THE MONOCOTYLEDONS 413 



glumaceous monocotyledons, are nearly related to these forms. 

 A striking contrast is presented in the anatomy of the true palms 

 and the Scitamineae. In these groups amphivasal strands seem 

 to be entirely lacking. In the Principes, or true palms, we find a 

 marked difference in anatomical structure from the western 

 tropical Cyclanthaceae, which have on floral grounds often been 

 considered to form a systematic link between the palmlike mono- 

 cotyledons and the aroids. The anatomical structure of Carlu- 

 domca and allied Cyclanthaceae is rather that of the aroids than 

 of the true palms, since amphivasal strands are conspicuously 

 present. Our knowledge of the development and comparative 

 anatomy of the groups which appear to lack amphivasal bundles 

 is still too meager to warrant any hypothetical conclusions as 

 to the phylogenetic significance of the apparent lack of amphivasal 

 fibrovascular strands in the conspicuously large-leaved forms, 

 which are united systematically under the headings of Principes 

 and Scitamineae. It may well be that the two large groups 

 above indicated, by the anatomical peculiarities revealed as a 

 result of an examination which is as yet only preliminary, occupy 

 a position high among the monocotyledonous orders. 



It will be convenient to elucidate in a general way by means 

 of diagrams the main anatomical conditions presented by the 

 monocotyledons. Fig. 286^ illustrates the distribution of amphi- 

 vasal regions in the stem of a sedge. In the reproductive axis 

 the amphivasal segments are remote and are clearly in the nodal 

 regions. In proximity to the substratum the nodes become more 

 approximated, and in the subterranean axis they are frequently 

 so closely disposed that amphivasal organization is often contin- 

 uous. This condition is well illustrated by the sedges and rushes 

 and less distinctly by the grasses, since the last have well-spaced 

 nodes. The next diagram (b) shows the situation commonest 

 among the monocotyledons. In this type of anatomical organ- 

 izations the amphivasal structures are found exclusively in the 

 perennial subterranean axis and do not appear in the annual 

 stem. In the last type (c) , which portrays the conditions apparently 

 characteristic of the true palms and the Scitamineae (bananas, 

 cannas, ginger, etc.), amphivasal regions are absent both in the 



