INTRODUCTION 



constituents of the plant ; they consist of carbon, hydrogen, nitrogen, oxygen, 

 sulphur, and possibly also phosphorus. 



Only a few examples of quantitative analyses of entire plants or of their 

 larger parts are available. Such analyses have been made mainly in connexion 

 with nutritive media, and are not of special interest at the moment, since 

 they take into account substances belonging to too few groups. Still we may 

 quote in this relation a short table illustrating such an analysis taken from 

 KoNiG (1882). 



Percentage composition of fresh material. 



^ This estimate is taken from Wiesner, Rohstoffe des Pflanzenreiches, 2nd ed. 



A few remarks may not be out of place with regard to the details of this 

 table (comp. Konig, 1897). In the first column the proportion of water 

 present is indicated, from which it will be apparent that every part of the 

 plant contains water, and that even in air-dried seeds it amounts to from 

 12 per cent, to 15 per cent, of the original weight, while plants in the Uving 

 condition contain at least 75 per cent, of water, and usually, as a matter of 

 fact, considerably in excess of that amount. The maximum percentage of 

 water, viz. 98 per cent., occurs, as might be expected, in aquatic plants (Algae). 

 Similarly, the last column teaches us that from no plant are mineral matters 

 entirely wanting. Neither of these columns, so far as analysis is concerned, 

 presents any difficulty, and both are of great physiological value. The case 

 is quite otherwise with columns II, III, IV, and V. In order to arrive at an 

 estimate of the nitrogenous constituents of the plant, the nitrogen itself was 

 determined, and the number so obtained was multiplied by 6-25, because it 

 was assumed in the first place that nitrogen occurred only in proteid, and, in 

 the second place, that proteid contained 16 per cent, of nitrogen (N.B. 6-25 x 16 =: 

 100 per cent.). Neither assumption, however, proves to be correct. Proteid 

 contains from 15 per cent, to 18-5 per cent, of nitrogen, and, further, nitrogen 

 occurs in amides and in other bodies as well, probably in relatively large quan- 

 tity. The information given in column II, therefore, is of limited value. 

 Column III shows how much material is soluble in ether, all of which, however, 

 is not fat ; it includes as well such bodies as wax, lecithin, cholesterin, hydro- 

 carbons, and chlorophyll. Column IV contains what is left over after sub- 

 tracting the sum of the contents of the other columns from 100. In it are 

 included by no means only carbohydrates, but everything soluble in dilute 

 solutions of sulphuric acid and caustic potash (1-25 per cent, solution). The 

 substances which resist such reagents are found in column V. 



Quantitative analysis of a plant, though far more detailed and accurate 

 than those given above, cannot give us any satisfactory insight into its 

 chemical mechanism ; for it must be obvious that materials which, in the 

 process of analysis, become united in the distilling apparatus, occur in the 



