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Overview
CHAPTER I.
INTRODUCTORY REMARKS.
Various means which favour or determine the cross-fertilisation of
plants.--Benefits derived from cross-fertilisation.--Self-fertilisation
favourable to the propagation of the species.--Brief history of the
subject.--Object of the experiments, and the manner in which they were
tried.--Statistical value of the measurements.--The experiments carried
on during several successive generations.--Nature of the relationship of
the plants in the later generations.--Uniformity of the conditions to
which the plants were subjected.--Some apparent and some real causes of
error.--Amount of pollen employed.--Arrangement of the work.--Importance
of the conclusions.
CHAPTER II.
CONVOLVULACEAE.
Ipomoea purpurea, comparison of the height and fertility of the crossed
and self-fertilised plants during ten successive generations.--Greater
constitutional vigour of the crossed plants.--The effects on the
offspring of crossing different flowers on the same plant, instead of
crossing distinct individuals.--The effects of a cross with a fresh
stock.--The descendants of the self-fertilised plant named
Hero.--Summary on the growth, vigour, and fertility of the successive
crossed and self-fertilised generations.--Small amount of pollen in the
anthers of the self-fertilised plants of the later generations, and the
sterility of their first-produced flowers.--Uniform colour of the
flowers produced by the self-fertilised plants.--The advantage from a
cross between two distinct plants depends on their differing in
constitution.
CHAPTER III.
SCROPHULARIACEAE, GESNERIACEAE, LABIATAE, ETC.
Mimulus luteus; height, vigour, and fertility of the crossed and
self-fertilised plants of the first four generations.--Appearance of a
new, tall, and highly self-fertile variety.--Offspring from a cross
between self-fertilised plants.--Effects of a cross with a fresh
stock.--Effects of crossing flowers on the same plant.--Summary on
Mimulus luteus.--Digitalis purpurea, superiority of the crossed
plants.--Effects of crossing flowers on the same
plant.--Calceolaria.--Linaria vulgaris.--Verbascum thapsus.--Vandellia
nummularifolia.--Cleistogene flowers.--Gesneria pendulina.--Salvia
coccinea.--Origanum vulgare, great increase of the crossed plants by
stolons.--Thunbergia alata.
CHAPTER IV.
CRUCIFERAE, PAPAVERACEAE, RESEDACEAE, ETC.
Brassica oleracea, crossed and self-fertilised plants.--Great effect of
a cross with a fresh stock on the weight of the offspring.--Iberis
umbellata.--Papaver vagum.--Eschscholtzia californica, seedlings from a
cross with a fresh stock not more vigorous, but more fertile than the
self-fertilised seedlings.--Reseda lutea and odorata, many individuals
sterile with their own pollen.--Viola tricolor, wonderful effects of a
cross.--Adonis aestivalis.--Delphinium consolida.--Viscaria oculata,
crossed plants hardly taller, but more fertile than the
self-fertilised.--Dianthus caryophyllus, crossed and self-fertilised
plants compared for four generations.--Great effects of a cross with a
fresh stock.--Uniform colour of the flowers on the self-fertilised
plants.--Hibiscus africanus.
CHAPTER V.
GERANIACEAE, LEGUMINOSAE, ONAGRACEAE, ETC.
Pelargonium zonale, a cross between plants propagated by cuttings does
no good.--Tropaeolum minus.--Limnanthes douglasii.--Lupinus luteus and
pilosus.--Phaseolus multiflorus and vulgaris.--Lathyrus odoratus,
varieties of, never naturally intercross in England.--Pisum sativum,
varieties of, rarely intercross, but a cross between them highly
beneficial.--Sarothamnus scoparius, wonderful effects of a
cross.--Ononis minutissima, cleistogene flowers of.--Summary on the
Leguminosae.--Clarkia elegans.--Bartonia aurea.--Passiflora
gracilis.--Apium petroselinum.--Scabiosa atropurpurea.--Lactuca
sativa.--Specularia speculum.--Lobelia ramosa, advantages of a cross
during two generations.--Lobelia fulgens.--Nemophila insignis, great
advantages of a cross.--Borago officinalis.--Nolana prostrata.
CHAPTER VI.
SOLANACEAE, PRIMULACEAE, POLYGONEAE, ETC.
Petunia violacea, crossed and self-fertilised plants compared for four
generations.--Effects of a cross with a fresh stock.--Uniform colour of
the flowers on the self-fertilised plants of the fourth
generation.--Nicotiana tabacum, crossed and self-fertilised plants of
equal height.--Great effects of a cross with a distinct sub-variety on
the height, but not on the fertility, of the offspring.--Cyclamen
persicum, crossed seedlings greatly superior to the
self-fertilised.--Anagallis collina.--Primula veris.--Equal-styled
variety of Primula veris, fertility of, greatly increased by a cross
with a fresh stock.--Fagopyrum esculentum.--Beta vulgaris.--Canna
warscewiczi, crossed and self-fertilised plants of equal height.--Zea
mays.--Phalaris canariensis.
