9i6 



A TEXTBOOK OF THEORETICAL BOTANY 



is often given to it. Balance and resistance to strain are functions which are 

 inherent in the whole structure of a land plant, just as much as are the 

 requirements of photosynthesis or of reproduction. 



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Fig. 897. — A, Theoretical transverse section of a reinforced shaft. The small 

 squares represent the iron rods (R). The concrete mass marked G. The 

 distribution of stresses is represented graphically on the right. TC =the 

 load line. C =; compression side. T = tension side. NN =the null line of 

 no load. In the stress diagram SG = stress in ground mass, SR = stress in 

 reinforcement. SRG= stress in combined materials. AB= equal stress 

 at points R and G which are equidistant from the null line. 



B, Diagrammatic transverse section of a stem of Scirpus caespitosus. 

 The sclerenchyma is coloured black. Symbols as in diagram above. 

 AB= stress (tension) at the outer side of bundle R, and A 'B'= stress 

 (tension) at the inner side of bundle R. Both sides of bundle R are in 

 tension ; it does not therefore act as a girder, the only bundles acting as 

 girders in this case are those lying on the line NN, of which one side is in 

 tension and the other side in compression. {After Rasdorsky.) 



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