406 



THE ANATOMY OF WOODY PLANTS 



clearly exemplified in certain species of Clematis. In the numerous 

 species in which the large rays are approximated in pairs there are 

 depressed segments in the stem; but in Clematis paniculata, in 

 which the large compound rays are equidistant, the segments of 

 the woody cylinder are all on a level and there are no depressed 

 regions. It is not possible to follow this subject further in the 

 present connection, but it is enough to point out that the facts 



f 



a 



FIG. 284. Diagram of the topography of the cylinder in Quercus and Aster. 

 Explanation in the text. 



entirely invalidate the interpretation of depressed segments ad- 

 vanced by Sanio, Sachs, and De Bary and now classic in botanical 

 textbooks. The view of these authors is that the depressed seg- 

 ments, where they occur, owe their topography to a later forma- 

 tion than the rest of the cylinder. This is distinctly not the case. 

 The classic view just mentioned further involves the equally 

 erroneous hypothesis that the continuous cylinder of woody forms 

 has been derived from the discontinuous one of herbaceous types, 

 a conclusion which, on the evidence furnished in the present and 

 previous chapters, is exactly opposite to the true situation. In 



