Internal Phloem in Gclscmhim sevipervhrns, Ait. 47 



Histology of a Nodal Section. 



Near a node the circle of wood and external phloem becomes 

 elliptical, and the patches of internal phloem lie at the ends 

 and sides of the ellipse. The end patches are considerably- 

 larger than the side ones and are further divided into a central 

 and lateral portion, the former for the petiole, the latter to 

 remain in the stem. Higher up, the ends of the ellipse curve 

 out more and more, and soon separate from the sides to form 

 the petiolar bundles. Each bundle is accompanied by a por- 

 tion of the internal phloem, so that at first the petiolar bundle 

 is composed of external phloem, wood and two small masses 

 of internal phloem. Left in the stem are the two long lateral 

 curves of wood and external phloem as before. The two 

 small groups of internal phloem that remained behind at each 

 end now move together to reconstitute the end patches. 

 Above the node the wood reunites into a continuous ring, 

 while at the next node above, the leaf bundles will be given off 

 from the opposite sides of the stem. 



The petiolar bundles are at first distinctly bicollateral. 

 Numerous patches of external phloem border upon the outer 

 or lower face of the wood, and on its inner or upper face are 

 two clearly defined patches of internal phloem. Almost im- 

 mediately after the petiole has separated from the stem, the 

 main petiolar bundle gives off two small lateral branches. 

 These bundles consist chiefly of external phloem with a little 

 xylem. They continue upward through the petiole and along 

 the sides of the leaf, where their branches anastomose with 

 branches from the main leaf bundle. A remarkable change 

 soon takes place in the main petiolar bundle of a kind which, 

 so far as I am aware, has not previously been described. 

 Just above the point where the lateral petiolar bundles branched 

 off, the two internal pJiloem patches, one after the other, pass down- 

 ward and outward through the wood to Join the external phloem. 

 In a transverse section of a petiole, the phloem strands may be 

 seen in longitudinal section passing between the xylem cells. 



