540 



ThK JoiRNAL OF HhRHOITY 



PROBABLY A CASE OF I.NFKCTIOl S CHLOROSIS 



One of the causes of variegated leaves in i)lants is infectious elilorosis, a disease which is not 

 inheritefl, but transmitted only by j^rafting. The leaf of Farfii^ium grande, here shown 

 natural size, ajjpcars to be thus infected. The spots start from the small capillary veins 

 and enlarge radially. "The white spots are surrounded by a border of yellowish green 

 where the chloroplasts are losing their color," Dr. Chapin notes. "One gets the im- 

 pression that the green cells are being bleached by a poison which diffuses slowly from 

 centers scattered about the leaf, and it is hard to account for this except by the parasitic 

 theory." (Fig. 13.) 



of at least one Z and two Ys. The 

 formula ZZ Yy NN j^ivcs "aiirea" 

 plants. 



It should be Ijorne in mind that the 

 Z, Y and N factors in Melandrium are 

 not necessarily the same as those in 

 other plants, such as Antirrhinum. 

 Baur and Correns seem to think that the 

 iiiht'ritanee f)f ehloro])hyll color is con- 

 nected directly with the inheritance of 

 the yellf)W ])ij,'ment, carotin. ShuU, 

 however, on the basis of his work with 

 Melandrium, believes that they are due 

 to indeijcndent factors. 



ATYPICAL .MKN'DKLIA.N TYPES. 



In the "variegata" form of Mirabilis: 

 jalapa, Correns (10, 12) shows a very 

 l)uzzlinjj; type of heredity. This race 

 of Fotn* O'Clocks differs from the 

 "chlorina" ty])e in having' ])atchcs of 

 jnire jj[reen scattered o\'er a backjjjroimd 

 of "chlorina" color on the leaves. The 

 ntnnber and size of these sjjots varies 

 j^reatly in dilTcrent i)lants and fluctuates 

 to some extent from leaf to leaf. Some 

 "varicfjata" plants are scarcely to be 

 distinj^jtiished from "chlorina." the green 



