288 REPORTS ON THE STATE OF SCIENCE, ETC. 
The conclusion that normal mycorrhiza formation is a factor that may become 
of critical importance to the growth of young trees under certain soil conditions is 
reinforced by observations on seedlings and young plants of Scots Pine from various 
stations where growth was unsatisfactory. 
In general, these showed that poor root development, stunted shoot growth and 
yellowing of the foliage were associated with abnormalities in respect to mycorrhiza 
formation and parasitisation of the roots amply sufficient to account for the appearance 
and behaviour of the plants. 
Evidence has been sought also in the case of Oak. 
A preliminary survey was made of the mycorrhizal condition of the roots in young 
plantations of Oak in various parts of the Forest of Dean. It has been ascertained 
that certain types of mycorrhiza are associated with vigorous growth of the young 
trees, a phenomenon strikingly manifested in the case of plantations showing marked 
inequalities of growth in different parts. The observations are significant, although 
there is at present no proof of a causal connection between the two sets of phenomena. 
The promising results obtained from this preliminary survey point to the necessity 
for more complete observations in this and other areas and more precise knowledge 
as to the identity of the fungi concerned in the mycorrhiza of Oak. 
2 (a). Presence or Absence of the appropriate Fungi. 
Mycorrhiza-forming fungi specific to Scots Pine are present in the Wareham and 
Ringwood areas. Observations on the hymenomycete flora of this district are at 
present fragmentary, and it would be rash to assume that optimum conditions in 
respect to the proximity of mycelium of suitable fungus species exist throughout the 
plantations. 
The two other pines under observation present a rather different problem. Both 
are exotics, and in neither case is there yet available exact information as to the 
identity of any root fungi associated with them under natural conditions. 
In Maritime Pine, mycorrhiza of a normal type is freely formed under certain 
ascertained conditions in the Ringwood area, although its formation is inhibited 
in seedlings or transplants elsewhere there and at Wareham. Experiments now in 
progress should throw light upon the causes of these discrepancies and indicate 
whether conditions in respect to this formal condition of mycorrhiza formation can 
be improved. 
In Corsican Pine observations lead to a somewhat different conclusion. Com- 
parative observations on roots from established stands in this country show that 
mycorrhiza of a normal type is formed, but suggest that disturbing conditions are 
not infrequently present. There is now available for the first time a standard of 
comparison provided by mycorrhiza collected in Corsican forests. It is possible that 
absence of appropriate fungus species or of a suitable grouping of such may be wholly 
or in part responsible for the observed abnormalities. 
At Wareham no improvement in growth or increase in dry weight has yet resulted 
from treatments with humus from pure stands in this country, thus providing a 
striking contrast with the case of Maritime Pine. The reaction of seedlings and young 
trees of Corsican Pine to treatments with Corsican humus known to contain the 
mycelium of specific mycorrhiza formers should permit of final conclusions. 
In view of the existence of healthy well-grown stands of Corsican Pine in this 
country it must be emphasised that the matter under consideration is likely to be 
of critical importance only in relation to the establishment of new plantations either 
by seed or planting on poor and unfavourable soils such as these under observation 
at Wareham and Ringwood. 
2 (b). Existence of inimical soil conditions. 
In the Wareham area and locally at Ringwood the existence of soil conditions 
inimical to mycorrhiza formation may be regarded as established. In the pines 
under consideration—notably in the two exotic species—absence of mycorrhiza 
is associated with an unhealthy and often moribund condition of the younger 
roots. 
Many of the morbid characteristics of seedlings in the field are reproduced in pot 
cultures, and the value of the latter as supplementary to field observations emphasises 
the need for a suitable shelter house for growing them under more satisfactory 
conditions. 
EE ——— 
a 
