34 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



gallons of hot water, then af^d two gallons of paraffin and mix 

 thoroughly until the ingredients do not separate on standing. 

 One gallon of the emulsion thus prepared should be diluted with 

 fourteen gallons of water, when it is ready for use. 



Recent investigations tend to show that the spruce-gall aphis 

 {Chermes abietis, L.), and the larch aphis {Chermes laricis, 

 Hartig), are alternating stages of one species. The sexual 

 generation occurs only on the spruce, the agamic generations, 

 consisting entirely of females, then migrating to the larch. 

 Under the circumstances a mixture of spruce and larch is not 

 to be recommended, as it furnishes the aphis with its two 

 necessary host-plants. 



As a safeguard against inoculation taking place through bark 

 fissures caused by late frosts, it is advisable not to form seed- 

 beds nor to plant larcli in low-lying damp localities, where not 

 only are the plants most exposed to frost, but such situations also 

 favour the presence of the aphis. 



In the case of larger trees there is no cure. If the trunk is 

 not seriously injured the tree may continue to grow and make 

 wood for many years after being cankered. However, it is very 

 important to remember that the toleration of canker-bearing 

 ascophores is a serious menace to surrounding trees. As the 

 spore is the only known means of transmitting the disease from 

 one tree to another in a state ot nature, therefore, whenever 

 practicable, all canker wounds should be cut away, and the 

 removed portions burned. Protect the cut surface with a coating 

 of gas-tar. 



In this country ascophores of the fungus are formed every- 

 where in abundance, independent of altitude. 



Literature Quoted. 



1. Hartig, R., Unters. Forsthot. Inst. Miinch, i. p. 63. 

 '1. Carruthers, J. B., Jour. Roy. Agric. Sac, ser. iii., vol. ii. 

 p. 299 (1891). 



3. Willkomm, M., Die mlkroskopischen Feinde des Waldes, Heft. 



II. p. 167 (1867). 



4. Ward, H. Marshall, Timber and Some of its Diseases, London 



(1889). 



5. Buckton, G. B., Mon. /British Aphides, vol. iv., pi, cxix. 



fig. 4. 



