Lecture VI —11— Environment 



sporophores of certain hymcnomycetes which form ectotrophic mycor- 

 rhizae with roots of trees. Guinier supposed that benefit of the 

 fungi to the higher symbiont consisted in accumulation of ammonia 

 in the soil. Mitchell (1937), in experimental studies with coniferous 

 seedling beds treated with various N, P, and K combinations found 

 that the benefits attributable to mycorrhizae, like their distribution in 

 nature, vary inversely as the concentration of readily available mineral 

 nutrients in the soil. As to what these mineral nutrients may be, a 

 paper by Chandler (1941) indicates that decay of leaf litter in a 

 central New York hardwood forest returns Ca to the soil in greatest 

 amount, N in the second greatest, followed by P, K and Mg. McComb 

 (1944) indicates P rather than N as incentive to good growth in 

 conifers. 



Soil Reaction: — Anyone who has worked wdth soil reaction tests 

 knows the difficulties of securing an accurate reading for that highly 

 buffered colloidal thing called soil ; and if he has studied the relation 

 of plants to soil /jH, knows further the wide tolerance most plants 

 show for h.i.c. He is not surprised that Biraghi (1936) reports 

 cereals growing in soils of /)H 5 to 8, and he has sympathetic under- 

 standing for the report that Pinus radiata was planted in grey sand of 

 pU 6.18. 



Long ago Melin (1925) stated that optimum conditions for fungi 

 of pine and fir are provided by pH values between 4.0 and 5.0 and he 

 noted with interest that this observation accorded well with observed 

 pH values for middle and northern Europe recorded by Hesselman. 

 Henry (1933) found trees and shrubs mycorrhizal on soils of pU 

 5.0 in Butler County, Pennsylvania. For Pinus Strohus, McArdle 

 (1932) reports a /)H of 6.0, a little lower for spruce. Germinating 

 seed and young seedlings of P. echinata cannot survive in culture 

 media having a soluble Ca content of approximately 500 p.p.m. or 

 more and a pH value of approximately 6.5 or more, or having either 

 of these characteristics. This condition was evidenced by behaviour 

 of seed in greenhouse cultures and of seedlings in nursery beds. With 

 P. caribaea in Australia, Young (1938) concluded from experiment 

 that "The efficiency of the mycorrhiza is increased with increasing 

 acidity up to pH 4.7 and thereafter is adversely affected." For orchids, 

 Burgeff (1932) found the optimum values lying between pH 5.0 and 

 6.0; while LaGarde (1929) said that h.i.c. is of the greatest impor- 

 tance in germination, growth being best at pK between 4.8 and 5.2; 

 and above 6.0 no germination took place. 



It is evident that soil reaction affects the fungal symbiont rather 

 than the higher plant because the latter is virtually isolated from the 



