1903.] with especial Reference to its Nitrogenous Metabolism. 461 



stimulated, and this is particularly rapid when grown upon nutrient 

 agar or gelatine to which glucose has been added. The liquid medium 

 par excellence for studying this organism, is sterilised sewage, in which 

 it preserves its normal form and characteristics. In solution A, it also 

 grows well, while if to the liquid a small quantity of glucose is added, 

 the growth is much stimulated, and the individuals assume the appear- 

 ance, described below, characteristic of growth in glucose media. 



Accompanying the much more abundant development, the nitrogen 

 assimilation is also increased, as will be seen later. 



Glucose-containing media (fig. 4). When grown upon media containing 

 glucose, while the general growth is much improved, and the individual 

 cells are also larger in size upon the whole, the green colour of 

 the cell-contents is much paler, and sometimes almost disappears, 

 while the chromatophore is much disorganised. The contents of the 

 cell appear to be segregated into a variable number of slightly 

 refractile bodies, usually pale greenish-yellow in colour, which are 

 apparently free in the cell. If when mounted in water under the 

 microscope, a slight pressure is applied .to the coverslip, the cell 

 envelope is easily ruptured, and these bodies are liberated, and float 

 'freely in the surrounding liquid. The protoplasm also, in the case of 

 glucose cultures, shows small granules, and the pyrenoid is no longer 

 to be traced, but a certain amount of staining with iodine may be 

 noticed in the granular protoplasm. These changes closely resemble 

 those noticed respectively by Krliger* in the case of his Clilorotliecium 

 saccharophilum and Chlorella protothecoicles, and by Matruchot and 

 Molliardf in the case of SUchococcus bacillaris, when these algse were 

 grown upon glucose containing media. 



The results of growing C. pyrenoiclosa upon media containing lactose 

 or saccharose also resembled those of the above authors. These two 

 sugars appear to possess a far lower nutritive value than does glucose, 

 Avhile the algal cells preserve their normal appearance. When grown 

 upon ammonium agar, the growth is comparatively slow, the 

 individuals appear larger in size than when grown upon ordinary 

 nutrient agar, their green is darker and the cell-contents are of the 

 normal type. 



Quantitative Chemical Experiments. 



The evident preference of this organism for ammoniacal culture 

 solutions seemed to be a reason for studying its nitrogen assimilation. 

 The absorption of ammonia by algse is not a new discovery ; it is well 

 known, from the researches of Letts and Hawthorne, t that Ulva latissima 



* Zopf's ' Beitrage z. Morph. u. Phys. Nied. Org.,' Leipzig, toI. 4, 1894, p. 91. 

 f < Bev. Gen. de Bot.,' vol. 13, 1902. 



X Letts and Hawthorne, ' Boy. Soc. Proc, Edin.,' 1901, p. 268 ; Letts, " Beport 

 on the Scheme of Sewage Purification proposed for Belfast, and its Probable 

 Effects on the Lough." 



VOL. LXXI. 2 L 



