THE HERBACEOUS DICOTYLEDONS 



405 



to pairs of these related to the foliar strands of diverse leaves at 

 different nodes. This phenomenon is rather rare in the herbaceous 

 type, but is occasionally found in the genera Aster and Solidago, 

 among the Compositae. Fig. 283 represents an axis of this type 

 in Aster multiflorus. There are five depressed segments correspond- 

 ing to five pairs of foliar traces, to be seen in the woody cylinder. 

 Fig. 2840 is a diagram of the topography of the axis in the oak. 

 The bark is represented as removed on the side toward the reader 

 and as still present on the 

 opposite side. To the 

 right on the distant 

 aspect of the stem is 

 shown a leaf base. Into 

 this run three traces. 

 Since the median one 

 passes out at a different 

 level from the other two 

 and exercises no impor- 

 tant influence on the 

 topography of the stem, 

 it is represented by a 

 dotted outline. It is to 

 be noted that the lateral 

 traces take their origin 

 from the foliar rays which are most remote from the median trace. 

 On the left of the posterior aspect of the axis is shown by a dotted 

 outline a leaf base of a succeeding node. The traces of this leaf 

 are plotted in by broken outlines, so as to indicate their relation 

 to the foliar rays of the stem. It is clear from the illustration 

 that the depressed segment lying uppermost in the diagram is 

 flanked by two foliar rays which belong to the lateral traces of 

 two successive leaves. The depressed segment of the woody 

 cylinder in this instance owes its position to the retarding effect 

 on growth of the two closely approximated foliar rays which bound 

 it on either side. In the case of stems in which the large rays are 

 equidistant there are no depressions, showing clearly that the 

 depressed segment is the result of growth mechanics. This is 



FIG. 283. Transverse section of the stem of 

 Aster multiflorus. 



