26 



FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



(in the course of the appearance of needles, and dwarfing the leading 

 shoot) sheathing shoots, which, however, usually reach no great age, but 

 are provisionally of much importance to the life of the tree. 



The loss of increase in size resulting from diseavse is twofold. Some- 

 times the shoots sufler in decrease in length, at others in shrinking in 

 size. The diminution of length is shown after the year succeeding that in 

 which the injury took place ; that in the terminal 

 shoot of the branch, and especially the topmost 

 shoot, the needles remain shorter. Not until 

 later do they again assume their normal length. 

 The fir also, whose topmost shoot is here repre- 

 sented (Fig. 5), after injury received in the year 

 1857 formed only short leading shoots, but in 

 1861 again formed a strong shoot. 



The diminution of the growth in diameter is 



especially noticeable in the loss of the foliage or 



needles, which sometimes occurs in the year of 



injury, but more decidedly the following year. 



After a greater loss of leaves the annual rings 



Fig. 6. 



Fig. 5. Terminal shoot of a 

 fir defoliated by the nun-cat- 

 erpillar in 1857, showing the 

 different lengths of the 

 year's growth. After Katze- 

 buig. 



The last seven rings of pine stem almost wholly defoliated in 

 1858, but not killed outright. After Ratzeburg. 



are smaller and feebler, and this may sometimes 

 last over for many years. (Fig. 6.) 



Nordlinger has repeatedly found signs of de- 

 foliation by the May beetle for three years on 

 oaks, also on Carya alba, in southern Germany, indicated by very small 

 annual rings. 



The counting of the annual rings to ascertain the age of the tree in 

 the practically so important matter of discovering its rate of growth is 

 rendered unsafe by the formation of double rings, which may result 

 from the sudden leaving-out in summer on young shoots, or by the co- 

 alescence of two annual rings in one, and sometimes even by the total 

 omission of a ring. The sharply-defined difference between the spring 

 and autumn growth of wood as denoted by the color, " white and brown 

 wood " of an annual ring, especially in the coniferous woods, enable 

 them to be very easily counted, provided there is no interruption in the 

 growth. In the deciduous trees the two layers of the annual rings are 



