September 28, 1900.] 



SCIENCE. 



471 



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 dis- 

 coveries in relation to the nutrition of 

 plants, but there are others of not less im- 

 portance 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 nutri- 

 tive 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 

 practiced by Duhamel (1768) and de Saus- 

 sure. Special interest centers around 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 ex- 

 pressed 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 ana- 

 bolic processes to those which are catabolic. 

 The discovery of the latter, just as of the 

 former, was arrived at by the investigation 

 of the gaseous interchange between the 

 plant and the atmosphere. In the eight- 

 eenth century Scheele and Priestley had 

 found that, under certain circumstances, 

 plants deteriorate the quality of air ; but it 



is to Ingen-Housz that we owe the discovery 

 that plants, like animals, respire, taking in 

 oxygen and giving off carbon dioxide. And 

 when Senebier (1800) had ascertained for 

 the inflorescence of Arum maculatum, and 

 later de Saussure (1822) for other flowers, 

 that active respiration is associated with an 

 evolution of heat, the connection between 

 respiration and catabolism was 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 that are designated 

 by the general term fermentations. The 

 first of these to be discovered was the alco- 

 holic fermentation of sugar. Towards the 

 end of the seventeenth century Leeuwen- 

 hoek had detected minute globules in fer- 

 menting wort ; and a century later Lavoi- 

 sier 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 simul- 

 taneously, Cagniard de Lateur, Schwann, 

 and Kiltzing discovered that Leeuwen- 

 hoek'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 organized 

 and unorganized ferments. The number of 

 the former was rapidly added to by the in- 

 vestigation more especially of the Bacteria, 

 in which Pasteur led the way. The exten- 

 sion of our knowledge of the unorganized 

 ferments, or enzymes, has been even more 

 remarkable : we now know that very many 

 of the metabolic processes are effected by 

 various enzymes, such as those which con- 

 vert the more complex carbohydrates into 

 others of simpler constitution (diastase, 

 cytase, glucase, inulase, invertase); those 



