900 



PHYSICAL BASIS OF HEREDITY 



mosaic seedlings with patches" of green and white on stems 

 and leaves (Fig. 104). When these seedlings grow into 

 plants, the color of the leaves will depend on the color 

 of that part of the stem from which the terminal bud, and 

 lateral buds grow out. If a bud lies in a green part of the 

 stem the new part will be green (Fig. 104, a) : if the new 

 bud lies in a white part of the stem the new part will be 

 white (Fig. 104, c) : and if it lies in a partly green, partly 

 white region the new part will have some white, some 



*t* ^^ ^^ 



Fig. 104. — Diagram to show how a sectorial chirnera may be produced. If the ter- 

 minal bud has come from a region of the seedling entirely green, all of the future leaves 

 will be green, a; if from a region without chlorophyll, all the future leaves will be white, c,- 

 but if the terminal bud lies partly in one, partly in the other region, some white and some 

 green leaves will arise, b. (After Baur.) 



green parts (Fig. 104, h). The only explanation that is 

 suggested by Baur is that in this plant the plastids are 

 transmitted both by the egg and by the pollen. The white 

 plant with defective plastids contributes part of the plas- 

 tids in the fertilized egg, the green plant with normal 

 plastids the other part. The fertilized egg contains there- 

 fore both kinds of plastids. During division of the egg and 

 embryo, the granules become irregularly distributed in 

 the cells. "Whenever a cell gets only defective granules, 

 it and its descendants are white, producing white parts : 

 when a cell gets mostly or only green granules, it and its 

 descendants are green, producing green parts. Hence 



