velamen

n. membrane or outer layer; membranous moisture absorbing layer on the aerial roots of some epiphytic plants (non-parasitic plants that grow on the surface of other things, such as rocks)

Special adaptations of roots are found among epiphytic or semi-epiphytic plants such as Orchid sp. and Clivia. Velamen is a spongy, multiple epidermis that covers the roots of some of these plants. The velamen of an orchid is the white or gray covering of aerial roots (when dry, and usually more green when wet as a result of the appearance of underlying photosynthetic structures). It is many cell layers thick and capable of absorbing atmospheric moisture and nutrients. Often, the roots of orchids are associated with symbiotic bacteria or fungi that may fix nutrients from the air. This functionality allows the orchid to exist in locations that provide a reproductive or vegetative advantage such as improved exposure or reduced competition from other plant species.
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n. sail

N
veil; for nun/Muslim); covering (esp. clothing for body/parts)

velamen /vi'leimən/
danh từ, số nhiều velamina (thực vật học) vỏ lụa (giải phẫu) màng (óc, phổi...)
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