1911-12.] BOTANICAL SOCIETY OF EDINBURGH 5 



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 places in this country we have examples of the 

 Alpine or northern form of the Scots pine planted where 

 they have no business to be. 



Plant Disuse. — In applied botany there is no depart- 

 ment of greater economic importance than that which deals 

 with plant disease, i.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 Ave can in words draw up a hard and 

 fast definition, as there is no hard and fast line of demarca- 

 tion 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 optimum 

 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 environ- 

 mental conditions may be grouped under two heads, namely, 

 physical and organic environment. The physical environ- 

 ment is supplied by the soil in all its variations of chemical 

 composition, depth, porosity, moisture, temperature, texture, 