CHAPTER VII.
SUMMARY OF THE HEIGHTS AND WEIGHTS OF THE CROSSED AND SELF-FERTILISED
PLANTS.
Number of species and plants measured.--Tables given.--Preliminary
remarks on the offspring of plants crossed by a fresh stock.--Thirteen
cases specially considered.--The effects of crossing a self-fertilised
plant either by another self-fertilised plant or by an intercrossed
plant of the old stock.--Summary of the results.--Preliminary remarks on
the crossed and self-fertilised plants of the same stock.--The
twenty-six exceptional cases considered, in which the crossed plants did
not exceed greatly in height the self-fertilised.--Most of these cases
shown not to be real exceptions to the rule that cross-fertilisation is
beneficial.--Summary of results.--Relative weights of the crossed and
self-fertilised plants.
CHAPTER VIII.
DIFFERENCE BETWEEN CROSSED AND SELF-FERTILISED PLANTS IN CONSTITUTIONAL
VIGOUR AND IN OTHER RESPECTS.
Greater constitutional vigour of crossed plants.--The effects of great
crowding.--Competition with other kinds of plants.--Self-fertilised
plants more liable to premature death.--Crossed plants generally flower
before the self-fertilised.--Negative effects of intercrossing flowers
on the same plant.--Cases described.--Transmission of the good effects
of a cross to later generations.--Effects of crossing plants of closely
related parentage.--Uniform colour of the flowers on plants
self-fertilised during several generations and cultivated under similar
conditions.
CHAPTER IX.
THE EFFECTS OF CROSS-FERTILISATION AND SELF-FERTILISATION ON THE
PRODUCTION OF SEEDS.
Fertility of plants of crossed and self-fertilised parentage, both lots
being fertilised in the same manner.--Fertility of the parent-plants
when first crossed and self-fertilised, and of their crossed and
self-fertilised offspring when again crossed and
self-fertilised.--Comparison of the fertility of flowers fertilised with
their own pollen and with that from other flowers on the same
plant.--Self-sterile plants.--Causes of self-sterility.--The appearance
of highly self-fertile varieties.--Self-fertilisation apparently in some
respects beneficial, independently of the assured production of
seeds.--Relative weights and rates of germination of seeds from crossed
and self-fertilised flowers.
CHAPTER X.
MEANS OF FERTILISATION.
Sterility and fertility of plants when insects are excluded.--The means
by which flowers are cross-fertilised.--Structures favourable to
self-fertilisation.--Relation between the structure and conspicuousness
of flowers, the visits of insects, and the advantages of
cross-fertilisation.--The means by which flowers are fertilised with
pollen from a distinct plant.--Greater fertilising power of such
pollen.--Anemophilous species.--Conversion of anemophilous species into
entomophilous.--Origin of nectar.--Anemophilous plants generally have
their sexes separated.--Conversion of diclinous into hermaphrodite
flowers.--Trees often have their sexes separated.
CHAPTER XI.
THE HABITS OF INSECTS IN RELATION TO THE FERTILISATION OF FLOWERS.
Insects visit the flowers of the same species as long as they
can.--Cause of this habit.--Means by which bees recognise the flowers of
the same species.--Sudden secretion of nectar.--Nectar of certain
flowers unattractive to certain insects.--Industry of bees, and the
number of flowers visited within a short time.--Perforation of the
corolla by bees.--Skill shown in the operation.--Hive-bees profit by the
holes made by humble-bees.--Effects of habit.--The motive for
perforating flowers to save time.--Flowers growing in crowded masses
chiefly perforated.
CHAPTER XII.
GENERAL RESULTS.
Cross-fertilisation proved to be beneficial, and self-fertilisation
injurious.--Allied species differ greatly in the means by which
cross-fertilisation is favoured and self-fertilisation avoided.--The
benefits and evils of the two processes depend on the degree of
differentiation in the sexual elements.--The evil effects not due to the
combination of morbid tendencies in the parents.--Nature of the
conditions to which plants are subjected when growing near together in a
state of nature or under culture, and the effects of such
conditions.--Theoretical considerations with respect to the interaction
of differentiated sexual elements.--Practical lessons.--Genesis of the
two sexes.--Close correspondence between the effects of
cross-fertilisation and self-fertilisation, and of the legitimate and
illegitimate unions of heterostyled plants, in comparison with hybrid
unions.
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