THE CELL 7 



simple on the side of the medullary-ray cells. Pits of this nature 

 are called half-bordered. 



In Fig. 5 simple and bordered pits are represented diagram- 

 matically side by side and from both profile and face view. Ob- 

 viously the simple pits in face view are single in contour, while 

 those which are bordered have a triple concentric outline, the outer- 

 most circle corresponding to the boundary of the broad membrane 

 of the pit, the innermost to the narrow mouth, and the intermediate 

 representing the outline of the torus. The distinction between 

 simple and bordered pits is an extremely important one, particularly 

 in the lower groups of vascular plants. In higher forms the dis- 

 tinction is of less value, but the presence of bordered pores in vas- 

 cular elements in general still indicates that an important function 

 of the element so provided is the transport of water. It should be 

 further noted that elements with bordered pits are usually without 

 intercellular spaces, while those in which the pits are of the simple 

 type normally possess such aerating cavities. Exceptions to this 

 statement are found ordinarily only in plants which have become 

 highly specialized in connection with resistance to drought. 



