336 FOREST ENTOMOLOGY. 



of larch disease. So far as the mixing of spruce with larch is con- 

 cerned, this theory does not square with actual results, inasmuch as 

 many instances of the " mixture " referred to may be seen throughout 

 the country, where, with spruce as an undergrowth, the larch is 

 practically free from disease, and likewise a very good commercial 

 crop. On the contrary, it is just possible that the under-crop of 

 spruce in a larch plantation, acting as a soil - protector, may have 

 proved a great stimulus to the larch crop, forming greater increment. 

 But while improved sylvicultural conditions may do much for the 

 prevention of insect or fungoid diseases, it must not be inferred from 

 the above remarks that spruce is the best mixture with larch, though 

 it must be borne in mind that larch is not a suitable tree to grow as 

 a pure crop. 1 



It might again be noted that this genus is, in general appearance, 

 practically identical with several other insect damage. Thus, for 

 example, Chermes corticalis may be common on Weymouth pine, and 

 Cryptococcus fcigi abundant on adjacent beech-trees ; but the one is an 

 Aphis and the other a Scale two quite distinct insects. Now this 

 is very important to the entomologist ; but it is often of far more 

 practical importance to the owner of trees, inasmuch as the imperfectly 

 trained entomologist is apt to make wrong deductions and prescribe 

 erroneous remedies. For example, I once knew of an expert ento- 

 mologist advising a landed proprietor to cut down Weymouth pines as 

 a remedy for the injuries of Cryptococcus fagi on beech, a most 

 absurd remedy, seeing that the two insects have no connection 

 whatever. 



Genus Phylloxera. 



Hitherto only one species has been found in this country, 

 and the generic characters may be characterised by moderately 

 long rostrum in the winged form, their jointed antenna?, eyes small, 

 legs very short, and tarsi apparently single-jointed, with a double 

 claw and pad. In this respect they come very near in structure to 

 the Coccida? or " scale- insects." As regards the wings, they are 

 decidedly of aphidian structure, inasmuch as we get a well-marked 

 cubitus, whence spring their straight veins. 



1 These remarks may be criticised by practical men, but in some cases the 

 success of this " mixture," as showing the absence of " larch disease," can be 

 seen in certain parts of the south of England. 



