ORGANIZATION AND GROWTH 243 
I II Ill 
3.3 g. NaCl 3.3 g. NaCl 1.6 g. NaCl 
100 c.c. fresh water 0.03 g. KCl 1.6 g. MgSO, 
100 c.c. fresh water 0.03 KCl 
100 c.c. fresh water 
No regeneration whatsoever occurred in the first solution; 
small and not entirely normal polyps formed in the second, 
but no growth occurred; normal regeneration and growth 
occurred in the third solution. 
3. It might be possible from these experiments that the 
MgSO, is essential for regeneration and growth, while KCl 
is only secondary. I therefore experimented with the follow- 
ing solutions: 
I II 
2.3 g. NaCl 2.3 g. NaCl 
1.0 g. MgSO, 1g. MgSO, 
100 c.c. fresh water 0.03 g. KCl 
100 c.c sea-water 
No regeneration whatsoever occurred in the first solution; 
but regeneration and growth were normal in the second. 
After six days I divided the first solution and the animals 
contained in it into two vessels, adding 0.05 g. of KCl to 
one of them, while I left the other unaltered. The animals 
contained in the dish to which I had subsequently added 
the KCl regenerated and grew in a normal way, while not 
even a suggestion of regeneration was apparent in the other. 
The presence of potassium in sea-water is therefore neces- 
sary for regeneration. 
4, It had still to be decided which constituent of MgSO, 
is essential for regeneration in Tubularia. I substituted 
Na,.SO, for MgSO,, and experimented with 300 c.c. of each 
of the following solutions: 
I II 
2.5 g. NaCl 2.5 g. NaCl 
0.8 g. Naz SO4 0.8 g. Naz SO4 
100 c.c. fresh water 0.03 g. KCl 
100 c.c. fresh water 
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