THE PROBLEM OF GRAFT HYBRIDS AND CHIMAERAS

Abstract

Summary.In the introductory paragraphs of this review, the question was discussed whether after grafting, any effect of scion on stock or vice versa was known to occur. It was indicated that apart from the infectious chlorosis, a supposed virus disease, any influence of stock on scion or scion on stock is generally regarded as nonexistent. Professor Daniel, however, who has had unrivalled experience of grafting, holds the opposite view and believes strongly in the intermingling of characters of stock and scion (hybridation asexuelle) caused particularly by his method of mixed grafting.The earliest graft hybrid which has been scientifically investigated, the so‐called “Bizzarria” Orange, is then described. It is regarded by some as a true graft hybrid, by others as a synthetic chimaera of periclinal constitution. Other instances of sectorially diverse oranges may be due to partial segregation of heterozygous forms of Citrus.The well‐known and much discussed Cytisus Adami seems according to the investigations of Buder (1910 and 1911) to be what Baur (1910) has called a periclinal chimaera with a core of the Common Laburnum surrounded by an epidermal layer of Cytisus purpureus.Though according to Baur (1919) and Meyer (1915) the Crataegomespili are also periclinal chimaeras with a core of the hawthorn surrounded by one or more layers of the medlar, the more recent investigations of Haberlandt (1926) and Weiss (1925) as well as previous observations by Daniel (1914) throw some doubt on the chimaeric structure of these so‐called graft hybrids.The constitution of Pirocydonia is still uncertain and the Amygdalopersica described by Daniel (1914) seems likely to be a heterozygous plant.Of the various forms of growth obtained by Winkler by grafting tomato on nightshade stock and vice versa, four seem to be definitely proved to be periclinal chimaeras, but the constitution of Solanum Darwinìanum is still doubtful, and it may possibly be a true graft hybrid formed by a union of vegetative cells.The formation of chimaeric growths of variegated plants both of sectorial and periclinal constitution was experimentally established by Baur (1909) for Pelargonium and further investigated by Bateson (1919 and 1920), Chittenden (1925) and others. This has led to interesting discussions and observations concerning the part played by the plastids in the reproductive processes of plants and generally in the inheritance of variegated leaves.A further point of interest is the suggestion made by Chittenden (1930) that certain eversporting forms of flowers may be of chimaerical constitution.