80 PLANT PHYSIOLOGY 



as other plants .associated with Mycorhiza fungi, are there 

 any grounds for assuming that we have other than patho- 

 logical conditions due to the interference of the fungi with 

 the normal independent habits of higher plants. So far as 

 the chlorophyll-containing plants are concerned, Mycorhiza 

 seems an affliction rather than a blessing, despite the claims 

 of Frank and of Stahl. Frank says the growth of seedlings 

 of beech and pine, cultivated in sterilized humus soil, is less 

 than of other seedlings of the same sort in the same soil 

 unsterilized. Stahl shows that plants ordinarily free from 

 Mycorhiza grow better in sterilized than in unsterilized 

 humus. It remains for experiment to show whether beech, 

 pine, and other plants with fungi usually on or in their 

 roots grow better in sterilized fertile soil free from humus 

 or in humus which has not been sterilized. Some green 

 plants are strictly humus plants, refusing to grow in other 

 soils, but one cannot now conclude from this that they are 

 dependent upon the fungi, rather than upon any other con- 

 stituent of the humus. Sterilizing a humus soil causes 

 changes in the physical arid chemical conditions of many 

 nitrogenous matters in the humus. Some plants are able to 

 accommodate themselves to these changes, others are not. 

 Sterilizing the humus causes the death, not only of the 

 Mycorhiza fungi, but also of the nitrifying bacteria and of 

 those other bacteria and fungi which directly or indirectly 

 produce ammonia from the organic nitrogen compounds. 

 These changes must profoundly disturb the balance of ac- 

 tivities in the soil. It is, therefore, much easier to under- 

 stand the benefit derived by the fungi from their intimate 

 association with the roots of plants able to manufacture 

 food for themselves, than to be convinced that the indepen- 

 dent green plants greatly benefit by association with de- 

 pendent ones. However, the subject deserves further investi- 

 gation. 



The association of high and low colorless plants in My- 

 corhiza is different only in degree, not in kind, from their 

 simultaneous occurrence in all places where there are highly 

 elaborated nitrogenous and non-nitrogenous materials. As 

 the nitrate bacteria can work only upon nitrites formed 



