9 



anatomical and physiological research we may discover why one 

 variety develops better in one climate than another and why it 

 produces a better product in one place than another and eventually 

 by careful selection acclimatize a large series of plants which at 

 present we can hardly induce to exist under special climatic condi- 

 tions. This conquest over nature will entail, however, a very large 

 amount of research, and a very big cultivation area under the hands 

 of scientific men whose time is exclusively employed in making such 

 investigations. The possibilities of the results, however, are enor- 

 mous, and will well repay the expenditure of time and money. 



H. N. R. 



PLANT LIFE AND DISEASE. 



A plant is a breathing feeding object with many activities or 

 functions ; it elaborates chemical compounds from the liquids it 

 absorbs from the soil and the gases it assimilates from the air ; it 

 grows, reproduces its kind, and is sensitive to changes in its sur- 

 roundings. If it cannot control its immediate conditions, it can to 

 a great extent adapt itself to them. 



Growth is probably the most dominant phenomenon we associate 

 with plants. It is affected by soil, water, air, light and heat. For 

 each of these factors there is a certain range within which the 

 functions of the plant regularly proceed. For each species of plant, 

 for example, there is a certain temperature below which it will not 

 grow, and likewise a definite temperature above which growth 

 ceases. Between these two extremes and near the middle is a 

 point — the optimum point — which is the most beneficial. There is 

 a most advantageous strength (concentration) for each of the 

 necessary salts in the soil, and optimum points for water and each 

 of the other faetors. If every factor is at its optimum the plant is 

 in the best position for growth; most likely this condition is never 

 realised in nature. 



Any prolonged derangement in the factors of growth usually 

 results in a curtailment of function and this must be looked on as 

 disease. From this point view a plant like the banana, which 

 seldom produces seeds capable of germinating, is diseased. Disease 

 is rather difficult to define, and for our purposes we may take it that 

 a plant is diseased which is not growing in what we know from 

 practice to be its normal manner. 



The causes of unhealthiness may be shortly put down as due to : 



( 1 ) Derangement of any or all of the factors of growth ; 



(2) Attacks of parasites (plant or animal). 



The question of the relation between the health of a plant and its 

 immunity, or the contrary, from fungal attacks is decidedly not 

 settled. It is held by many experts that fungal infection is due to 



