SOME MODERN ASPECTS OF APPLIED BOTANY 27. 
Scots pine, as it furnishes a splendid example of the value of ceco- 
logical studies to a practical industry like forestry. He has shown 
that the tree occurs in several cecological forms, among which two 
well-marked cecological types can be readily distinguished. The one 
a strong-branched, strong-crowned tree, which is the typical form in 
Scotland ; the other a slender, pyramidal-shaped tree, which is typical 
of the Baltic provinces. Such types are found to be hereditary, and 
are not altered by altered climate and soil. The Scottish type is 
better adapted to hold its own in the struggle for life in milder 
localities, whereas the slender, pyramidal type is better able to hold 
its own under more rigorous conditions, where wind, and especially 
heavy snowfalls, constitute the primary dangers. Great care should 
therefore be exercised in selecting seed or in planting seedlings, of 
whichever form is better suited to a definite locality. 
In many placesin this country we have examples of the Alpine or 
northern forms of the Scots pine planted where they have no 
business to be. 
Plant Disease.—In applied botany there is no department of 
greater economic importance than that which deals with plant 
disease, z.e. plant pathology. 
Plants of all kinds as living things are subject to disease. It 
is difficult to give a short, concise definition of disease. ‘The 
following is a dictionary definition: ‘ A derangement in the structure 
or the function of any organ belonging to a vegetable or animal,” 
but this does not convey any definite or clear meaning. After all, 
probably it does not matter much whether we can in words draw up 
a hard and fast definition, as there is no hard and fast line of de- 
marcation between health and disease. Let us for the present 
understand by disease any marked deviation of the vital functions 
from the normal. We may have various stages of healthiness, from 
the perfectly healthy body or organ, through less healthy conditions, 
till a diseased state is reached, and likewise we may have various 
stages of disease, from slight to severe. For health, the living body 
and its organs must be normal, and the environmental factors and 
conditions must approach as near the opf/imum in each case as 
possible. Otherwise, signs of unhealthiness may appear, probably 
not sufficient at the moment to cause much alarm to the practical 
cultivator, but the scientist knows that plants, even though slightly 
weakened, may have developed a predisposition to unhealthiness, and 
crops, though not actually diseased, may nevertheless be liable to an 
epidemic attack, the conditions for which may be made favourable 
through loss of vigour of the plants. 
Loss of vigour and subsequent unhealthiness in plants may be 
caused by unfavourable environment. In the plant kingdom, as in 
the animal kingdom, unfavourable environmental conditions may be 
grouped under two heads, namely, physical and organic environment. 
The physical environment is supplied by the soil in all its variations 
of chemical composition, depth, porosity, moisture, temperature, 
texture, air-content, etc. Then we have the atmospheric conditions, 
