APHIDILXK, 



195 



to fully clear up the life-history of this hitherto partially studied 

 genus. The aspiring student should therefore collect the various 

 species of what hitherto has been termed stem-mofhers on different 

 trees, boil them in caustic potash, and stain with Crawshaw's magenta 

 penny dye, as recommended for scale-insects, and try to verify the 

 various minute points of structural difference as shown in fig. 280 

 from Judeich and Nitsche, carefully noting and tabulating the results 

 of his observations. Such a method would obviously be highly 

 interesting and important, as in searching for the various anticipated 

 alternating stages of the same insect on different trees, confirmation -of 

 the same creature changing from host-plant 

 to host-plant Avould obviously be ratified. 



Importanx'e of the Genus Chermes 

 IN Forestry. 



This genus is exclusively arboreal, and 

 should be specially studied from a practical 

 and scientific point of view. To the 

 scientist the various species of insects 

 change from one tree to another, and thus 

 our so-called species are simply various 

 stages of the same insect. But the prac- 

 tical man, often indifferent to specific dis- 

 tinctions, recognises the injurious effects 

 on certain trees, and thus prefers to 

 identify the species as coincident with 

 the food - plant. Thus Chermes Jaricis 

 may often be found very injurious to young 



larches of from ten to fifteen years of age, more especially on those 

 trees growing in hollows or in damp spots; Chermes viridis on spruce- 

 trees which are not growing in suitable places, and often in young 

 spruce -trees in the nursery-lines; and (7/ier??ies picece is often found 

 on young silver- firs in the nursery, and on young trees of A. Nord- 

 onanniana. C. stroUlohius is perhaps more destructive to young trees 

 in the wood, especially those too much overshaded and not thriving 

 well. The dead galls adhere very closely to the twigs, and can often 

 be seen after the infested tree is partially dead. 



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



