NATURAL WOUNDS. 207 



which the various species of Grapholitha or Carpo- 

 capsa are conspicuous : the fallen fruits show a 

 small hole leading by a labyrinth of passages to 

 the " core " or " stone," and in which the grub and 

 its excrement are visible. The cuttting off of the 

 vascular bundles and disturbance of the water 

 supply only partly explain the premature fall. 



Pith-flecks are minute brown specks or patches 

 found in the wood-layers of many trees, and 

 consist of dead parenchymatous thick-walled cells, 

 reminding one of the structure of pith. They are 

 explained as due to the borings of minute insects, 

 Diptera or Beetles, the larvae of which pierce the 

 cortex and phloem and bore their way into the 

 cambium. The latter then occludes the tunnels 

 by filling them up with cells, and continuing its 

 wood-forming activity gradually buries them 

 deeper and deeper in the wood. Such pith-flecks 

 are common in Willow, Birch, Alder, Sorbus, etc. 

 It is possible that they may be due to other causes 

 also in other trees. 



Erosions or irregular wounds on leaves are 

 caused by large numbers of grubs and caterpillars 

 and other insects, such as earwigs, as well as 

 slugs, snails, and other animals ; but it must by 

 no means be assumed that all marginal leaf 

 wounds, for instance, are caused by animals, since 

 many fungi which rot the tissues, as explained 

 below (p. 208), also cause such erosions, the 

 putrescent parts falling out ^.^. the Potato 

 disease. 



Skeleton leaves frequently result from the 



