TREES AND SHRUBS 



The spores gain access through a wound, such as a broken branch or an 

 unprotected surface exposed by pruning. The mycelium attacks the heart- 

 wood, changing its colour to a clear reddish-brown, and causing it to crack 

 and decay. 



Parts exposed by pruning, and the ends of broken branches, should be 

 protected by the use of a fungicide. All specimens of the polypore should 

 be removed and burned, and the surrounding wood cut away to the depth 

 of an inch, the cut surface being washed with a saturated solution of cor- 

 rosive sublimate in methylated spirit, and afterwards painted over with tar. 



The Spruce Nectria (Nectria cucurbitula) attacks the Norway Spruce, 

 and sometimes the Silver Fir and Scots Pine. It is a wound parasite, gaining 

 entrance by means of cracked branches, bruises caused by hail, and on the 

 Continent through wounds made by the larvae of a Tortrix moth (GraphoMtha 

 pactolina). The fungus chiefly affects the cortex, but when this is killed 

 the wood may also dry up and wither, and in this way the top of a tree 

 often becomes yellow, withers and dies. The mycelium is most active in 

 the soft bast ; and when the dead bark is almost constantly damp, numerous 

 small cushion-shaped or mushroom like bodies called stroma burst through 

 to the surface. These at first bear numerous conidia, followed at a later 

 period by red perithecia, which produce colourless sporidia contained in asci. 

 To prevent the spread of the disease it is considered advisable to cut off 

 and burn the tops of dead trees. 



Sycamore-leaf Blotch (Rhytisma acerinum) is common on the upper surface 

 of the leaves of Sycamore, as well as at least three other species of Acer, 

 viz. the Common, Norway, and Red Maples. On their first appearance in 

 June or July the blotches are yellow, but soon change to pitch-black, the 

 surface becoming wrinkled or corrugated and scab-like. Within the scab- 

 like covering or stroma are cavities from which there ooze out minute curved 

 spores or spermatia. During the winter an ascigerous form of fruit is pro- 

 duced on the fallen leaves, the sporidia being needle-shaped and colourless. 

 All diseased leaves should be collected and burned before the ascospores are 



liberated in the spring. 



lxxvi 



