334 



FOREST ENTOMOLOGY. 



Now the question is, how are we to deal practically with those 

 pests, having regard to recognised systems of " mixing " with those 

 very trees which act as host-plants in the alternation of the species 1 

 Much has yet to be learnt from good sylviculture! conditions, careful 

 work in planting with well-rooted plants, and also from experiment 

 and observation. Take, for example, a suggestive case in point viz., 

 the growing of young silver firs. On many estates very fine examples 

 of old silver fir trees can be found, and the modern forester Avith his 

 high-class sylviculture cannot grow it. Without giving any definite 

 opinion, much might be done in the younger stages by growing under 

 shade of hardwoods in the nursery say, plant a row of hardwoods, 



Fig. 309. Hibernating winter forms of four species o/Chermes. 



a C. abietis; b, C. strobilobius ; c, C. coccineus; d, C. siliricns ; together with a highly 



' magnified single chitin plate of each species. Copied from Judeich and Nitsche. 



two or three rows of silver fir, and again a row of hardwoods, and so 

 on throughout the nursery plot. Perhaps, also, an exception may be 

 made to the general rule of much transplanting in the nursery. This 

 tree should not be too often moved, but plants should be specially 

 carefully taken up when they are lifted. Again, when transplanted 

 in the forest, the silver firs should not be planted in the open, but 

 as shade - bearers in late filling up, or otherwise solely as under- 

 planting. 



Then as regards the injurious effects of C. abietis as compared with 

 C. strobilobius, it may be said, so far as real injuries are concerned, 

 that the former is often injurious in the nursery-lines, more especially 

 to those plants standing in the rows for three consecutive years, and 



