| The American Heritage® Book of English Usage. |
A Practical and Authoritative Guide to Contemporary English. 1996.
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4. Science Terms: Distinctions, Restrictions, and Confusions
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| § 45. xylem / phloem |
| Up the xylem, down the phloem may sound like a call to woodland insurrection. Instead, it is a useful device for determining which of these botanical terms is involved in what type of botanic activity. The vascular system of a plant consists primarily of the sturdy upward-conducting tissue known as xylem (from the Greek word xulon meaning wood) and the soft downward-conducting tissue known as phloem (from the Greek word phloios meaning bark). In herbaceous plants, for example, water moves from the roots to the leaves by way of the xylem. Nutrients from the leaves are, in turn, distributed down and throughout the plant via the phloem. | 1 |
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| The American Heritage® Book of English Usage. Copyright © 1996 by Houghton Mifflin Company. All rights reserved. |
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