ISBN-10:
0226044408
ISBN-13:
9780226044408
Pub. Date:
04/28/2002
Publisher:
University of Chicago Press
The Rose's Kiss: A Natural History of Flowers / Edition 1

The Rose's Kiss: A Natural History of Flowers / Edition 1

by Peter BernhardtPeter Bernhardt

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Overview

"An engaging botanical overview of flowers."-New York Times Book Review

In The Rose's Kiss, Peter Bernhardt presents a fascinating and wide-ranging look at the natural history of flowers—how they look, what they do, and their often hidden interactions with the surrounding environment and other living organisms upon which they depend for their survival. You'll discover why flowers are so colorful, how they evolved, and how insects exploit them for their nectar. This is a book for all flower lovers, from naturalists and gardeners to poets and botanists.

Product Details

ISBN-13: 9780226044408
Publisher: University of Chicago Press
Publication date: 04/28/2002
Edition description: 1
Pages: 290
Product dimensions: 5.50(w) x 8.25(h) x 0.70(d)

About the Author

Peter Bernhardt is a professor of biology at St. Louis University and a research associate at both the Missouri Botanical Garden of St. Louis and the Royal Botanic Gardens of Sydney, Australia. He is the author of Wily Violets and Underground Orchids: Revelations of a Botanist and Natural Affairs: A Botanist Looks at the Attachments Between Plants and People.

Read an Excerpt


The Rose's Kiss



A Natural History of Flowers


By Peter Bernhardt


University of Chicago Press



Copyright © 2003


University of Chicago
All right reserved.


ISBN: 0-226-04440-8





Chapter One


When to Bloom

"Just at this time the hundred years had nearly come to a close, and the
day at last arrived for Briar Rose to be awakened from her long sleep.
On this very day the prince started on his enterprise and on reaching
the hedge of thorns, what was his surprise to find it covered with
delicately-beautiful flowers."

-Jacob and Wilhelm Grimm, "The Sleeping Beauty in the Wood"

A tropical tree drops all its leaves as the season turns hot and dry but
quickly reclothes itself in thick clusters of flowers. A snow crocus
pushes yellowish buds through defrosting soil until they reach the weak
light of a February morning. Although these displays occur on different
continents, both will enjoy human admirers.

Most people welcome the sight of flowering plants after a drab,
uncomfortable season and are willing to extend the display by playing with
plant heredity. For example, some collectors prefer the older breeds of
roses, extolling their hardiness, strong scents, and fine colors.
Unfortunately, most of these old forms stay in flower for just two weeks
each year. Go to yourlocal nursery and you'll find it's the finicky
modern breeds that sell out because they promise "repeating roses" from
late spring through autumn.

Where are flowers made in a plant? They seem to rise up magically out of
the bare earth or, more often, appear to emerge out of formless masses of
stems and leaves.

Branches, leaves, and flowers all derive from the same microscopic source.
They are manufactured by the reduced tip of a stem. This tip is hard to
see with the naked eye, as it is often covered by developing leaves during
the growth season or by bud scales during periods of dormancy. The tip is
properly known as the shoot meristem, a name derived from the Greek word
merizein, "to divide." By cutting thin longitudinal sections of a shoot
and staining them, botanists can locate the regions of most intensive cell
division, since meristems are the dominant centers of growth in plant
bodies. Meristems are composed of rapidly dividing cells called initials.
The shoot tip of a flowering plant is always made of layered initials.

The outermost initials form the tunica. Tunica initials are small and, as
their name suggests, well organized into tight but orderly layers, like
the clothes covering your body. Most tunica initials divide to make plant
skin and all the hairs, glands, and bud scales on the outer surface of the
plant. Below the tunica is a mass of packed, swollen initials that make up
the body, or corpus, of the shoot. Corpus initials divide at various
angles and planes, adding bulk to the inner parts of the plant by forming
pith and vein tissues. Working together, the tunica and corpus increase
the length of the primary stem and manufacture all leaves and new lateral
buds. A lateral bud usually appears at the base of each new leaf. This new
bud waits patiently for the central stem to age until it is permitted to
sprout by itself, forming its own leafy lateral branch.

The tunica-corpus spends most of its active life adding foliage and length
to the stem, until it receives signals to change production. When these
signals arrive, the cells in the shoot narrow and stretch so much that
leaves and lateral buds are unable to form. It's then time for meristem
initials to make flowers, flower stalks, and those flat, protective
enveloping structures (bracts) that appear at the base of most flower buds
or their stalks.

This transition from leafy stem to flowering branch is usually permanent,
but there are two developmental extremes. Sex and death are linked in many
of the plants sold as bedding annuals. Alyssums (Alyssum), marigolds
(Tagetes), tufted pansies (Viola cornuta), and zinnias (Zinnia elegans)
convert all their shoots on every stem into flowering branches as they age
over a single growing season. Unable to make leafy stems after
reproducing, annuals die of old age even if the frost doesn't kill them.
The life cycle of a zinnia, then, is similar in some ways to the lives of
most insects or Atlantic salmon. That's why the only way to keep your
favorite potted coleus (Solenostemon rotundifolius) alive indefinitely is
to pick out every flowering stalk as soon as flower buds are visible. By
removing a flowering stalk, you trigger the activity of lateral buds lower
down on the stem, encouraging them to sprout and make new leafy stems.

