146 



BOTANY OF THE LIVING PLANT 



Each develops from a single embryonic, or cambial cell. As it elong- 

 ates, its pointed ends slide between those of other fibrous cells, taking a 

 sinuous course. The result is that the cells of the strand interlock, and 

 when a longitudinal strain is applied, the resistant rods press laterally 

 upon one another, so that the greater the strain the more closely are 

 they united. Mechanically such strands act like solid metal wires. 



3. 



Fig. 105. 

 A , Transverse section of sclerenchyma of stem of Sunflower. Tlie larger sections 

 show cells cut through the middle of the fibre, the smaller near to the pointed end. 

 B, the same in longitudinal section, showing the pointed ends of the cells. Small 

 pits are present, in surface view, and in section. F. O. R. ( ■ 300.) 



This comparison has been pursued into measurements which bring 

 out the characteristic features of the resistance of plant-fibres, as 

 contrasted with those of certain metal wires of similar transverse 

 section. The figures in the subjoined table show how different is 

 the behaviour of the two under strain. 



Limit of Elasticity 

 in Kg. per sq. mm. 



IVeaking strain in 

 Kg, per sq. mm. 



I Elongation at limit 

 j of Elasticity per 

 1000 units of length. 



