100 



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 



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 



