products of biological origin. The factors inhibiting the activity of
the fungi can be removed by the application of comparatively small
amounts of organic composts which produce dramatic and lasting effects
on the growth of roots and shoots.

The special composts used are prepared from organic materials such as
straw, hop waste and sawdust. The mechanism by which they stimulate
growth is still obscure. All of them contain small amounts of directly
available plant foods such as phosphates and potash, but careful
investigation both in laboratory pot cultures and in the field, has
shown that these can account for only a relatively temporary effect on
growth. It is suggested that the composts act mainly by modifying the
course of humus decomposition, thus bringing about drastic changes in
the biological activities of the organic substrate of the soil.

This demonstration of the profound influence of biological factors on
the nutrition of trees challenges the attention of foresters and has
important practical applications. By making use of suitable composts, it
will be possible to carry out the successful afforestation of land
formerly regarded as wholly unproductive.

For further information see "Problems of Tree Nutrition"[5].

From the two foregoing examples it is seen that in the case of banana
blight, fungi had to be suppressed by bacteriae, but that for pine trees
on poor English soils fungi had to be activated for proper tree
nutrition.

4) Inorganic Tree Nutrients

Other information also from England concerns the use of so-called
"minerals" which I prefer to call "essential inorganic nutrients," and
name by the element or the compound in which the element is contained.
"Minerals", strictly speaking, refers to compounds formed by nature as
rocks, ores, brines, salt deposits, etc.

Professor Wallace, Director of Britain's Long Ashton Research
Station[6], has laid the foundation for diagnosing mineral deficiencies
by leaf symptoms. These are reliable indicators of what nutrients to
furnish plants when they are distinct and easily recognized. But for
subacute deficiencies, plant analysis and injections are resorted to.
Injections of manganese sulphate as pellets into holes drilled in trunks
of cherry trees caused orchards that had been barren, to bear heavy
crops a few months later.

Manganese, boron, zinc, copper, iron, magnesium also lend themselves
quite readily for applications as nutritional sprays, when