102 C. D. Shekbakoff 



possible, these transfers were made from the very margin of the colony. 

 But if in a colony there were apparently two or more organisms growing 

 together, this method would invariably lead to isolation of the rapidly 

 growing one and loss of the slower-growing one. In order to save the 

 latter also, the plates with origmal plantings were kept for a long time 

 after the first transfers were made, and now and then dilutions were 

 made from the old colonies. In the majority of cases this work was 

 useless, but in two cases there were isolated verj^ slow-growing fungi ■ — 

 F. dimerum var. Solani and F. udum var. Solani — which otherwise 

 would have been missed. 



The cultures obtained by transfers from original plantings seemed to 

 be, and usually were, pure cultures from the start. Nevertheless it was 

 evident that some method of obtaining cultures from single spores must 

 be employed before a comparative study of the organism could be profit- 

 ably begun. 



In those few instances in which a culture did not produce any spores for 

 a long time and which appeared to be a mixture of more than one fungus, 

 an attempt was made to separate the organisms by the mere planting 

 of a small bit of the fungous growth in the center of a newly poured plate. 

 In only one case was the result satisfactory. This was when a bit of 

 mixed growth of F. arcuosporum and Ramularia Magnusiana, on being 

 planted in a plate, produced from the start on one side a pure gro^^i;h of 

 one fungus and on the other side a pure grow^th of the other fungus. 

 In all the other cases a culture, if transferred mto several different media, 

 sooner or later always produced a sufficient number of spores; and in 

 order to obtain a pure culture the poured-plate method of dilution was 

 invariably employed. 



Considerable economy of time and labor was effected bj^ placing a number 

 of separate drops of sterile water in a sterile plate. By transferring 

 spores from drop to drop, a drop is soon secured in which the number 

 of spores is such that a small loopful transferred to a drop in another 

 plate will contain onlj^ thirty or forty spores. The melted and properly 

 cooled medium is then poured into the plate, and distribution of spores 

 is effected by giving the plate a rotary motion before the medium has 

 hardened. 



The first observation of the dilution plates was made about a day later. 

 At this time most of the spores had germinated and could be observed 