At the other end of the spectrum are some Australian members of the myrtle
family (Myrtaceae), especially shrubs such as bottlebrushes (Callistemon)
and honey myrtles (Kunzea). In these plants, a stem shoot converts itself
into a flowering stalk, but the flowering stalk "reconverts" into a leafy
stem shoot as soon as its flowers form fruits. No one is really sure how
they do this. However, since these evergreen bushes usually bloom only
once a year, the age of a bottlebrush branch can be determined by counting
the number of hard fruit clusters on it, since each cluster represents one
year of reproductive effort.

Most perennial herbs, shrubs, trees, and woody vines prefer an
intermediate path to flowering. Secondary branches and twigs flower,
fruit, and die, but primary stems and trunks are preserved to increase
growth and extend the plant's life span. Many wildflowers return year
after year because they keep their primary stems underground and poke only
their seasonal secondary stems up into the air. The primary stems form
rounded bulbs, pointed corms, lumpy tubers, or jointed, creeping
structures known as rhizomes.

What signals "convince" a stem to make flowers? Although different plants
grow at very different rates, we recognize that our local vegetation
experiences peaks when the flowers of many different species bloom
together. These annual miracles are so dependable that some people travel
abroad just to enjoy the flowers of rural England in April, those of
Mexico at Christmas, or those of South Africa in September.

Supernatural explanations for this phenomenon dominated imaginations until
people began to experiment seriously with plants. Cultures recognizing
many gods or spirits assigned the annual flower show to some minor deity,
often female. The ancient Greeks said that Princess Chloris became the
goddess of flowers after the death of her mortal family. The Romans
worshiped the nymph Flora, who exhaled petals and left flowers in her
footprints. Her lively festival began on April 28 and continued for six
days while celebrants played games, exchanged floral crowns, and invited
prostitutes to undress in public. The Chinese Fairy-of-a-Hundred-Flowers
was a strict bureaucrat who made sure that each blossom didn't open until
its appropriate season. Japanese parents once told their children of
Konohana-sakuya Hime (Princess Blossoms of the Trees), the lady who causes
trees to bloom. A tribe of Koori people in Australia believed that flowers
were a gift from the spirit of a powerful male shaman. Byamee received
messages from the bees before he made the east wind blow the rain down the
mountain to soften the hard ground and bring forth flowers that his bees
could visit to make honey.

During the twentieth century, scientists began to understand how
environmental cues stimulate flowering. Clearly, plants do not respond to
external cues as quickly as animals do. Plants tend to require a rhythmic,
repetitive cycle over a period of weeks or months before they make buds or
become ready to open them. This period, in which a plant's physiology must
follow the rhythm of the cue, is known as entrainment. Eventually, flower
development becomes synchronized with one or more cues that are repeated
every twenty-four hours. Plants that entrain to the same cue or cues show
peak bloom around the same season, regardless of species.

Cues encourage plants to make new hormones and suppress old ones. In some
plants, hormones may move to and from the meristem through the cells that
link up to form the young veins. Since the early 1930s, plant
physiologists have tried to isolate the hormone that turns leafy shoots
into flowering stalks. They call this mystery chemical anthesin, but I
don't think they'll ever isolate it. Research suggests that different
plants require different hormone mixes to bloom. Some plants need
gibberellins, a class of hormones that make cell walls stretch. Others are
content with ethylene, surely one of the shortest compounds made by a
plant (CH2=CH2). Ethylene is such a lightweight molecule that it may
escape from one plant only to be absorbed by another. For example, ripe
apples give off ethylene, and an old but effective trick to make
bromeliads bloom is to lay a piece of apple on the plant and cover them
with a paper bag for a short time.

In the Northern Hemisphere, most research on flowering has concentrated on
the cue of light and dark cycles. Plants that respond directly to these
cycles fall into two broad categories. Short-day plants form flower buds
when synchronized to a cycle of reduced critical day length. Most
short-day plants bloom in early spring or fall, often requiring fewer than
fourteen hours of light each day. Cockleburs (Xanthium strumarium),
strawberries (Fragaria), primroses (Primula), a type of morning glory
(Ipomoea hederacea), and some breeds of tobacco (Nicotiana) are among the
best studied of the short-day species.

Long-day plants require entrainment periods opposite those of their
short-day cousins. They need daylight cycles that exceed some critical
interval, usually blooming during summer. Lettuce (Lactuca), most of the
older breeds of potato (Solanum tuberosum), barley (Hordeum vulgare), and
spinach (Spinacia oleracea) are among the best-known of the long-day
plants.

Light cues tend to explain some odd features of agriculture and
horticulture in the Northern Hemisphere. For example, few people who live
in farming regions where the summer season is brief ever see the bluish
purple flowers of potatoes. That's because the wild ancestor of the
domesticated potato evolved in the Andean highlands of South America,
where longer days are the rule.

