. -SO JIE RECENT RESEARCHES IN PLANT PHYSIOLOGY 



THE STARCH OF THE LEAF. 



When the above-mentioned research was begun, it had 

 been already proved by the work of Bokorny (1891) that 

 starch could be produced in the chloroplasts of Spirogyra 

 from formaldehyde by supplying the alga with a nutrient 

 solution containing a compound of formaldehyde united 

 with sodium bisulphite, which on warming with water is 

 hydrolyzed to give the original components in the free 

 state. At air temperature the amount of free formaldehyde 

 in such a solution is very small, but the supply is con- 

 tinuous, for as the substance is removed by the plant more 

 is set free by hydrolysis to restore the disturbed chemical 

 equilibrium. By thus ingeniously avoiding poisonous con- 

 centrations of the aldehyde, Bokorny showed that starch 

 was formed by Spirogyra majuscula in the absence of any 

 other possible source. This afforded evidence in favour of 

 Bayer's view that plant carbohydrates are formed by 

 polymerization and condensation of formaldehyde. But 

 the intermediate steps remained quite unknown, while even 

 the first one could not be regarded as conclusively estab- 

 lished. Accordingly the problem which presented itself to 

 Brown and Morris was to determine what sugars were 

 utilized by the chloroplasts in the formation of starch, and 

 what the down-grade products were when starch was 

 brought into solution for respiration or translocation. In 

 addition to this they had to examine the possibility of the 

 formation of starch without intermediate sugar, for there 

 was no conclusive evidence on this point, although J. A. 

 Bohm (1877, 1883) and A. Meyer (1886) had shown that 

 starch could be elaborated by leaves in the dark and in 

 absence of carbon dioxide. Bohm found that the chloro- 

 plasts of the leaves of seedlings of Eaphanus sativus, 

 Lepidium sativum, and Pkaseolus multiflorus, which still 



