276 THE WOODLANDS. 



CHAPTER XVII. 



GALLS AND PARASITES. 



CERTAIN plants are liable to be punctured in their 

 soft parts by insects, for the purpose of depositing 

 their eggs under such conditions that when hatched 

 they may procure food. The violation caused by the 

 insertion of this foreign substance results in the accu- 

 mulation of an abnormal quantity of tissue in the 

 neighbourhood of the puncture, and a swollen body, 

 termed a " gall," is formed. These galls, therefore, 

 indicate the presence of some insect parasite upon the 

 plant so affected. Some plants are more subject than 

 others to these parasites, as, for instance, the family of 

 Oaks. We have a catalogue of no less than forty-one 

 kinds of gall, which are found upon different species 

 of oak, and this is probably now below the real 

 number known. Amongst herbaceous plants those of 

 the composite family seem to be peculiarly liable to 

 such excrescences. 



Not only have we insects parasitic upon plants, but 

 also some plants are parasitic upon others; as the 

 mistletoe and dodder not to mention many species of 

 fungi. 



Then, again, animals are parasitic upon each 

 other : many gall insects have their special parasites ; 



