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ON MYCORRHIZA IN RELATION TO FORESTRY. 287 
Mycorrhiza in Relation to Forestry.—Report of Committee (Mr. 
F. T. Brooks, Chairman; Dr. M. C. Rayner, Secretary; Mr. W. H. 
GUILLEBAUD). Drawn up by the Secretary. 
THE grant was allocated as a contribution toward the current expenses of an 
investigation, the purpose and scope of which were explained in a report presented 
last year. 
In this first report the main objects of research were thus summarised :— 
1. To ascertain whether the formation of normal mycorrhiza may fairly be regarded 
as a causative factor in the healthy growth of young trees, it being already assumed 
that it is an invariable concomitant of such growth. 
2. To determine whether the absence of mycorrhiza associated with unsatisfactory 
growth is related to :— 
(a) absence of the mycorrhiza-forming fungi appropriate to the trees; or 
(b) the existence of soil conditions inimical to the formation of functional 
mycorrhiza of a beneficial type. 
3. To ascertain whether it is practicable to supply deficiencies or ameliorate 
existing soil conditions by experimental treatment of nursery stock or in other ways. 
The present position of the work may be dealt with conveniently under these heads. 
1. Mycorrhiza as a causative factor. 
Evidence bearing on this problem has been sought in relation to three species of 
pine, sown or planted in the Wareham and Ringwood plantations of the Forestry 
Commission, viz., Scots Pine (P. silvestris), Maritime Pine (P. pinaster), and Corsican 
Pine (P. laricio) by means of humus treatments. 
In the case of the first-named species, humus regarded as suitable for inoculation 
purposes was available in the spring of 1930. For corresponding treatments of 
Corsican Pine and Maritime Pine it has been considered advisable to examine 
mycorrhizas and collect humus containing them in habitats native to the species. 
For this purpose the forests of Aitone, Valdoniello and Vizzavona in Corsica were 
visited in the spring of 1931. From the nature of the case, evidence derived from 
the use of material collected in Corsican forests is not yet available. That already 
obtained from field experiments of Scots Pine supports the view that the formation 
of normal mycorrhiza is a causative factor of great importance to the growth of young 
trees. 
The nature of this evidence may be judged from the fact that the relative dry 
weights of sample seedlings on treated and untreated plots were in the ratio 2:1 
after eight months, and the disparity now, after fifteen months’ growth, is much 
greater. In respect to vigour of growth, root and shoot development, and colour of 
foliage, comparison of the growing plants provides irresistible evidence of the 
beneficial effects associated with induced mycorrhiza formation in seed plots of Scots 
Pine on the soils in question. This conclusion is confirmed by the results of pot 
experiments. 
Corresponding experiments on other types of soil are desirable and are in progress, 
but results have been greatly delayed owing to the hampering conditions under which 
the work has been carried on. 
In the case of Maritime Pine, humus treatments have likewise given positive 
results of a less marked kind. Using humus from a young natural stand in this 
country, the dry weight ratio of sample seedlings in treated and untreated plots was 
3:7: 1 at eight months, and is roughly 3:2 at fifteen months. The experiments 
have been tentative in character, and a full report of the reaction shown by seedlings 
of this pine to humus inoculation with material known to contain mycelium of specific 
root-fungi must await the results of experiments now in progress. 
Treatments of Corsican Pine with humus from stands in this country have not 
given noteworthy results, the average dry weight ratio of treated and untreated 
seedlings after fifteen months being practically unity. As was anticipated, therefore, 
a full report on this pine must await the results of field experiments with soil known 
to contain the mycelium of mycorrhizal fungi appropriate to the species. 
