250 Forestry Quarterly. 



turning points of the tunnels are semi-circular instead of pointed. 

 The histological modifications which result from the mining of the 

 Opostega larva are fundamentally the same as those described 

 above. 



Grossenbacher reports the presence of cambium miners in the 

 following trees : Prunus mahaleb, seedlings of P. avium, P. 

 serotina, P. virginiana, Crataegus oxyacantha, and other species 

 of Crataegus when among infested P. avium or P. mahaleb. They 

 were also found in P. cerasus and P. domestica of some nurseries. 

 The mines and larvae were present in various sized stems, 

 branches and shoots of the above hosts from the surface of the 

 ground (even underground) up to nearly 3 meters above. 



Various writers have referred to pith flecks in describing wood. 

 Laslett^^ notes their occurrence in "many Birches, Alders, Haw- 

 thorns, Poplars, etc." and considers them "points of structure 

 that help the expert to determine the nature of a piece of wood." 

 Boulger^ (page 33) : "Another character of some value in dis- 

 crimination is the occurrence of pith flecks, or medullary spots, 

 dark rust-like patches, which occur in Alder, Hazel, Hawthorn 

 and some species of Willow, Poplar, and Pyrus. They are sup- 

 posed by some authorities to originate in passages bored by the 

 larvae of a species of Tipula (wire worm) which live in the 

 cambium, these passages becoming filled up immediately with 

 cellular tissue ; but their origin requires further investigation." 



In his classification of woods Boulger makes the presence or 

 absence of pith-flecks the basis for separating certain species of 

 Acer, of Populus and of Pyrus. Acer barbatum Mich. (A. 

 saccharum March), for example, is said to be without pith-flecks, 

 thereby distinguishing it from A. campestre L. and A. pennsyl- 

 vanicum L. The present writer, however, has observed pith- 

 flecks in the wood of A. saccharum Marsh, and it is probable that 

 their use in the other instances referred to is equally unreliable. 



Stone* recognizes the pathological origin of pith flecks but 

 states (pages XVI-XVH) that they "are as characteristic of the 

 species as any other feature because the grub is faithful to its 

 special tree and prefers it to all others, therefore as a series of 

 years can hardly pass without the presence of the grub, no log of 

 wood of a susceptible species of tree will be found without these 

 traces." 



Opposed to this statement are the observations of Kienitz^^ 



