Chapin: Heredity in Chimeras 

 Table 3. Variegated Pigweeds IB and IC. 



535 



Fifty-seven green seedlings of the 

 original pigweed 1 were raised until 

 they had five or more leaves. None of 

 them showed the least variegation with 

 white tissue, however. Twenty of 

 these plants were placed together in 

 a box where there was abundant oppor- 

 tunity for cross as well as self pollina- 

 tion. No attempt was made to avoid 

 foreign pollen as this would come from 

 green plants anyway and would not be 

 likely to prevent the formation of 

 white or variegated plants, if such 

 could occur. As a matter of fact there 

 were no wild pigweeds growing within a 

 hundred feet of them. From the mixed 

 seed of these plants a large sample was 

 planted and I obtained 3492 seedlings, 

 which were all green, none variegated 

 or white. 



From this it would appear in the case 

 of these pigweeds that green tissue 

 produces only green plants and white 

 tissue only white plants when fertiliza- 

 tion takes place between germ cells 

 which come from the same tissue. 

 Variegated plants are most likely formed 

 from a cross between germ cells which 

 come one from green and the other 

 from white tissue. I have experiments 

 planned for the future to determine 

 this point, which will be the subject of 

 another paper. 



A word should be said as to the ac- 

 curacy of these figures. I believe that 

 they are essentially correct. The white 

 seedlings always wither before the new 

 leaves appear and if a way could be 

 found to raise them some might prove 

 to be variegated. This seems unlikely, 

 however. A more important source of 

 error consists in overlooking variegated 

 plants which have only a little white in 

 their cotyledons and counting them as 

 green. I doubt if this error would 

 amount to half of one per cent at the 

 most. 



The important thing is that we have 

 here a race of plants with different 

 hereditary characteristics on different 

 branches. They are in fact natural 

 chimeras, in distinction to those chi- 

 meras which are formed by grafting. 

 If we could graft the white plants on 

 green plants we might expect to get 

 just such sorts of variegated individuals 

 from adventitious shoots which included 

 tissue from both stock and scion. 



Baur (4) has reported a very similar 

 condition among geranitrms. Pelargon- 

 ium zonale, which have white-edged 

 leaves. The whole subject is so inter- 

 esting from a genetic standpoint that I 

 shall attempt a review of the main 

 features of chlorophyll inheritance, and 

 the hypotheses put forward to explain 

 them. Besides the cases which I have 

 given in this review others have been 

 reported which do not seem to belong 

 to any of these types. H. Mohsch (13), 

 for instance, has reported cabbages 

 which develop variegated leaves on the 

 approach of cold weather. The leaves 

 become green again if the temperature 

 is raised. The plants are true to seed, 

 but no crosses with green plants were 

 reported. Shull (16) also reports some 

 very interesting variegations in the 

 leaves of Melandrium. 

 classification of chlorophyll inheritance. 



1. Infectious Chlorosis. Not inherited. 

 Transmitted only by grafting. 



2. Mendelian Types of Inheritance. 



(a) Chlorophyll albinos. Forms which 

 lack chlorophyll entirely. Known only as 

 seedlings which soon die. 



(b) "Chlorina" and "Pallida" types. 

 Leaves have less chlorophyll than normal. 

 Leaf color fairly uniform. 



3. Atypical Mendelian Types. Represented 

 by the "Variegata" form of Mirahilis jalapa — 

 Correns (10). 



4. Non-Mendelian Types. 



(a) "Albomaculata" type. Variegated 

 leaves. Inheritance through the mother. No 

 segregation in the F2 generation. 



(b) Sectorial and periclinal chimeras. 



