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1a Be ee ere 
aa eS 
ON MYCORRHIZA IN RELATION TO FORESTRY. 289 
In the case of Scots Pine, field plots have yielded evidence that, whereas mycorrhiza 
formation can be freely induced experimentally, soil factors inimical to its maintenance 
and free functioning are present in the Wareham soil. 
With regard to the nature of these factors, there is little doubt that bad aeration 
from several causes contributes directly and indirectly to the unhealthy condition 
of the roots. Improvement in this respect in pot cultures in the case of Maritime 
Pine alleviates the symptoms and permits a relatively free development of mycorrhiza. 
This activity is not maintained, and other factors are undoubtedly concerned. 
In this connection great importance is attached to observations on the effects 
produced by supplying phosphates in various forms, alone, or in conjunction with 
humus treatments. 
In respect to soil factors generally, field observations confirm the results of 
laboratory experiments with pure cultures and provide independent proof of the 
extreme sensitiveness of tree mycorrhiza to environmental conditions. 
At Wareham there has been observed a remarkable correlation between vigorous 
spontaneous growth of the trees in localised areas and the appearance of the sporo- 
phores of certain fungi known to be mycorrhiza-formers. This supplies confirmatory 
evidence for the view held that the formation of normal and functional mycorrhiza 
of a type beneficial to the trees is not a resultant merely of the presence of appropriate 
mycelium in proximity to the roots, but is a complex phenomenon controlled by soil 
factors intimately affecting the physiology of both trees and fungi, and ultimately 
determining the behaviour of the mycelium and the reaction of the roots when 
attacked. 
3. Possibility of effecting improvement. 
Certain definite conclusions have been reached respecting the inimical causes 
operating in the Wareham plantations. It is believed that experiments on the lines 
of these now in progress will demonstrate conclusively that the unfavourable conditions 
undoubtedly present can be ameliorated by methods practicable under field conditions 
and not prohibitive in cost. 
Consequently it should be possible to prevent the loss due to death or more or 
less complete stagnation of growth with irregular and sporadic emergence from this 
condition of check, at present observable. 
Comparative observations on a number of geographical races of P. silvestris in 
respect to differences of growth and mycorrhiza-forming capacity are being continued. 
A full account of the work will be published in due course. 
This report offers an opportunity to acknowledge once more the help and 
co-operation received from officers of the Forestry Commission in this country and 
from Mr. Forbes, late Director of Forestry in the Irish Free State. 
The two grants allocated to this research committee by the British Association 
have facilitated the accumulation of evidence indicating that a clearer understanding 
of the relation of mycorrhiza formation to tree growth may be of importance in 
helping to solve the practical problems presented by the afforestation of uncongenial 
soils in Great Britain. 
With their help it has been possible to lay the foundations of a comprehensive 
scheme of intensive research. 
The grant of £40 provided by the British Association has been fully expended. 
It was hoped that it would be unnecessary to ask for the reappointment of the 
- Committee, as it was understood that the Forestry Commissioners were willing to 
make a grant which would enable the work to be carried on and extended. Owing, 
however, to the present financial position, the question of a grant will have to be 
eee asdered by the Commissioners, and it is very unlikely that this will be made. 
if 
The Committee ask for reappointment and for the renewal of a grant of £40 to enable 
_ essential observations on existing plots to be carried out. 
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1931 U 
