65 TEXTURE OF VEGETABLES. 



lation. But it has been observed that the pith of a 

 whole branch does not in many cases, contain sufficient 

 moisture to supply an hour's perspiration of a single 

 leaf; and an opinion, whose absurdity is thus easily 

 demonstrated, must be forever relinquished. 



SECTION 5. 



VEGETABLE FIBRE. 



In the pith of the Indian Corn, we have seen a num- 

 ber of large insulated fibres, passing longitudinally 

 throughout its whole extent. In the leafstalk of Cel- 

 lery, in the stem of the common Brake, and also in 

 most herbaceous plants, we meet with similar fibres. 

 Viewed with a microscope, they are found to beabun- 

 dle of very slender fibres firmly connected together, 

 and forming a thread, which is usually elastic and fre- 

 quently strong. This thread is capable of repeated 

 subdivisions, but no art can divide the component fibres 

 to which it may easily be reduced. 



In a similar way the net work of fibres which com- 

 pose a portion of the wood, and those of the silver- 

 grain, by which the former are intersected, may be re- 

 peatedly subdivided, and it is found that they differ not 

 only in structure and arrangement, but also in their de- 

 cree of strength. " This is obvious, from the well 

 known fact that wood may be easily split, in the direc- 

 tion of its longitudinal fibres, but not in the direction of 

 the transverse plates, owing evidently to the strong 

 and tough fabric of the former and to the slender and 

 delicate contexture of the latter."* 



* Keith 



