•2310 Journal of Applied Microscopy 



the importance of having absolutely pure culture, without any possibility of con- 

 tamination, cannot be over-estimated. The only excuse for publishing them at 

 this time, rather than in connection with the investigation with which they prop- 

 erly belong, is that the numerous requests for some artificial medium to be used 

 in growing algae makes it seem probable that a wider use of certain methods 

 may lead to more definite and satisfactory results in the study of these forms, 

 and that our knowledge of them may be rapidly and accurately increased. It 

 should be said at once that there is no one method or medium which is equally 

 well adapted to all algae. The slightest modification in concentration or ingre- 

 dient is often sufficient to preveat luxuriant growth, and the advantage of 

 special formulae for certain groups and genera becomes more and more evident 

 as one's experience increases. 



Beyerinck was perhaps the first who successfully attempted the growth of 

 algae in artificial media. His earlier method was to use sterilized ditch water 

 with 10 per cent, gelatine, a drop of water containing the algae to be studied be- 

 ing added just before the mixture hardened. The chief objection to this nutri- 

 ent solution, aside from its uncertainty and indefiniteness, is the great difficulty 

 of properly sterilizing the ditch water. Spores of certain blue green algae are 

 tremendously resistant to even boiling temperature, and the constancy with 

 which one gets a blue green culture after having inoculated with a grass green 

 organism is calculated to produce a certain degree of patience with the authors 

 of such articles as " Algae, the Spawn of Mosses," etc. A modification of the 

 ditch water method, wherein the gelatine has been previously liquified by pan- 

 creas, is supposed to induce more luxuriant growth, but it seems to possess no 

 particular advantage over the unmodified gelatine. 



Perhaps the best known artificial medium for growing algae is that devised 

 by Knop and frequently referred to in subsequent literature. The formula for 

 this, as generally given, is : 



4 parts calcium nitrate, 

 1 part magnesium sulphate, 

 1 part potassium nitrate, 

 1 part potassium phosphate. 



It is much better, however, to prepare 10 per cent, solutions of all these 

 salts, and obtain the desired dilutions before adding ihe calcium nitrate to the 

 other three. In this way the insoluble precipitate formed by the calcum phos- 

 phate will be reduced to a minimum. Solutions containing from .1 to .5 per 

 cent, of the magnesium and potassium salts, with four times as much calcium 

 nitrate, are suitable for the cultivation of algae, but higher concentrations may 

 be used with some forms. Unfortunately, this solution, which is comparatively 

 well known, is perhaps the least well adapted for growing many species, particu- 

 larly in connection with a solid medium. 



The source of nitrogen is naturally of considerable importance, it being par- 

 ticularly necessary in growing blue green algae, and calcium nitrate does not 

 seem to be the most suitable salt for this purpose. A much more satisfactory 

 solution, which is a modification of another of Beyerinck's, is : 



