442 THE ANATOMY OF WOODY PLANTS 



an oil-secreting system are occasionally found in the root only. 

 Even in the chicory itself some slight indications of oil canals are 

 sometimes discovered in the roots, although these are never func- 

 tional as in the salsifies. 



It will be apparent from the various illustrations and state- 

 ments of the foregoing paragraphs that in the Compositae the 

 oil canals of the lower forms tend to perpetuate themselves in a 

 vestigial fashion in certain conservative parts and organs of the 

 higher types belonging to the Cynareae and the Cichorieae. The 

 general situation can best be visualized by means of a diagram 

 which is made in accordance with the data supplied by the French 

 artichoke, Cynara Scolymus, since this form on the whole reveals 

 the anatomical situation in the fullest manner. In the center 

 of Fig. 306 appears a somewhat conventionalized external view 

 of the species under discussion. The regions which are of critical 

 importance are indicated by dotted lines, marked by letters from 

 A to D. At the sides are shown diagrammatic transverse sections 

 of the regions indicated by the letters. In A is seen a view of 

 the root, conforming to the general structure of such organs and 

 at the same time showing a series of oil canals just external to an 

 outer circle indicating the endodermis. In B appears a view of 

 the lower region of the axis showing leaf traces, either present in 

 the cylinder of the stem or lying externally in the cortex. In 

 every case the foliar strand is accompanied by oil canals, which 

 are entirely absent in the bundles of the stem. In C is represented 

 a section through the high aerial portion of the stem. Here the 

 leaf traces, whether still within the cylinder or passing outward 

 in the cortex, are conspicuously without accompanying oil canals, 

 as are also those of the axis proper. In D, which illustrates a 

 region of section through the base of the reproductive axis, the 

 oil canals appear again in relation to the traces of the involucral 

 appendages, but are as clearly absent in the axial bundles as they 

 are in the lower parts of the stem. It is accordingly obvious that 

 the various canons of comparative anatomy stated in chapter xvii 

 are as well illustrated by that very high dicotyledonous group, 

 the Compositae, as they are by the conifers and calamites. More- 

 over, while it is true that in the case of the high dicotyledonous 



