592 



FARMERS' REGISTER 



No. 11 



Fig. 8, 9, 10. 



the tubes, which he has called simple tubes, 

 seem to contain the resinous or oily fluids peculiar 

 to different plants. 



The porous tubes likewise contain these fluids; 

 and their use is probably that of conveying them 

 into the sap for the production of new arrange- 

 ments. ° 



The tracheffi contain fluid matter, which is al- 

 ways thin, watery, and pellucid; and these organs, 

 as well as the false trachea?, probably carry off wa- 

 ter from the denser juices, which are thus enabled 

 to consolidate fbr the production of new wood. 



In the arrangement of the fibres of the wood, 

 there are two distinct appearances. There are 

 series of white and shining lamina?, which phoot 

 from the centre towarde the circumference, and 



these constitute what is called the silver grain ot 

 the wood. 



There are likewise numerous series of concen- 

 tric layers, which are usually called the spurious 

 grain, and their number denotes the age of the 

 tree.* 



The silver grain is elastic and contractile; and 

 it has been supposed by Mr. Knight, that the 

 contractions produced in it by changes of temper- 

 ature are the principal causes of the ascent of the 

 sap. 



The silver grain is most distinct in forest trees; 

 but even annual shrubs have a system of fibres 



* Fig. 8. represents the section of an elm branch, 

 which exhibits the tubular structure and the silver 

 and spurious grain. 



