Recent Work on Endotrophic Mycorhiza. \ 63 
rhiza. The narration of them is a fascinating chapter in the history 
of biological research, and the facts themselves have an immediate 
and practical bearing on the problems of soil ecology. 
From 1887 onwards, researches on mycorhiza fall naturally 
into two groups : viz., those dealing with the ectotrophic and endo¬ 
trophic forms respectively. Despite the accumulation of a large 
number of facts bearing on the physiology of the relationship it is 
not yet clear whether, in the case of the ectotrophic forms, we are 
dealing with an association between plant and fungus differing only 
in degree from that in endotrophic forms, or whether the two types 
became differentiated at an early stage in their evolutionary history 
and differ from one another, not only in degree, but also in the 
essential character of the infection. 
Stimulated by the researches of Frank, records of many obser¬ 
vations on endotrophic mycorhiza were published during the last 
decade of the 19th century. For a detailed list of these reference 
may be made to the papers by Gallaud, Burgeff and Rayner named 
at the end of this review. Among them may be mentioned those 
of Groom on the saprophytic Monocotyledons and Thismia aseroe 
(1894, 1895); Thomason Corallorhiza (1893); Janse on the endo¬ 
phytes of many Javanese plants (1896); Chodat and Lendner on 
Listera cordata (1898); Nobbe and Hiltner on Podocarpus (1899) ; 
Magnus, who published an exhaustive study of the mycorhiza of 
Neottia nidus-avis (1900), and Stahl (1900) whose treatise “ Der 
Sinn der Mykorrhizenbildung ” is in part a record of the author’s 
experimental investigations and in part a comprehensive account 
of the interpretation of the physiology of the relationship which 
he based upon them. The views of Stahl on the subject of 
mycorhiza have been widely quoted in botanical text-books. Certain 
of his experimental observations and conclusions are, however, at 
variance with those recorded in one of the more recent papers here 
reviewed. A brief discussion on the matter under dispute will be 
found towards the end of the present paper (p. 173). 
These earlier researches'showed that the relation between plant 
and fungus—more obviously in the case of plants like the saprophytic 
orchids and Thismia —are intimate and complex, with apparently a 
balance of profit on the side of the higher plant. There is frequently 
a definite succession of phases in the life-history of the fungus, 
the predominance of one or other of these phases being expressed 
by a differentiation of the invaded tissues of the root into morpho¬ 
logical regions. 
In the first phase the mycelium vegetates actively in the living 
