30 



MISC. PUBLICATION 110, U. S. DEPT. OF AGRICULTURE 



slightly sinuous leaf margins which 

 bend moderately inward and outward 

 in succession are repand. (Fig. 60, 



Figure 60. — Two types of leaf mar- 

 gin : A, serrate ; B, repand, or 

 undulate 



B.) Repand, however, is not so 

 deeply wavy as is sinuate. 



Resin-duct: A canal, tube, or vessel in 

 which resin is secreted. Resin ducts 

 are exemplified in the leaves, wood, 

 and bark of conifers. 



Resiniferous: Bearing or yielding 

 resin. 



Respiration: Literally, breathing. In 

 plants, the taking in of free oxygen 

 from the air and the giving off of 

 carbon dioxide (C0 2 ) (both in rela- 

 tively much smaller quantities than 

 in animals), with some rise in tem- 

 perature as a result of oxidation 

 (combustion) ; the diffusion and in- 

 terchange of gases between the at- 

 mosphere and the intercellular 

 spaces of plants, especially in the 

 leaves. In photosynthesis (a reverse 

 process) plants utilize so much car- 

 bon dioxide (C0 2 ) and give off so 

 much oxygen that they may be said 

 to purify the air. The hotbed of 

 gardeners takes advantage of the ac- 

 tive respiration of certain bacteria 

 to produce higher growing tempera- 

 tures. 



Reticulate(d) : Net veined, the leaf 

 veins like a network. 



Retrorse : Directed back or downward ; 

 as retrorse hairs or spines. 



Retuse: With a rounded summit very 

 shallowly notched at apex. (Fig. 

 61, A.) 



Revolute: Rolled backward (as a leaf) 

 from the margin or apex upon the 

 lower surface. The opposite of in- 

 volute. 



Rhaphe: Same as raphe. 



Rhizome: A rootstock. In its simplest 

 form, merely a creeping, usually 

 thickened stem or branch growing 

 partly or entirely beneath the sur- 



face of the ground. That a rhizome 

 is really a stem and not a root is 

 evident from its manner of growth, 

 from its consisting of a succession 

 of joints, and from the scales which, 

 as true though degenerated leaves, 

 are borne at these joints and which 

 often have buds in their axils. 



Rhombic: Literally, having the form 

 of a rhombus, an equilateral paral- 

 lelogram differing from a squa re in 

 having the angles oblique ^^ ^^ 

 instead of square ; but used broadly 

 as diamond shaped, or lozenge 

 shaped. 



Rhomboid(al) : Literally, having the 

 form of a rhomboid, but used broadly 

 for an elongated figure roughly quad- 

 rilateral, having the opposite sides 

 equal, the angles oblique, and the 

 adjacent sides unequal. / / . 



Rootstock: A rootlike stem or branch 

 under or sometimes on the ground ; 

 a rhizome. 



Rosette: A dense basal cluster of 

 leaves, as in the common dandelion, 

 caused by dwarfing of the true 

 (leafy) stem, and so named because 

 of its resemblance to the petals of 

 a double rose. Rosettes are common, 

 for example, among winter annuals 

 and alpine herbs. 



Rostrate: Beaked, as the rostrate keel 

 of crazy weed or Lambert loco ( Oxy- 

 t rop is lambe rtii ) . 



Rotate: Wheel 

 shaped ; having 

 the parts hori- 

 zontally flaring. 

 A term often 

 used for gamo- 

 petalous corollas 

 having a much re- 

 duced tube and a 

 widespread limb. 

 For example, cer- 

 tain genera in the 

 Gentian family 

 (e. g., Frasera, 

 Sabbatia, and 



Swertia) are largely distinguished 

 by their rotate corollas. 



Rugose: With wrinkled or creased sur- 

 face ; roughened by wrinkles. 



Rugulose: Minutely rugose; slightly 

 wrinkled. 



Runcinate: Coarsely and pinnately 

 lobed with the pointed lobe tips 

 curved toward the base of the leaf, 

 as in the common dandelion. (Fig. 

 62.) 



Runner: A long, slender, tendrillike 

 leafless form of creeping branch, 

 prostrate on the ground. Each run- 



Figure 61.— Two 

 degrees of ter- 

 minal notching, 

 as in leaves, 

 petals, etc. : A, 

 Retuse; B, 

 emarginate 



