536 



The Iournal of Heredity 



VARIATION IN PI(;WEKD CHIMERA SEEDLINGS 



Seeds of the green and white pigweed chimera as shown in the frontispiece were planted and 

 produced about three-fourths green and one-fourth white plants. A few of the plants 

 were variegated, and it is believed that these were produced by the union of germ cells 

 from green tissue and germ cells from white tissue. The patterns of the cotyledons of 

 these variegated seedlings are shown in the above diagram, a pure white and pure green 

 plant being sketched in the lower corners, for comparison. The heredity of these seedlings 

 docs not follow any mathematical law for the plants as a whole, but the relative number 

 of white and green seedlings produced by a chimera depends largely on the ratio of wliite 

 to green tissue. (Fig. 10.) 



INFECTIOUS CHLOROSIS. 



Under this heading Baur (1 and 2) 

 describes a jjeculiar disease amonj; 

 Abutilons and other plants in which the 

 leaves are i^reen with white spots. The 

 disease may be transferred to healthy 

 ^reen leaved ])lants l)y j^Taftinj^, but in 

 no other way. Healthy ]:)lants are not 

 infected by contact with s])otted jjlants 

 even when j^rown to}.;ether in the same 

 pot. Baur was also unable to infect 

 healthy jjlants by injectinjj them with 

 tissue juices of chlorotic individtjals and 

 for this reason he believes that it is not 

 a j.(erm disease, although its ability to 



spread from plant to jslant b\- ijjraftinj^ 

 would lead one to suppose so. It seems 

 to me ]x)ssible, however, that the disease 

 is due to an organism which li\'cs in the 

 vasctilar ducts and is so delicate that 

 it is killed by the cell juices when the 

 tissues are crushed. Infectious chlorosis 

 is not inherited. Seedlings from infected 

 jjlants are all green and normal. 



CHLOUOI'lIVLL .M.mXOS. 



The Mendclizing forms which lack 

 chlorophyll entirely cannot be used in 

 crosses because of their early death. 

 We know of their existence only through 

 the iichavior of green or yellowish-green 



