. A textbook of botany for colleges and universities ... Botany. go2 ECOLOGY evidence for either. The exact cause of petalization is unknown, but in many cases it appears to be inherent, double flowers usually being regarded as sports or mutants, since they often may be reproduced by seed as well as by cuttings.^ In other cases, petalization clearly is due to external factors, notably in a number of species in which plants whose roots are infested with certain parasitic fungi (as Heterodera radicicola) develop double flowers. Saponaria sometimes has double flowers when the roots are infested w
. A textbook of botany for colleges and universities ... Botany. go2 ECOLOGY evidence for either. The exact cause of petalization is unknown, but in many cases it appears to be inherent, double flowers usually being regarded as sports or mutants, since they often may be reproduced by seed as well as by cuttings.^ In other cases, petalization clearly is due to external factors, notably in a number of species in which plants whose roots are infested with certain parasitic fungi (as Heterodera radicicola) develop double flowers. Saponaria sometimes has double flowers when the roots are infested with Fusarium. In the tulip, petalody is facilitated by good nutrition, especially if there is an abundance of nitrogenous sub- stances in the soil. In some cases parasites cause not only ordinary doubling, but also the development of green foliage leaves in place of floral organs, the phenomenon being known as sepal- ody or greening. In parasitized in- dividuals of Heli- anlhus strumosus, greening is a common phenomenon, and not infrequently green foliage leaves are intermingled with ligulate flowers in place of the usual disk flowers. One of the most remarkable of all reproductive variations is that in which flowers are replaced by bulbils, as in the wild garlic (Allium cana- dense, fig. 1203), in whose umbels some primordia develop into flowers and others into bulbils. Sometimes most or even all of the primordia develop 1 Obviously, completely petalized flowers can be reproduced only by cuttings. In the double petunia, which usually is propagated from seed, seeds are saved from flowers that are almost double, and only 20 to 30 per cent of the progeny have double flowers. In the composites complete doubling does not necessarily prevent seed production, double asters, daisies, and sunflowers being raised regularly from Figs. 1201, 1202. — Flowers of Narcissus, illustrating petalody: 1201, an ordinary single flower with a six-parted perianth (p) and a crown or corona (c
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
