276 



PRIMA R}- ARRANGEMENT OF TISSUES. 



lateral bundles. The leaf-trace is here much contracted, and usually forms by 

 coalescence one single mass. The six bundles of one pair of leaves thus go through 

 only two internodes before they coalesce with lower ones, and the transverse section 

 through an internode shows twelve bundles (Fig, 127), of which six pass out at the 

 next node and six at the node above it. These twelve bundles would be arranged in 

 a circle if they had a radially perpendicular course. But this is not the case : they 

 penetrate further into the pith as they pass down lower. Their radially oblique course 

 is however restricted almost entirely to the nodes : the same bundle thus appears at 

 unequal distances from the centre in the two internodes. The lateral bundles, which 

 in their first internode are nearer the centre than the median ones, differ still more from 

 them in this respect in the next lower internode. The transverse section through an 



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i-ijj. 126. 



Fig. 127. 



I-IGS. 126, 127. — Dioscorea Batatas, with decussating pairs of leaves; after NSgeli. Fig. 126. Scheme of the 

 vascular bundle-system in the end of a shoot, the cylindrical surface being reduced to a single plane. Fig. 127. 

 Transverse section through an internode, the same bundles being indicated by the same letters as at the bottom 

 of Fig. 27 ; further explanation in the text. 



internode therefore shows four bundles which project further inwards and form a 

 rectangle, — these are the lateral bundles of the next higher pair of leaves, — and eight 

 outer bundles. 



On the longitudinal course where the leaves in Dioscorea are arranged spirally, 

 and on Tamus. compare Nageli, I.e. 



The course of the bundles in IMonocotyledonous stems has recently been the 

 subject of extended researches by Falkenberg^ The chief result of that work which 



' P. Falkenberg, Vergl. Unteisuchungen uber den Ban der \egLtationsorgane der Monocotyle- 

 donen, Stuttg. 1876. 



