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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.在木质部导管和...[继续阅读]
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...[继续阅读]
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.).研究群体内对大多数人...[继续阅读]
See auditory capsule.参阅66页auditory capsule。...[继续阅读]
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...[继续阅读]
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...[继续阅读]
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...[继续阅读]
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...[继续阅读]
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