2oS DISEASE IX PLANTS. 



ravages of caterpillars, which leave the coarser ribs 

 and veins untouched, but much finer skeletons with 

 the minute veins almost intact may be found on 

 plants infested with certain insects e.g. Selandria 

 on Cherries. Skeletonised patches on Cherry 

 leaves, often pink or brown-pink, are eaten out 

 by this grub. 



Shot-holes are perforations in leaves presenting 

 the appearance, from their more or less rounded 

 shape, of gunshot wounds. They may be due 

 to insects which bore through the young leaves 

 while still folded in the bud e.g. Willow Beetle 

 or which gnaw out the tissue e.g. the Beech 

 Miner. Similar but usually more torn and 

 irregular holes are eaten out by many cater- 

 pillars e.g. the Cabbage Moth. 



Shot-holes on Peas may be the work of Thrips. 



Leaf perforations are commonly caused by 

 severe hail-storms, the hail-stones beating right 

 through the thin mesophyll. Certain chemicals 

 used for spraying have also been known to cause 

 shot-holes by killing the tissue beneath the stand- 

 ing drops. 



There Ts, however, a class of shot-holes in thin 

 leaves which are due to the action of minute fungi, 

 the mycelium of which so rots the tissues in a more 

 or less circular area round the point of infection, 

 that, in wet weather, the decomposing mass falls out 

 and leaves a round hole e.g. certain Chytridiaceae, 

 Peronosporeae, Gloeosporiuin, Exoascus, etc. If dry 

 weather supervenes these holes frequentl}- dr\' at 

 the edges, and the leaves appear as if eaten out. 



