CHAPTER V 



HOW PLANTS OBTAIN FOOD FROM THE AIR 



WE have seen that plants obtain both food and 

 water from the soil by means of the roots. Is this 

 the only way in which they obtain food, or are they 

 also able to feed on air ? 



We have often seen mustard or cress grown 

 upon a piece of moist flannel, the tiny seeds spring- 

 ing in a rich mass of green foliage. How have those 

 plants been supplied with food 1 



Let us try a few experiments with a view to 

 understanding exactly what happens when cress is 

 grown in this way. 



But in the first place, let us examine a seed itself, 

 with a view to finding what it contains, and whether 

 it plays any part in feeding the young plant. 



If we select a large seed, such as a bean, and cut 

 it neatly in half, we notice in one corner near the 

 margin a small speck. This is the young plant 

 which, if the seed be kept warm and moist, will 

 begin to grow. The rest of the seed is 'merely a store 



