JuLy, 1922.} THE ORCHID REVIEW. 199 
is nevertheless true that failure of germination is more common than 
success, even when the fungus is provided. Bernard’s experiments reveal 
case after case, in which the introduction of the fungus was followed by 
death of the seeds or failure to germinate. He states as follows :— 
“The germination by inoculation is not obtained without certain 
difficulties. For five years I have sown seeds of diverse species of Orchids 
in culture tubes, each of which contained roo seeds, and these I have 
inoculated with Rhizoctonia obtained from the roots. Altogether, I have 
obtained a few hundreds of seedlings, but I underestimate when I place 
the number of seeds used in my experiments at 50,000. For the majority 
of the seeds, the association with the fungus that 1 have placed in their 
presence has been merely passive and without effect, or impossible, or 
rapidly injurious to the embryos.” 
It would be well not to lay undue stress upon this statement. Bernard 
was probably too much imbued with the idea of the identity of fungi of 
merely similar appearance. Flasks showing percentages of germination in 
Odontoglossum, hardly dreamed of by Bernard, have been repeatedly 
exhibited during the last eighteen months : those in the Scientific Tent at the 
Chelsea Show last year, were in no wise picked flasks, save that they were 
chosen to illustrate certain points—they were typical rather than exceptional. 
Moreover, during the last few months, such success has been obtained with 
Cattleyas, that Bernard’s further idea that in this genus more certain and 
regular results are obtained by stimulating seeds chemically, than by sowing 
them on the fungus must be abandoned. 
Bernard believed that the action of the fungus was physico-chemical : 
the fungus causes an increase in the concentration of the cell sap, and 
induces germination and protocorn formation, in a way similar to that in 
which the forms of unicellular alge are changed by increasing the 
concentration of the external solution. Knudson believes that the fungus 
may bring about germination in another way. Bernard used salep in all 
his media. ‘In view of the fact that organic matter is present, it is 
conceivable that the influence of the fungus might be to digest some of the 
starch, pentosans, and nitrogenous substances ; which digestion products, 
together with secretions from the fungus or products produced on decom- 
position of the fungus, might be the cause of germination. In brief, it is 
conceivable that germination is induced not by any action of the fungus 
within the embryo, but by products produced externally on digestion or 
secreted by the fungus.” 
Knudson faces many of the difficulties which his theory meets with in 
interpreting various results obtained both by Bernard and by Burgeff, but 
is hampered in not knowing whether certain results were typical, or 
anomalous. 
