436 THE ANATOMY OF WOODY PLANTS 



belongs. The circular zones of darker elements mentioned above 

 represent not only the distribution of the laticiferous tissue, but 

 that of the sieve tubes as well, which cannot be clearly distinguished 

 from the latter. The subject of the relation between characteristic 

 elements producing latex and sieve tubes needs further investiga- 

 tion with the improved methods now in vogue. Former statements 

 that the development of the milk system is in inverse proportion 

 to that of the sieve tubes, which have been both denied and 

 affirmed, may advantageously be controlled by examination of 

 more perfect sections. In Fig. 298 is seen a magnification of the 

 laticiferous system of the black salsify (Scorzonera).. It is here 

 obvious that the secretory system with dark contents no longer 

 shows the identity of its originally separate elements, so com- 

 pletely has cellular fusion taken place. 



A consideration of the subfamily Cynareae of the Tubuliflorae 

 will next occupy our attention. Here we have to do with a group 

 which is transitional anatomically from the Tubuliflorae to the 

 Liguliflorae, since it possesses partially the oil canals of the lower 

 Compositae and likewise the laticiferous system which is a feature 

 of organization of the higher members of this important group. 

 Fig. 299 illustrates a portion of a transverse section of a root of 

 the so-called French artichoke, Cynara Scolymus. Three oil 

 canals are to be seen in the upper region of the section. We may 

 now pass advantageously to a consideration of the common bur- 

 dock, Arctium minor. In this species the root resembles that of 

 the artichoke, figured above, in the possession of oil canals. The 

 stem of the burdock in its lower and first-formed region presents 

 some interesting features of organization, which are illustrated 

 in Fig. 300, showing part of a transverse section through the 

 axis. In the lower region of the figure appear the outer parts of a 

 number of fibrovascular bundles belonging to the stem. It is 

 clear that none of these shows the presence of any oil canals. 

 In the phloem may be seen dark dots, which indicate laticiferous 

 elements. Above the zone of stem bundles lies a single leaf trace 

 in the cortex. Along the outer margin of this appears a row of 

 secretory canals. The nature of these is more clearly seen in 

 Fig. 301, representing the transverse view of the foliar trace under 



