i68 BOTANICAL GAZETTE [September 



of Stipules, the small cortical strands are few and wanting, even in 

 species which possess them abundantly in the leafy shoot. (2) As 

 will be pointed out later, in P. naians, P. Nuttalliij etc., the cortical 

 strands spread upward into the peduncle, but fuse with the strands 

 of the vascular ring (see below) or fade away soon after reaching 

 the fertile part of the axis, (3) As stated above, small bundles are of 

 constant occurrence in the petioles and stipules, even if the stem is 

 free from them. 



The creeping stem. — According to Irmisch (12), this does not 

 represent the main stem, but certain lateral members of the extensively 

 branched system. The structure differs in several noteworthy respects 

 from that of the leafy stem. The central cylinder is flattened in 

 accordance with the dorsiventral nature of the stem, as is seen in the 



piilcher {fig 



(fig 



somewhat masked by the large size of a dorsal and a ventral bundle. 

 These two bundles may meet in the center of the stele in case the stem 



I 



is much flattened. All of these are cauline strands, whose disposition 



is practically unaffected by the entrance of the insignificant leaf traces 



from the thin deciduous scale leaves. Hence there is no ^'trio" of 



bundles, and the disturbing elements are branches, not leaves. Con- ^ 



sidering a node lacking a branch, the large dorsal and ventral bundles 



are seen in a series of sections to pass through the node sometimes 



without anastomosis with other bundles; they swerv-e slightly toward 



the middle of the stele, while the lateral bundles partly close the gaps 



thus left in the vascular ring, and give off roots on all sides of the stele. 



In case a branch is present at a node, the dorsal and ventral bundles 



much 



oem (fig 



am 



vasal bundles. These anastomose with peripheral bundles of the 

 stele and with the bundles of the branch which enter at this point. 

 The bundles at the base of the branch likewise show a greatly swollen 

 phloem, which is a conspicuous feature in the figure. It will be 

 recalled that owing to the distichous arrangement of the leaves, the 

 ascending stem shows two bundles on opposite sides of the central 

 cvlinder, which bundles are the median traces of the two next hisher 



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