GRAFT-HYBRIDS AND OTHER CHIMERAS 



379 



green varieties of geranium (Pelargonium zonale). From his study of 

 seedlings ^f the white-edged variety he had come to realize that the 

 color of the leaves on a seedling depends entirely upon the nature of the 

 cells composing the vegetative cone or plumule. This led him to examine 



6 c d 



FIG. 154. Leaves of the Cratsegomespili of Bronvaux and their components, a, 

 Mespilus germanica (Medlar); d, Cratcegus monogyna (Whitethorn); b, Crataegomespilus 

 Dardari, with two outer layers of medlar cells; c, CratcBgomespilus Asnieresi, with one outer 

 layer of medlar cells. (After Buder.) 



the cells in white-edged and green leaves and he found that in a white-edged 

 leaf there is an extra layer of colorless cells in addition to the true epidermis 

 (see Figs. 155, 156 and 157). He concluded that a plant bearing all white- 

 edged leaves must have a complete peripheral layer of the colorless cells 

 just below the epidermis as shown in Fig. 157, a, and that a plant differing 



FIG. 155. Leaves from periclinal chimeras of the white-edged geranium ; a, from a plant 

 with two white peripheral cell-layers; 6, from a plant with only one epidermal layer of 

 colorless cells. (After Baur.) 



in this respect from a normal green plant should be considered a peri- 

 clinal chimera. He had observed sectorial chimeras among his geranium 

 seedlings and found that occasionally a plant having some of its leaves 

 entirely green and some of them entirely white would produce a shoot 

 bearing white-edged leaves. He found that such shoots arose near the 



