The Sexual Reproduction of Ranunculus Ficaria

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Abstract
Lack of viable seed in Ranunculus Ficaria, which is especially characteristic of forms which bear tubercles in the axils of the cauline leaves, is chiefly due to various forms of degeneration in the embryo-sac or nucellus which are fully described. The fact that ovules frequently become disorganized, even when active pollen tubes are present, shows that degeneration is not due to lack of viable pollen. The process of fertilization in normal embryo-sacs is described. Fertilization is not a necessary preliminary to the formation of endosperm, and definite proof was obtained that embryos sometimes arise from unfertilized eggs. Seed which is apparently viable is not always capable of germination for reasons which are fully described. Forms of R. Ficmia with axillary tubercles appear to be almost absent from certain localities in Devonshire and Somerset, although there are districts in other parts of the country where they are dominant. In other places forms with or without aerial tubercles appear to exist side by side in about equal quantities. In parts of central Europe, records show that the species almost invariably bears axillary tubercles. I am indebted to all those who have assisted in various ways with this investigation. Thanks are due especially to Sir Arthur W. Hill for his interest and advice in the preparation of the manuscript. Also to Mr. E. M. Marsden-Jones who carried out the pollination experiments, fixed material, and supplied living plants from the Potterne Biological Station. Dr. W. B. Turrill's suggestions and criticisms have also been most helpful. I am also grateful to Mr. G. Atkinson for advice and assistance in preparing the illustrations.