EXPERIMENTAL RESULTS 117 



the crenulata (cren) species in nuclear transplant experiments. The 

 main conclusion is that the addition of a homologous nucleus has 

 no appreciable effect on protein synthesis. The rate of the latter is 

 the same whether the alga contains two or a single nucleus from the 

 same species. In the heterologous med cren combination, the cren 

 nucleus speeds up protein synthesis, a fact which is in agreement 

 with the observation that protein synthesis is faster in Acetabularia 

 crenulata than it is in Acetabularia mediterranea. 



The biochemical results just described are in good agreement 

 with the observations of Beth (1953a) who showed, in Acetabularia, 

 that the presence of the nucleus exerts an inhibitory effect on cap 

 formation; this process is initially speeded up when the stalk is 

 severed from the rhizoid just before the formation of the cap. 



Extensive experiments by Beth (1953b, 1955) have disclosed 

 another interesting fact. Cap production markedly depends on the 

 amount of light received by the algae. Intense illumination produces 

 algae which have a short stalk and a large cap; insufficient light 

 supply results in the formation of very long algae with small caps. 

 The phenomenon studied by Beth (1953b, 1955) also occurs in 

 nature: algae collected in the Mediterranean a few feet deep are 

 short and have large caps in July; those obtained by dredging or 

 deep-diving have long stalks and smaller caps. 



These observations by Beth (1953b) have led Brachet et al. (1955) 

 to a study of the regenerative capacities of the enucleate fragments 

 which had been left in the dark during increasing lengths of time 

 prior to exposure to light in order to induce regeneration. The ex- 

 periments showed that the same percentage of caps is obtained with 

 the stalks which had been kept two weeks in the dark as with those 

 which had been immediately illuminated. But the regenerative po- 

 tencies of the algae which are kept in the dark for periods longer 

 than two weeks soon decrease ; they disappear after 4 v/eeks. It may 

 be concluded that the substances of nuclear origin which are re- 

 quired for regeneration disappear at the same rate in the light and 

 in the dark; their maintenance is apparently not linked with the 

 energy supply in the cytoplasm. 



The chemical nature of the substance responsible for cap forma- 



References p. 1331135 



