XTL THE STRUCTURE OF ECONOMIC PLANTS 



the lower leaves may appear to be in approximate pairs. The 

 trace of each young leaf consists of a large median bundle and two 

 smaller lateral ones, but at maturity this number is considerably 

 increased so that there are several bundles in the semicircular base 

 of the petiole at its point of divergence from the stem. The course 



of the bundles in the Chenopodiaceae 

 and in the genus Beta has been in- 

 vestigated by Fron (8), Wilson (xi), 

 Artschwager (x), and others. The 

 accounts are in agreement except for 

 differences in the course of the 

 median bundle as reported by Fron 

 who worked with Beta cycla. Art- 

 schwager's report, based on Beta 

 vulgaris, is here given in part: 



"Occupying the corners of the ir- 

 regular polygon are five large cauline 

 bundles alternating with an equal 

 number of strands, usually somewhat 

 smaller in size, which represent the 

 median traces of the first five leaves. 

 Flanking the sides of the cauline 

 bundles are small strands of vascular 

 tissue which represent the lateral 

 traces." (Fig. 135.) 



Considering only the three main 

 bundles of each trace and disregard- 

 FiG. 135. A portion of floral axis ing variations which occur, 



five internodes in length showing vas- 

 cular anatomy. Cauline bundles are "the derivation of the traces accords 

 solid black, median traces of leaves are • u u r 11 • 1 r- u 



■^ 1 I I , , I u ji f I With the rollowinff plan. Each new 



stippled, and lateral bundles of leaves 1 1 r 



are white. (Redrawn after Artschwa- median trace IS derived from a left 

 g£r,Jour. Agr. Res.') cauline bundle (viewed from the stem 



apex) a little distance above the node, 

 it ascends without fusion or forking for five internodes and passes into 

 the leaf without branching. The left lateral trace is derived from the 

 cauline bundle next it, passes through three internodes, and usually 

 branches several times before entering the leaf. The right lateral 

 trace is also derived from its adjacent cauline bundle. It passes 

 through only two internodes, but otherwise conforms to the left 

 lateral trace. The length of the lateral trace is, however, subject 

 to variation since it often remains a part of the cauline bundles for 

 a longer or shorter portion of their ascent. 



