28 NATURE'S TEACHINGS. 



which is coated with a very thin shell of flint, or " silex " as it 

 is scientifically termed. The result of this structure is that the 

 stem possesses strength, lightness, and elasticity, so as to be 

 equal to the burden which is laid upon it. 



Then there is the common Bamboo, which is little more than 

 a magnified straw, being constructed in much the same manner, 

 and possessing almost the same constituents of vegetable matter 

 and silex. 



Perhaps the most extraordinary of the tubal system is to be 

 found in the remarkable plant of Guiana called by the natives 

 Ourah, and scientifically known by the name of Arundinaria 

 Schomburgkii. Like the bamboo, it grows in clusters, and has 

 a feathery top, which waves about in the breeze. But, instead 

 of decreasing gradually in size from the base upwards, the 

 Ourah, although it runs to some fifty feet in height, is 

 nowhere more than half an inch in diameter. The first joint 

 is about sixteen feet in length, and uniform in diameter 

 throughout. 



It is scarcely thicker than ordinary pasteboard, and yet so 

 strong and elastic is it, that it can sustain with ease the weight 

 and strain of its feathery top as it blows about in the breeze. 

 The natives of certain parts of Guiana use this reed as a blow- 

 gun, and I have a specimen, presented to me by the late Mr. 

 Waterton, which is eleven feet in length. 



So the reader will see that when engineers found that hollow 

 iron beams were not only lighter, but stronger than solid beams, 

 they were simply copying the hollow beams formed by Nature 

 thousands of years ago. 



ANOTHER great improvement in ship-building now comes 

 before us. 



We have already seen that the earliest boats were merely hol- 

 lowed logs, just as Robinson Crusoe is represented to have made. 

 But these had many disadvantages. They were always too 

 heavy. They were liable to split, on account of flaws in the 

 wood, and if a large vessel were needed, it was difficult to find 

 a tree sufficiently large, or to get it down to the water when 

 finished. 



So the next idea was to build a skeleton, so to speak, of light 

 wooden beams, and to surround it with an outer clothing, or 



