The seeds, or properly fruits, are contained singly in a stony involucre or bract, which does not open until the enclosed seed germinates.
The young involucre surrounds the female flower and the stalk supporting the spike of male flowers, and when ripe has the appearance of bluish-white porcelain.
The Ctenopoda comprise two families: (a) the Holopediidae, with a solitary species, Holopedium gibberum (Zaddach), queerly clothed in a large gelatinous involucre, and found in mountain tarns all over Europe, in large lakes of N.
America, and also in shallow ponds and waters at sea-level; (b) the Sididae, with no such involucre, but with seven genera, and rather more than twice as many species.
- 1, Female catkin (enlarged); 2, Pair of fruits (nuts) each enclosed in its involucre (reduced).
Resembling leaf-buds, and have protruding crimson stigmas; the minute inner bracts, by their enlargement, form the palmately lobed and cut involucre or husk of the nut.
The filbert, 2 among the numerous varieties of Corylus Avellana, is extensively cultivated, especially in Kent, for the sake of its nuts, which are readily distinguished from cob-nuts by their ample involucre and greater length.
The cup-shaped involucre of Cornucopia is a dilatation of the axis into a hollow receptacle with a raised border.
In Cynosurus (Dog's tail) -- C the pectinate involucre which conceals the spikelet is a barren or abortive spikelet.
The remarkable ovoid involucre of Coix, which becomes of stony hardness, white and polished (then known as " Job's tears," q.v.), is also a modified bract or leaf-sheath.
In Setaria and allied genera the spikelet is subtended by an involucre of bristles or spines which represent sterile branches of the inflorescence.
12); C. tribuloides (bur-grass) and other species are troublesome weeds in North and South America, as the involucre clings to the wool of sheep and is removed with great difficulty.
At the base of the general umbel in umbelliferous plants a whorl of bracts often exists, called a general involucre, and at the base of the smaller umbels or umbellules there is a similar leafy whorl called an involucel or partial involucre.
15), neither involucre nor involucel is developed.
In Compositae the name involucre is applied to the bracts surrounding the head FIG.
- Compound umbel of Common Dill (Anethum graveolens), having a primary umbel a, and secondary umbels b, without either involucre or involucel.
This involucre is frequently composed of several rows of leaflets, which are either of the same or of different forms and lengths, and often lie over each other in an imbricated manner.
The leaves of the involucre are spiny in thistles and in teazel (Dipsacus), and hooked in burdock.
In Compositae besides the involucre there are frequently chaffy and setose bracts at the base of each flower, and in Dipsacaceae a membranous tube surrounds each flower.