24 E. G. PRINGSHEIM 



means negligible, and their spectral emanation is less in con- 

 formity to the absorption of algal pigments than that of incan- 

 descent lamps. Moreover a great number of culture vessels can be 

 arranged at equal distances around a bulb, and lower intensities 

 obtained in greater distances; whereas the distribution of light 

 from a number of tubes involves complications. 



General rules about light intensity cannot be given. Most 

 Cyanophyta, Chrysophyta, Chrysomonadaceae, the Euglenophyta 

 and the Cryptophyceae, as well as the majority of other filamen- 

 tous algae cannot be made to multiply more quickly by employ- 

 ing bright light. Many Volvocales, however, maintain a better 

 growth at a high intensity. Most of our strains, on the contrary, 

 are removed from their places of cultivation before they are at 

 the height of their development and are kept in a dimly lighted, 

 cool place. 



We have had no experience with cold water algae. Except in 

 hot summers all our algae grow well at "room temperature" 

 (18-22° C. in England) and there is no indication that lower 

 temperatures are better for their multiplication, although most 

 of them live longer when the temperature is not high. 



A great difficulty is evaporation. Agar dries out; liquid cul- 

 tures often produce a growth near the water margin which is 

 lost when the level drops. Caps of wax paper fastened with rub- 

 ber bands reduce evaporation and soiling by dust. Carbon dioxide 

 seems to penetrate sufficiently, although in soil-water cultures 

 CO2 is also provided from the mud-base. Tubes with plastic 

 screw caps are still better, provided they have cardboard washers. 

 Their necks, however, make them less useful for soil-water cul- 

 tures than for agar and liquid media. 



Application 

 More algal species can be grown in soil-water cultures than 

 in all other media combined, among them some delicate ones, 

 although experience is still limited. The following summarizes 

 some of our experiments: 



CHRYSOPHYTA (Chrysophyceae) : Ochromonas, Urogle- 

 na, Synura, Coccolithophora, and among colorless forms, Monas, 



