210 GEOLOGICAL SURVEY OF NEW JERSEY. 



course, some sort of draft upon the tree. The least drain, per- 

 haps, is made by the gall wasps, or Cynipidcz, where the larvae 

 seem to feed chiefly upon a secretion in the central cell and not 

 upon the gall tissue itself. 



Plant-lice have been mentioned as gall-makers, but they occur 

 also in great numbers, living freely upon the leaves or succulent 

 growing shoots. No kind of tree is free from one or more 

 species of these pests, and no sort of insect makes a more con- 

 tinuous drain upon the vitality of the attacked plant. Individu- 

 ally insignificant, their numbers make them dangerous, and 

 their habit of excreting the plant juices in the form of " honey- 

 dew " gives them the power of disposing of their food material 

 more rapidly and in greater quantity than any other kind of 

 insect. And they attack all parts of a tree : not only are they 

 abundant among the foliage and branches, but even under- 

 ground among the roots, and the latter are among the more 

 serious forms. Of course, seasons affect the number of species 

 and specimens of a species, to a very large extent. In wet 

 seasons one set will become troublesome ; in a dry season 

 another will be in evidence while the former can scarcely main- 

 tain itself. And so of the trees : in some seasons plant-lice 

 attack will be serious ; in the ensuing, scarcely a trace of aphid 

 injury may be found in the district. 



Scale insects belong to the same general category as the plant 

 lice in so far as they are suckers of the plant juices, but they 

 are more dangerous because their attack is more continuous > 

 because they are less exposed to adverse climatic conditions, 

 and, perhaps, because some, at least, do exercise a really poison- 

 ous influence upon the plants. Soft scales are comparatively 

 rare in the forest, and only the Tulip tree, Liriodendron Tulipi- 

 fera, is seriously attacked in New Jersey. Of the armored scales 

 the oyster-shell bark-louse, Mytilaspis species, is sometimes 

 seriously destructive in the more northern sections on the 

 walnut and butternut trees. Willow and poplar, which are also 

 attacked, seem to stand the injury better. The nut trees are of 

 comparatively slow growth, and when the twigs or smaller 

 branches become thoroughly encrusted with scales, death is only 

 a matter of time, usually a short time. 



