370 Stout: Bud-variation in Pelargonium 



In the light of Baur's anatomical studies this sort of bud-varia- 

 tion is readily understood as due to a mechanical readjustment of 

 the two kinds of cells already in the growing points. This par- 

 ticular type involves more extensive rearrangement than the 

 cases where pure green or pure white branches are produced by 

 the development of a bud containing only one kind of cells to the 

 exclusion of the other. For the development of a branch re- 

 versing the position of the two kinds of cells as described above 

 there must be a breaking out of the enclosed green cells in the 

 growing point and a growth of both green and white cells' in such 

 a manner that the green cells surround the white cells. It may be 

 that in this case the green cells break forth at two separate points 

 not far distant and that in further growth they meet, enclosing 

 the white cells. 



On the main portion of the plant here shown, the mature 

 leaves possess over their whole surfaces two peripheral cell-layers 

 that are white. To maintain this relationship the cell divisions 

 which give rise to these layers must occur only in p'anes wdiich are 

 at right angles to the surface of the leaf. The outer layers do not 

 contribute to the vascular t'ssues and the inner green tissue does 

 not form epidermis, a fact clearly shown by Baur. In the sporting 

 branch, however, the green cells get to the surface and form the 

 epidermis as well as some of the mesophyl and vascular tissue, 

 while the white cells cease to form epidermis and now contribute 

 only to the inner tissues. The cells preserve the green and white 

 character of their chromatophores but take on different structures 

 or different functions according to position and environment. 



In his interesting report of results of anatomical and hereditary 

 studies of variegated varieties of Pelargonium., Baur was not 

 especially concerned with the evidence of interaction between the 

 two kinds of cells, the white and the green, where both exist in 

 the same leaf. His photographs, however, show the same sort of 

 difference which have appeared so strikingly in the case here under 

 consideration. 



The marked differences between the two kinds of leaves pro- 

 duced on this plant (plate 20) make it clear that the outer layers 

 largely determine the size of the leaves and the depth of the lobing. 

 When the green is outside the leaf is larger, more deeply lobed and 



