686 - Appendix 2 



Autocatalvsis. Capacity of certain substances to 

 catalyze the production of themselves. 



Autonomic nervous system. A system of neurones 

 innervating the visceral organs, connected with 

 the central nervous system by axons of intermedi- 

 ate neurones of the central nervous system. 



Autosomes. Chromosomes that are not sex chromo- 

 somes. 



Autotrophic. Able to synthesize all substances re- 

 quired for nutrition from inorganic food substances. 

 (cf. Heterotrophic.) 



Auxin. A plant hormone, or growth substance. 



Auxocytf. A germ cell in the growth period, during 

 which synapsis and tell. id formation occur. 



Axon. A long unbranched or sparsely branched nerve 

 fiber, usually carrying impulses away from the cell 

 body of a neuron. 



Backcross. A cross between an individual whose 

 genetic constitution is to be tested and one that 

 is homozygous for all recessive genes involved in 

 the experiment. 



Bacterial transformation. The induction of a new 

 heritable property in bacterial cells by DNA, trans- 

 mitted via the culture medium. 



Bacteriophage. A virus parasitic in bacteria. 



Base. A substance that dissociates, yielding hydroxyl 

 (OH~) ions (but not hydrogen (H + ) ions). 



R\st. The phloem. 



Bilateral symmetry. Symmetry with reference to a 

 plane. In a bilaterally symmetrical body (e.g., a 

 spoon), only one plane can be found that will divide 

 it into symmetrical halves. 



Bile. The external secretion of the liver, secreted 

 through the bile duel to (he small intestine. 



Biology. The scientific study of living things. 



Bivalent, A pair of homologous chromosomes joined 

 in synapsis, (cf. Univalent.) 



Blastocoel. The cavity within a blastula. 



Blastopore. The external opening of the entcron of 

 a gastrula. 



Blastula. An embryo after cleavage and before gas- 

 trulation, typically a single layer of cells forming a 

 hollow sphere. 



Blood. A fluid tissue consisting of the blood cells, or 

 corpuscles, and a liquid intercellular material, the 

 plasma. A form of connective tissue. 



Brain. The enlarged anterior end of the central 

 nervous system. 



Brownian movement. The continual random move- 

 ment of small particles suspended in a fluid me- 

 dium, due to their bombardment by the molecules 

 of the medium. 



Bud. (1) A young individual produced by bud- 

 ding, before it is completely detached from 

 the parent. (2) The end of a stem or branch, en- 

 closed by young leaves; this may develop into 

 a leafy stem (leaf bud) or into a flower (flower 

 bud) . 



Budding. The asexual production of a new indi- 

 vidual by the splitting off of a relatively small por- 

 tion of the parent organism. 



Bulb. A subterranean leaf bud or flower bud. 



Calorie. A quantity of heat required to raise the 

 temperature of 1 kilogram of water 1 degree centi- 

 grade; this is the "large Calorie," the unit employed 

 in connection with nutrition. 



Calyx. The outermost whorl of parts in a complete 

 flower. Consists of sepals. 



Cambium. A layer of embryonic tissue between the 

 xvlem and the phloem in dicotyledonous plants. 



Capillaries. Very small, thin-walled blood vessels, 

 penetrating the intercellular spaces of all organs, 

 through whose walls exchanges occur between the 

 blood and the tissue cells. 



Carbohydrates. Compounds of carbon, hydrogen, 

 and oxygen in the proportions of about lC:2e:10; 

 including sugars, starch, glycogen, cellulose, etc. 



Carpel. A macrosporophyll of a flowering plant, one 

 of the innermost whorl of flower parts. 



Catalysis. The action of a catalyst. 



Catalyst. Any substance tnal modifies the rale of 

 a chemical change without being itself used up in 

 the process. 



Cell. A structural unit of protoplasm, consisting 

 typically of nucleus and cytoplasm. 



Cell sap. The fluid in the large vacuoles of plant 

 cells; a watery solution of salts, sugars, etc. 



Cell Wall. The rigid external covering of a plant 

 cell. 



Cellulose. An insoluble complex carbohydrate 

 (polysaccharide) , the chief component of most 

 plant cell walls. 



Centrvi. nervous system. The main part of the nerv- 

 ous system in most animals, containing the cell 

 bodies of most of the neurones. 



Centrum. is. "Division centers" found at the ends of 

 the spindle during mitosis and meiosis in animal 

 cells; display a complex structure (Fig. 3-5) when 

 studied by electron microscopy. 



Cen i rough iial egg. An egg cell containing a large 

 amount of volk concentrated toward the center. 



Centrosome. The body or region at the center of 

 an aster. 



Cephyliz ation. The concentration of the sensory 

 and nervous systems at the head end of animals. 



Cerebellum. An expansion of the dorsal side of the 

 brain near its hind end, the coordinating center for 

 proprioceptive stimuli and complex muscular move- 

 ments. 



Cerebrum. An expansion of the dorsal and lateral 

 sides of the brain at its front end; the chief center 

 for conditioned, or learned, responses. 



Chemical reaction. A change of one or more sub- 

 stances into different substances, by recombination 

 of their constituent atoms into different kinds of 

 molecules. 



Chemoiropism. Movement whose direction is deter- 

 mined by the unequal concentrations of some par- 

 ticular substance on the two sides of an organism. 



Chlorophvll. The green pigment of plant cells 

 which catalyzes photosynthesis. 



Chloroplvst. A plastid containing chlorophyll. 



Cholestfrol. A sterol found in the cells of many 

 organisms. 



Chromatin. A substance found in all living cells, 

 which stains deeply with certain dyes; the charac- 



