THE LARCH CANKER. 



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brilliant orange colour. The whole flattened portion of the stem 

 or branch is nearly all the time exuding resin, just as it would 

 from an accidental injury, and if steps are not taken to rid the 

 tree of its unwelcome visitor the deformation increases with more 

 or less rapidity, nearly always ending in the death of the tree, 

 and in every case rendering the timber well-nigh valueless. 



The cup- shaped fungus on the bark is the only part of this 

 parasite which can be observed by the naked eye ; but though 

 important as the means of reproducing and spreading the disease, 

 it is not the most important part of the fungus. The damage is 

 done by the root portion, or mycelium, of the fungus, which has 

 complete possession of the bark, and reaches to the cambium 

 layer of the tree, abstracting all available nourishment and killing 

 all adjacent cells, causing a darkening of a reddish colour, which 

 can easily be observed if a portion of the bark is cut off and the 

 cambium exposed. As the fungus grows year after year it 

 pushes its borders wider and increases the affected portion — the 

 tree at the same time attempting, by means of a callus, to cover 

 up the wounded portion, and also putting on a larger quantity 

 of wood on the side of the stem opposite to the cankered spot, in 

 order to maintain a vital connection and to afford the necessary 

 mechanical support. Thus we have a swollen condition of the 

 tree on the side of the stem opposite to the cankered area. The 

 fight goes on in some cases for a great number of years, but in 

 most instances the fungus will in the end succeed in " ringing " 

 the tree, though it is possible that the tree might be able to close 

 over the wound and form healthy wood on the outside of the 

 canker, and thus immure it. 



The spread of the fungus is naturally a most important 

 point, and in order to understand with what remarkable pro- 

 lificness the parasite will reproduce itself it is necessary to describe 

 the cup- shaped fruits which produce the spores or seeds of the 

 fungus. Each cup has a rim or margin surrounding the orange - 

 coloured part which contains the spores. The spores (which are 

 oval in shape) are enclosed in sacs or asci, eight in each ascus, 

 some ten to fifteen thousand of which are contained in each cup, 

 so that the number of spores produced in every cup is very great, 

 and if one spore in every ten thousand is successful in innocu- 

 lating a new tree the spread of the disease is very rapid. It 

 must, however, be borne in mind that this fungus, like most 



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