328 GLIMPSES INTO PLANT-LIFE 



such a large proportion of atmosplieric air. When 

 therefore a farmer sows his wheat in a field pre- 

 viously occupied by clover he finds the clover roots 

 left in the soil contribute the best possible supply 

 of nitrogen to the wheat crop. This seems a 

 remarkable fact, since vegetable physiologists have 

 hitherto insisted upon the fact that plant-life is 

 unable to make use of the free nitrogen of the air. 

 The other instance of strange habit is that of a 

 symbiosis,! which exists between certain trees on 

 the one hand and the threads of spawn of some 

 fungi on the other. If the roots of the white 

 poplar are examined minutely, quite a mantle of 

 whitish threads will be found covering the growing 

 point. It is said by that eminent botanist. Pro- 

 fessor Kerner, and^ by others that, as the roots are 

 developed from the young seedling-tree, they are 

 enclosed in the meshes of the fungus, and that this 

 particular fungus is always a close associate of the 

 roots as they grow in all directions. This fact we 

 can see when we dig up the roots, but the most 

 striking part of the story is this, that between this 



' A word meaning two plants living together and deriving mutual 

 benefit. 



