IMPORTANCE OF MYCORRH1ZAE TO FORESTRY 311 



nature is not satisfactorily explained by these experiments of 

 Knudson. 



Importance of mycorrhizae to forestry. Evidence from ob- 

 servations extending over a period of years has been accumulating 

 which tends to show that mycorrhizae plav an important role in 

 reforestation and afforestation. As long ago as 1917 [Hatch 

 (1937)] Aielin noticed that seedlings of pine and spruce, started 

 from wind-distributed seed in recently drained peat bogs, ex- 

 hibited nitrogen starvation and eventually died unless they be- 



O J J 



came invaded with mycorrhizal funoi. Seedlings in entire nur- 

 series in Australia, southern Rhodesia, the Netherlands East Indies, 

 and the Philippines remained unthrifty when the nurseries were 

 located outside the natural range of the species being grown 

 [Hatch (1936)]. When soil from established nurseries or from 

 sites where the species was endemic was incorporated as inoculum 

 in these seed beds, however, the seedlings recovered and grew 

 normally. Similarly, non-mycorrhizal seedlings made poor 

 growth in plantations until they were inoculated with small quan- 

 tities of soil containing mycorrhizal fungi. 



More convincing evidence of the beneficial nature of mycor- 

 rhizae has been supplied by Rayner (1934, 1936, 1939), Hatch 

 (1936, 1937), and Young (1940). Rayner reported experiments 

 in which she applied pure cultures of mycorrhizal fungi to soils 

 in which seedlings were making poor growth and in which my- 

 corrhizae were infrequent. As a result of such inoculations, seed- 

 ling growth was markedly stimulated, and correlated mycorrhizal 

 formation was abundant. 



Since transplants in the Prairie States grew poorly, Hatch 

 planted Finns strobus seed in pots of prairie soil in an effort to 

 determine the cause. The seedlings grew poorly, and mycor- 

 rhizae were lacking. He then inoculated a portion of the pots 

 with pure cultures of mycorrhizal fungi. The inoculated seed- 

 liners responded by increased growth over the uninoculated ones 

 to the extent that, after two months, analyses showed the inocu- 

 lated seedlings had 75% more potassium, 86% more nitrogen, and 

 234% more phosphorus than the uninoculated. Young grew 1600 

 Pinus caribaea in soil that had never grown pines. He mixed 

 manure and pine needles with the soil to supply organic materials. 

 As inoculum he used 7 mycorrhizal fungi. In all cases the un- 

 inoculated controls made the poorest growth, with best growth 



