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- The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom - 1/96 -
THE EFFECTS OF CROSS & SELF-FERTILISATION IN THE VEGETABLE KINGDOM.
CHARLES DARWIN, M.A., F.R.S., ETC.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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