| 词汇 | xylem |
| 释义 | xylem noun[ U ] biology specializeduk /ˈzaɪ.ləm/ us /ˈzaɪ.ləm/ the type of plant tissue that carries water and minerals from the roots to the leaves and gives support to the stem or trunk（植物的）木质部 Compare phloemspecialized Biochemistry adipose adrenalin albumin aldosterone amino acid endonuclease endorphin enzymatic enzymatically enzyme messenger RNA mRNA mycoprotein non-enzymatic nuclease serotonin spike protein T level testosterone trace element xylem | American Dictionaryxylem noun[ U ] us/ˈzɑɪ·ləm, -lem/ biology the plant tissue that carries water from the roots to the leaves and gives strength to the stem or trunk Examples of xylemxylem This may open the way to finding relatively distinct growth rings in the xylem of some evergreen species in these forests. The influence of these nematodes on cytokinins in the host's xylem exudate was not nearly so pronounced. In tangential section, preserved rays in the secondary xylem are relatively low (mean height: 86.9 m) compared to those of other specimens. But the same increase would double the food supply for a xylem-feeding insect. Most bark was eaten down to the xylem and the volume eaten was estimated from the mean bark thickness. The entire feeding areas were outlined, irrespective of depth, but feeding marks generally extended down to the xylem on the feeding substrate used. Secondary xylem ranges from 1.2 to 2 mm in thickness and is relatively evenly distributed around the primary strands. Features of the secondary xylem in radial section are not easily observed due to mineralization of the cell walls. As the tissues dehydrate, leaves shrink, chlorophyll is degraded, sucrose accumulates, the xylem cavitates eventually and the plants become desiccated. In transverse section, primary xylem strands rarely exceed 300 m in their smallest dimension and 2.5 mm in the largest. The second xylem element is of the dense, helicoidal type, which occurs in bundles comprised of numerous individuals, and remains active until maturity. Vascular bundles show a large number of xylem vessels of different diameter. Stomatal sensitivity to abscisic acid imported from the xylem sap. In particular, spittlebugs should be susceptible to manipulation of xylem transport solutes. Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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