464 Miss H. Chick. On a Unicellular- Green Alga, [Feb. 28, 



means easy, for the quantities treated are exceedingly small, the 

 methods of analysis adopted demand a comparatively large margin of 

 experimental error, and the length of time, over which many of the 

 experiments must continue, is also a drawback. The sterilisation of 

 flasks and pipettes must also introduce a slight error where such small 

 quantities of ammonia are concerned. The estimation of the albuminoid 

 ammonia is frequently rendered troublesome by the tendency of the 

 liquid to bump while distilling. It has been found that this difficulty 

 is usually obviated if the ammonia-free water used for dilution is well 

 aerated, and if, from time to time, small quantities of fresh aerated, 

 ammonia-free water are added during the distillation. 



The absorption of ammonia, as this alga grows in ammonia-contain- 

 ing culture liquids, is well shown by the results of the analyses in 

 Tables I — VII. At the same time, the amount of albuminoid ammonia 

 present steadily increases, and, on the whole, a fairly even balauce 

 is maintained, which can be seen by comparing the quantities of total 

 nitrogen. 



The evident preference of Chlorella pyrenoidosa for its nitrogen as 

 ammonia, rather than in an oxidised form, is seen from Tables II, III, 

 IV. In Table III an impure culture of the alga was allowed to grow 

 alongside the pure culture, and it will be seen that similar changes 

 had been taking place in the former, although they were not so well 

 marked. In the case of the pure culture, nearly all the free ammonia 

 was absorbed in six weeks, a considerable amount of albuminoid 

 ammonia was produced, while the nitrates and nitrites appear to have 

 remained free from any attack on the part of the alga. In the case of 

 the impure culture less free ammonia was absorbed, less albuminoid 

 ammonia formed, and some of the oxidised nitrogen present in the 

 solution had been assimilated. 



The presence of a small proportion of glucose (0*25 per cent.) has a 

 very remarkable effect in stimulating the nitrogen assimilation of the 

 plant (see Tables VI and VII). In these two cases, cultures were 

 started in exactly similar solutions, except that to the one set the 

 above small amount of pure glucose was added. In this case 

 (Tables VI b and VII b), practically all the free ammonia was absorbed, 

 and largely converted into albuminoid ammonia in an extremely 

 short time, when compared with the cultures grown in the solutions 

 containing no sugar. The glucose cultures showed evidence of much 

 more growth, and the individual algal cells were also much paler in 

 colour. 



It appeared to be a point of interest whether this albuminoid 

 ammonia, so invariably formed in these cultures of Chlorella injrenoi- 

 dosa, corresponded to nitrogenous substances formed within the plant 

 cell and kept there, or whether such substances were formed, and then 



