D

day-neutral plant. Plant in which flowering does not depend on length of day or night.

deciduous. Refers to the shedding of leaves, usually during the autumn, dehiscent. Splitting open along predeterminable lines, dehydrogenase. Enzyme involved in the removal of hydrogen atoms from a compound. Plays an important role in biological oxidation-reduction processes.

dehydrogenation. The removal of hydrogen atoms from a compound, deletion. A form of chromosomal anomaly wherein part of a chromosome breaks away and is therefore unable to go through the events of mitosis, deliquescent. Becoming dissolved in moisture absorbed from the atmosphere. Also, repeated division of branches, deoxyribonucleic acid. See DNA.

deoxyribose. A 5-carbon sugar having one less oxygen atom than does the sugar ribose.

dephlogisticated air. An ancient name for oxygen (phlogiston being an ancient name for carbon dioxide), deplasmolysis. Plasmolysis being a process wherein cytoplasm is separated from the cell wall because of a loss of water, this is the reverse process brought about by the intake of water, diakinesis. The final stage of meiotic prophase preceding the formation of the metaphase plate. During this stage, there is a marked contraction of the bivalents.

dialysis. The separation of substances in solution by means of a selectively permeable membrane, diastase. An enzyme that converts starch to maltose, diatom. A member of the group of golden-brown algae having siliceous cell walls fitting together much as do the halves of a pill box. dichotomous. Branching into two more or less equal portions, dicot. A plant having two cotyledons in the seed. A shortened form of dicotyledonous. dicotyledonous. Having two cotyledons in the seed, dictyosomes. See Golgi bodies.

dikaryotic. Binucleated, the paired nuclei usually deriving from different parents: one male and one female, dinoflagellate. A group of chiefly marine, solitary plantlike flagellates having cells typically enclosed in a cellulose envelope, dioecious. Literally, "in two houses"; here, having separate sexes: male and female. In reference to flowers, staminate and pistillate flowers are on different plants.

dipeptide. A union of two amino acids, the linkage made through a nitrogen atom.

diplococcus. Bacteria in which the cells occur in pairs or, sometimes, in short chains.

diploid. Having two sets of chromosomes, one of maternal origin and the other of paternal origin. Occurs in the sporophyte generation, diplotene. That stage in the meiotic prophase immediately following pachytene and when the homologous chromosomes tend to repel one another.

disaccharide. A sugar that yields two monosaccharides upon hydrolysis, most commonly a 12-carbon sugar that yields two molecules of 6-carbon sugar upon hydrolysis, dispersed phase. When the colloidal form (that is, the finely divided particles) is dispersed in a liquid medium, distal. Located away from the site of attachment. The opposite of proximal. distromatic. Referring to a thallus two cells in thickness, diurnal. Having a recurrent daily cycle of change.

DNA. Deoxyribonucleic acid. That molecule in chromosomes that governs the manufacture of protein and serves as the carrier of genetic information. Composed of phosphate, sugar, and bases, and capable of self-replication.

dominance. In genetics, when a gene expresses itself to the entire suppression of its allele.

double fertilization. A process occurring in flowering plants and involving two sperm cells: one fertilizing the egg and the other uniting with the polar nuclei to form endosperm, drupe. A one-seeded, fleshy fruit.

duplication. A form of chromosomal anomaly wherein a segment of a chromosome is represented twice, dwarf male. Occurs in the Oenogodiaceae. Several cells form an androspore near the oogonium.

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