THE LEAVES 65 



green stuff cannot make starch. Plants like the mush- 

 room that have none of this green stuff live on the 

 food stored up by green-leaved plants. 



4. Nor can a leaf that gets no sunlight make starch. 

 This can be proved by testing the leaves of a plant 

 that has been kept in the dark for a few days ; but 

 this also is too difficult for you just now. 



5. You have heard that all the forces that we use^ 

 steam force, water force, and so on, are got from the 

 sun. So also, you can now see, is the force that is 

 stored up by the plant in starch. "WTien you eat the 

 starch in a potato, you are taking in the sun-force that 

 enables you to run about. "When a plant pushes out 

 shoots, it does it by sun-force ; and the horse that 

 eats the plant obtains the force — sun-force, that 

 enables it to gallop round the field. Every grain of 

 starch won by the leaf is so much sun-force ready to 

 be packed away in twig or stem or root or seed for 

 present work or future work.* On a sunny day, a 

 strong vegetable-marrow plant takes in sun-force so 

 quickly that you can almost see the plant growing. 



6. Try to see in your mind what is going on in that 

 marrow plant. Ten thousand root-cells are receiving 

 water and passing it up and on ; through a million 

 breathing pores the water is escaping into the air ; 

 through a million mouths the leaves are taking in 

 air-food; at a thousand points the work goes on of 

 building new roots, new cells, new buds, new shoots, 

 new flowers, new marrow-fruits "What a scene of 

 busy work ! And all done by sun-force ! The marrow 

 is a beautiful living sun-machine. 



* A beautiful demonstration of sun-force can be given by the radiometer. 

 This is a very small machine like a windmill, but driven, not by the "wind, 

 but by the impact of the sun's rays. 



