flower; inner circle of leaflike flower parts, 

 usually of some color other than green. 

 coronary (kor'o-ner-y) : applied to arteries which 

 start from the aorta and supply the heart tis- 

 sues. Coronary thrombosis (throm-boh'sis) : 

 clot forming in one of these arteries. 

 corpuscles (core'pus-ls) : blood cells of verte- 

 brates. Red corpuscles carry oxygen to the 

 body cells; white corpuscles defend against 

 bacteria, 

 cortex: the "rind" (outer layers) of an organ such 

 as the brain or kidney. In a root or stem the 

 region between the conducting tissue and the 

 epidermis. 

 cortin: hormone extracted from the cortex cells of 



the adrenal glands. 

 cotyledon (cot-e-lee'don) : undeveloped leaf in the 

 embryo of a seed plant ; a monocot has one 

 cotyledon, a dicot has two, and gymnosperms 

 more. 

 cranium (cray'nee-um) : that part of the verte- 

 brate skull that contains the brain. 

 cretinism (cree'ti-nism) : abnormal condition in 

 humans in which from birth there is a great 

 deficiency of thyroxin, resulting in dwarfism 

 and idiocy; an individual having such a con- 

 dition is called a cretin, 

 crop: plants (or plant products) cultivated to 

 supply food or materials for man or domesti- 

 cated animals. Cover crops: plants raised 

 principally to bind the soil and prevent its 

 loss. Rotation of crops: planting different 

 crops in one field in regular order year after 

 year so that the soil's minerals may be nsed 

 up more slowly or restored. Crop is also part 

 of the digestive tract in many animals, 

 cross: mating two organisms. 

 crossbreeding: mating two individuals that belong 

 to the same species or even the same variety 

 but which have no family relationship; also 

 outbreeding, 

 crustaceans (crus-tay'shuns) : members of a class 

 within the phylum arthropoda; mostly water- 

 living forms with firm shells, such as lob- 

 sters. 

 culture: the sum total of ways of living of a group 

 of human beings handed on from one genera- 

 tion to another; also the growth of micro- 

 organisms or tissues for scientific study. Cul- 

 ture medium: a prepared material for raising 

 microorganisms. Pure culture: a culture of 

 only one kind of organism. 

 cytoplasm (sigh'toe-plasm) : that part of the liv- 

 ing matter of a cell that surrounds the nu- 

 cleus. 

 deciduous (de-sid'you-us) : shedding the leaves 

 every year, as occurs in many trees and 

 shrubs. 

 deficiency (de-fish'en-see) disease: illness caused 

 by an insufficient supply of some necessary 

 substance in the diet, such as A vitamins. 

 dendrites (den'drights) : thickly branched pro- 



jections from the body of a nerve cell which 

 carry impulses into the cell body. 



denitrifying (dee-ny'tri-fy-ing) : breaking down 

 nitrates into nitrites, ammonium compounds, 

 or free nitrogen by microorganisms in the 

 soil. 



dentine (den'teen) : a hard substance making up 

 the greater part of -the tooth in vertebrates. 

 In the crown it is covered by enamel; in the 

 root, by cement. 



dermis: in mammals a form of epithelium lying 

 under the thinner epidermis and containing 

 such structures as the roots of hairs, oil 

 glands, secreting cells of sweat glands, etc. 



diabetes (dye-a-bee'teas) : disease in which sugar 

 is not used normally because of a deficiency 

 of insulin. 



diaphragm (dye'a-fram) : thick sheet of muscle 

 separating the chest from the abdominal cav- 

 ity in mammals. 



dicotyledons (dye-cot-e-lee'dons) or dicots: mem- 

 bers of a subclass of angiosperms which have 

 two seed leaves in the embryo, net-veined 

 leaves, and stems which can form annual 

 rings. 



differentiation (diff'er-en-she-a'shun) : processes 

 by which embryonic cells develop the shapes 

 and structures of specialized cells such as 

 muscle and nerve cells. 



diffusion (dif-you'shun) : spreading of molecules 

 from a region where they are more concen- 

 trated to where they are less concentrated; 

 this may occur through a membrane. 



digestion: changing larger molecules into smaller 

 molecules; this is often necessary to enable 

 food to diffuse through a cell membrane and 

 to make it usable by the cell. 



dihybrid (die-high'brid) : an organism that is hy- 

 brid with respect to the two contrasting char- 

 acters of a pair. 



dinosaurs (die'no-sores) : extinct dragon-like rep- 

 tiles of many species that lived toward the 

 end of the Mesozoic era; some, such as 

 Brontosaurus, were of gigantic size. 



diploid number: number of chromosomes nor- 

 mally found in each of the cells of an organ- 

 ism other than the sex cells; a number twice 

 as large as the number of chromosomes in a 

 sex cell. 



disinfectant: substance that destroys all bacterial 

 life. 



dominant: in genetics, that character which, when 

 combined with the contrasting character, 

 shows up in the hybrid offspring; applied 

 also to the gene of any pair of genes that 

 produces the character that shows up. 



donor: person furnishing blood for transfusions. 



dorsal: in animals, applied to the back region as 

 opposed to the under or ventral side. 



ductless gland also gland of internal secretion or 

 endocrine gland: gland that secretes a hor- 

 mone directly into the blood stream. 



587 



