The Cytoplasm as Specific Substrate 235 



pretation such as those of Noack and Renner (see Renner, 1936). 

 However, such and other imaginable comphcations would not change 

 the fact that genetically diflPerent and constant plastids exist. Rhoades 

 (1946) pointed out that in view of the lack of visible differences 

 between the plastid types and the exclusive presence of differences of 

 reaction with a definite cytoplasm, we cannot exclude the possibility 

 that different plasmagenes are present which may be sorted out — a 

 dangerous terminology, I think, because it suggests a segregation of 

 plasmagenes, comparable to segregation of nuclear genes (whether 

 this is intended or not). Therefore I prefer to speak of genetically 

 different plasmons which may be mixed and separated; this amounts 

 to an explanation in terms of Correns' view, though with a different 

 terminology. 



A further step in the analysis of genetic properties of plastids has 

 been made in Schwemmle's work with crosses of Oenothera Berteriana 

 and odorata (see Schwemmle, Hanstein, Sturm, and Binder, 1938), in 

 which plastid behavior and plasmon inherited characters were studied 

 simultaneously. According to Renner's experiments a hybrid plant may 

 contain the plastids of the two parental species in the maternal cyto- 

 plasm (plastids introduced by egg and pollen). This results in a 

 variegated plant; and, in proper plastid distribution (i.e., sorting out), 

 pure pale or green branches may be formed, which can be propagated. 

 Thus from the cross A X B a line can be obtained with A cytoplasm 

 and B plastids plus different genomes. Accordingly, many Hues of 

 O. Berteriana X odorata were established in diverse combinations. 

 This allows distinguishing the maternal effects due to cytoplasm (of 

 the substrate type) from those which must be due to plastids. It was 

 found that leaf shape is influenced by the plastids present, which 

 must interact in some way with the genome in the control of a mor- 

 phological character, certainly a remarkable fact. This may sound less 

 astonishing if we realize that a difference in physiological function of 

 plastids will necessarily result in some biochemical difference of the 

 surroundng cytoplasm, which then acts as a different substrate for 

 genie function, just as in the cases studied above. It would be wrong 

 to consider these plastids as part genetic determinants for leaf shape. 

 Their role is better compared with a temperature or chemical action 

 upon cytoplasm, which, as we saw, shifts genie effects in a quantitative 

 way. 



The next consequence of such facts is to look for plastid muta- 

 tions. This is not an easy task. It is well known that plastid characters 

 may be controlled by genie changes. In such well-analyzed plants as 



