|
|
This Project Gutenberg Etext was prepared by Sue Asscher asschers@dingoblue.net.au
The Effects Of Cross And Self-Fertilisation
In The Vegetable Kingdom
By Charles Darwin, M.A., F.R.S.
Second Edition
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.
