THE WATER IN TREES 



sucking in water,^ and eventually they are so full and dis- 

 tended within, that the internal pressure becomes almost 

 incredible. Wieler found in the young wood of a Scotch fir 

 that the pressure was sixteen atmospheres, or 240 lb. to the 

 square inch. Dixon, when experimenting with leaf-cells, 

 found ten, twenty, or even thirty atmospheres (150 to 

 4501b. to the square inch). No locomotive engine has 

 cylinders strong enough to resist such internal pressures as 

 these. It is an extraordinary fact, and one almost incredible, 

 that the cells can stand such pressures. 



Yet these minute living cells not only exist but work at 

 this high tension, and, in some cases, they live to about 

 fifty years. 



In this favoured country of Great Britain, it is unusual to 

 find any serious lack of water. But in Italy or Greece, every 

 drop of it is valuable and carefully husbanded. 



Sometimes in such arid dry countries, a small spring of 

 water will form around itself a refreshing oasis of greenery 

 surrounded everywhere by dreary thorn-scrub or monotonous 

 sand. All the plants in such a spot have their own special 

 work to do : the graceful trees which shade the spring, the 

 green mosses on the stones, the fresh grass and bright flowers 

 or waving reeds, are all associated in a common work. They 

 protect and shelter each other ; their dead leaves are used to 

 form soil ; their roots explore and break up the ground. It 

 is true that they are competing with one another for water 

 and for light, but they are all forming a mutual protection, 

 and producing an annual harvest. 



In a climate like our own we cannot, like the Greek, 

 suppose a Nymph in the shape of a lovely young woman 



^ The ascent is assisted by the osmotic absorption of water at the root 

 and by evaporation at the leaves. 



25 



