Stout: A Graft-Chimera in the Apple 



135 



ange which appeared in Florence, Italy 

 about 1644. On some of its branches 

 oranges are produced, on others citrons 

 develop, and on other branches the 

 fruits are part orange and part citron 

 as shown on page 522 of Vol. 5 of this 

 Journal (December, 1914). Another 

 plant known as Cytisus Adami origin- 

 ated in 1825 as a branch of a plant 

 grown from a graft between Cytisus 

 pur pur ens and Laburnum vulgar e. 

 Some branches of this plant are pure 

 Cytisus purpureus, others are pure 

 Laburnum vulgar e, others are various 

 mixtures of the two, and others bear 

 leaves that are intermediate in charac- 

 ter. Several types of plants are known 

 which appear to be mixtures of the two 

 species Crataegus monogyna and Mespi- 

 lus germanica. All of these have been 

 propagated vegetatively and have been 

 objects of more than usual interest. 

 How these plants originated has been 

 a matter of no little discussion and 

 speculation among botanists and horti- 

 culturists. 



GRAFTING TO PRODUCE CHIMERAS 



The experimental production of 

 chimeras in rather recent years has 

 shown very clearly how such plants can 

 arise incidentally through the practice 

 of grafting. By a simple but ingenious 

 arise incidentally through practice of 

 grafting. By a simple but ingenious 

 method of experimentation Dr. Wink- 

 ler, now Director of the Botanical 

 Garden at Hamburg, produced such 

 plants under observation and control. 

 He used the tomato and nightshade, 

 two distinct and well-known species 

 with marked differences in leaves, 

 flowers and fruit. He made grafts, 

 and when the scions were well estab- 

 lished he decapitated the branches by 

 cutting through the points of contact 

 between scion and stock, thus exposing 

 on the cut surface the two kinds of 

 tissue and the lines of contact between 

 them. On this surface a callus formed 

 from which buds arose. If a bud arose 

 entirely from the part that was night- 

 shade the branch was nightshade only; 

 if from tomato tissue the branch was 

 pure tomato. If, however, a branch 



arose over the line of juncture it was 

 composed partly of tomato and partly 

 of nightshade tissue. 



TWO KINDS OF CELLS IN SAME BRANCH 



Such branches were called "chime- 

 ras." The simpler of these show 

 vertical lines of differentiation; one 

 sector bears the leaves, flowers, and 

 fruits of the tomato while the rest of 

 the branch bears those of the night- 

 shade. Such branches and the plants 

 grown from them by vegetative propa- 

 gation are called "sectoral chimeras." 

 In such an association of two kinds of 

 cells, each sort retains its own character 

 and the leaves, flowers, and fruits of 

 the two sectors are readily to be 

 identified. 



Occasionally, however, branches 

 arose which produced leaves, flowers 

 and fruits that were intermediate or 

 mixed in character. One of these 

 (named Solatium tubingense) bears 

 simple leaves like the nightshade but 

 the leaves are more or less lobed and 

 are hairy as the tomato. Another 

 (Solatium proieus) resembles the to- 

 mato more than the nightshade; the 

 stems and leaves are hairy but the 

 fruits are smaller than those of the 

 tomato. Several types of intermediates 

 were produced and for a time it was 

 believed that these were true graft- 

 hybrids resulting from the actual 

 fusion of certain vegetative cells of the 

 tomato and the nightshade in the 

 region of contact in the graft. Later, 

 however, a study of the internal and 

 minute structure of the cells in these 

 plants revealed that the two kinds of 

 cells characteristic of the tomato and 

 the nightshade are both present, and 

 that one kind exists as one or more 

 continuous layers covering the other 

 kind. It was found that Solatium 

 tubingense has one outside or periclinal 

 layer of tomato cells covering a core of 

 nightshade tissue and that 5. proteus 

 has two such periclinal layers. Other 

 types of the intermediates have one or 

 more outermost layers of nightshade 

 cells covering tissue of the tomato. 

 The plants were thus found to be 

 periclinal chimeras. A photo of four 



