THE CHROMOSOMES 139 



again there are mosaic branches, white branches, and 

 also green branches. Flowers on green branches 

 crossed with flowers on white branches give mosaic 

 plants, irrespective of which way the cross is made. 

 A self-fertilized flower from a green branch gives rise 

 to a plant with purely green leaves. If a flower from 

 a checkered branch is self-fertilized it produces a 

 checkered plant. If a flower from a white branch is 

 self-fertilized it gives rise to a white plant. 



Baur suggests tentatively, the following hypothesis 

 to explain the case of Pelargonium. The green color 

 of this plant, like that of all flowering plants, is due 

 to chlorophyll grains and these grains multiply, 

 supplying all the cells in generations that subse- 

 quently arise with their quota of grains. In the 

 white parts these grains are defective in the sense 

 that they fail to produce the green color, but retain 

 their power of multiplying. If now it is assumed 

 that the pollen as well as the egg may transmit some 

 chlorophyll grains the results can be explained. For, 

 in the division of the cells that contain both green 

 (normal) and white (abnormal) grains there will 

 arise at times an unequal distribution of the grains, 

 and in extreme cases two kinds of branches may arise, 

 one with green and the other with white grains. The 

 hypothesis calls for transmission through the cyto- 

 plasm of the pollen as well as through that of the 

 egg cell. Baur states that until this fact can be 

 established the interpretation must be uncertain. 



