68 BOTANICAL GAZETTE [JULY 
NOTES FOR STUDENTS. 
IN SEARCH of an explanation for mycorhiza Dr. E. Stahl has made a 
comparative study of broader scope than any involved in the previous 
researches upon the subject.” The interesting conclusion of extended observa- 
tions upon the distribution of mycorhiza is that, hydrophytes aside, the large 
majority of vascular plants possess it. Its occurrence, in the words of the 
author, “has an intimate relation with increased difficulties of nutrition.” 
That photosynthesis is so intimately conditioned by transpiration as to 
be approximately in direct proportion to it is a fundamental premise of 
Stahl’s conception. Further, it is assumed as demonstrated that the host, in 
the presence of mycorhiza, possesses a nutritive advantage. Now if it be 
found that mycorhiza is coincident with low transpiration, may not the nutri- 
tive advantage of the former provide a certain compensation for the weakness 
of the latter? Indeed the author seeks to refer the inception of mycor 
hiza to comparative weakness of absorption as an original cause. For, he 
argues, a root system unable to supply the green parts with a transpiration 
stream carrying nutrient salts commensurate with the demand would at once 
induce a need for equivalence of organic substances which it is the function 
of the mycorhiza habit to supply. Holding with Frank that the humus soil 
of forests is in large part “a living mass of innumerable fungal hyphe, — 
the discussion of competition for nutrient salts upon forest floors leads to the 
conclusion that, unless possessed of root-systems of exceptional absorbent 
