116 The Nature of Biological Diversity 



was, so to speak, dominant. That is, either the nucleus or the cyto- 

 plasm of med plants sufficed to establish the med phosphatase as ex- 

 clusively characteristic of the hybrid plant. The acic enzyme rapidly 

 disappeared from the graft combination at a rate far in excess of its 



MED 



ACIC 



M 



I I A^° 



FIG. 11. Diagram of zymogram patterns of acid phosphatase in two species of 

 Acetabularia. Each species contains a single acid phosphatase with a characteristic 

 electrophoretic mobility in starch gel. Strips 1 and 6 show the pattern obtained 

 from mixed homogenates of the two species. Strip 2 depicts the conversion of the 

 acic enzyme to the med type when a med nucleus is substituted for the acic nucleus. 

 Strip 3 shows that the med enzyme persists even after the med nucleus is replaced 

 by an acic nucleus. Strip 4 shows that only med enzyme is found in hybrid cyto- 

 plasm regenerated in the presence of one nucleus from each species. Strip 5 shows 

 the intermediate phosphatase band frequently observed when two acic nuclei and 

 one med nucleus collaborate in the production of new cytoplasm. This band ap- 

 parently represents an intermediate stage in the conversion of acic enzyme to med 

 enzyme. 



normal diminution in enucleated acic plants. This rapid disappearance 

 suggests that some mechanism in the med cytoplasm converts the acic 

 enzyme to the med type. This mechanism must be initiated by the 

 nucleus because the med nucleus, by itself, is sufficient to bring about 

 the conversion of acic phosphatase to the med type. An intermediate 

 step in this conversion is visible after electrophoresis of graft com- 



