GRAFT-HYBRIDS AND OTHER CHIMERAS : 379 
green varieties of geranium (Pelargonium zonale). From his study of 
seedlings of 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 
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a 6 Cc d 
Fie. 154.—Leaves of the Crategomespili of Bronvaux and their components. a, 
Mespilus germanica (Medlar); d, Crategus monogyna (Whitethorn); 6, Crategomespilus 
Dardari, with two outer layers of medlar cells; c, Crategomespilus 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 
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