Dec. 9.1918 Seedling Diseases of Conifers 527 



of the artificial media used. In typical experiments the inoculum 

 fragments were distributed among the seed over a sector of the pot 

 approximately one-fourth the area of the surface sown. In special 

 cases the inoculum was limited to one or two fragments, while in other 

 experiments fragments were distributed over the entire surface of the 

 soil. In a few of the earlier experiments pots were covered, except 

 during the seed-sowing process, until germination. Stands whose legs 

 were set in pans of water were used in most of the experiments to exclude 

 slugs and ants. In the majority of the inoculations the control pots 

 were given sterile agar from the same lot as that serving as substratum 

 for the cultures placed in the inoculated pots. Results in such experi- 

 ments were not noticeably different from those in which the controls 

 received no agar. In the later experiments all watering was with heated 

 water, resulting in a decrease in the amount of contamination as indi- 

 cated by a lesser damping-oflf occurring in the control pots. 



Reisolations, like the original isolations, were made by planting re- 

 cently affected seedlings in solidified agar plates and transferring from 

 the advancing margins of the resulting growth. Reisolations were made 

 only in experiments in which the control pots had remained free from 

 disease. 



DEFICIENCIES IN STANDARD METHOD 



The above method of conducting inoculations, involving sterilized soil, 

 heated water, heavy seeding, and heavy inoculation, is a convenient one. 

 The first two of these features are necessary when it is desired to keep 

 the controls entirely free from disease and reisolate the organisms used 

 in the inoculation work. It is the method which has been used by most 

 recent experimenters with root parasites. Attention should, however, be 

 called to the fact that it is not a reliable index of what takes place in 

 ordinary seed beds unless supplemented by experiments under more 

 nearly natural conditions. It is well established that as a substratum 

 for the growth of either higher plants or of fungi steamed soil is a very 

 different thing from normal soil. The quantity of water-soluble matter, 

 both organic and inorganic, is changed; the composition of the organic 

 and inorganic matter is changed; and the effects of destruction of the 

 original microflora and fauna, which can be hardly reestablished for 

 several months in the original composition and balance, can scarcely fail 

 to be reflected upon both hosts and parasites grown in the steamed soil. 

 That the changes due to steaming are of more than theoretical importance 

 is shown by the comparison of results of inoculations on steamed and 

 unsteamed soil. Successful inoculation, at least with some of the para- 

 sites, seems much easier to secure in steamed than in normal soil. A 

 further indication that heating soil is likely to abnormally favor damping- 

 off parasites is seen in the heavy spontaneous losses occurring on soil 

 subjected to temperatures of only 80° to 90° C. at some nurseries. In 



