51 



Series J. Left exposed to the air. 



Series II. Covered with soil. 



Series IIT. Covered with 'dead leaves. 

 After one year had elapsed, namely in the middle of September. 

 1927, a careful inspection of the inoculations was made. The 

 results showed that where the roots had not dried out unduly due 

 to exposure to the wind, the fungous growth was slight. Where 

 the roots had become somewhat dried, the fungous growth was 



In the belief that the presence of much water in the tissues of 

 normal roots might have a deterrent effect on the fungous growth, 

 inasmuch as the water would tend to shut out air. an experiment 

 was now set up in the laboratory at the Carden, which would test 

 this point, as well as the tannic-acid hypothesis. A set of 15 



autoclaved and inoculated with the fungus. 



The rather remarkable result, in view of all previous hypoth- 

 eses, was that the fungus now <wcw and sporulated much more 

 luxuriantly on the root segments than on the stem. This seemed 

 to dispose of the tannic acid hypothesis once for all, unless, indeed, 

 sterilization had changed the nature of the tannin compounds. 

 making them less effective. It also disposed of the hypothesis that 

 the greater amount of water in the root tissues may be inimical to 

 the fungus on account of exclusion of air, for during the process 

 of sterilization in the autoclave, both root and stein segments be- 

 came pretty well waterlogged. 



The experiment was now tried out again on the living material 

 in the laboratory, where it could be under constant surveillance 

 segments of live roots and stems of similar diameters being care- 

 fully washed in bichloride of mercury (1-1000), rinsed 3 times 

 in sterile water, stabbed and inoculated from a pure culture of 

 Endothia in oat agar, and placed in sterile test tubes. Under these 

 conditions the results paralleled those obtained in the field: in the 

 majority of cases the fungus made only slight growth on the roots, 

 but had an opposite effect on the stems. That the fungus \va> 

 nevertheless present in the roots was proved by the presence 

 usually of one or more tiny fruiting bodies around the inoculation 

 ; discoloration. Some of these root- 



