294 REPORTS ON THE STATE OF SCIENCE, ETC. 



original sowings, and also from those associated with the existence of local 

 areas of soil toxicity probably mainly due to defective aeration, it is believed 

 that the condition of the moribund and semi-moribund plants described is 

 a starvation phenomenon — in large part probably one of nitrogen starvation. 



Tentative experiments with inorganic nitrogenous fertilisers have con- 

 firmed the results obtained by others both in field and laboratory cultures — 

 viz. that it is difficult to make good deficiencies in this way without serious 

 disturbance of the root-shoot growth ratio in species of Pine. 



It is believed that on soils poor in inorganic nitrogen of this type the 

 nutrient requirements of the young trees are normally made good by a 

 profuse development of mycorrhiza. This view is confirmed by examination 

 of the roots of Scots Pine and Maritime Pine in the area adjoining the 

 plantations in question, by that of patches of young trees on the sown or 

 planted areas that have made surprisingly good growth, and by the remark- 

 able fact that the condition of arrested growth described can be relieved in 

 the course of one growing season by induced mycorrhiza formation following 

 suitable humus inoculation. 



It is not believed, however, that this treatment alone will permanently 

 remove the trouble on soils where mycorrhiza formation by young trees is 

 inhibited or markedly delayed. 



In the area under consideration the view has been reached that the factors 

 permitting healthy mycorrhiza formation annually and, therefore, deter- 

 mining healthy growth must be sought in the condition of certain organic 

 constituents of the humus following upon abnormal decomposition changes. 



Attention is now focused on this aspect of the problem. Following the 

 adoption of a working hypothesis, a series of experiments has been carried 

 out involving the application of certain organic composts. The materials 

 for these composts are of the nature of waste products. 



The treatments have been applied to experimental plots which reproduce 

 certain features of the Wareham area as originally sown, and also to sowings 

 on a section recently tractor-ploughed. Each connpost treatment will be 

 applied in duplicate, one series compost alone, the other the same compost 

 inoculated with known mycorrhiza-formers of the trees concerned, either 

 from pure cultures or from humus material from a native habitat of the 

 species. It may be noted that the cultivation of specific root fungi on 

 composted and other organic materials has provided and is likely to continue 

 to provide a number of independent and intricate problems. 



These field experiments have been duplicated in pot cultures using soil 

 from the same area, and this essential part of the work could not have been 

 undertaken without the provision of a suitable shelter house such as has 

 been erected this summer. 



Existing experimental plots at Wareham and Ringwood are still under 

 observation, and intensive study of the roots of seedling Pines from these 

 plots is likely to yield interesting comparative data on the causes underlying 

 inhibition of mycorrhiza formation, and interference with its normal 

 structure and functioning when induced artificially by humus treatments of 

 the soil. 



Humus inoculation of exotic Pine species. — This aspect of the work was 

 considered in the report presented at the London meeting in 193 1. It 

 raises a matter of considerable practical importance involving the desirability 

 or otherwise of applying appropriate humus treatments to seedlings in the 

 nursery stage. The experimental data now available in respect to Corsican 

 Pine and Maritime Pine at Wareham and elsewhere may be summarised as 

 follows : 



(i) The addition to seed-beds of small quantities of the appropriate humus 

 in the right condition produces a markedly beneficial effect upon the seed- 



