FIBROVASCULAR TISSUES: PHLOEM 



121 



panion cells. In the tangential aspect the terminal sieve plate, 

 since it is radial in position, is shown in profile. The protoplasm, 

 present more densely in the region of the terminal plates, is pur- 

 posely omitted in order that the sculpture of the lateral walls may 



FIG. 92. Tangential section of the phloem of the linden. Explanation in the 



text. 



be apparent. There are manifestly strongly punctuated areas in 

 the side walls of the sieve element. These represent sieve plates 

 which have more or less completely lost their function as a result 

 of degeneracy. In herbaceous types lateral sieve areas frequently 

 have no longer even a morphological expression, the structural 



