THE SAP 



fungus. Very soon the mushroom-like heads of this fungus 

 begin to swell and elongate; they burst through the bark 

 and form a clump of reddish-yellow Paddock-stools. A fly 

 comes to the fungus and lays an egg in it. This egg 

 becomes a fat, unpleasant little maggot which eats the fun- 

 gus, and amongst others devours our carbon atom, which 

 again becomes fat in its body. Then a tomtit or other 

 small bird comes along and eats the maggot. That bird 

 stays out too late one evening and is eaten by an owl. The 

 owl, satisfied with a good meal, allows itself to be surprised 

 and shot by a keeper. When its body is nailed to a door 

 and decays away, the carbon atom again takes up oxygen 

 and becomes carbonic acid gas, which escapes into the atmo- 

 sphere, and is ready for a fresh series of adventures. 



We must now consider the water which with carbonic acid 

 gas makes up sugar, etc. All plants contain a large per- 

 centage of water. This may be as much as 95 to 98 per 

 cent in water plants, and 50 to 70 per cent in ordinary 

 tissues ; it is contained in every sort of vegetable substance. 



But there is also a stream of water or sap which is almost 

 always entering the roots, rising up the stem, and passing 

 into the lieaves. On these leaves there are hundreds of 

 minute openings called stomata, by which the water escapes 

 as water- vapour into the atmosphere. A single oak leaf may 

 have 2,000,000 of these stomata. 



It is this current of sap which keeps the leaf fresh and 

 vigorous ; it is also by this current that every living cell is 

 supplied with water and kept in a strong, healthy condition. 



The amount of water used in this way is very great ; in 

 four months an acre of cabbages will transpire or give out 

 through its leaves 3,500,000 pints of water and an 

 acre of hops from 5 J to 7 millions. A single oak tree, 



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