NUTRITION IN THE LOWER PLANTS 77 



advantage of the fungus and that mycorrhiza are more parasitic 

 than mutualistic. 



In some cases, e. g., the heaths, the green plants are possibly 

 dependent upon the presence of the fungi. This is said by many 

 workers to be the case with Calluna. Here the entire plant may 

 be permeated by the fungal filaments and when the seeds are formed 

 some of the mycelial strands are already present, ready to develop 

 parallel with the plant. This obligate condition is considered of 

 value to Calluna in that the fungus can fix free nitrogen (Chap. IX) 

 and also aids the heath to absorb soluble compounds from the 

 acid soil where it grows. Knudson (1929), however, insists that 

 this plant can grow without the mycorrhiza if the acidity and iron 

 nutrition are handled properly. While this may be true in cul- 

 tural conditions, this does not preclude the possibility that the 

 two are valuable to each other as found in nature. A similar sit- 

 uation may be true in regard to the relation between some or- 

 chids and their mycorrhiza; they can get along without the my- 

 corrhiza if the proper conditions are met, but the mycorrhiza, 

 nevertheless, aid them in nature where the " proper conditions" 

 happen to be lacking. In the case of Cattleya, the fungus seems to 

 assist in the mobilization of the reserve foods in the seed at the 

 time of germination. 



The dependence of plants upon their mycorrhiza may explain 

 in part why such plants are extremely hard to transplant. When 

 taken from their native environment, the young roots are likely 

 to be broken off and with them the mycorrhiza. They are then 

 often placed in a soil which may lack completely all of the co- 

 operating fungi, in which case death is almost sure to result. Such 

 transplantings should be made with due care to keeping intact 

 as many of the feeding roots as possible, and some of the same 

 soil from the original locality may profitably be placed around the 

 roots in the new location. It might be added at this point that 

 Martin-Zede (1922) showed that success in transplanting was 

 connected also with the orientation of the tree. When trees were 

 oriented as they had been before, the mortality was only 7%, 

 while if they were placed in a different position in regard to the 

 points of the compass, 50% died. 



The bacteria which live in the nodules on the roots of legumes 

 (Chap. IX) are another excellent example of mutualism. These 

 bacteria receive organic food from the legume and in turn produce 



