52 



A TEXT-BOOK OF BOTANY 



(phloem).* A vascular bundle, therefore, is made up of 

 wood and bast, which differ from one another in the work 

 of conduction, the wood chiefly conducting the water that 

 enters the plants by the roots and is passing to the leaves, 

 and the bast chiefly conducting prepared food. 



The cells of the wood that conduct water are called 

 tracheary vessels. They are more or less elongated and 

 have very thick walls, upon which there appear markings 

 of various kinds. These markings may be seen in a 



B 



FIG. 53. Vessels: spiral (A) and annular (B) vessels; dotted vessel (C) ; sieve 

 vessel (D) and sieve plate (E) from pumpkin. A and B after BONNIER and 

 SABLON ; C after DE BARY ; D after STRASBURGER. 



longitudinal section through the wood. Some of the vessels 

 are marked by a spiral band that extends from end to end, 

 and are called spiral vessels (Fig. 53, A); others show a 

 series of thickened pngs, and are called annular vessels 

 (Fig. 53, B); while others, and among them the largest, 



If a cross-section of a pine twig be stamen first with safranin and 

 afterward with Delafield's haematoxylon, the xylem will become bright 



red and the phloem rich violet. 



