52 BIOLOGICAL LECTURES. 



Hypopitys by Kamienski in 1881. Frank, in a series of studies 

 published between 1885 an d 1891, originated the theory that 

 the higher plant is really parasitic upon the fungus, inducing it 

 to grow on and in its roots, and finally yield its components to 

 the higher plant, and he termed the arrangement a " fungus 

 trap." Recently Janse has endeavored to prove that mycor- 

 rhizas sustain the same functions as leguminous tubercules 

 (1896). The theory of Janse has been found to hold true 

 of Podocarpus and the peronosporous fungus with which it 

 forms mycorrhiza only, although it may be applicable to a few 

 other special forms. 



So far as the mutual dependence of the mycorrhizal symbionts 

 upon each other is concerned, it may be stated, with a fair 

 degree of certainty, that all of the fungi are capable of more or 

 less extended periods of growth and endurance in the soil ; 

 though to what extent has not been ascertained. The higher 

 plants which habitually form mycorrhizas are capable of devel- 

 opment in sterilized soils, but according to Frank's experi- 

 ments they do not attain the size of specimens united with 

 fungi in the usual manner. This applies only to those species 

 which are furnished with chlorophyl, and Frank's experiments 

 were made with coniferous trees. The capacity of such chlo- 

 rophylless forms as Monotropa and Pterospora for growth in 

 sterile cultures has not yet been determined, though I hope to 

 have some results wifhin the coming season. It is pertinent 

 to recall in this connection the fact that when spruces or other 

 coniferous trees with mycorrhizal roots are cut down, the stump 

 often forms a callus plate, which finally covers the entire in- 

 jured surface, and it continues to live without forming leaves 

 or other organs for constructing food from the air. This was 

 thought by Frank to demonstrate that the living stump was 

 parasitic on the fungus attached to the roots. This conclusion 

 did not take into account the comparatively enormous amount 

 of food stored in the roots of the tree, or of probable metabolic 

 capacities of the protoplasm of the tree not possessed by the 

 fungus. 



Omitting the discussion of the anatomical details of the 

 union of the two plants which form a mycorrhiza, I may say, 



