688 - Appendix 2 



Ducr. (1) A long, hollow, woody tube, in the xylem 

 portion of a vascular bundle (also c. tiled a vessel) . 

 (2) The tubular outlet of a multicellular gland of 

 external secretion. 



Ecological. Pertaining to the relations of organisms 

 to their environments. 



Ecology. Study of the adaptations of organisms to 

 their environment. 



Ecosystem. A more or less isolated system constituted 

 by the sum total of interactions between a particu- 

 lar environment and all the organisms inhabiting 

 this environment. 



Ectodfrm. The outer layer of cells in the gastrula 

 or, less accurately, the tissues derived from this 

 layer. 



Effector. A structure specialized for the production 

 of some particular kind of response; e.g., movement, 

 secretion, etc. 



Efferent fiber. A nerve fiber carrying impulses 

 from the central nervous system to an effector. 



Egestion. The elimination of waste material from 

 the digestive cavity. 



Egg ceil. A large, usually nonmotile gamete, con- 

 taining abundant cytoplasm and yolk. (cf. Sperm 



CELL.) 



Electrolyte. A substance whose molecules dissoci- 

 ate into ions, especially in aqueous solution. 



Electron. A particle of negative electricity; one of 

 the particulate constituents of matter. 



Element. A substance constituted of only one kind 

 of atom. 



Embryo. A young organism before emerging from 

 the egg, the seed, or the body of the mother. 



Embrio sac The female gametophyte of a seed 

 plant. 



Emulsion. A dispersion consisting of small droplets 

 of one liquid in another. 



Endocrine organ. A gland of internal secretion, pro- 

 ducing a hormone or hormones. 



Endodfrm. The inner lavcr of cells in the gastrula. 

 The tissues derived from this laser. 



Endodermis. The differentiated innermost layer of 

 cells of the cortex of stems and roots. 



Endoplasmic reticulum. A svstem of double mem- 

 branes revealed bv electron microscopic studies 

 in cells generally; closely affiliated with the ribo- 

 somes. 



Endosperm. A mass of cells, containing stored food 

 substances, developing from part of the female 

 gametophyte and, unless fully resorbed, filling all 

 the seed outside the embryo. 



Energy. The capacity to do work; i.e., to produce 

 movement. 



Enteron. The digestive cavity of multicellular ani- 

 mals. 



Enzyme. An organic catalyst produced by living 

 cells. 



Epicotyl. The part of an embryonic seed plant, 

 above the point of attachment of the cotyledons. 

 (cf. Hypocotyl.) 



Epidermis. The outermost layer of cells of a plant or 

 animal. 



Epithelial tissues. Surface tissues in which the cells 



form one or more regular layers, with very little in- 

 tercellular material. 



Epithelium. An epithelial tissue, covering an ex- 

 ternal or internal surface. 



Erepsin. A group of enzymes secreted by the intes- 

 tine, which hydrolyzes peptones to amino acids. 



Esophagus. The portion of the enteron between the 

 pharynx and the stomach. 



Eustachian tube. A passage connecting the tympanic 

 cavity (middle ear) with the pharynx; developed 

 from the most anterior gill slit of the embryo. 



Evolution. Process bv which organisms change, by 

 the origin of new genotypes and phenotvpes. with 

 partial or complete extinction of old ones. 



Excitation. The state of a cell immediately after 

 being stimulated, involving an increased rate of 

 metabolism, increased permeability, and an altered 

 electric membrane potential. 



Excretion. Elimination of waste products of metab- 

 olism (except CO.) . 



External secretion. Secertion to the outside of the 

 body or into the cavity of the enteron. Any sub- 

 stance or mixture thus secreted. 



Family. A taxonomic group, between order and 

 genus; names of plant families end in -acme, those 

 of animal families in -idae. 



Fa is. Lipids that can be hvdrolyzed to glycerol and 

 fatty acids, each fat molecule yielding one ghcerol 

 molecule and three fatty acid molecules (alike or 

 different) . (The term fats is sometimes used to in- 

 clude all lipids.) 



Faitv aiids. Organic acids containing a single car- 

 boxvl radical (COOH) and otherwise only carbon 

 and hydrogen; there are many different fatty acids, 

 differing in the number of carbon and hvdrogen 

 atoms. 



Fixes, The material egested from the enteron. 



Female. An individual that produces egg cells but 

 not sperm cells. 



Fertility. Ability to reproduce. 



Fertilization. Fusion of two gametes, especially of 

 their nuclei. 



Fibrils. Small fibers or threads within cells. 



Fission. Asexual reproduction bv division of an or- 

 ganism into two or more equal, or nearlv equal, 

 parts. 



Flagellum. A protoplasmic process, longer than a 

 cilium. whose movements usually effect locomotion 

 of a cell. 



Floral envelopes. The calvx and corolla; i.e., the 

 outer whorls of flower parts, not directly concerned 

 in reproduction. 



Flower. A group of modified leaves of several kinds, 

 including sporophylls, arranged in concentric 

 whorls; a complete flower consists of calyx, corolla, 

 stamens, and carpels, but in many flowers some of 

 these are absent. 



Food. Any material that the organism obtains from 

 the environment and that can either yield energy 

 for the activities of the organism or supply matter 

 for its growth. 



Formed bodies. Localized differentiated regions or 

 structures within the cytoplasm. 



