178 THE GYPSY MOTH. 



the exudation of crude sap, commonly called "bleeding," and 

 is not open to the objection which applies to grafting wax. 

 Paint is often used. Thick mineral paint mixed with linseed 

 oil has given satisfactory results at the Massachusetts Agri- 

 cultural College at Amherst, and is recommended by Prof. 

 S. T. Maynard. Coal tar has been long used in Europe 

 as the best substance known for this purpose. It needs 

 no preparation aside from an occasional warming in cold 

 weather, and may be readily applied with a painter's lirush. 

 This substance will not injure the wood, but, on the con- 

 trary, is one of the most perfect wood preservatives known. 

 If pruning is done with discretion at the right season, 

 the trunk being not already decaj^ed, and if the tar is 

 applied at once on the removal of the branch, the wood 

 will remain sound, and, except in the case of very old 

 and feeble trees, the new growth Avill in time cover the 

 wound. Decay may be prevented or delayed even in old 

 trees by such treatment. Coal tar should be used with some 

 caution on cherry and plum trees, as it may injure the tree 

 if applied to the bark. Wounds on the maple and elm, 

 which often "bleed," may need more than one application 

 of coal tar to stop the "bleeding." In such cases the first 

 coat of tar should be well rubbed oft' before the second 

 application. 



The two most essential rules in regard to removing limbs 

 are followed in the pruning done in the gypsy-moth work. 

 Although known and practised in this country at the begin- 

 ning of the present century, they have been ignored by most 

 American writers on tree pruning. Yet Wm. Coxe of 

 Burlington, N. J., wrote in 1817 : — 



In cutting off a bvaueh, it should be done as close as possible, 

 never lea^dng a stump, for the bark cannot grow over it, and 

 disease in the wood will inevitably follow. If the wound produced 

 by the separation be very large, cover it with tar or thick paint.* 



The principles of pruning were ably set forth in 1861 by 

 De Courval, as practised with perfect success for more than 

 forty years in the forest of his vast estate of Pinon (Aisne), 



* Coxe on " Fruit Trees," 1817, page 41. 



