THE ANGIOSPERMAE 1115 



flowers, so that the top-knot of sterile flowers makes up an " advertisement " 

 of the inflorescence which attracts the notice of polhnating insects. 



Fig. loyo. — Heracleiim sphondylium. Umbel showing irregular 

 exotrophic development of the lateral flowers. 



THE ANATOMY OF THE FLORAL AXIS AND THE FLORAL 



RECEPTACLE 



The anatomy of the pedicel or the peduncle does not itself call for much 

 special remark. As a rule it shows a vascular arrangement closely resembling 

 that of a young vegetative stem of the same plant. It is in fact a one- 

 internode stem, with a single ring of bundles in Dicotyledons and concentric 

 rings in Monocotyledons. Pedicels of the latter group usually have a simpler 

 structure than the vegetative axis, frequently with only a single ring of 

 bundles as in the stems of Dicotyledons. When several rings are present 

 they are clearly concentric, an arrangement which is often disguised in the 

 stem by the flexures and changes of direction of the leaf-trace bundles at 

 the nodes. Where the pedicel or peduncle is long, it may possess a better 

 developed stereome system, both of sclerenchyma and collenchyma, than 

 does the stem. It is also not uncommon to find independent phloem strands, 

 alternating with the normal bundles or scattered in the medulla or the cor- 

 tex, especially where large fruits, or a large number of fruits, are developed. 



Occasionally anomalous structures may be present, as in Utriciilaria and 

 Adoxa, where each bundle is surrounded by an individual endodermis, 

 producing what may be called either a polystelic or an astelic structure 

 according to the point of view. In Dicotyledons secondary thickening may 



