THE FOOD OF FLINTS. 47 



small or very insignificant quantities of starch, or even no starch 

 at all. In the afternoon of a hot summer day we collect, e.g., 

 during the same hour leaves of Tropseolum majus, Phaseolus 

 multifiorus, Helianthus annuus, of a Polygonum, of a Gentian, of 

 Tamus communis, and of Allium Cepa. It is best if the plants from 

 which we take the leaves have grown under conditions as nearly 

 similar as possible, such as are afforded for example in botanic 

 ir.-irdens. It is also to be observed that we must always work with 

 fully developed leaves. On testing the material, in the manner 

 described in 14, macroscopically or microscopically, we find that 

 the leaves of Tropaeolum, Phaseolus and Tamus contain copious 

 quantities of starch in their green cells, while those of Helianthus 

 already contain less. The quantity of starch in the leaves of 

 Polygonum is still less, that in Gentian leaves very small, and the 

 leaves of Allium prove to be completely free from starch. 



To obtain further information, we perform the following in- 

 structive experiment. A large quantity of Helianthus tuberosus 

 leaves are gathered on the afternoon of a hot summer day, and 

 after removal of the leaf-stalks are cut into small pieces, and 

 crushed between folds of linen in a hand press. We measure the 

 volume of the dark-coloured juice obtained, boil it, allow to cool, 

 then replace the water lost by evaporation, and filter. We prepare 

 in exactly the same manner juice from leaves of Allium Cepa 

 collected at the same time as the Helianthus leaves. We now 

 determine the quantities of juice necessary for the reduction of 

 10 c.c. of Fehling's solution, and find that a large quantity of the 

 Helianthus juice is required, but only a very small quantity of the 

 Allium juice.* Leaves which produce large quantities of starch 

 contain therefore but little glucose ; leaves which form no starch 

 are very rich in glucose. In fact, as Sachs l long ago declared, 

 and as Arthur Meyer specially determined, 2 the glucose present 

 in the leaves of Allium and other plants is to be regarded as a 

 product of assimilation. 



We may also conduct the investigations on the quantity of 

 starch and sugar in assimilating leaves as follows, again employing 



* Hand presses and cloths are to be obtained from G. Wenderoth in Cassel 

 (see price list No. 2907). If the juices after filtering are very dark in colour, 

 it is well to treat them with Lead acetate, filter, precipitate the lead with ELS, 

 and free the solution from H 2 S by passing a current of air. On the preparation 

 of Lead acetate, see C. Wolff, Anleitung zur Untersuchung landwirthschl. wich- 

 tifjer Stoffe, 1875, p. 188. The Fehling's solution is prepared in the manner 

 given in Section III. 



