The most extensive formof thickening found in xylem vessels and tra-cheids,where all the inner wall is thickened a-part from small areas called pits. It is common-ly found in secondary xylem and in the lastformed metaxylem. See xylem. See also pit.在木質(zhì)部導(dǎo)管和...[繼續(xù)閱讀]

    1 . Any of the narrow threadlike out-growths from the skin of mammals,consistingof dead cells containing large amounts ofhorny keratin (a protein) and granules ofpigment. The presence of hair reduces heatloss from the skin.See also hair follicle,se-baceou...[繼續(xù)閱讀]

    The study of diseases affect-ing large numbers within a population. Theseinclude both epidemics of infectious diseasesand also diseases associated with environ-mental factors and dietary habits (e.g. lungcancer,some forms of heart disease,etc.).研究群體內(nèi)對(duì)大多數(shù)人...[繼續(xù)閱讀]

    See auditory capsule.參閱66頁(yè)auditory capsule。...[繼續(xù)閱讀]

    A process fol-lowed when tissues are prepared for perma-nent microscope slides. Water is removed byimmersing the tissue in increasing strengthsof ethyl alcohol. The alcohol concentrationmust be increased gradually as otherwise thecells would dehydrate too...[繼續(xù)閱讀]

    The marine environment from lowwater level to a depth of about 200 m,a zonethat in many areas corresponds to the extentof the continental shelf. It makes up lessthan 1 % of the marine environment.Nutri-ents are relatively abundant in this zoneand it is pe...[繼續(xù)閱讀]

    Darwins theory of evolu-tion through natural selection,modified andexpanded by modern genetic studies arising from the work of Mendel and his successors.Such studies have answered many questionswhich Darwins theory raised,but could notadequately explain b...[繼續(xù)閱讀]

    acid (pteroylglutamic acid) One ofthe water-soluble B-group of vitamins. Theprincipal dietary sources of folic acid areleafy vegetables,liver,and kidney. Defi-ciency of the vitamin exhibits itself in anemiain a similar manner to vitamin B12 deficien-cy,wh...[繼續(xù)閱讀]

    The breakdown of complex organ-ic foodstuffs by enzymes into simpler solublesubstances,which can be absorbed and as-similated by the tissues. In most animals (e.g. vertebrates and arthropods) it is extracel-lular,occurring in an alimentary canal or gut in...[繼續(xù)閱讀]

    A periodic physiological or be-havioral change that is controlled by a biolog-ical clock. Circadian rhythms,hibernation,and migration are examples.由生物鐘控制的生理或行為周期的變化。晝夜節(jié)律、冬眠、遷徙都是生物節(jié)律的例子。...[繼續(xù)閱讀]