20 E. G. PRINGSHEIM 



than with Jacobsen's technique. It was soon found, moreover, 

 that by omitting organic matter other than that contained in the 

 soil, many more algae could be grown in clonal cultures, pro- 

 vided the isolation of algal species was secured by a repetition of 

 the isolation procedure. 



The advantages of this bi-phasic soil-water technique were 

 found to be manifold. Its adaptibility permits one to grow almost 

 any species of small organisms, especially algae. Healthy material 

 for morphological investigations and for further culture experi- 

 ments can be grown with a longevity that surpasses isolates 

 grown in mono-phasic solutions. A strain once put into culture 

 does not get lost easily. The rich and homogeneous growth can 

 be investigated in all of its developmental stages under condi- 

 tions resembling those of the natural habitat. The technique is 

 easy to employ inasmuch as it does not require bacteriological 

 sterility. It can be employed, therefore, without elaborate equip- 

 ment and on a wider scale than with the pure culture technique, 

 and by maintaining many strains in test-tubes it permits the com- 

 parison of related species. 



This technique was described, mainly as a preparatory method 

 before final purification (Pringsheim, 1946). Its adaptability 

 to ecological studies and its application to various needs have 

 been shown in other papers. Herein I shall give an account of 

 further experience. 



Media 



The imitation of natural conditions will provide a miniature 

 artificial pond. It is not possible in many cases to give in a liquid 

 medium all nutrients required by an alga because many species 

 cannot adapt themselves to other than very dilute solutions. Also, 

 such indispensable elements as calcium, iron, magnesium, phos- 

 phorus tend to precipitate. Nutrient solutions of a suitable pH 

 therefore are soon exhausted. In nature substances from the mud- 

 phase replenish nutrients taken up from the water by organisms, 

 and organic compounds keep indispensable chemical elements, 

 especially iron and manganese, in solution. This takes place also 

 in soil-water cultures where the mud-phase serves as an accumu- 



