40 WONDERS OF PLANT LIFE 



plant perishes under the attacks which the min- 

 ute creatures make upon it. Mostly, however, 

 the plants seem to be neither better nor worse 

 for having to develop the little houses in which 

 the insects find a residence. Everyone must be 

 familiar with the large round " gall nuts " which 

 are found on the twigs of the Oak. Whilst these 

 are, of course, produced by the plant, the under- 

 lying cause of growth consists in the irritation 

 set up by the minute gall wasps when the insects 

 lay their eggs in the buds. These particular galls 

 are but types of an immense number of examples 

 exhibiting a wide range of form and size. More- 

 over, the life histories of the insects with which 

 they are associated are in many cases imper- 

 fectly understood. 



A very singular case of partnership between 

 plants is that which is seen in the case of the 

 Lichens. These used to be regarded as distinct 

 individuals, capable of definite classification on 

 the lines of other plants. It has been established 

 that this is entirely a mistaken impression. 

 Researches have shown that the Lichen is not a 

 separate plant at all in the ordinary sense of the 

 word. Rather must it be regarded as a case of 

 that which has been called " symbiosis " liter- 

 ally, the living together of two very distinct 



