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METABOLIC PROCESSES IN THE PLANT. ">17 



139. Experiments with Leaves. 



The starch formed in the leaves by assimilation is only em- 

 ployed to a very small extent for the development of the leaf 

 itself. The bulk of the starch leaves the leaf; ifc travels thence 

 into other organs of the plant, in order to render possible their 

 development. The starch in many cases undoubtedly passes into 

 solution as glucose, which is formed by the action on the starch 

 of diastatic ferments present in the leaves (see 112). 



Leaves of TropaBolum, Solanum or Cucurbita are cut off in the 

 evening of a warm summer day. We boil them with water, treat 

 with alcohol in order to remove the chlorophyll, and lay a few 

 of them in Iodine solution (see 14) to prove the presence of large 

 quantities of starch in their cells. The rest of the leaves after 

 treatment with alcohol are washed with water and left for a few 

 hours in a freshly prepared extract of malt at a temperature of 

 45 C. If we now lay the leaves in Iodine solution, they give no 

 starch reaction, or at most only a weak one, from which it follows 

 that diastase can bring about the solution of the starch developed 

 by assimilation in the cells of the leaf. This process of solution 

 often goes on with quite remarkable rapidity. 



We cut in the evening of a very warm summer day in June or 

 July a few leaves of very vigorous plants of Solanum, Nicotiami, 

 Atropa, Cucurbita, or Phaseolus, growing in the open, and at once 

 examine them macroscopically for starch by the method described 

 in 14. They are found to be very rich in starch. If the next 

 morning at sunrise we again remove a few leaves from the plants, 

 and test them, we find no starch in their cells if the night was 

 warm; it has been dissolved during the night, and has travelled 

 from the leaves into other organs. 



The following investigation which I made with vigorous pot- 

 plants of Tropa^olum majus is very instructive. We first make 

 sure by macroscopic tests that the leaves of the plants contain 

 large quantities of starch. A few leaves are cut off, placed under 

 a bell-glass on a moist surface, and screened from the light. The 

 plants themselves are then likewise placed in the dark. After 

 some time (in my investigations, which \vere made at a tempera- 

 ture of only 12-15 C., at the end of five days) we test macro- 

 scopically for starch in the cut leaves, and also in leaves which 

 were not separated from the parent plant. The latter contain 

 starch only in the nerves, while the cut ones are still more or less 



