452 Prof. H. Marshall Ward. On Pure Cultures 



Tube-cultures. 



In order to obtain more decisive answers to such questions as Are 

 any of the results obtained on plants in the open, or merely covered 

 with bell-jars and so forth, due to spores accidentally introduced, or to 

 mycelium, &c., already in the plant ? a number of infections were 

 made on seedlings germinated and grown anti-septically in tubes as 

 follows : 



As a preliminary trial, to test whether grass seedlings would live 

 long enough in tubes and show the results of infection, I placed seed- 

 lings, all similar, and bearing three to four leaves, in test-tubes, the 

 roots, carefully washed free of soil, resting on wet cotton wool, and 

 the orifice of the tube plugged. The results of two series apparently 

 showed that spores from B. mollis infect B. mollis and B. sterilis* 

 B. secalinus and B. arvensis, but not B. inermis, while spores grown on 

 B. sterilis only infected B. secalinus and B. arvensis (see Table I). 



It is a striking fact that under the conditions afforded by these 

 closed tubes, with their stagnant moist atmosphere, spores from B. sterilis 

 apparently succeeded in infecting B. secalinus and B. arvensis. The 

 pustules were small, and it is significant that it took 14 days' incuba- 

 tion to establish the mycelium, against 9 days in the case of spores 

 from B. mollis. 



There are, however, other slight departures from the usual course of 

 events e.g., spores from B. mollis failed on B. arvensis and succeeded 

 on B. sterilis which may point to the probability that these uprooted 

 seedlings in tubes are not in their normal conditions. The facts seem 

 worth recording in this connection. 



I varied these tube-cultures by placing them, after infection, under 

 cuvettes filled with copper sulphate (blue light) or bichromate of 

 potassium (orange light). The results were somewhat contradictory 

 as regards the blue, but it did appear that the spores coming from 

 B. mollis can infect B. sterilis as well as B. secalinus, as the following 

 Table II shows. 



It is important here to bear in mind the origin of the seedlings 

 themselves, however, as a serious source of error was discovered in 

 these uprooted seedlings, previously exposed to possible infection in 

 the open. 



The same criticisms, in fact, apply to these transplanted garden 

 seedlings in tubes as I have given elsewhere regarding such experi- 

 ments in pots, viz., it was always possible that the seedling was already 

 infected, or had wind-blown spores on it when removed from the beds. 

 At the same time the long incubation period, 14 days in some cases, 

 fails to support this. 



* An exceptional circumstance, as numerous experiments have shown, and 

 itself sufficient to raise the criticism which follows. 



