of a Uredinc, Puccinia dispersa (Eriks.}. 459 



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,* though of course the length of time 

 occupied in a large series of cultures and infections will prove trouble- 

 some, 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 con- 

 firmatory 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 infec- 

 tion 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 nutri- 

 tive 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 incuba- 

 tion 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. 



