1922] - KNUDSON—ORCHID SEEDS 23 
infected. The diameter of the embryos in this case reached from 
0.6 to 0.8mm. in the same time. With infection still more 
advanced, but less than normal, a few seeds had leaves after seven 
‘months. Normally infected embryos produced leaves, and embryos 
that adhered to the wall of the tube likewise germinated. An infec- 
tion more advanced than normal caused the same development as 
an infection slightly less than normal. When from one-half to 
two-thirds of the embryos became invaded, growth was less than 
in the embryos not infected, and in another case the seeds were 
killed outright. 
As stated, certain facts from these experiments make it difficult 
to explain the action of the fungus as purely external. If so, why 
should the fungi behave so differently in inducing or retarding 
germination? Unfortunately BuRGEFF gives no details so that one 
may judge whether or not these results could be duplicated on 
second trial. Another difficulty is an adequate explanation for 
the germination of seeds adhering to the inner surface of the culture 
tube. It is possible, of course, that decomposition products of the 
fungus growing on the surface of the tube may have been the cause. 
It is desirable to await experiments with the fungus before attempt- 
ing to discuss these points further. 
There are other phases of the problem presented by BERNARD, 
especially the loss by the fungus of its capacity to induce germina- 
tion after prolonged culture in the laboratory. It is entirely 
possible that there has been no loss in the fungus, but that at the 
time of inoculating the culture the physiological state of the embryos 
was such as to resist or permit of infection. Those in which the 
infection was confined to the lower cell could still germinate despite 
the fungus. Those invaded to a greater extent would be killed. 
These and other experiments of BERNARD and BURGEFF suggest 
that one of the causes for the failure of germination is the parasitic 
character of the fungus. In other words, it is possible that the 
fungus, instead of being an aid in normal germination, is a factor 
in the death of the embryos and consequently in the failure of 
germination. 
In conclusion, it may be stated that the evidence for the 
necessity of the fungus for germination has not yet been conclusively 
proved. The evidence is conclusive that under conditions of pure 
