174 PLANT LIFE. 



In some cases, it is suggested that the ultimate particles 

 of each layer are really arranged in spirals, which 

 run in different directions in different layers. If this 

 is correct, then the structure of a woody tracheid-wall 

 is produced in a manner similar to that employed in 

 the manufacture of cannon, where each successive shell 

 is made by winding a wire round the core. There is 

 no doubt that the strength of the woody fibres and 

 even of other vegetable tissues is very great. 



The table on page 173 is given by Haberlandt from 

 his own experiments and those of Schwendener, Wein- 

 zierl, Firtsch, and others. 



The ingenious methods by which these results have 

 been obtained and other details are to be found in 

 Haberlandt's text-book. The above examples are 

 sufficient to show the extraordinary tenacity of vege- 

 table tissues. To this, and to the application of 

 strength in the exact position where it is most required, 

 is due the extraordinary engineering seen in such cases 

 as the Ryeplant, which, with a diameter at base of only 

 3 mm., may spring to a height of 1500 mm. A 

 factory chimney 3 67 J feet high supposed to be the 

 tallest in England has a diameter at base of 57 feet. 



The extraordinary flexibility of woody tissues is 

 quite as remarkable as their strength, as can be easily 

 realised by watching the branches of Birch and Ash on 

 a stormy day. The toughness and strength of wood 

 renders tree-stems invaluable to mankind ; and it seems 

 unfortunate, in view of the coming scarcity of timber, 

 that some seven acres of forest trees, eighty years old, 

 should be destroyed for a single day's issue of a New 

 York paper. 



