SOMATIC MUTATION 



germ layer. In any case only one layer is changed and hence gives 

 rise to a chimaera with, mixed tissues: a layer of mutant lies inside 

 or outside a layer of the unchanged type. 



Chimaeras can be produced artificially as graft-hybrids or by any 

 treatment which alters the chromosomes. Most old vegetatively 



i 



Fig. 22. — Leaves and fruits of 2x Solatium sisymbrifolium {.<), 6x S. nigrum (/;) and 

 the graft-hybrid or chimaera with one layer of ^ over n which sorts out to give 

 pure nigrum in parts of its leaves (after Jorgensen and Crane, 1927). 



propagated plants such as pelargoniums and potatoes have become 

 chimaeras owing to somatic mutation at some time in their history. 

 When they are propagated from root-cuttings (or from disbudded 

 tubers) shoots grow out of the concealed irmer layers which reveal 

 the chimerical structure and the ancient mutations of these plants. 

 The elucidation of these properties by Baur, Bateson, Winkler and 

 Crane has enabled us to understand that natural changes in the 

 arrangement of tissues lead to the repeated appearance of "sports" 



III 



