Some aspects of the mycorhiza problem 



* 



Benjamin C. Gruenberg 



The roots or underground stems in many families of plants 

 exhibit the constant presence of a symbiotic fungus. Mycorhiza 

 has been described in liverworts and ferns as well as in over twenty 

 families of flowering plants, including gymnosperms, monocoty- 

 ledons, and dicotyledons. With very few exceptions, mycorhiza 

 is not characteristic of the plants of a whole family, that is, in 

 most families of plants examined, some species have the myco- 

 rhiza, and some have not There are even species of plants in 

 which the presence or absence of the root fungus seems to be de- 

 termined by external conditions; symbiosis is facultative, so far at 

 least as the phanerogam is concerned. 



The identity of the fungus in the mycorhiza has been the sub- 

 ject of many investigations, but has not been definitely determined 

 for more than a very few cases, and even in these not with satis- 

 factory certainty. The chief difficulties in the way of identifying 

 the mycorhiza fungus lies in the fact that the mycelium cannot be 

 readily isolated and made to sporulate. The frequent finding of 

 Ftisariuin forms in cultures of mycorhiza fungus leads to the sus- 

 picion of foreign contamination. The spores of PeyiiciUium are 

 common in the soil and various moulds frequently appear in cul- 

 tures even after great pains have been taken to free specimens from 

 adhering soiT particles or other foreign matter. All groups of 

 fungi, from bacteria and slime-moulds to Pyrenomycetes and 

 agarics have been declared to form the mycorhiza in different 

 plants by different observers. It is impossible to identify the 

 fungus from the mycelium alone, although recent examinations of 

 forest trees have shown the presence of characteristically colored 

 mycelia which were believed to be connected w^ith sporocarps in the 



• • 



vicmity. 



As to the relationship between the fungus and the higher plant 



* Read before Section G of the American Association for the Advancement of 

 Science at the Baltimore Meeting, December 31, 1 908. 



1G5 



