Rachis. The prolongation of the peduncle through a flower cluster, or of a petiole 



through a compound leaf (fig. 121). 

 Radiate. Disposed in a plane from a common center like the spokes of a wheel; 



also said of inflorescences in which the marginal corollas spread in this manner 



(figs. 444. 741). 

 Ray. Any spreading segment of a radiate structure; often used specifically for the 



marginal, ligulate corollas of the Compositae (fig. 741 ). 

 Ray flower. One of the marginal flowers in Compositae when the flower head 



bears ligulate corollas, in contrast to the tubular disk corollas of the central 



flowers (fig. 741). 

 Receptacle. The axis of a flower and its toral proliferation that bears the flower 



parts; term also applied to the discoid platform which bears a group of flowers 



in the headlike inflorescence of members of the Compositae (figs. 377, 741). 

 Recurved. Turned backward in a curving manner. 

 Reflexed. Turned backward from the point of attachment. 

 Regular. Said of a flower or of parts of a flower when the members within each 



whorl are alike. 

 Remote. Separated from one another. 

 Reniform. Kidney-shaped (fig. 787). 

 Repand. Exhibiting a slightly uneven margin when viewed at right angles to the 



plane (fig. 787). 

 Repent. Creeping (prostrate and rooting). 

 Replum. The marginate septum of certain pods that persist after the valves have 



fallen, as in the fruit of Cruciferae. 

 Resaca. A former course or channel of a stream, commonly water-filled to form 



narrow oxbow or meandering lakes. 

 Resupinate. Upside down, inverted by the twisting of the pedicel, as the flowers 



of orchids. 

 Reticulate. Netted. 



Retrorse. Having hairs or other processes turned or pressed toward the base. 

 Retuse. With a shallow, rounded notch at the apex (fig. 787). 

 Revolute. Said of margins that are rolled backward (toward the abaxial side), as 



in some leaves. 

 Rhizome. A horizontal underground stem. 

 Rhombic. Somewhat diamond-shaped. Rhombiform: rhomb-shaped. Rhomboidal: 



a solid with a rhombic outline. 

 Rib. A thickened structure, usually surrounding a primary vein on a leaf; also, 



one of more or less parallel ridges on fruits, seeds, or stems 

 Ringent. Gaping, as the mouth of an open-throated bilabiate corolla. 

 Rootcap. Large cells that form a caplike covering for the smaller cells in rear 



(growing point). 

 Rootstock. A horizontal underground stem bearing both roots and aerial stems 



along its axis or from its tip. 

 Rosette. A group of organs, such as leaves, clustered and crowded around a com- 

 mon point of attachment. 

 Rosulate. Having the form of a rosette. 

 Rotate. Radiately spreading in one plane. 



Rudimentary. Said of organs in which development has been arrested. 

 Rugose. With a wrinkled surface. 



Runcinate. Deeply incised, with the segments directed toward the base. 

 Runner. A horizontal stem with long internodes that trails along the surface of 



the ground (fig. 789). See Stolon. 



1725 



