GLOSSARY AND INDEX. 283 



raphe, the continuation of the stalk of the ovule extending from hilum to 



chalaza, 3. 

 raphides, needle-shaped crystals, 164. 



ray flowers, the strap-shaped marginal flowers of CompositsB, 258. 

 receptacle, torus ; the axis on which the parts of a flower or on which 



the flowers of a head are borne ; among cryptogams applied to various 



spore-bearing structures, 

 regular, having the parts of each whorl alike in form and size, 74. 

 reniform, kidney-shaped, 58. 

 reserve materials, 18. 

 respiration, the process in plants that corresponds physiologically to 



breathing in animals ; it consists in the absorption of oxygen, the 



oxidation of organic materials, and the release of carbon dioxide and 



other products of oxidation, 65. 

 retinaculum (pi. retinacula), one of the delicate bands connecting the 



poUinia of Asclepias with the corpusoulum, 229 ; a structure of simi- 

 lar function in orchids, 

 rhizoids, root-like organs of various cryptogamous plants ; organs having 



the same function as roots, but a different structure, 121, 133. 

 rhizome or rhizoma, a thickened subterranean stem ; rootstook. 

 rhizophore, an organ resembling a root, from the end of which true roots 



arise, 141. 

 root, 29. 



absorption, 30, 34. 



adventitious, 32, 36. 



aerial, 31, 36. 



as storehouse, 34. 



mechanical function, 31, 35. 



mode of growth, 30, 35. 



parasitic habits, 36. 



primary and secondary, 36. 



shape, 34, 35. 



root-cap, the protective cap-like structure covering the tip of the 



root, 32. • 



root-hairs, the absorbing cells growing from the surface of nearly all 



young roots, 29, 34. 

 rotund, rounded, 58. 



samara, a winged, indehiscent fruit. 

 saprophyte, a plant that lives on dead organic material, 

 sclerenchyma, tissue composed of thick-walled, indurated cells, such as 

 constitute the hard parts of stone-fruits, etc. 



