Lecture VI — 89 — Environment 



nurseries in Western Australia with the appropriate fungi, thus obtain- 

 ing normal growth of the tree seedlings (Kessell, 1938). The inocu- 

 lated plants when put out in the forest are said to infect the soil quite 

 satisfactorily. Rayner (1938) gathered together various reports on 

 soil inoculation from nurseries and plantations, particularly from the 

 British Empire. In northern Rhodesia it was found that Pinus 

 halepensis only amongst several exotic pines made any growth beyond 

 the seedling stage without soil inocula, whereas inoculation with soil 

 from a southern Rhodesian P. radiata plantation caused remarkable 

 stimulation in growth in several spp. of pine. In Nyasaland, all species 

 of pine observed except P. longifolia and Araucaria failed to grow 

 without inoculation. At Buitenzorg in Java, P. Merkusii is completely 

 dependent on the presence of mycorrhizal infection for normal de- 

 velopment, inoculation resulting in vigorous growth and rapid spread 

 of infection from plant to plant. In New Zealand, inoculations of 

 P. radiata with Boletus-'miected soil gave positive results (whatever 

 that means), the control plots remaining free from infection. In India, 

 Casiiarina flourished after inoculation whereas controls died within 

 three years. Caragana became established in Canada after use of soil 

 inocula. At a new forest tree nursery in Iowa, pine seedlings failed 

 to grow unless they developed mycorrhizae (McComb, 1943). On the 

 other hand, S. A. Wilde remarked in a recent review that "99 percent 

 of all practicing foresters will not have to lose any sleep over the 

 problem of mycorrhizal inoculation." 



Compost Studies: — But soil inoculation with mycorrhizal fungi 

 does not necessarily lead to mycorrhizal formation because the soil it- 

 self may be unfavourable to such formation even though the appro- 

 priate fungi are present. Thus, in Rayner's heath soils mentioned 

 in an earlier paragraph, it was the inhibitory effect of the soil that 

 prevented mycorrhizal formation. Rayner therefore initiated studies 

 of "organic composts" in relation to growth of young trees. Her 

 general conclusion after several years' experiments is that an increased 

 supply of nutrients plays a relatively insignificant part in improved 

 fertility of the soil studied, induced by addition of composts. In the 

 soil are substances deleterious to growth, but their action is obviated 

 by addition of compost although addition of the equivalent amount of 

 salts had no effect. Rayner considers that the striking effects on 

 tree growth brought about by composts on natural soils do not depend 

 to any extent upon the addition of nutrients, but are directly associated 

 with qualitative changes in the humus constituents and with the bio- 

 logical activities related with these changes. They may also, possibly, 

 be associated with the presence of growth-promoting substances in 



