vil] MYCORHIZA 207 



by transpiration less readily. Though many excep- 

 tions can be observed, there seems to be a very 

 general association of the development of mycorhiza 

 with a diminished transpiration and the absence of 

 starch from the leaf, especially among plants like the 

 orchids, lilies, iris, etc., which often grow in dry or 

 shady situations, such plants being further distinguish- 

 able by a shiny, glossy leaf surface. Stahl has again 

 shown that the average proportion of ash to dry 

 matter in the leaf is lower for mycotrophic than for 

 normal plants; the former grow, as a rule, in situa- 

 tions containing but little mineral salts, particularly 

 in humic soils, where, in addition, the plant is put 

 into competition for whatever nutriment may be present 

 with the mycelia of fungi, which everywhere traverse 

 humus in its natural state. By direct experiment, it 

 has been shown that normal plants grown in humus 

 develop better when the humus is previously sterilised 

 by long exposure to chloroform vapour than when it 

 is in its fresh condition, full of living mycelia com- 

 peting successfully for the nutriment. The absence 

 in the leaf of calcium oxalate and of nitrates is 

 particularly characteristic of mycotrophic plants. 



Stahl concludes that symbiosis between the roots of 

 plants and the mycelia of fungi is a very general 

 phenomenon, especially characteristic of plants growing 

 in soils subject to drought, or poor in mineral salts, 

 or rich in humus. These mycotrophic plants are 

 generally of slow growth, possess a feeble transpiration, 

 and limited root development ; their leaves rarely con- 

 tain starch ; they are also characterised by containing a 

 comparatively small proportion of mineral salts, among 

 which calcium oxalate and nitrate are notably absent. 



To the mycorhiza associated with plants of the 

 genus Erica the power of fixing atmospheric nitrogen 



