VALUE OF CULTURAL CHARACTERS. 



179 



few cultures, he will then in all probability have covered only a fraction of the curve 

 A B, let us say between C and D, and not the whole curve of growth. If, now, 

 another worker should happen to experiment with potatoes capable of giving rise in 

 the organism to phenomena represented by that part of the curve lying between A 

 and A', he would get somewhat different results and yet this would not prove 

 steamed potato to be a worthless culture-medium. The only real facts in the sup- 

 posed case are that neither person has experimented sufficiently to draw up a proper 

 description of the characteristics of the given organism on potato. Let us suppose 

 we have to do with a yellow organism, e. g., Bacterium phaseoli and that A to A' 

 represents a pale yellow growth, with no graying of the potato, while D to B repre- 



Fi g . 142.* 



sents a very deep yellow growth, with very decided graying of the potato. The 

 cultures look like different organisms, but they are not. The descriptions would 

 differ. Neither account alone would form a proper description of the behavior of 

 this organism on potato, but there should be rather a combination of the two and 

 of all intermediate stages, viz Potato : Color van-ing from pale to deep yellow, 

 flesh of the potato usually grayed, but sometimes remaining unchanged, etc. The 

 same remarks apply to other non-synthetic media. 



*Fic. 142. Iris-rhizome rot. A dense sowing of the organism in an agar-plate culture after 45 

 hours at 25 C. The buried colonies small. Not van Hall's organism, which, as received from 

 Krai of Prague, is non-pathogenic in my hands. 



