FISHERIES, GAME AND FORESTS. 405 



case of two organisms taking advantage of one another, because both are modified in 

 a slight degree, at least to suit one another's needs. In the cases of which I shall 

 speak later, it seems that the host-plant, or tree on the roots of which these fungi or 

 micro - organisms live, gives little in return for what it receives. It would seem, 

 therefore, that the tree is more of a parasite, if it is at all parasitic, than the fungus 

 which lives upon its roots. The organs on the roots of plants, or rather the formation 

 which is produced by the union of root and fungus, have been named " mycorhiza " or 

 fungus-roots. One class of these mycorhiza is abundant on the roots of certain 

 plants and lives in the humus of the soil, acting as intermediate agents in supplying 

 nutritive material, especially nitrogen, that most essential ingredient of plant-food. 

 According to several authorities, these mycorhiza may be found on the roots of almost 

 all trees. Experiments seem to show that the rapid growth of several species of trees, 

 especially the beech, is due to their presence. 



It is on the roots of leguminous plants where the action of micro-organisms is most 

 marked. They are extremely common on the roots of locust trees in the form of 

 tubercles containing masses of these organisms, which are called "bacteriods" because 

 of their resemblance to bacteria. It is in fact a bacterium, and has received the name 

 of Rhizobium leguminosarum. It is to the presence of these organisms that the rich- 

 ness in nitrogen of leguminous crops is due. They give to clovers their great value 

 as green manures and soil-improvers. What clovers are to the agricultural world, 

 leguminous trees are or may be to the forester. It is due no doubt to the presence of 

 these organisms that the locust tree is able to grow in sterile places. The locust produces 

 one of our most durable woods, with an ash richer in inorganic constituents than most 

 of our hardwoods. It grows with great rapidity on poor soils. This is probably, at 

 least in part, due to the presence of these bacteriods on its roots. What is true of the 

 locust is probably true also of many other leguminous trees. 



A very great deal in reference to these mysterious beings, in comparison with 

 what will probably soon be known, is still unknown. I have mentioned these agents 

 which work in the humus of soil to show that when we destroy or remove the humus 

 from the soil we remove a whole menagerie of living things which are constantly 

 working for the betterment of the soil and the life of the forest which covers it. 

 When farmers say that fire " cooks the life " out of a sandy soil they are saying what 

 is literally correct. 



