Recent Work on Endotrophic Mycorhiza. 167 
without making any definite suggestion as to their systematic 
affinities. 
The experimental evidence obtained by Bernard and Burgeff 
is contradictory with regard to the practicability of maintaining the 
fungus in pure cultures without impairment of its power of effecting 
germination. For example, Bernard found that a root-fungus isolated 
from Cattleya was scarcely capable of inducing germination after 
17 months in pure culture outside the plant. Burgeff, working with 
another orchid, found the powers of the fungus unimpaired after 
26 months cultivation on artificial media. This author also expresses 
the opinion that in certain cases the fungus isolated from endemic 
species can be used for inducing germination of the seeds of tropical 
species—an observation which bears out the earlier observations of 
Bernard and is of practical interest to orchid-growers. 
Such inconsistencies suggest that the degree of dependence 
varies in different orchids. The more specialized the relation 
between the two partners, the more easily is the adjustment thrown 
‘ out of gear’ by cultivating the fungus outside the plant. 
Until 1915, the case of the orchids remained unique as being 
the only one in which the endophyte had been isolated and in which 
an obligate relation between the two symbionts had been experi¬ 
mentally demonstrated, but in that year Rayner (14) showed that a 
similar condition of obligate symbiosis existed in Ericaceae. It was 
proved experimentally that seedlings of Calluna vulgaris , raised 
under aseptic conditions from sterilized seeds do not develop beyond 
the seed-leaf stage and are incapable of forming roots. The infecting 
fungus was isolated, grown in pure culture and proved to have the 
morphological characters of the genus Phoma, a member of the 
Hyphomycetes. Sterile seedlings growing in suitable media under 
aseptic conditions and inoculated from such pure cultures formed a 
vigorous root-system, and developed into normal plants. 
The case of Calluna is probably characteristic of ericaceous 
plants in general. The relations between fungus and plant are as 
specialized and remarkable as in the orchids, although in many 
respects different, and are of considerable interest ecologically in 
view of the edaphic peculiarities of ericaceous plants. 
The occurrence of endotrophic mycorhiza in the roots of 
Ericaceae had long been known, and the more obvious facts described. 
Such cytological observations as had been made, however, gave 
no clue to the nutritive relations, nor was anything known experi¬ 
mentally of the physiology of the relation in this family of plants. 
The facts brought to light are striking and in some respects 
