CHAP, v HOW PLANTS OBTAIN FOOD FROM AIR 39 



of food, from which the seedling is supplied until it can 

 obtain food for itself. 



This food store may be largely oil, as in linseed, 

 or starch and other vegetable substances. 



Experiment 24 



Let us take, for instance, some linseed and crush 

 them in a mortar. Now place the crushed seed in a 

 bottle, pour a little ether upon it, cork the bottle 

 and shake it vigorously. After shaking it for a few 

 minutes, empty the contents of the bottle on a filter- 

 paper, and collect the ether running through. Place 

 the ether out in the sun, exposed in a shallow dish. 

 In a short time the ether will evaporate and leave 

 behind a yellow oil. This oil has been dissolved by 

 the ether from the seed, leaving behind a brown- 

 coloured substance, similar to that of which linseed 

 cake is made by pressing hot seed. 



A store of food is therefore contained in the 

 seed, and with this and with water the cress grow- 

 ing on flannel has been supplied. Can we regard 

 such a store of food as sufficient, or must we search 

 elsewhere to find other sources from which the 

 plant has been fed 1 



Let us try to find out the answer to this question 

 by another experiment. 



