SOIL ALGAE 219 



Beijerinck 10 was the first to isolate algae in pure culture, using a 

 medium consisting of ditch water, to which 10 per cent gelatin had 

 been added. The liquid media given above are well suitable for the 

 cultivation of algae. An alkaline reaction is most favorable, since algae 

 are usually injured in acid media. 



The agar plate method for the isolation of pure cultures of algae 

 has been successfully employed. 11,12 The broken-up mass of algal 

 material can be streaked out several times upon the surface of a 

 solidified agar plate, so that each streak carries less of the inoculum 

 than the preceding one. The inoculum may also be placed in a tube 

 of melted and cooled agar; then a series of successive transfers are made 

 into other tubes, so as to obtain a series of dilutions. These agar 

 tubes inoculated with successively decreasing portions of material 

 are poured into sterile Petri dishes. The streak method allows the 

 development of surface colonies and the tube method of deep colonies. 

 The plates are then exposed to light, so as to stimulate the development 

 of the algae and to prevent the growth of other organisms. When the 

 colonies have developed sufficiently they are transferred into liquid 

 media. Algae are usually provided with a more or less highly dev- 

 veloped exterior mucilaginous investment, either in the form of a 

 sheath or of a mere gelatinization. They also develop much more 

 slowly than fungi. Both of these factors contribute to the difficulties 

 encountered in pure culture work with algae. 13 When the life-history 

 of the organism is known, the best period for obtaining it free from 

 bacteria can be readily determined. 



Schramm 13 used, for the isolation of algae, the medium recommended by Moore 

 with the addition of 10 gm. of agar. The latter is carefully washed first in tap 

 water, then in distilled water, 14 so that the medium can be cooled down to about 



10 Beijerinck, M. W. Kulturversuche mit Zoochlorellen, Lichengonidien, und 

 anderen niederen Algen. Bot. Ztg. 48: 725-785. 1890; Also Centrbl. Bakt., 

 13: 368-373. 1893. 



11 Tischutkin, N. Ueber Agar-Agarkulturen einiger Algen und Amoben. 

 Centrbl. Bakt. II, 3: 183-188. 1897. 



12 Ward, H. M. Some methods for use in the culture of algae. Ann. Bot. 

 13: 563-566. 1899. 



13 Schramm, J. R. Some pure culture methods in the algae. Ann. Mo. Bot. 

 Gard. 1: 23-45. 1914. 



14 Richter, O. Reinkulturen von Diatomeen. Ber. deut. bot. Gesell. 21 : 

 493-506. 1903; Die Ernahrung der Algen. Monograph. Abhandl. Int. Rev. 

 Hydrobiol. Hydrogr. 2: 31. 1911. 



