34 



THE AGRICULTUR\L XKWS. 



February 1, 1913. 



elements in the food bodies (nutrients), or the tissues; 

 intramolecular respiration causes these to be broken up, 

 and simpler substances are formed which are poisonous 

 and have to be reiiiave<l as fast as they are produced, or 

 thev will kill the prnt<ipla<ni in the cells, and may cause 

 the death of the whole or<,'anism If these substances 

 are removed ronlinually aiicl proper nutrietiis supplied, 

 the cells will continue to live, even with little dirt^ct 

 respiration: but there will be no form ition of new tissue 

 (growth). Direct respiration is necessary for growth. 



In respiration by either means, the first result is to 

 take away, by oxidation and by the remo\al of the 

 elements of water (dehydration), a part of the nutrients 

 in the cell sap and to replace them by water. The 

 strength, or concentration, of the cell sap is thus 

 reduced below that of the surrounding Huids, so 

 ihat fresh supplies of nutrients move in (by osmosis) 

 through the cell wall. The general effect is that 

 respiring cells are continually receiving fresh nutrient 

 •material, while water formed by the changes due to 

 respiration (metabolic water) is constantly moving 

 away. The weakening of the cell sap by metabolic 

 water is the actual means which determines the pro- 

 vision of the cells with food materials. 



The sources of water for the living being are, 

 then, direct provision and the changes involved in 

 respir.iiion. It has now to be considered in what wa3's 

 the water is used: that is, what are the functions of the 

 water. One of the most obvious of these is the dis- 

 solving of nutrients, and a second correlated with this 

 is the distribution of the nutrients throughout the 

 organism. In animals', water dissolves the digested 

 food and travels in the blood stream: in plants it forms 

 solutions that comprise the cell sap, and moves from 

 cell to cf'll (by osmosis) and in special tubes in the 

 wood and bast. Another use of water is the removal 

 of poisonous waste products from the cells in which 

 they are formed; it has been indicated already. 

 Water also controls the temperature to a certain extent, 

 by evaporation: this has been shown to be esjiecially 

 important in the case of plants in tropical sunlight, 

 where the evaporation from transpiration takes place 

 at a very ra]iid rate. A last use of water in living 

 organisms is confine<l to green plants, where it forms 

 a source of material that is used in building up 

 erganic substances in sunlight — an operation that is 

 caiie I photosynthesis. These are the general and more 

 <3irecD functions of water. Attention will now be given 

 t« some of its uses that are less direct and obvious. 



Insoluble food bodies that arc taken in by animals, 

 or produced in the cells of jjlants, must be changed 

 into forms that are soluble before they can be used in 

 nutrition. 'I'his change consists in the employment of 

 water to form new compounds that are soluble; the 

 process is called hydrolysis, and is described more 

 accurately by saying that the elements of water are 

 addfd to the molecular stiuct.ure of the insoluble 

 substances so that entirely new compounds which are 

 Soluble are formed. A familiar example is the conver- 

 sion of starch into sugar: by hydrolysis, water is used in 

 such a way, under the proper conditions, that an 

 insoluble body is caused to form a totally different, 

 soluble body, that can be used directly in nutrition. 

 Changes of this nature are brought about by unor- 

 ganized ferments called enzymes; they are entirely 

 chemical in nature, and contact with living tissues 

 is not necessary for them to take place. A use- 

 ful example is the malting of barley, where the 

 germ is actually killed by heat before the enzymes are 

 allowed to act on the starch in the grain and turn it 

 into the sugar which will be eventually converted into 

 alcohol by yeast. 



The employm<nt of nutrients in the proper condi- 

 tion, that is after their rligcstion, results in growth, or 

 repair which is only a special form of growth. Water 

 is again necessary for this to take place. In this case, 

 however, the elements of water are removed frou, the 

 old compounds and new oms are formed: it is freed, not 

 used up as in hydrolysis. This dehydration, as it i* 

 called, requires energy, and the energy is set free 

 through respiration. Carbon dioxide and water have 

 been mentioned already as products of respiration. 

 Another product is heat, and it is in this form that 

 the energy is supplied for dehydration, and therefore 

 for growth. Kitlier direct or intramolecular respiration 

 is effective, and unlike hydrolysis for nutrition, dehydra- 

 tion for growth almost always recjuires the presence of 

 living protoplasm. 



What has been said forms a general summary of 

 the part played by water in the life-processes of animals 

 and green plants. ( )pportunity will be taken in the 

 next issue of the Agricultural Nca-s, to consider ia 

 a similar way the application of this information to 

 several interesting examples in the plant and animal 

 kingdoms that are of importance to the agriculturist, a.s 

 well as to all others who are interested in the problems 

 of life and growth. 



