298 FOREST ENTOMOLOGY. 



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

 the country, wliere, 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 health stimulus to the larch crop, forming greater 

 increment, and thus jji-obahly rendering the larch less liable to disease, 

 inasmuch as the vigour of the larch is encouraged and the dreaded 

 effects of the disease considerably minimised. Where spruce is used 

 as a mixture with larch it would be Avell also to add a sprinkling of 

 beech, because the addition of beech foliage as surface litter con- 

 siderably improves the soil conditions by accelerating decomposition, 

 and the manurial action of the humus is therefore intensified, 

 liut while improved sylvicultural conditions may do much for the 

 jirevention 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 p\ire crop,^ more especially after the cro]) of young larches has 

 passed through the pole stage. 



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 

 Cryptococciis fagi 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 Crijptococcus 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 



^ 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. 