This also explains the proliferation of greenhouses with white-painted
panes that shut out much of the sunlight. Within these greenhouses are
tropical plants receiving fixed cycles of lamplight so they will bloom for
winter sales. The beloved poinsettia (Euphorbia pulcherrima) is actually a
short-day plant, but it won't survive long outdoors in a November freeze.
It requires the same critical intervals of light its parents receive in
Mexico, so the potted plants must be placed on an artificial cycle to
produce Christmas flowers.

Green leaves "measure" the cycles of light and day. This is to be
expected, since it is the green leaves that capture light energy to make
sugars. During the 1930s, the humble cocklebur was subjected to a series
of laboratory tests. Cockleburs are so tough that they will continue to
live even if they are completely defoliated. However, a cocklebur can't
flower if its leaves are removed during the critical cycle of short days.
Scientists snipped pieces off cockleburs' leaves and learned that only
one-eighth of a mature leaf on a stem was needed to receive the light cue
and trigger the flowering process.

The response of leaves to light cycles seems to be very localized.
Kalanchoe blossfeldiana is a succulent from Madagascar popular as a
houseplant because it produces reddish flowers in winter. You can take a
single plant and expose its leaves to two separate light cycles by
shutting different branches of the plant in separate light boxes.
Flowering stems will develop only near those leaves that receive a
short-day cycle. Flowers won't form on shoots whose leaves are exposed to
a long-day cycle.

Many plants require two periods of entrainment, and that often means
exposure to two different cues at two different times. The first cue
induces the development of flower buds, while the second cue encourages
the buds to swell and open. Many trees and shrubs of the Northern
Hemisphere respond to light cycles, producing their flower buds by late
summer or autumn. The buds of lilacs (Syringa), ornamental quinces
(Chaenomeles), and breeds of Asian magnolia are easy to find on autumn
branches once the leaves have fallen, but they remain as buds until
spring. Having produced their buds, the plants require entrainment by a
cycle of low temperatures. After a couple of months of cold weather, they
will be ready to swell and pop as days grow warmer.

There are problems with this double cycle when plants are grown outside
their natural distribution. In the St. Louis area, fruit crops are more
likely to be devastated by mild seasons than by frigid weather. Buds start
expanding during extended thaws in early March, but opened flowers are
slaughtered if hard frosts return unexpectedly in April. Cinema fans may
remember the Sardinian peasants in the beautiful film Padro Padrone, whose
hopes for a better life are crushed after a mild winter. They lose a
year's olive crop when the early flowers are killed by a freeze so hard it
turns a pitcher of goat's milk into sorbet.

Temperature cues are all some plants need to stimulate flowering. This
helps explain how bulbs and tubers ready their flowers, since these
underground stems lack aerial leaves for most of the year. Daffodils
(Narcissus), tulips (Tulipa), hyacinths (Hyacinthus), and bulb iris (Iris
reticulata
) are descended from wild plants native to true Mediterranean
zones. These regions experience hot, dry summers and cool, wet winters.
The commercial bulbs gardeners purchase each autumn have already received
their first hot cue. In some cases, the bulbs were dug up after the spring
leaves withered and stored in a dark, dry warehouse for a week or more at
80-85 degrees Fahrenheit. That's all that is needed to simulate the
natural conditions of clay and sandy soils baking under a Mediterranean
sun. Cut a heat-treated bulb in half lengthwise and you'll find embryonic
flower buds embedded inside.

Planted in the moist autumn soil of a temperate garden, a bulb begins to
grow roots at its base. Although some grape hyacinths (Muscari) and hardy
cyclamens (Cyclamen) will poke tough leaves above the ground by late
autumn, a bulb's flowers won't appear until after a cold cue. Gardeners
must remember that northern winters are so severe that imported
Mediterranean bulbs often delay flowering for weeks or months after their
usual period of cold entrainment has ended. In fact, most garden bulbs and
tubers are bred from wild ancestors that bloom best if they are entombed
in a frigid dirt for less than twelve weeks. Take a winter holiday in a
Mediterranean zone and you may see that some native species complete their
flowering before spring.

Continues...




Excerpted from The Rose's Kiss
by Peter Bernhardt
Copyright © 2003
by University of Chicago.
Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

Introduction - Beyond the Florist's Shop
1. Brotherhoods and Sisters' Rooms
2. Limits to Perfection
3. The Pig in the Pizza
4. When to Bloom
5. When to Die
6. Of Pollen, Perpetrators, Politics, and Piety
7. Fruitful Union
8. The Primary Attractions
9. Rewards
10. Unloved but Efficient
11. Psychoanalysis and Serenades
12. The Faithful and Unfaithful Bee
13. The Squawking Tree
14. F is for Fake (and Flower)
15. Into Thin Air
16. Self-Made Marriages and Virgin Births
17. The First Flowers
Glossary of Flower Terms
Annotated Bibliography
About the Author
Index

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