328 Studies in Forestry [CHAP. xiv. 



The caterpillars of the former are thus prevented from ascend- 

 ing the stems in spring after hibernating under the layer of 

 moss on the ground ; whilst the same is also the case when the 

 latter spin themselves down to the ground on cocoon-like 

 threads (like some of the Tortriddae]. This they practically do 

 at least once before they lose the power of spinning their 

 gossamer filaments or get too heavy to be supported and 

 borne downwards by the latter; and these transformations 

 occur simultaneously, though gradually, about the third time 

 of changing their skins. 



The essential requirement about good viscous tar is that it 

 should remain sticky, and without either running or getting 

 hard and dry from exposure to rain and sun. Its efficacy is not 

 dependent on the mechanical action of its stickiness, but on 

 some inherent smell of one or more of the ingredients that is 

 exceedingly repulsive to the caterpillars till the ring becomes 

 hard and dry. Even if individual caterpillars can be found 

 to face and cross it, their feet and mandibles get clogged with 

 the gluey composition, and they die of inability to procure 

 food for themselves. It is therefore essential that the rings or 

 narrow girdles should remain sticky until the larval state of 

 development has been completed, that is to say, for at least 

 six to eight weeks (although practically good patent tar remains 

 active about three times as long) without the surface oxydizing 

 or becoming covered with a skin. It is a patent composition, 

 whose ingredients must, however, be a very open secret, as 

 over a dozen firms advertise it throughout Germany for delivery 

 at about 75. 6d. per cwt. This quantity suffices for about 

 2\ acres on the average, although of course young crops 

 require more per acre than older woods \ 



Previous to the application of the patent viscous tar the 

 bark of the stem requires to be cleaned, or cleared of loose 



1 For the benefit of those who may wish to try the effects of this patent 

 tar or ' Raupenleim/ the following addresses of manufacturers may be 

 given : L. Polbora, I Kohlenufer, Berlin S. ; Schindler and Miitzel, Stettin ; 

 and J. M. Witzemann, Stuttgart. 



