FIBRO-VASCULAR BUNDLES 51 



net-work (rcticiJate). Vessels have the same function as tra- 

 cheids, that is, they condiiet water. In vessels a lonoitudinal 

 channel is formed which has a greater diameter than thai of 

 the tracheids, i.e. 300 to 700 /x. Owing to the cavity of the 

 vessels being continuous from end to end the vessels are more 

 efficient as water-conduits than the tracheids and throu<.Ii 

 them most of the water passes. "^ 



Fm. 14. Leaf of Plane, Platanus orientalis, showing the fibres and vascular 



bundles. From Ettingshausen. 



The organic food material is conveyed throughout the plant 

 by the sieve-tubes. These are formed of rows of cells whose trans- 

 verse walls are pierced by a number of minute holes as a sieve 

 is. These are called sieve-plates, and through the holes in them 

 the protoplasm of one cell is continuous with that of the next. 



All the three conducting tissues, tracheids, vessels and 

 sieve-tubes help to form the " fibro-vascular bundles" which 

 traverse the plant from the root tip to the leaves. 



