THEIR RELATION TO PLANTS 41 



as they did in primitive times when dampness, mud 

 and ooze were prevaihng conditions and vegetable 

 life just established, they were fitted to live and gain 

 their subsistence in disorganized tissue: they were 

 simple forms of scavengers, and so they are to-day in 

 most cases. They are always found where there is 

 moist vegetable decay and sometimes, in manure beds, 

 they occur in countless numbers. In fermenting sap, 

 under bark of trees undergoing moist decay, in masses 

 of leaves and similar localities, these species may gen- 

 erally be sought. Their direct influence upon growing 

 vegetation is extremely small. 



In the Neuroptera there has been an advance, al- 

 though, as these were also primitive species and largely 

 adapted to aquatic or semi-aquatic life, the vegetable 

 feeders are in the minority. Almost everywhere the 

 larval life is more or less predatory in tendency and 

 in some, hke the Odonata or dragon flies, this predatory 

 character is carried into the adult stage. The feeders 

 on vegetable matter, like Psocids and Termites, usually 

 attack dry or dead tissue or feed upon Lichens and 

 similar material. None of them rank as destroyers of 

 the higher forms of plant life, although Termites do in 

 some instances attack growing vegetation. 



In the Hemiptera we have a well-developed series 

 of terrestrial species, the vast majority of which are 

 feeders on plant life or on plant juices drawn from 

 living plants. The mouth structure of the insects is 

 such that they can feed only on the liquid which they 

 draw from a punctured tissue, whether vegetable or 

 animal, and therefore, primarily, the injury is due to 

 a withdrawal of sap, severe in proportion to the amount 

 of liquid thus withdrawn. Secondarily, injury is caused 

 by an interruption of the circulation in the plant, due 

 to a hardening of the exhausted tissue, or the drying 



