90 



VEGETABLE HISTOLOGY. 



The following scheme shows the types of bundles and their 



distribution : 



COLLATERAL BUN- 

 DLES. -- Stems and 

 leaves of nearly all 

 flowering plants, a 

 few ferns, as the gen- 

 era Ophioglossum 

 and Osmunda and 

 stems of Equiseta- 

 ceae. 



I. Ordinary Bun- 

 dles. Having one 

 phloem and one 

 xylem mass. 



II. Bicollateral 

 Bundles. Chiefly 

 stems of Cucurbi- 

 taceae (gourd fam- 



a. Open Bundles. 

 Stems and leaves 

 of woody dicotyls. 

 (Cambium zone 

 present.) 



6. Closed Bun- 

 dles. Most mono- 

 cotyls, the ferns 

 mentioned and 

 stems of Equiseta- 

 ceae. (No cambium 

 zone present.) 



CONCENTRIC BUNDLES. 



I. Bundles with xylem central. 

 Stems and leaves of nearly all ferns 

 and club mosses. 



II. Bundles with phloem central. 

 Stems and leaves of some mono- 

 cotyls. 



RADIAL BUNDLES. Roots of all phanerogams and pterido- 

 phytes and stems of Lycopodiaceae. 



COLLATERAL BUNDLES. 



CLOSED BUNDLES. Harden a stout piece of the stem of Spider- 

 wort ( Tradescantia Virginica) in alcohol and make thin cross- 

 sections. (This is a monocotyl). Stain with phloroglucin. 



The greater portion of the section is made up of large ordinary 

 parenchyma cells containing starch. Scattered among these 

 cells over the entire section are numerous rounded areas of 

 smaller cells containing no starch. These are the closed col- 

 lateral bundles. In the xylem, which faces towards the center 

 of the section, will be found from three to five thick-walled 

 ducts, which in many of the bundles are arranged in the form 

 of a V. In some of the bundles the xylem completely surrounds 

 the phloem. On the side of the xylem towards the center of the 

 section there is usually found a large intercellular space. This 

 is often found in closed collateral bundles. 



The phloem is composed of small cells, which are mostly 

 sieve cells, accompanied by some parenchyma cells. There is 

 no growing or cambium zone between the phloem and xylem. 



