Chapin: Heredity in Chimeras 



539 



Some of the earliest work on chloro- 

 phyll color was done by Baiir (3) with 

 an "aurea" form of snapdragon, Antir- 

 rhinum majus. The leaves of the 

 "aurea" plants were yellowish green or 

 golden in color and they had less 

 chloroph}'!! than normal, green plants. 

 Baur's experiments showed that the 

 "aurea" plants were to be regarded as 

 heterozygotes, for when self fertilized 

 they produced green, "aurea" and 

 yellow seedlings in the ratio of 1 : 2 : 1 . 

 The yellow seedlings soon died, as they 

 had no chlorophyll in their leaves, but 

 only a yellow pigment, carotin, which 

 gave them their color. The cross be- 

 tween green plants and "aurea" plants 

 gave green and "aurea" offspring in 

 equal numbers. Evidently this case 

 is like that of the famous Andalusian 

 fowl. 



"chlorina" and "pallida" types. 



Plants which have less than the 

 normal amount of chlorophyll in their 

 leaves, are true to seed and behave as 

 typical recessives when crossed with 

 normal green plants, have been described 

 by Baur, Correns, Shull and others. 

 "Chlorina" forms have been described 

 by Baur (5, 6) for Antirrhinum majus 

 (Snapdragon) and Aquilegia vulgaris; 

 by Correns (9, 10) for Mirahilis jalapa 

 (Four O' Clocks) and Urtica pilulifera 

 and U. dodarti and by Shull (16) for 

 Melandrium. The "pallida" type has 

 only been reported by Shtdl for Melan- 

 drium. Price and Drinkard (15) report 

 a case of yellow leaved tomatoes which 

 appears to belong in this class. 



Correns' "chlorina" type of Mirahilis 

 jalapa has pale green leaves which con- 

 tain 28 to 30% of chlorophyll. The 

 plants and their flowers are smaller than 

 usual on this account. The color seems 

 to be fairly uniform, though it varies 

 somewhat in different plants. In Me- 

 landrium Shull says the "chlorina" 

 plants have about 43% of chlorophyll 

 in their leaves. The color varies con- 

 siderably in intensity in different plants 

 and even in different parts of the same 

 plant. They also have a tendency to 

 bleach in strong sunlight, especially 

 near their centers. The "pallida" type 

 of Melandrium differs from "chlorina" 



in having rather darker leaves (about 

 65% chlorophyll) which do not fade in 

 sunlight. The color is more unifbrm 

 than in "chlorina." 



the mendelian explanation. 



If we let X represent the sum of all 

 the unknown factors for chlorophyll 

 color, then the following formulas will 

 explain Shull's results with Melandrium. 



1. XX ZZ YY NN produces normal, 

 green leaves. 



2. XX ZZ YY NN forms a white 

 plant without chorophyll which soon 

 dies because it lacks the Z factor. 



3. XX Zz YY NN is green like no. 1 

 but differs in being a heterozygote. Its 

 offspring are green plants and white 

 plants in the ratio of 3 : 1. 



4. XX ZZ yy NN gives the "palhda" 

 form. 



5. XX ZZ Yy NN represents the 

 hybrid between green and "pallida." 

 It has green leaves and produces green 

 and "pallida" offspring in the ratio of 

 3 : 1. 



6. XX ZZ YY nn gives the "chlorina" 

 form. Like "pallida" it behaves as a 

 simple recessive to normal green. The 

 cross between "chlorina" (XX ZZ YY 

 nn) and "palHda" (XX ZZ yy NN) 

 produces a green leaved plant with the 

 formula : 



7. XX ZZ Yy Nn whose offspring in 

 the F2 generation are composed of green, 

 "chlorina" and "pallida" plants. The- 

 oretically the ratio should be 9 : 3 : 3 : 1 , 

 the one plant in 16 being a new type of 

 the formula: 



8. XX ZZ yy nn which Shull calls 

 "subchlorina." Unfortunately he was 

 unable to distinguish the "subchlorina" 

 plants from the others. The number of 

 green and pale leaved plants agreed very 

 well with the expected ratio of 9 : 7, 

 however. 



Baur (6) says that a factor Z is neces- 

 sary for the production of chlorophyll. 

 Plants which do not possess it are pure 

 white and cannot live. Factor Y is only 

 active in the presence of Z. Plants with 

 Z but not Y are yellow and cannot live. 

 Factors Z and Y without N produce the 

 pale green "chlorina" color. Factor N 

 produces a green plant in the presence 



