54 BIOLOGICAL LECTURES. 



tropacece), formerly included with the heaths, comprise nine 

 genera, Allotropa, Monotropa, Pterospora, Hypopitys, Sarcodes, 

 Newberrya, Schweinitzia, Pleuricospora, and CheilotJieca, all of 

 which have lost their chlorophyl and depend upon the fungi 

 symbiotic with their roots for organic nutriment. All of these 

 genera are inhabitants of the north temperate zone, arranged 

 in a belt which circles the globe, but with the greater number 

 of species and genera in western North America. 



Hitherto all chlorophylless seed plants which were not para- 

 sitic have been classed as saprophytes, but in some recent pub- 

 lications I have been able to show that this term may be applied 

 only to one species of seed plants, Wullschlczgelia apJiylla. 

 All other so-called saprophytes are found to be symbiotic with 

 fungi in such manner as to form mycorrhizas. The tendency 

 to form mycorrhizas is most marked among species living in 

 humous soils. The percentage of the flora with the mycor- 

 rhizal habit increases from the arctic circle to the equator 

 as a consequence of this fact. Hoveler describes mycorrhizas 

 on 24 of the 72 species, native and cultivated, which he exam- 

 ined in northern Germany. Schlicht found 70 of the 105 

 species native to northern Europe to be provided with mycor- 

 rhizal adaptations. The writer found 13 of the 15 selected 

 species growing in the United States to be mycorrhizal. 

 Janse found mycorrhizas on 69 of the 75 species growing in 

 Java, which he examined. Wahrlich examined 500 species of 

 orchids, chiefly from the tropics, cultivated in the greenhouses 

 at Moscow, all of which he reports as being furnished with 

 mycorrhizas. 



The identity of the greater number of fungi which enter 

 into mycorrhizal combinations is unknown. Present informa- 

 tion leads us to believe that each species of the higher plants 

 forms mycorrhizas with one, or at most two or three fungi only 

 in the different parts of its range. On the other hand, it is 

 fairly probable that one species of fungus is capable of enter- 

 ing into such combinations with several of the higher plants. 



Tulasne noted the fact that Elaphomyces forms the ecto- 

 tropic mycorrhizas on the roots of pines, to which Boudier 

 attributed a parasitic relation. Reissek determined the fungus 



