ARTIFICIAL INFECTION 



83 



and specific needs. In particular work the surface thus injured 

 should be washed, cleansed with a disinfecting solution, if the struc- 

 ture will permit, and again washed with distilled water before the 

 inoculation is made. In work of this character the spores or 

 mycelium for inoculation should be taken from a pure culture ; 

 indeed, pure cultures should always be used if the fungi are cul- 

 turable, except where the only 

 material available is hopelessly 

 mixed, and the inoculation is 

 only desired to eliminate some 

 of the saprophytic forms. It is 

 usually well to covet the wounds 

 with grafting wax (Fig. 18), or 

 some other similar adhesive con- 

 taining no injurious substance. 

 This will be possible in the case 

 of stem diseases. In this case 

 the control experiments should 

 be wounded and covered with 

 wax as well, so that the condi- 

 tions may be quite the same. In 

 some instances absorbent cotton 

 may replace the wax. 



Whenever the air may too 

 readily serve as a source of con- 

 tamination, plants of large size may be fairly well protected from 

 this source of danger by using practically air-tight glass frames, into 

 which the air may enter only after filtration through cotton, and 

 smaller plants may be accommodated under bell glasses with open 

 tops loosely plugged with cotton. 



Certain disease organisms gain entrance through the roots, as 

 in the case of Neocosmospora vasinfccta. It will be evident in 

 such cases that the soil should be inoculated. If possible, the plants 

 to be inoculated should be grown in sterilized soil, but another con- 

 sideration of importance frequently is to have the soil conditions 

 imitate as closely as possible the conditions under which the disease 

 was developed in the field ; thus the type of soil and the percentage 

 of soil moisture are important. 



Fig. 18. The Use of Grafting Wax 

 in Inoculation Experiments 



