no DISEASE IN PLANTS. 



another year, or at most so little that only feeble 

 plants come up. 



In the case of a tree the case is different, and 

 since most large trees in full foliage have far more 

 assimilatory surface than is actually necessary for 

 immediate needs, a considerable tax can be paid 

 to parasites or predatory insects before the stores 

 suffer perceptibly. Still, it should be recognised 

 that the injury tells in time, especially in seed 

 years. 



Many larvae of beetles, moths, etc., bore into 

 the bark and as far as the cambium or even into 

 the wood or pith of trees, the local damage in- 

 ducing general injuries in proportion to the number 

 of insects at work : moreover, the wounds afford 

 points of entrance for fungi and other pests. 



Galls and similar excrescences result from the 

 hypertrophy of young living tissues pierced by the 

 ovipositors of various insects, and irritated by 

 the injected fluid and the presence of the eggs 

 and larvae left behind. They may occur on the 

 buds, leaves, stems, or roots, as shown by various 

 species of Cynips on oak. Phylloxera on vines, etc., 

 in all cases the local damage being relatively 

 small, but the general injury to assimilator}-, 

 absorptive, and other functions is great in propor- 

 tion to the number of points attacked. 



Many grubs larvae of flies, beetles, etc. bore 

 into the sheaths or internodes of grasses, or the 

 pith of twigs, or into buds, fruits, and other organs 

 of plants, and do harm corresponding to the kind 

 and amount of tissues injured. 



