550 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



way they are formed, the transformations they undergo, and 

 their significance in the economy of the plant, and in so do- 

 ing gives an interesting summary of the past progress and 

 present status of our knowledge of these subjects. 



Chlorophyl and the Formation of Starch. 



At the beginning of the present century, the sum total of 

 the knowledge on this point was due to the observations of 

 l)e la Hire, Priestley, Ingenhousz, Senebier, and De Saussure, 

 and amounted to this that the green parts of plants exposed 

 to sunlight decompose the carbonic acid of the air, evolve 

 oxygen less, however, than was in the carbonic acid and 

 at the same time increase in weight. Since then it has been 

 observed by Mohl, and later by Nageli and Cramer, that 

 starch grains are formed in the chlorophyl corpuscles ; by 

 Sachs, that this formation of starch is dependent upon light; 

 by Godlewsky, that it goes on only when carbonic acid is 

 supplied; by Nobbe, that the agency of potassium is neces- 

 sary to the process ; and by Moll, that the carbonic acid from 

 which the starch is formed is imbibed by the leaves, and not 

 by the roots. In short, we know now that carbohydrates, 

 chiefly starch, are formed in the chlorophyl grains of the 

 leaf; that the process is dependent upon light, supply of car- 

 bonic acid, and co-operation of potassium ; and that the car- 

 bonic acid probably comes from leaves alone. 



It is still a question whether chlorophyl is transformed 

 itself into starch, or is only an agent which effects the com- 

 bination of carbon and carbonic acid with hydrogen and oxy- 

 gen of water into starch. Sachsse favors the view that chlo- 

 rophyl is first formed by union of carbonic acid with water, 

 and then turned into starch or other carbohydrates, and 

 gives good grounds for his belief. His latest investigations 

 strengthen this hypothesis. 



What Becomes of the Carbohydrates that are Formed in the 



Leaves 2 



The fate of the carbohydrates, the raw material of the 

 plant, is probably as follows : 



]. One portion is transformed into cellulose, and goes to 

 form the cell-walls in growing organs. This cellulose is sub- 

 sequently converted into lignine or cork, gum, and mucilage. 



