THE FOOD OF PLANTS. 



seen to be very 

 rich in starch 

 (see Fig. 17). 



It is further im- 

 portant to satisfy 

 ourselves that 

 plants are unable 

 to form starch 

 when exposed to 

 the light in an 

 atmosphere free 

 from Carbon di- 

 oxide, and indeed 

 that the starch 

 which may al- 

 ready be present 

 disappears under 



FIG. 17. A leaf of Tropteolum tested wicn Iodine. In the 

 white parts starch formation has been suppressed by cutting off 

 the light, as described in the text. 



these conditions from 

 the chlorophyll bodies. 

 We fill small flower- 

 pots with ignited sand 

 saturated with the 

 ordinary food solution 

 used for water-culture 

 experiments, but di- 

 luted with water, and 

 sow in them a few 

 seeds of Raphanus 

 sativus or other plants 

 (with special success 

 I experimented with 

 Lepidium sativum). 

 When the cotyledons 

 have fully developed, 

 the seedlings, in whose 

 cotyledons we can 

 easily detect large 

 quantities of starch, 

 are placed in the ap- 

 paratus represented 

 in Fig. 18. The glass 



Fir. 18. Apparatus for the culture of plants in absence 

 of Carbon dioxide. 



