156 



MECHANICAL SYSTEM 



that fully developed fibrous tissues consist of nothing but a frame- 

 work of dead cell-walls which are no longer capable of growth. One 

 need only try to form a mental image of a young elongating organ 

 strengthened with strands of bast-fibres, in order at once to realise 





Fio. 49. 



Collenchyma. A. Collenchyma from the petiole of Salvia Sclarea in L.S. B. Collen- 

 chyma from the petiole of Salvia'Sclarea in T.S. C. Lamellar collenchyma from the 

 petiole of Astrantia major in T.S. D. Tubular collenchyma from the petiole of Petasite* 

 nivens in T.S. (Intercellular spaces shaded in D.) 



the absurdity of such a combination. One of two things would 

 inevitably happen in the circumstances suggested. Either the bast 

 would offer such resistance as to prevent any appreciable elongation 

 of the organ : or else the fibres would give way and so be permanently 

 deprived of their mechanical usefulness. Organs which are still 



