I 



Livingston : Chemical stimulation or 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^^^ 5, 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- 



o 



a 



o o 



o 



© 



4 



a, <& % 



© 



^ 



(?) 



0(s> 

 CO 



^ a 





a 



Figure 3. Palmella and dead cells from 5/7/100,000 Al^(SO^)3. 



Figure 4 

 Figure 5 



Palmella and dead cells from 5^/100,000 Al2(N03)6 

 Palmella and zoospores from «/ioo,ooo Al2(N03)g, 



5 



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

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

 000 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. Aliuniniiim sulfate (Al2(SO^)3). — This salt acts in the same 

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

 Jig, J, showing a large group of palmella still exhibiting traces of 



