NATURAL WOUNDS. 205 



blood, etc., as in animals ; the danger consists, 

 rather, in their affording access to other injurious 

 agents, especially fungi, and the treatment of 

 wounds frequently resolves itself into cutting or 

 pruning in order to get clean surfaces which can 

 heal readily. 



Wounds on leaves imply loss of foliar surface 

 i.e. of chlorophyll action and the remarks on 

 page 193 apply. 



Burroivs may be taken as comprising all kinds 

 of tunnel-like excavations in the various organs 

 of plants, including those cases where insects 

 burrow into hollow stems of grasses, etc., as 

 indicated by the perforations they make in the 

 outer tissues. 



Bark-boring is done by many species of beetles, 

 especially Scolytidae, which excavate characteristi- 

 cally formed branching passages tangentially in 

 the inner bark of Conifers and other trees. Some 

 of them also bore down to the surface of the sap 

 wood (e.g. Toinicus bidentatus) or even burrow 

 right into the latter (e.g. T. lineatum). It com- 

 monly happens that the external apertures show 

 up clearly, ownng to the brown dust and excre- 

 ment, sometimes accompanied by turpentine, 

 which exude from them. Many of these Bark 

 beetles only attack trees which are already injured 

 by fire, lightning, etc. ; possibly they cannot bore 

 through a cortex which swamps them with sap, 

 as a vigorous one might do. 



Wood-boring is also done by many of the bark- 

 beetles as well as by Longicorns, e.g. Saperda in 



