BORDERED PITS. 



159 



thickening, which traverses the wall transversely. If the canal be equally wide 

 throughout or narrowing outwards, we have a non-bordered pit. On the other hand, 

 the term bordered pit is applied to those in which the canal widens suddenly towards 

 the outside, i. e. towards the non-thickened part of the membrane, so that it is here 

 broader than at the part of the canal bordering on the internal cavity. In the 

 surface view of the wall the boundary of the unthickened portion of the membrane 



HiC. 58.— Pinus sylvestris ; radial longitudinal section through 

 the wood of a branch ; a — e ends of tracheides with bordered 

 pits (/', t" in surface view ; c b piece of a young wall of a 

 tracheide, with still iwimature bordered pits; further^ develop- 

 ment of these, successive narrowing of the canal a — *:; d and e 

 mature condition ; st large pits on the limiting surface be- 

 tween tracheides and cells of medullary rays {550). From Sachs' 

 Textbook. 



<1) 



@) 



Fig. S9- — Ephedra helvetica. Wood (230) ; 

 a member of a vessel, b tra-jheides seen from 

 the radial side, isolated by maceration with 

 Schultze's mi.\ture ;y the oblique ends oi the 

 member of the vessel in surface view, with 

 two rows of large open bordered pits ; at x, x 

 two closed bordered pits. Of the traclieides, 

 b is only drawn in 9utline, the surface of the 

 other is put in. (The direction of the split- 

 like pits is reversed ; they rise in reality frou» 

 left to right.) 



may be seen surrounding the limit of the section of the canal like a border or 

 halo. (Fig. 58). The widened outer part of the pit, the limit of surface of which 

 is the halo, is called the cavity of the pit; in the canal itself may be seen the 

 outer aperture, which leads into the cavity of the pit, and the inner which borders on 



