SIEVE-TUBES 117 



mount as before. The oblique walls are here cut longi- 

 tudinally ; the sieve-plates are often callous, especially 

 in autumn. 



Note the form of the segments of sieve-tubes ; it 

 is fundamentally the same as that of the cambium cell 

 as seen in tangential section (compare Fig 9, C, D). 



