332 INTRODUCTION TO CYTOLOGY 



be carried from one generation to the next in the egg cytoplasm, causing 

 a direct inheritance of the disease. But such pathological cases are not 

 to be confused with, or thought to contradict, normal Mendelian heredity, 

 which, as will be seen in the following chapter, is closely bound up with 

 nuclear phenomena. They are rather to be regarded as examples of 

 repeated reinfection. 



Results differing from those of Correns were obtained by Baur (1909) 

 in his researches on Pelargonium zonale albomarginata. This form, which 

 is characterized by white-margined leaves, often has pure green and pure 

 white branches, as in Mirabilis. Crosses either way between flowers on 

 these two kinds of branches result in every case in mosaic (green and 

 white) offspring: inheritance is here not purely maternal as in Mirabilis. 

 Although Baur admits for this case the possibility of a Mendelian inter- 

 pretation if a segregation of factors for greenness and whiteness in the 

 somatic cells be allowed, he thinks it more probable that inheritance in 

 this instance is not a matter of chromosomes and Mendelism at all, but 

 is rather due to a sorting out of green and colorless plastids, themselves 

 permanent cell organs, in the somatic cells. In order to account for 

 inheritance through both the male and the female, Baur assumes that 

 primordia of plastids are brought in through the male cytoplasm as well 

 as the egg cytoplasm, a conclusion directly contradictory to that of 

 Correns. Ikeno (1917), working on variegated races of Capsicum annum. 

 obtained results similar to those of Baur on Pelargonium, and concluded 

 that transmission of variegation is not through the nucleus, but through 

 plastids contributed by both parents. 



Although the results and interpretations of Correns and Baur are at 

 present irreconcilable except on the basis of assumptions not warranted 

 by known facts, they agree in the conclusion that plastid inheritance is 

 not Mendelian, but is due rather to extra-nuclear factors. Baur reports 

 corroborative evidence in Antirrhinum (1918). Opposed to this con- 

 clusion is that of Lindstrom (1918), who has clearly shown in the case of 

 certain variegated races of maize that the inheritance of characters due 

 to unusual plastid behavior is strictly Mendelian. This means that the 

 distribution or degree of prominence of the plastids, although these may 

 be organs with their own individuality, depends upon the activity of 

 Mendelian factors in the chromosomes, which represent the only known 

 cell mechanism in which there is at present any hope of rinding an expla- 

 nation for the distribution of Mendelian characters (Chapter XV). In 

 Lindstrom's plants plastid inheritance appears to be as much a nuclear 

 matter as the inheritance of any other character manifested in the extra- 

 nuclear portion of the cell. 



On the basis of the data at hand the tentative conclusion seems fully 

 justified that all cases of chlorophyll inheritance do not belong to one 

 category. Some of them are clearly to be accounted for on the same basis 



