926 REPORT — 1900. 



mann (188/!-84) based on his ingenious Bacterium-method, have confirmed the 

 views of Lommel and of Miiller, and have placed it beyoud doubt that the import- 

 ance of light in the assimilatory process is that it is the form of kinetic energy 

 necessary to effect the chemical changes, and that the function of chlorophyll is 

 to serve as the means of absorbing this energy and of making it available for the 

 plant. 



These are perhaps the most striking discoveries in relation to the nutrition of 

 plants, but there are others of not less importance to which brief allusion must be 

 made. We owe to de Saussure (1804) the first clear demonstration of the fact 

 that plants derive an important part of their food from the soil ; but the relative 

 nutritive value of the inorganic salts absorbed in solution was not ascertained until 

 Sachs (1858) reintroduced the method of water-culture which had originated 

 centuries before with Woodward (1699) and had been practised by Duhamel 

 (1768) and de Saussure. Special interest centres .iround the question of the 

 nitrogenous nutrition of plants. It was long held, chiefly on the authority of 

 Priestley and of Ingen-Housz, and in spite of the contrary opinion expressed by 

 Senebier, Woodhouse (1803), and de Saussure, that plants absorb the free nitrogen 

 of the atmosphere by their leaves. This view was not finally abandoned until 

 1860, when the researches of Boussingault and of Lawes and Gilbert deprived it 

 of all foundation. Since then we have learned that the Free nitrogen of the air 

 can be made available for nutrition — not indeed directly by green plants themselves, 

 but, as Berthelot and Winogradsky more especially have .shown, by Bacteria in the 

 soil, or, as apparently in the Leguminosse, by Bacteria actually enclosed in the roots 

 of the plants with which they live symbiotically. 



We turn now from the nutritive or anabolic processes to those which are catabolic. 

 The discovery of the latter, just as of the former, was arrived at by the investiga- 

 tion of the gaseous interchange between the plant and the atmosphere. In the 

 eighteenth century Scheele and Priestley had found that, under certain circum- 

 stances, plants deteriorate the quality of air ; but it is to Ingen-Housz that we owe 

 the disccivery that plants, like animals, respire, taking in oxygen and giving off 

 carbon dioxide. And when Sen6bier (1800) had ascertained for the inflorescence 

 of Arum maculatum, and later de Saussure (1822) fir other flowers, that active 

 respiration is associated with an evolution of heat, the connection between respiration 

 and catabolism %yas established for plants as it had been long before by Lavoisier 

 (1777) in the case of animals. 



Among the catabolic processes which have been investigated none are of greater 

 importance than those which are designated by the general term fermentations. 

 The first of these to be discovered was the alcoholic fermentation of sugar. Towards 

 the end of the seventeenth century Leeuwenhoek had detected minute globules in 

 fermenting wort ; and a century later Lavoisier had ascertained that the chemical 

 process consists in the decomposition of sugar into alcohol and carbon dioxide ; but 

 it was not until 1837-38 that, almost simultaneously, Cagniard de Latour, Schwann, 

 and Kiitziug discovered that Leeuwenhoek's globules were living organisms, and 

 were the cause of the fermentation. Shortly before, in 1833, Payen and Persoz 

 extracted from malt a substance named diastase, which they found could convert 

 the starch of the grain into sugar. These two classes of bodies, causing fermentative 

 changes, were distinguished respectively as organised and unorganised ferments. 

 The number of the former was rapidly added to by the investigation more espe- 

 cially of the Bacteria, in which Pasteur led the way. The extension of our knowledge 

 of the unorganised ferments, or enzymes, has been even more remarkable : we now 

 know that very many of the metajjolic processes are eflected by various enzymes, 

 such as those which convert the more complex carbohydrates into others of simpler 

 constitution (diastase, cytase, glucase, inulase, invertase) ; those which decompose 

 glucosides (emulsin, myrosin, &c.) ; those which act on proteids (trypsins) and on 

 fats (lipases) ; the oxidases, which cause the oxidation of various organic substances ; 

 and the zymase, recently extracted from yeast, which causes alcoholic fermentation. 



The old distinction of the micro-organisms as * organised ferments ' is no longer 

 tenable ; for, on the one hand, certain of the chemical changes which they effect 

 can b« traced to extractable enzymes which they produce ; and, on the other, as 



