166 Gruenberg : Some aspects of the mycorhiza problem 



(commonly called the host although it is not commonly supposed 

 that the relationship is a parasitic one) there have been offered 

 many theories. In 1846 Reissek declared that the root fungus 

 was a normal phenomenon in the life of the plant, Hke the produc- 

 tion of flowers : it is not necessary to the existence of the plant 

 but is produced under certain conditions, spontaneously. Schaclit 

 in 1852 and Irmisch in 1853 described the fungus in many orchid 

 roots and rhizomes and concluded that the fungus was not para- 

 sitic, but offered no definite explanation of the constant presence 

 of the fungus in the orchid. 



In 1877 Pfeffer suggested that as root hairs were absent from 

 the roots or rhizomes bearing fungi, the fungi perform the absorb- 

 ing function of root-hairs. In 1882, Kamienski, studying Mono- 

 tropa^ concluded that the relation between this plant and its root 

 fungus is a mutual symbiosis, and in 1885 Brunchorst ascribed 

 a similar nutritive function to the symbiont of the Papilionaceae. 

 In 1886 Miiller inferred from the behavior of the roots of forest 

 trees that the fungus serves to disintegrate the soil. Frank in 

 1888 thought that the root fungus is of special service to its sym- 

 biont in absorbing nitrogen compounds from the soil, or from the 

 humus. It has since been definitely determined that the organ- 

 isms in the root-tubercles of leguminous plants, as well as other 

 fungi, have the ability to fix atmospheric nitrogen, and this ca- 

 pacity is of sufficient advantage to compensate for any carbohy- 

 drate the fungus may obtain from its partner. 



There is probably no need to consider, nowadays, some of the 

 earlier theories of spontaneous generation of autonomous organ- 

 isms within the tissues of the seed plant ; or the idea that the fun- 

 gus-infested tissue is the result of degeneration or the gall of an 

 insect All the probabilities point to some nutritive relation be- 

 tween two autonomous organisms, including under the concept 

 *' nutritive" water and salt relations. However, there is no reason 



my 



O 



consider the case of plants entirely free from chlorophyl. The 

 case of Monotropa was interpreted by Kamienski as follows : 

 The Monotropa derives its organic nutrients from the humus 

 through the Intermediation of the fungus, which obtains from the 



