448 TEXTBOOK OP BOTANY 



Pyrenoid. A small body found in the cells of green algse, whose func- 

 tion is the manufacture of starch. It is very commonly imbedded 

 in a chloroplast. 



Race. A group of plants or animals, very similar and closely related. 

 Raceme. An elongated flower cluster, with many short pedicels borne 



at different levels upon the peduncle. 

 Radicle. That part of an embryo below the seed leaf or leaves. 

 Respiration. The breaking down of living substance and food in a 



living organism, as a result of which energy is set free for the use 



of the organism. Commonly respiration involves the taking in 



of oxygen and the giving off of carbon dioxid. 

 Response. The change produced in a cell or organism as the result of a 



stimulus ; also called a reaction. 

 Rhizoid. An elongated cell or row of cells by means of which a plant 



absorbs food materials from th« soil or water. 

 Root cap. The protective cap-like mass of cells covering a root tip. 

 Rudimentary. Not fully developed. 



Sap. The liquids of a plant, especially those found in the vascular 

 bundles. The water and dissolved substances transported through 

 the wood constitute the crude sap; the manufactured foods trans- 

 ported in the bast are the elaborated sap. 



Saprophyte. A plant which obtains its food from dead or decaying 

 organic materials. 



Sapwood. The moist, usually comparatively soft, outer layers of the 

 wood of the trunk and larger branches of a tree or shrub. 



Scion. The shoot or bud which is grafted upon a stock. 



Secondary leaf. Any leaf formed later than the primary leaf or leaves. 



Secondary root. Any root formed later than the primary root. 



Seed. A structure developed from an ovule ; it consists of a small 

 plant (the embryo), surrounded by nutritive and protective layers. 



Seed leaf. The first-formed leaf, or one of the first-formed leaves, of an 

 embryo. 



Seedling. A young plant just beginning to grow from a germinated 

 seed. 



Selection. The choice of plants (or animals) having certain desirable 

 qualities, to be used as the parents for the next generation ; a 

 method used in the production of improved strains and breeds. 



Self-pollination. The falling or depositing of the pollen from an anther 

 upon a stigma of the same flower. 



