204 



THE SECOND BOOK OF BOTANY. 



into fibres, as well as by their union and modification 

 in various ways, that all the elements of vegetable 

 structures are produced. 



FIG. 867. 



FIG. 863. 



FIG. 869. 



FIG. 870. 



FIG. 871. 



Fibres vary in length, and their walls thicken 

 with age by the deposit upon their interior of new 

 layers filling up the cavity. As long as any cavi- 

 ty remains it will be round, while, by pressure, the 

 external wall becomes flattened and prismatic (Fig. 

 372). In fibrous tissue (Fig. 373) you see the taper- 

 ing, overlapping extremities, making the texture 

 close and solid. The largest fibres of wood are found 

 in trees of the pine family cone-bearing trees 

 where they are as much as -g-J-g- or ^-i-g- of an inch in 

 diameter. Their size varies in different families of 



