Livingston : Chemical stimulation of a green alga • 11 



y. Ammonium sulfate ( (NH 4 ) 2 S0 4 ). — The results are the same 

 as for the nitrate. {Fig. J shows palmella, several fairly typical 

 filamentous cells, and sporangia.) 



5. Barium nitrate (Ba (N0 3 ) 2 ). — With this salt, ;// 100 kills 

 practically all cells, although sometimes a few of the palmella form 

 will survive. The palmella form is typically produced in 5;// 1,000, 

 and more slowly in 0/1,000. In 5// 1,000 to some extent, but 

 especially in 0/1,000, there is again an acceleration of zoospore 

 production, which activity falls back to normal at a concentration 

 of 5/?/ 1 0,000. 



6. Calcium nitrate (Ca (N0 3 ) 2 ). — This salt is a component of 

 the nutrient solution itself and therefore it is difficult to determine 

 its effect upon the plant without having recourse to other methods 

 than the ones here used. The experiments indicate that it pro- 

 duces palmella at 5;// 100, and that there is a zoospore acceleration 

 from 0/100 to 5//. 1,000. The palmella response is perhaps partly 

 due to osmotic pressure. 



7. Cadmium nitrate (Cd (NO s ) 2 ). — The lowest dilution pro- 

 ducing death to all cells is 0/ 10,000, usually 50/ 100,000 kills 

 the majority of the cells. The typical palmella form is produced 

 in concentrations of from 50/100,000 to 0/ 100,000, and zoospore 

 acceleration appears in the latter concentration and continues in 

 weaker ones till the cultures become normal in the vicinity of 

 50 1,000,000. It is often difficult to tell where acceleration of 

 zoospore production actually ceases ; the markedly increased activ- 

 ity of the higher concentrations grades almost imperceptibly into 

 the normal production of these bodies in the weaker ones. 



8. Cobalt nitrate (Co(NO a ) 2 ). — The killing strength is from 

 0/1,000 to 50/10,000. The palmella form is produced in 50/10,- 

 000 to 0/100,000, and zoospore stimulation at 0/10,000 to 50/1,- 

 000,000, below which concentration the cultures are normal. {Fig. 

 8 shows palmella from 0/10,000 concentration.) 



g. Cobalt sulfate (CoSOj. — The responses here follow accur- 

 ately those with the nitrate. {Fig. 9 shows palmella in 50/1,000,- 

 OOO, while fig. 10 shows nearly normal filaments in one fifth of 

 that strength.) 



10. Copper nitrate (Cu(NO s ) 2 ). — The killing strength is from 

 0/100,000 to 50/1,000,000. In the latter strength sometimes a 



