SOIL ALGAE 233 



came to the conclusion that Chlamydomonas pisiformis Dill, forma 

 minor Spargo, Protosiphon botryoides (Kiitz) Klebs, Chlorococcum humi- 

 cola (Nageli) Rabenh., Chlorella vulgaris Beij., Stichococcus bacillaris 

 Nag., Chlorella sp. and Kirchneriella sp. are unable to fix free atmos- 

 pheric nitrogen in the complete absence of combined nitrogen. Wann, 53 

 however, working in Schramm's laboratory claims to have found that 

 seven species of algae exhibited the ability to fix atmospheric nitrogen, 

 when grown in pure cultures on mineral nutrient agar media containing 

 either ammonium nitrate or calcium nitrate, as a source of nitrogen, and 

 a small amount of glucose. A gain of 1 to 12.5 mgm. of nitrogen per 

 flask was obtained. In the absence of glucose, growth and nitrogen- 

 fixation were only slight. When urea, glycocoll, asparagine or am- 

 monium sulfate was supplied as a source of nitrogen, either with or with- 

 out glucose or mannite, no fixation took place; one species caused a loss 

 of nitrogen. Positive nitrogen-fixation by algae has also been claimed 

 recently by Moore and Webster. 54 The fact, however, that bacteria 

 were present in the cultures and that these were exposed to the air, from 

 which traces of ammonia could be absorbed, would tend to invalidate 

 these results. Bristol and Page, 55 in a series of carefully controlled 

 experiments, repeated Wann's work, using four different species of 

 algae, each growing on six different media selected from among those 

 used by Wann. They found no evidence to indicate any fixation of 

 atmospheric nitrogen. In the presence of combined nitrogen, good 

 growth was obtained, but only the original nitrogen was recovered 

 even where it had originally been present in the form of nitrate. Bris- 

 tol and Page pointed out a serious source of error in the chemical method 

 used by Wann for the determination of the initial nitrogen content of 

 media containing nitrates and suggested that his apparent fixation of 

 nitrogen was probably the outcome of a faulty chemical technic since 

 they completely failed to corroborate his results. They also suggested 

 that the results of Moore and co-workers was of doubtful validity, since 

 their cultures of algae were probably not free from bacteria. Bacteria 

 can develop in the gelatinous sheaths of algae and need, therefore, not 

 cause any turbidity of the medium. 



"Wann, 1921 (p. 221). 



64 Moore, B., and Webster, T. A. Studies of photosynthesis in fresh-water 

 algae. I. The fixation of both carbon and nitrogen from the atmosphere to 

 form organic tissue by the green plant cell. Proc. Roy. Soc. B. 91: 201-215. 

 1920; also 92: 51-60. 1921. 



56 Bristol, B. M., and Page, H. J. A critical inquiry into the alleged fixation 

 of nitrogen by green algae. Ann. Appl. Biol. 10: 378-408. 1923. 



