THE GIPSY MOTH AS A FOREST INSECT. 15 



Siiice hemlock is better liked than pine by the caterpillars, a mixed 

 growth of oak and hemlock is much more likely to be destroyed com- 

 pletely than a mixed growth of oak and pine; and since gray birch 

 is not so favorable a food plant as oak, a birch and pine mixture is 

 not nearly so likely to suffer as a mixed stand of oak and pine. 



Apparently no fear need be felt as to the safety of any mixture 

 whatever of which all the component parts could be considered as 

 resistant if they were standing in pure growth. As to the greater 

 resistance of an oak tree when standing surrounded by chestnut and 

 hickory, as compared with another of the same species and vigor 

 surrounded by oak, there is room for further investigation. It can 

 only be said that the protection thus afforded to oak through being 

 associated witli other trees is not particularly striking. 



RELATION OF UNDERBRUSH TO THE FOREST. 



It is interesting, in connection with the relative resistance of forest 

 trees, to note that the sprouts and, to a less extent, the seedlings, are 

 not so liable to mjury as are larger trees of the same species. This 

 is true even of pme, unless the writer has misinterpreted his field 

 observations. 



It is also true that for the most part the common species of shrubs 

 to be found growing as underbrush in a forest are unfavorable as 

 food for the gipsy moth — that is to say, they may be classed with 

 the resistant species of trees. It is certainly logical and, to that 

 extent, reasonable to suppose that underbrush will be found to play 

 quite an important part in the protection of the forest. Caterpillars 

 falling from trees in a pure stand of oak devoid of underbrush will 

 find their way back to oak and be little the worse for the adventure. 

 Caterpillars falling in a similar manner in a forest full of underbrush 

 will not find their way back so readily, and the eating of strange 

 food for a tune will render them less resistant to disease, more likely 

 to die, and thereby more likely to transmit the germs of disease to 

 their fellows. 



It is a subject well worthy of further study and experimentation 

 and one to which it is hoped to devote considerable attention in the 

 course of the coming year, the more so since it has special bearing 

 upon the suggestion that oak might possibly be protected by adopt- 

 mg the method of cutting so as to leave reserve trees. 



RELATIVE RESISTANCE OF DIFFERENT TREES OF THE SAME SPECIES. 



It would appear from numerous obsei-vations that certam indi- 

 vidual trees (of red oak, for example) are much better able to with- 

 stand the attack ot the gipsy moth than othei-s of the same species 

 growing m the same wood lot. These trees, although they are sub- 

 jected to the same degree of defoliation, will live when all around 



