CHAP, xiii.] Fungoid Diseases of Trees 295 



the occurrence of yellowish-green loranthus-like deformities 

 or twig-clusters of a more bushy appearance than the normal 

 branches from which they protrude at right angles ; the yellow- 

 ish-green needles, growing closely and all round the twigs, are 

 shed during the first autumn. These deformities always have 

 their origin in a swelling or node within which the mycelium 

 of the fungus infests the bark, liber, and young wood, and 

 from which it annually extends to the young twigs and needles 

 till the disease dies out. 



Whether a canker-spot or a twig-deformity will be produced 

 by the fungus depends on the nature of the place in which the 

 mycelium develops. Should the latter in extending itself effect 

 an entrance into a bud still capable of development, a deformed 

 twig-cluster is the result; but when the shoots are already 

 formed, the mycelium is principally confined to the bark, and 

 a cankerous swelling is there produced. In either case infec- 

 tion seems only possible at wound-surfaces. The receptacles 

 (spermogonia and stylospores) develop in the diseased leaves of 

 the youngest shoots, appearing on the lower side of the needles 

 in June in the shape of red or orange cups (aecidia\ which 

 burst and scatter their spores. All attempts hitherto to pro- 

 duce the disease directly by means of infection with these 

 spores have failed, as a heteroecious change of generation is 

 necessary ; but the intermediate form of the fungus and the 

 host on which it produces itself remain, for the present, 

 unknown to mycologists. 



The formation of mixed forests is the best prophylactic 

 measure against this disease; whilst the removal of twig- 

 clusters in June and July, and the cutting out of cankerous 

 stems, should be undertaken, wherever possible, in order to 

 check its spread. 



5. Nectria cucurbitula, Fr., the Spruce-bark Fungus. This 

 is a cankerous disease occurring principally on the stems of 

 young Spruce from about 3 to 15 ft. in height, especially in 

 localities exposed to danger from frost. Infection can only 



