs of apple-trees often have the whole of their 

 bark ringed by the fungus, especially near the tips, so that they 

 die, and in this case it is generally held that frost has caused 

 their death. It will be found that the fungus, as a rule, is 

 located near and round the shoots or twigs, because the cuticle 

 there is tender and to some degree extravasated and liable to 

 receive injuries from frost or hail, making it a convenient nidus 

 for the spores of the fungus, which commences life as a 

 saprophyte — i.e., a feeder on decayed substances. 



Canker attacks some varieties of apple-trees more than 

 others. Those which yield the best eating apples are most 

 liable to it. Cox's Orange Pippin is a variety subject to this 

 disorder, as is also the Ribston Pippin, while the Golden Pippin, 

 and several of the Rennets,, or Eeinettes, notably Reinette des 

 Carmes, are somewhat liable to canker. Trees with the thinnest 

 and smoothest bark are most liable. In France, trees bearing cider 

 fruit are not usually cankered as much as those growing fruit 

 for the table. Varieties of the Reinette type are specially 

 attacked, as well as some of the Calville tribe ; and in Germany, 

 according to Goethe, Reinettes, especially the Reinette de 

 Canada, are most frequently infected. Goethe states that canker 

 is very common in Alsace, and in the Rhine districts of Prussia, 

 where thousands of trees succumb every year to this malady. 

 He adds that there are certain regions where the apple trees 

 most liable to infection cannot be cultivated. 



Pear-trees are affected by Nectria clitissima in the same way 

 as apple-trees. Fortunately in this country the attack on pear- 

 trees is not so frequent as on apple-trees, though in France it 

 appears to affect both pretty equally. The effect of the fungus 

 and its methods of attack are precisely the same as upon 

 apple trees. 



This fungus is also desti'uctive to oak, beech, ash, hazel, and 

 lime trees. 



Description and Life History. 



The perithecia, or spore-bearing cases, of the fungus appear 

 first as minute red dots, as shown at B (Fig. 1). From the 

 spores emanating from these a mycelium is produced, which 

 penetrates the rind and wood, whose juicy tissues are dried up 

 and destroyed. The action of the mycelium in course of time, 

 though it moves slowly, causes distortions and malformations of 

 the surrounding parts, and death to all the branch above the 

 centre of its action. Perithecia, or spore-bearing cases, are 

 formed on the surface of the rind after a time (D,, Fig. 1). 

 They are crimson, and are found in small groups ; they are 



