626 Staber : The anatomy of Sesban macrocarpa 



mapped out on paper. In this way any section could be cut and 

 Its position in the plant ascertained and recorded. Microtome 

 sections were prepared by embedding in paraffin, this method be- 

 ing found suitable even for the older, tougher portions when the 



harder paraffin was used. 



The general structure of the stem was determined by a trans- 

 verse section at 5 cm. from the tip. - This showed 39 definite 

 open collateral bundles arranged in a circle about a central cylin- 



der of pith (figure i). These were enclosed by a stereome ring 



separated from the cortex by an endodermis. To determine the 

 changes which had taken place in the development of the stem, a 

 section was taken just above the root (figure 3). Here the bun- 

 dles had enlarged considerably, forming a complete woody cylin- 

 der by the growth of interfascicular cambia, and not by the inter- ^ 

 polation of new bundles; the width had increased from 67.8 fx 

 to 2.36 mm. The first evidence of a complete woody cylinder 

 appeared at 88.5 cm. from the base, or at 16.5 cm. from the tip. 

 Another change was in the broken appearance of the stereome, 



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which at 17 cm. from the base showed 44 groups, giving evidence 

 of the inability of these cells to stretch with the growth of the 

 stem in circumference. Besides this a superficial periderm had 

 formed, just above the roots, of six or seven layers in thickness. 

 In several places where wounding had occurred it was deep 

 enough to cut off a portion of the stereome. Very prominent, 

 because of their brown color, were cells filled with tannin, occur- 

 ring in the cortex, leptome, and pith. In the cortex the tannin 

 filled separate cells without particular order, but in the leptome 

 long ducts, usually three to each bundle, formed a ring concentric 

 With the epidermis, stereome, and cambium. Besides this, single 

 ducts appeared in the periphery of the pith at the base of the large 



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bundles (see figure 2). As the general plan of the plant has 

 been given, the separate elements will now be considered in detail. 

 The pith, constituting the central cylinder of the stem, was 

 formed of more or less spherical cells, the llgnified walls of which 

 were very delicately pitted. In the older stem the cells at the 

 periphery contained considerable starch. The diameter of the 

 pith averaged thirty-nine cells throughout, the increase in the size 

 of the cells causing the enlargement in the diameter of the stem. 



