226 



THE AGRICULTURAL NEWS 



JlLV 



1918. 



I'lant physiology has as an object the stuily of 

 the nianner in which the lives of plants are iutluenceil 

 by temperature, soil, and moisture. 



The study of the conditions under which the lite 

 of the plant can be best maintained has had the most 

 important bearing on agriculture. It is only within 

 the last 200 years that the manner in which plants 

 obtain the substances necessary for health and growth 

 has been scientifically studied, and accurate results 

 obtained. Up to the end of the seventeenth century 

 it was believed that plants obtained all their food from 

 the soil, although the elements constituting even the 

 food so obtained were not then known. In fact, it may 

 be said that not until the middle of the nineteenth 

 century did the researches of Liebig and Boussingaulti 

 on the subject of plant nutrition, afford such infor- 

 mation on the point, that the knowledge could be of real 

 profit to agriculture. From that time on, however, 

 rapid progress has been made in the study of the 

 complex chemical and physiological problems relating 

 to the assimilation by plants of the several food ele- 

 ments necessary to their growth under various condi- 

 tions, and which are derived from various sources. 



The demonstration of the requirements necessary 

 for the growth of most cultivated plants has given to 

 the agriculturist the knowledge of the means essential 

 to maintain and increase the fertility of the soil. In 

 fact, in many cases, soils that were long considered 

 hopelessly barren have been rendered fertile by putting 

 into practice the knowledge thus acquired. The know- 

 ledge too that plants need light and air, and that 

 really the larger portion of their food is obtained by 

 them from the atmosphere, has in many ca.ses led id 

 a considerably greatly increased yield of certain crops, 

 by a modification of hitherto practised method.s of 

 cultivation, each individual plant being now given 

 more room in which to grow. The art of feeding 

 plants, based on the scientific knowledge of plant 

 nutrition, has developed remarkably of late years. As 

 an article in the yearbook of the United States 

 Department of Agriculture, iy()4, puts it: the well 

 infiirmed farmer now knows that the varying combina- 

 tions of essential conditions .-iiid elements that occur 

 naturally in different soils and climates are an index- 

 to the adaptability of these climates and soils for 

 special crops. He knows also that these condi- 

 tions can be modified favourably or uti favourably by 

 cultivation and fertilization. He understands the 

 importance of a physical and chemical examination of 

 soils as indicating the presence or .absence, and the 

 jelative proportions »f the essential elements of plant 

 iood.' 



Whether certain crops, however, are adapted to 

 particular conditions, or whether the conditions may 

 be made more favourable, has to be determined under 

 actual trial: and this is really the work of the plant 

 physiologist. His examination of this question would 

 al<o relate to the determination of the micro-organisms 

 present in the soil, and the beneficial or injurious 

 changes which they might produce. Some bacteria and 

 fungi cau^e the decay of organic remains of animals 

 or plants, leaving the nitrogen and other elements of 

 plant food in forms available for assimilation by other 

 plants. < )n the other hand, there are organisms which 

 produce conditions of soil directly or indirectly un- 

 favourable to crops. The work of the physiologist 

 is to study the life-history and habits of all these forms 

 so as to put the useful kinds to work, and to eliminate 

 the injurious ones. 



Investigations of plant physiologists on the causes 

 prevention, and cure of plant diseases, have also been 

 of immense benefit to modern agriculture. This scien- 

 tific investigation of plant diseases, which has been 

 conducted for little more than half a century, has 

 already residted in the discovery of remedial nreas- 

 ures which have been the salvation of many crops 

 in various countries. 



In this connexion it appears that the best results 

 have been obtained because physiologists are concern- 

 ing themselves in enquiries into the life condition of 

 the plants affected by disease, rather than confining 

 their attention to the diseases themselves. 



It will thus be seen that agriculture is much 

 indebted to the development of the science of plant phy- 

 siology, which, first, has very greatly increa.sed the 

 power of the practical agriculturist to secure harmony 

 between crop and environuK'nt: in the second place, 

 it has enabled him to maintain and increase the 

 fertility of soils by the knowledge of the elements 

 required for their nutrition: and thirdly, it has shown 

 him how to increa.se the yield and ijuality of crops 

 by .setting to work to improve nature's machinery 

 toi- the accumulation in the soil of compounds 

 available to the plants. Plant physiology also has • 

 discovered the causes of, and found remedies for 

 many of the most destructive diseases of all kinds of 

 crops. The result of this is that in modern times the in- 

 telligent planter or farmer is enabled to protect and 

 control his crops to a wonderful degree, so that it may 

 be well said that scientific agricultiire is fast becoming 

 if it has not already become, one of the .safest forms of 

 investment of capital and labour. 



