Livingston : Chemical stimulation of a green alga 9 



the cells become spherical or nearly so but a number still die. 

 Also, there is here a marked production of zoospores, which form 

 spherical cells immediately after germination, usually by the time 

 they have reached the two-celled stage. (See fig. j. Here the 

 dead filament-cells are denoted by dotted contents, the same 

 methods will be used in the following figures. A number of 

 empty sporangia are shown at a, together with zoospores in var- 



X^<2&& 





O o 



O So 



o 



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o 



o ° 



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&> a 

 6 © 



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Figure 3. Palmella and dead cells from 5«/ioo,ooo A1.,(SQ 4 ) 3 . 

 Figure 4. Palmella and dead cells from 5;//ioo,ooo A1,(NC\) 6 . 

 Figure 5. Palmella and zoospores from «/ioo,ooo A1 2 (N0 3 ) 6 . 



ious stages.) In weaker concentrations the filaments persist, zoo- 

 spore acceleration being still evident in 5;// 1,000,000. In ;^/i,ooo,- 

 OOO the culture is normal for a weak solution. Here zoospores are 

 produced but not as soon nor in such great number as in the 

 stimulated cultures. 



2. Aluminium sulfate (A1 2 (S0 4 ) 3 ). — This salt acts in the same 

 way as does the nitrate, and at the same concentrations. (See 

 fig. j, showing a large group of palmella still exhibiting traces of 



