THE PRESERVATION OF CHLOROPHYCEAE 



227 



ing a more or less transparent 3'ellowish tinge. The mixture does 

 not color the cytoplasm, but the nucleus is frequently tinged a 

 faint ydlow brown. This slight staining of the nucleus is not 

 marked enough to be a disadvantage; on the other hand it brings 

 out more strongly an organ of the cell that is usually difficult to 

 see. The pyrenoids, as a rule, are rendered less refractive by the 

 action of the mixture, so that they do not stand out as well as in 

 the living material. However, they are not so far obliterated 

 as to render them difficult of observation. There is not as great 

 a difference as would be expected between the action of a 2 % 

 and that of a 20 % concentration of the mixture. The retention 

 of the color in the mixtures below a concentration of 5 % is not as 

 good as in concentrations of from 5 % to 20 %. In the 2 % and 

 the 4 % solutions there was a tendencj^ towards a blackening of 

 the colorless cytoplasm and an olive coloration of the chromato- 

 phores. The best results were obtained in a concentration of 

 from 10 % to 20 %. The doubling or the tripling of the amount 

 of the copper salts, leaving the other constituents unchanged, 

 gave unfavorable results. The use of the double or the triple 

 copper-lacto-phenol (mixtures no. 27 and no. 28) frequently caused 

 the chromatophores to change their color to olive or brown, while 

 the amount of plasmolysis was also increased. 



The nature of the mixture obtained, when the different constitu- 

 ents of the copper-lacto-phenol are added to one another, is hard 

 to determine. The point at which plasmolysis occurs with each 

 of the individual components of the mixture was determined in 

 the case of Spirogyra. The concentration of the mixture causing 

 plasmolysis was also determined and found to be somewhat greater 

 than the concentration obtained by computation from plasmo- 

 lytic data with the individual components. This may be due to an 

 antagonistic action between different substances in the mixture 

 similar to that which exists between calcium and sodium as has 

 been shown by Osterhout.* This difference is not marked 

 enough to justify one in calling the copper-lacto-phenol mixture 

 a ''balanced solution." 



' Osterhout, W. J. V. On tho importance of physiologically balanced solutions 

 for plants. II. Fresh water and terrestrial plants. Bot. Gaz. 44: 259-272, 1907. 



