What is "radical vessels"

Radical \Rad"i*cal\ (r[a^]d"[i^]*kal), a. [F., fr. L. radicalis having roots, fr. radix, -icis, a root. See Radix.]

1. Of or pertaining to the root; proceeding directly from the root.

2. Hence: Of or pertaining to the root or origin; reaching to the center, to the foundation, to the ultimate sources, to the principles, or the like; original; fundamental; thorough-going; unsparing; extreme; as, radical evils; radical reform; a radical party.

   The most determined exertions of that authority, against them, only showed their radical independence.
   --Burke.

3. (Bot.)

   1. Belonging to, or proceeding from, the root of a plant; as, radical tubers or hairs.

   2. Proceeding from a rootlike stem, or one which does not rise above the ground; as, the radical leaves of the dandelion and the sidesaddle flower.

4. (Philol.) Relating, or belonging, to the root, or ultimate source of derivation; as, a radical verbal form.

5. (Math.) Of or pertaining to a radix or root; as, a radical quantity; a radical sign. See below.

   Radical axis of two circles. (Geom.) See under Axis.

   Radical pitch, the pitch or tone with which the utterance of a syllable begins.
   --Rush.

   Radical quantity (Alg.), a quantity to which the radical sign is prefixed; specifically, a quantity which is not a perfect power of the degree indicated by the radical sign; a surd.

   Radical sign (Math.), the sign [root] (originally the letter r, the initial of radix, root), placed before any quantity, denoting that its root is to be extracted; thus, [root]a, or [root](a + b). To indicate any other than the square root, a corresponding figure is placed over the sign; thus, [cuberoot]a, indicates the third or cube root of a.

   Radical stress (Elocution), force of utterance falling on the initial part of a syllable or sound.

   Radical vessels (Anat.), minute vessels which originate in the substance of the tissues.

   Syn: Primitive; original; natural; underived; fundamental; entire.

   Usage: Radical, Entire. These words are frequently employed as interchangeable in describing some marked alteration in the condition of things. There is, however, an obvious difference between them. A radical cure, reform, etc., is one which goes to the root of the thing in question; and it is entire, in the sense that, by affecting the root, it affects in an appropriate degree the entire body nourished by the root; but it may not be entire in the sense of making a change complete in its nature, as well as in its extent. Hence, we speak of a radical change; a radical improvement; radical differences of opinion; while an entire change, an entire improvement, an entire difference of opinion, might indicate more than was actually intended. A certain change may be both radical and entire, in every sense.