PLANT TISSUES 



117 



bium and phloem with crude sap which passes up ma inly through the 

 tracheae and tracheids from the absorptive regions of the roots. 

 They furthermore serve as storage places for starch, alkaloids, resins, 

 and other substances. 



Fibro-vascular Bundles are groups of fibers, vessels and cells cours- 

 ing through the various organs of a plant and serving for conduction 



PIG. 54. Diagrams illustrating the arrangement of the regions in different 

 types of nbrovascular bundles. In each diagram x represents xylem; P, phloem 

 and C, cambium. A, Radial bundle; B, concentric bundle of fern stem type; 

 C, concentric bundle of monocotyl type; D, closed collateral bundle; E, open 

 collateral bundle; F, bi-collateral bundle. 



and support. According to the relative structural arrangement of 

 their xylem and phloem masses they may be classed as follows: 



I. Closed collateral, consisting of a mass of xylern lying alongside 

 of a mass of phloem, the xylem facing toward the center, the phloem 

 facing toward the exterior. Stems of most Monocotyledons and 

 Horsetails. 



II. Open collateral, consisting of a mass of xylem facing toward 

 the pith and a mass of phloem facing toward the exterior and sepa- 

 rated from each other by a cambium. Stems and leaves of Dicoty- 

 ledons and roots of Dicotyls and Gymnosperms of secondary growth. 



III. Bicollateral, characterized by a xylem mass being between 

 an inner and an outer phloem mass. There are two layers of cam- 

 bium cells, one between the xylem and inner phloem mass, the other 



