RELATION OF THE PLANT TO JHE SOIL 121 
air will be discussed, it will be shown that this substance is 
carbon dioxide. The important point now is, that plants grown 
in the light do get food from the air. | 
| Plant ten cress seeds, the weight of which 
has been ascertained, in moist earth, and keep 
them in the dark for a week. Then weigh the seedlings. 
Result. | The seedlings are heavier than the seeds. 
The seedlings must have taken up something 
~~ from the soil. . | 
We have already seen in the preceding chapter that plants 
do take in water through their root-hairs. Water is not the 
Experiment III. 
Conclusion. 

Fig. 141.—Srepuine = Fig. 142. SEEDLING 
IN WATER CUL- IN- DISTILLED 
TURE SOLUTION. WATER. 
only substance the plant gets from the soil. To prove this 
experimentally plants have been grown in solutions contain- 
ing those substances which enter into the composition of the 
plant. The solution which is generally used is the one 
recommended by the German botanist Sachs, see Appendix A. 
It will be referred to in future as the ‘Water Culture Solu- © 
tion.’ 
