306 The Physiology of Plants BOOK'HI 



the non-assimilating starch corpuscles, the material for the 

 formation of starch consists of sugar. The question now 

 remains, therefore, how does the sugar itself arise by 

 assimilation ? I hold it as probable even now that in this 

 process the proteid substance of the assimilating chlorophyll 

 itself co-operates and undergoes a change.' We have here 

 something akin to Vines's theory of starch formation, to 

 which allusion has been made. 



The view that sugar is the immediate forerunner of 

 starch was soon supported by experiment. Boehm, in 

 1883, was the first of a long series of workers who estab- 

 lished it. Boehm's researches proved that when green 

 leaves, which have been depleted of starch by being kept 

 in darkness, are put in contact with solutions of cane sugar 

 or of glucose, or when their stalks are immersed in such 

 solutions, starch reappears in the cells. Similar results 

 were obtained in 1885 by Meyer and by Schimper, in 1887 

 by Laurent, in 1888 by Klebs, and in 1890 by Acton. 

 They all showed that starch formation takes place as soon 

 as a plant is supplied with various carbohydrates in 

 appropriate solutions. 



Meyer's results proved that during photosynthesis large 

 quantities of soluble carbohydrates are formed in plants 

 without the inevitable appearance of starch, and that these 

 same substances occur in plants together with starch. 



Sachs made an observation in the course of his early 

 work to which he did not seem to have attached the 

 importance it deserves in the light of these later re- 

 searches : 



' In some cases it is impossible directly to observe starch 

 as the product of the assimilation in the chlorophyll grains. 

 I found this to be the case in the leaves of our common 

 onion (Allium Cepa), where, however, large quantities of 

 glucose (sugar) are to be recognized as the result of assimila- 

 tion.' 



