EXPERIMENTAL RESULTS 113 



Further analysis of the problem by Hammerling (1943, 1946) and 

 his colleagues (Beth, 1943 ; Maschlanka, 1946) includes very interest- 

 ing experiments on interspecific grafts. For instance, binucleate 

 grafts containing one A. mediterranea (med.) and one A. crenulata 

 (cren) nucleus form "intermediate" caps; trinucleate grafts con- 

 taining two cren and one med nucleus give, as would be expected, 

 caps which more resemble normal cren. If now an enucleate cren 

 stalk is grafted with a med nucleate rhizoid, intermediate caps of 

 various types are formed. If this first intermediate cap is removed, 

 the new cap which forms is always a typical med cap. These results 

 led Hammerling (1953) to the following important conclusions. 

 The nucleus-controlled morphogenetic substances show species- 

 specificity; in binucleate grafts, distinct substances are produced by 

 the two nuclei and intermediate caps of constant types are formed. 

 In uninucleate grafts, the enucleate cytoplasm contains a store of 

 morphogenetic substances of its own species ; if this store is large 

 enough, an *'intergrade" cap is formed as a result of the competi- 

 tion between the substances stored in the enucleate piece and the 

 substances produced by the grafted nucleus. Since the structure of 

 the cap is obviously a hereditary character, it can be concluded 

 (Hammerling, 1953) that the substances produced under the in- 

 fluence of the nucleus are "products of gene action, which stand 

 between gene and character". It should, however, be borne in mind 

 that in these experiments it is not the nucleus alone which is trans- 

 planted: cytoplasm surrounding the nucleus is also grafted and it 

 cannot be entirely excluded that cytoplasmic particles endowed 

 with genetic continuity are also involved in the specific regenerative 

 processes. 



After this summary of the main facts concerning regeneration in 

 Acetabularia mediterranea, we can now go into the RNA and pro- 

 tein metaboHsm of this organism. ^ 



Unfortunately, accurate RNA estimations are difficult to carry 

 out in Acetabularia, which contains little RNA and a wealth of 

 substances interfering with the assay methods. The first measure- 

 ments, made by Brachet et ah (1955), indicated that there is ^^yJ^^vrTT" 

 synthesis of RNA in enucleate halves during the first ^^^^^'^^ji^^^^^r^;^^^ 



References p. 133/135 / Qq 



2^ 



