HEREDITY IN CHIMERAS 



Pigweed with Variegated Leaves Proves to Be Sectorial Chimera— Variegated 

 Plants Probably Produced by Mating of Green and White Gametes — Re- 

 view of Present State of Knowledge of Chlorophyll Inheritance. 



Dr. WiLLiAiM S. Chapin, Vanderbilt, Mich. 



IN AUGUST, 1912, I found three 

 variegated-leaved pigweeds, Ama- 

 rantlnis retroflexits, growing within a 

 yard of each other in a neglected 

 comer of an old garden. I removed the 

 healthiest plant to a large flower-pot in 

 the house, where it started to blossom 

 a week later. Beyond keeping it in the 

 window, I made no effort to protect it 

 from wind-borne pollen from outdoors. 



The peculiar thing about these three 

 pigweeds was their leaves, many of 

 which had irregular patches of white 

 where the chloroplasts had failed to 

 develop. A few leaves were pure white 

 while those on the other side of the 

 stem were pure green. The white 

 tissue, not being able to elaborate 

 carbohydrates for itself, had to depend 

 for food on that brought to it from the 

 green portions of the plant. Conse- 

 quently the white patches showed less 

 growth than the rest of the leaf and 

 this often caused the leaves to bend 

 or curl toward the white areas. Such 

 variegated plants are handicapped in 

 the "Struggle for Existence" when in 

 competition with green plants which 

 have no parasitic white tissue to sup- 

 port and, if they have a large proportion 

 of white tissue, are delicate and hard 

 to raise. 



The side branches also bore the char- 

 acter of the leaves from whose axils 

 they sprung: e. g., pure green branches 

 came from the axils of pure green 

 leaves, pure white branches from the 

 axils of pure white leaves, while from 

 the axils of variegated leaves there 

 might appear pure white, pure green or 

 variegated branches depending on cir- 

 cumstances. It is believed that in such 

 plants the apical cone, or mass of 



embryonic cells at the tip of the stem, 

 is composed of two kinds of cells, some 

 of which are able to produce green 

 tissue while the others can only produce 

 white. If all the white tissue embryonic 

 cells happen to be bunched together on 

 one side of the apical cone, the leaves 

 formed from these cells alone will be 

 pure white, while leaves on the other 

 side of the stem formed only from green 

 tissue embryonic cells will be pure 

 green. Leaves formed from both sorts 

 of cells are variegated and their pattern 

 depends on the relative number and 

 position of the green and white cells. 



VARIATION IN THE LEAVES. 



If the white and green embryonic 

 cells always maintained their relative 

 numbers and position in the apical 

 cone, then theoretically each leaf on a 

 stem might have the same pattern as 

 the leaf directly below it. There is in 

 fact a very strong resemblance between 

 such leaves, but there is always some 

 inequality in the growth of the cells of 

 the apical cone with a consequent 

 change in the pattern of the leaves. In 

 some cases the green embryonic cells 

 crowd the white ones entirely out of 

 the apical cone or vice versa and the 

 rest of the stem and leaves becomes 

 pure green or pure white as the case 

 may be. Such branches have never 

 again become variegated so far as I 

 have observed. In many variegated- 

 leaved plants the white embryonic 

 cells form a layer over the green ones 

 in the apical cone. The leaves in such 

 cases are a lighter green with white 

 edges, the green cells being sandwiched 

 in, so to speak, between an upper 



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