IOO 



THE ANATOMY OF WOODY PLANTS 



In this case the wall to the left has been in contact with a ray, as 

 evidenced by the grouping of the pits. The region of the lateral 

 wall to the right has been in contact with another vessel and is 



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FIG. 77. Various types of vessels in the dicotyledons. Explanation in the text 



conspicuous, not only by reason of the characteristic arrangement 

 of the pits, but also by the presence of a somewhat spiral internal 

 sculpture, the so-called tertiary thickening, which always marks 

 (when present) the contact or "party wall" between vessel and 

 vessel. Those surfaces of the vascular element which are in contact 



