CHAPTER III. ORGANS OF PLANTS. 185 



In the stems of a few Ferns there is more than one circle of 

 ■fibro -vascular bundles. In the stems of Lycopodiums and Selagi- 

 nellas there may be a single bundle, and this may be either con- 

 centric or radial, or there may be two or more concentric 

 bundles placed side by side, as in Fig. 445. In the stems of 

 Equisetums, a transverse section of the internode shows a single 

 circle of poorly developed collateral bundles surrounding a cen- 

 tral hollow and enclosed by a common endodermis. Within 

 each bundle at the inner side is an intercellular space, produced 

 by the breaking down of the earlier formed xylem elements. 

 A longitudinal section shows that the bundles run parallel in the 



internodes, but anastomose 

 at the nodes where the 

 bundles are received from 

 the leaves. 



The Palm or Monocot- 

 yledon Type is the preva- 

 lent one in the sub-class 

 of flowering plants called 

 Monocotyledons. Here the 

 fibro-vascular bundles are 

 usually of the collateral 



Fig. 445 — Transverse section of stem of Selagi- type, and of that Variety of 



nella denticulata, showing two concentric fibro- . , . , , 



vascular bundles side by side. Magnified about 65 it Which, When mature, pOS- 



diameters. • . .• 



sesses no menstem tissue 

 between xylem and phlcem. They are, therefore, closed bundles. 

 As viewed in a cross-section of the stem they do not show 

 a circular arrangement, but are scattered with little or no 

 apparent order through the fundamental system of tissues. The 

 phloem part of each bundle usually faces radially outward or 

 toward the periphery of the stem, and the xylem inward or 

 toward the centre. The bundles of the stem are all continuous 

 with those of the leaves. From them they pass obliquely down- 

 ward, or sometimes nearly horizontally inward, in a radial direc- 

 tion, toward the centre of the stem ; thence they bend in a 

 downward direction, and then, in a long curve, sweep gradually 

 outward toward the circumference of the central cylinder, where 

 they finally terminate, after coalescing with other bundles which 

 originate from leaves higher up. The bundles do not all pene- 



