274 



THE ANATOMY OF WOODY PLANTS 



hence are to be regarded as Lycopsida. The comparative anatom- 

 ical evidence on this point is equally unequivocal. In the repro- 

 ductive axes or cones of both Calamitaceae and Equisetaceae the 

 strands typically fail to alternate at the nodes, and the traces of 

 the sporophylls are consequently quite without corresponding gaps. 

 There apparently can be no question on anatomical grounds that 

 the Equisetales are justly included in the Lycopsida. 



If the evidence as to the 

 relationship of the Equisetales to 

 the phylum Lycopsida is clear on 

 anatomical grounds, it is equally 

 definite from a consideration of 

 the features of organization of the 



FIG. 197. Longitudinal section of bundle in vegetative and reproductive leaves 

 of Equisetum (after Earnes). 



cones. In the Sphenophyllaceae and Calamitaceae the sporangia 

 or sporangiophores are known to be ventral appendages of the 

 sporophylls and thus present the condition characteristic of the 

 Lycopsida. On the basis of both reproductive and anatomical 

 features the group under discussion clearly belongs under the large 

 heading of Lycopsida. 



The leaf in the genus Equisetum is of considerable interest in 

 view of the fact that it displays the presence of centripetal or 

 cryptogamic xylem which has entirely disappeared in the stem. 

 Fig. 197^ illustrates the organization of the trace of the vegetative 

 leaf of E. maximum. It is obvious that the xylem includes a central 



