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BOTANY 



PAKT I 



arrangement is due to the varying distances to which the bundles of the 

 leaf-traces penetrate into the central cylinder of the stem. A common 

 arrangement of the bundles in monocotyledonous stems is that of the 

 so-called Palm type, in which each leaf-trace consists of the numerous 

 bundles which pass singly into the stem from the broad leaf-base. The 

 median bundle penetrates to the middle of the stem. The depth to 

 which the lateral bundles penetrate varies with their remoteness from 

 the median bundle. In their descending course the bundles gradually 

 curve outwards, and finally join other bundles near the periphery of 



Fig. 132. — Diagram showing the course of the vascular bundles in a shoot of Taxus baccata. 



the stem. The number of internodes, therefore, through which a bundle 

 passes before coalescence is variable ; the median bundle, however 

 continues distinct for the longest distance. The deeper penetration 

 and greater length of the median bundle become apparent in a median 

 longitudinal section of such a stem (Fig. 133). In addition to the 

 leaf-trace bundles or common bundles, which are common to both leaf 

 and stem, there are others, called CAULINE bundles, which belong solely 

 to the stem, and again others, foliar bundles, which, on entering the 

 stem from the leaf, at once coalesce with other bundles and have no 



