438 



In another class of yellowish-green races, which are in a sense 

 constant, the yellow-green plants are all heterozygote and Men- 

 delize into one fourth clear yellow incapable of development, 

 one fourth pure green, constant in later generations, and two 

 fourths yellow-green, which splits again as above. This case was 

 treated of by Dr. Baur in a former paper. 2 



Many other types of variegation exist. One of them is re- 

 ported in the review of Professor Correns's paper below. The 

 present paper of Dr. Baur's deals with another type of variega- 

 tion, namely: white margined leaves, such as those found in 

 varieties of Acer negundo, Comas alba, Pelargonium zonale and 

 numerous other species. The investigation was confined largely 

 to the last-mentioned species. Little was previously known of 

 the inheritance of this character. Several authorities had stated 

 that such plants (with white margined leaves) produce only 

 seedlings that are pure white and incapable of development. 



Dr. Baur's studies show that the white margined plants of 

 P. zonale are covered with two or three layers of cells containing 

 colorless chromatophores which can not assimilate C0 2 but which 

 can manufacture starch from sugar. The whole plant is covered 

 by this white tissue. Near the leaf margin the two white layers 

 form the whole of the tissue and thus give the peculiar marking 

 on these leaves. 



The line of demarcation between the white cells and ordinary 

 cells is definite. One gets the impression that all the descendants 

 of a white cell are white and all those of a green cell are green. 

 This can not be definitely determined by microscopic study, but 

 the experimental results reported below practically prove that 

 such is the case. 



Four white margined plants obtained from different sources 

 all, when self-fertilized, produced only white seedlings, which 

 soon died because they were incapable of assimilating C0 2 . Some 

 of these plants occasionally produced green branches which arose 

 by the green tissue breaking through the superficial covering of 

 white. Seed from these green branches produced normal green 

 plants which propagated true to seed. On the other hand, white 

 branches, when close fertilized, produced only white seedlings. 

 (An occasional branch was pure white without the underlying 

 green tissue.) 



*Ber. d. Den. Bot. Gesell, 25, 1907, p. 442, and Zeitsch. f. Abst, u. Ver, 

 1, 1908, p. 124. ' 



