Pl. comæ. [a. L. coma, a. Gr. κόμη hair of the head, also applied to foliage, etc., and to the tail of a comet.]
1. Bot. a. A tuft of silky hairs at the end of some seeds, as those of Epilobium. b. A tuft of bracts occurring beyond the inflorescence, as in the pineapple; ‘the crown of sterile flowers on the top of some forms of inflorescence’ (Syd. Soc. Lex.). c. The arrangement of the leafy branches forming the head of a tree.
1669. Rowland, trans. Schroder’s Chymical Dispens., 2. Coma, in plants, signifies the tops.
1770. C. Milne, Bot. Dict., s.v. Bractea, Large bracteæ, which, from their resemblance to a bush of hair, are denominated coma.
1830. Lindley, Nat. Syst. Bot., 236. Cyrtandraceæ … Seeds … naked, or with a coma.
1870. Bentley, Bot., 102. The head of a tree is called a coma.
1872. Oliver, Elem. Bot., II. 172. The silky coma surrounding the top of the seeds of the Willow-herbs.
2. Astron. The nebulous envelope surrounding the nucleus of a comet, and forming the outer portion of the ‘head.’
1765. Maty, in Phil. Trans., LV. 307. The nucleus could not be distinguished from the coma.
1878. Newcomb, Pop. Astron., III. v. 365. The tail is a continuation of the coma.
fig. 1815. W. Taylor, in Monthly Mag., XXXIX. 309. It is not everywhere possible for the most ingenious critic to distinguish … the nucleus from the coma.
3. The blurred appearance surrounding an object seen under a microscope when the lens is not free from spherical aberration.
1867. J. Hogg, Microsc., I. ii. 64. If the greater expansion or coma be when the object is without the focus.
