6 THE ORCHID REVIEW. (January, 1918. 
with mycorhiza, but Kusano demonstrated a remarkable case of symbiosis 
between it and the fungus known as Armillaria mellea (one of the Agarics), 
a common fungus on dead and living roots of Quercus in the neighbourhood, 
and which is recorded as a troublesome parasite on the potato-tuber on 
farms near the woods. The history of the association is given, and it is 
said that without infection by the fungus the Orchid is incapable of 
flowering. After infection, food materials, derived from the fungus? 
accumulate in the cells, serving ultimately for the development of the 
inflorescence and for the nutrition of the daughter-tubers. The latter 
continue to grow as long as they remain attached to the parent-tuber, but 
afterwards the majority (failing infection) undergo a gradual diminution in 
size from lack of food material, and die without flowering. 
It is a complex relationship. The fungus is parasitic in its mode of 
entry and in its behaviour in certain zones of the infected cells, but in 
another region there is accumulation of food material brought in by the 
fungus, and the mycelium is ultimately digested. Upon this food the 
production of flowers and the nutrition of the offsets, or young tubers, is 
entirely dependent, and the Orchid must be regarded as completely parasitic 
on the fungus during part of its life history. The fungus, however, is 
entirely unmodified by the association, and produces normal fructification, 
a condition unique among fungi forming endotrophic mycorhiza. 
Nothing is yet known of the behaviour of the germination of the seeds of 
this curious Orchid, but it is remarked that in view of the dependance of 
the majority of Orchid seeds upon infection at a critical stage of germina- 
tion, and of the observed facts of vegetative infection of the Gastrodia tuber, 
the results of experimental seed culture will be awaited with particular 
interest. Kusano, indeed, suggests that in Gastrodia there is represented 
the first step in the formation of a special mode of parasitic life, which 
gives rise ultimately to a reciprocal exchange of food-materials, hence he 
regards the arrangement as probably a primitive stage, but Rayner well 
remarks that the conclusions are open to criticism in view of the extreme 
specialization and reduction of the Orchid, and difficult to maintain after 
his demonstration that the réle of ‘‘ host”’ is played by the fungus and not 
by the Orchid-tuber. 
We would add that Gastrodia elata also flourishes in the Himalayas, 
and it would be interesting to know if the same fungus also serves there as 
host. The relationship is not necessarily exclusive, and in any case 
Armillaria mellea is a widely-diffused fungus in temperate regions, extending 
far beyond the limits of the Gastrodia. G. elata, again, is only one of at 
least a dozen species of a genus that extends from Japan and North India 
through the Malay Archipelayo to Australia and New Zealand, so that 
there is a wide field for observation. 
