pure cultures of the host-plants, and since we can do this, there is no reason why the infection of Uredineae should not be conducted as rigorously and exactly as that of bacteria. As matter of fact, I have succeeded in proving that it can,[1] though of course the length of time occupied in a large series of cultures and infections will prove troublesome, and it remains to be seen whether we can get such plants to flower.
The following Table IV gives the results of an additional series where B. secalinus was the host, and spores from the same used as as infecting material. In this case the tubes used were closed from the first (see fig. 2). These results appear to me to dispose effectually of the question as to whether or not pure cultures of Uredineae can be obtained.
A number of isolated tube-cultures were made with spores from B. sterilis, B. mollis and B. sccaliiuts, and arranged similarly, and confirmatory results obtained. Moreover, I was able in several cases ta transfer successfully spores from these pure tube-cultures to other tubes of pure cultures of seedlings, and to prove that the spores raised under strictly antiseptic conditions are capable of germination and infection.
At the same time, it was noteworthy that in several cases the anti-septically raised spores were not always successful in infecting the seedlings, and it remains for further investigation to determine whether this was due to the conditions of culture of the fungus or the host or both.
Experiments with Mineral Supplies.
The question arose during some of the tube-experiments, Do infection and incubation occur normally if the host-plant is suffering from a lack of any particular ingredient in the soil e.g., one of the essential minerals ? To answer this, I prepared tube-cultures as before as in experiments Nos. 711 and 713, &c. substituting for the normal nutritive solution, in some of the tubes, the same solution minus calcium, or minus potassium, or magnesium or phosphoric acid, respectively, with the results shown in the following Table V. The only positive result was with spores from B. mollis, which infected B. mollis in spite of the lack of Mg salts. In other cases flecks only were developed.
This experiment cannot be regarded as very decisive, but it at least shows that infection can occur when Mg is lacking, though the incubation period (13 days) was somewhat long. As the pot-cultures show, no positive results were to be expected with B. waximus infected from B, mollis.
- ↑ I.e., of course so far as fungi are concerned : the antiaeptic treatment adopted does not always exclude harmless bacteria.
