Recent Work on Rndotrophic Mycorhiza. 165 
them up in any kind of evolutionary sequence or make clear the 
bionomics of mycorhiza in vascular plants. 
The necessity for such evidence was first clearly recognized 
by Noel Bernard (1—12) whose work marks the beginning of a new 
stage in the history of research on mycorhiza—another landmark 
in the field of investigation opened up by Frank and his fellow- 
workers nearly twenty years earlier. 
When Bernard undertook his researches into the bionomics of 
the relationship between plant and fungus in the orchids, it must 
be realized that no information was available as to time or mode of 
infection of the orchid seedling, nor was anything known of the 
degree of dependence—if any—of the two organisms upon one 
another, or of the systematic position of the fungi concerned. 
On the other hand great difficulty was experienced by orchid- 
growers in germinating the seeds of certain species,—a source of 
much loss and inconvenience in this branch of horticulture. Bernard 
very sagaciously assumed that this practical difficulty might have 
to do with a critical stage in infection by the appropriate fungus 
and directed his researches with the view of proving this hypothesis 
experimentally. 
He thus summarized the chief objects of his investigation. 
1. To germinate seeds of the orchids under aseptic conditions 
on sterilized media suitable for their culture. 
2. To isolate the root-fungi, grow them in pure culture and 
identify them with certainty. 
3. To compare—for each orchid species—the behaviour of 
aseptic cultures with those of seeds infected by the endophyte. 
By using seeds removed aseptically from sterilized capsules 
and sown under aseptic conditions, Bernard demonstrated the 
impossibility of raising uninfected orchid seedlings and showed 
incidentally that infection takes place subsequent to seed-sowing. 
He then proceeded to isolate and cultivate the root-fungi from 
various species of orchid, and was successful where all previous 
workers had failed. He tested the identity of the fungi isolated in 
this way by inoculation of sterile seeds, induced successful germin¬ 
ation of the most refractory species by this means, and so 
demonstrated conclusively the obligate nature of the association. 
In later papers he described the details of infection in various 
orchids and the germination thereby effected, together with many 
interesting observations showing the delicacy of the physiological 
adjustment. For example, early experiments with Ccittleya and 
Cypripedium showed that the fungus from Cattleya was effective in 
