Rayner.—Obligate Symbiosis in Calluna vulgaris. 103 
With this exception, in spite of the large and constantly increasing 
number of plants which are known to possess an endotrophic Fungus in the 
root tissues, nothing is known with certainty of the systematic position 
of the Fungi concerned. 
Many workers have endeavoured to isolate the Fungus concerned 
in endotrophic mycorrhiza. and the history of these efforts is not without 
interest. 
The task of isolating the Fungus from pieces of Orchid root was essayed 
by Wahrlich (1886) ( 21 ), Chodat and Lendner (1898) ( 22 ), and Bernard 
(1903) ( 23 ), and in all three cases resulted in the extraction of a species of 
Fusavium , which was believed for a time to be the true endophyte. 
Gallaud (1905) (20), in a series of researches extending over several 
years, worked on thirty-five species of flowering plants of widely separated 
affinities. From the roots of thirty of these he isolated with great 
regularity a species of Fusarium , which he obtained also but with rather 
less regularity from the roots of four of the remaining species. 
His cultures showed that, in addition to Fusarium , a number of other 
Fungi were constantly present on washed roots ; among the more 
common genera were Mortierella, Trachoderma , Cephalospermum , and Glio- 
cladium , with which are constantly associated species of Alternaria, Acro- 
stalagmus , &c. 
Inoculation experiments showed that Fusarium and the other species 
named were not the true endophytes, and established the fact that the 
species obtained in this way are constituents of the mycelial flora habitually 
associated with roots growing in ordinary soils. 
Gallaud concluded that it was impossible to extract the endophyte 
directly from the roots, and believed the difficulty to arise in some degree 
from the alteration or partial digestion undergone by the Fungus in the cells 
of the plant, and its subsequent inability to grow out of the cells. 
Bernard, in 1903 and succeeding years, isolated fungal species from 
the roots of various Orchids ; using a pure culture of the appropriate 
Fungus, and sterile seeds removed from unopened capsules with aseptic 
precautions, he was able—for the first time—to effect the synthesis of 
Orchid plant and Fungus, and thus to induce successful germination of the 
former. He referred these Fungi provisionally to the genus Oospora ( 24 ). 
In the course of subsequent researches (1905, 1906) ( 25 ) Rhizoctonia 
was suggested as the nearest generic ally among free-living Fungi for 
species isolated from Phalaenopsis , Odontoglossum , and Cattleya. 
Burgeff holds that the endophytic Fungi of the Orchids are to be 
regarded as forming a group morphologically and physiologically distinct, 
for which he suggests the generic name of Orcheomyces , leaving the 
correct systematic position of the genus an open question ( 14 ). 
Ternetz ( 26 ), working at the root Fungi of Ericaceae, isolated pycnidia- 
