ON TROPICAL FRUITS 
The full power of the molecular forces that, 
acting jointly, carry the water to the tree tops 
will best be understood when it is recalled that if 
a rubber tube is put tightly about the end of an 
amputated twig, water in this tube will be forced 
upward by the pressure of water in the cells of 
the twig. This experiment, first made by Hales 
in 1727, in itself shows how utterly different are 
the conditions of water in the tree from the mere 
mechanical condition of pressure that governs the 
water in a closed tube, or otherwise standing in a 
single receptacle. 
Titanic MoLecuLar Forces 
Many boys have made the experiment of burst- 
ing a barrel by the pressure of water in a small 
iron pipe projecting upward from the barrel. 
Whoever has seen the experiment will not 
doubt that the physical laws governing the water 
in the trunk of the tree are quite different from 
those that govern the water in the iron tube. And 
the difference is due, the physicists assure us, to 
the interposition of the molecular forces. 
Whether or not the laws of osmosis, above out- 
lined, as discovered by Vant Hoff, give full expla- 
nation is matter for the physicists to decide. As 
yet they are not quite sure about it. But that the 
osmotic forces are at least partly instrumental in 
lifting the water, all are agreed. 
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