16 PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



visible in them. a A very striking feature was the long-continued 

 persistence of turgor under these conditions, this being due to the 

 cytoplasm remaining alive for a considerable time. In equally diluted 

 solutions of tartaric acid most of the cells were perfectly normal after 

 nine days, which shows that the character of acidity at this high dilu- 

 tion exerted merely a secondary iniluence and that this alone can not 

 account for the action of the highly diluted oxalic acid. 



FORMATION OF LIME INCRUSTATIONS. 



It may not be out of place here to say a few words about the forma- 

 tion of incrustations of calcium carbonate on certain aquatic plants, 

 especially Chara — a phenomenon which PringsheimHries to explain on 

 the hypothesis that by assimilation of the dissolved carbonic acid the 

 neutral calcium carbonate is produced from the bicarbonate. However, 

 the fact that not every plant growing in the same water and near 

 Chara shows the incrustation must lead to the assumption that either 

 the assimilation is of much greater energy in Chara than in many other 

 plants, or that the surface of this plant is especially adapted for the 

 absorption of the neutral calcium carbonate. 



Hassack ( ' advanced another hypothesis, that is, that the plants 

 secrete an alkaline carbonate, which decomposes the calcium bicarbon- 

 ate. This view, however, the writer has proved to be entirely erro- 

 neous/ 7 The reaction with phenol -phthalein, which Hassack used, 

 is not due to an alkaline carbonate, but to neutral calcium carbonate 

 in a colloidal condition. Even the warming of ordinary water rich in 

 calcium carbonate will produce ephemerally a red color with phenol- 

 phthalein. e 



CAN CALCIUM IN PLANT CELLS BE REPLACED BY STRONTIUM? 



It has long been recognized that calcium salts can not be replaced 

 by potassium or sodium salts. Were it a well-founded hypothesis that 

 calcium salts serve only for certain phases of metabolism and arc not 

 connected with more important properties of the protoplasm itself, 

 then there might be taken a plain chemical view of the matter, that is, 

 that the action of the bivalent elements is often different from that of. 

 the monovalent elements. Thus, for example, dextrose yields sac- 

 charin^' when treated with lime, but not when treated with potash 



a Considerable swelling of the nucleus took place in a solution of 0.01 per cent 

 oxalic acid. 



''Jahrb. f. Wiss. Bot., Vol. XIX, p. 138. 



'•Unters. aus d. Bot, Instil, Tubingen, Vol. II, pp. 469-475. 



''Flora, 1893, No. 4. 



'Possibly the alga produces acids which form insoluble compounds with lime, and 

 hence the absorbed lime accumulates. By gradual oxidation of such salts calcium 

 carbonate is produced and is then excreted. 



/This product is not the sweet saccharin of commerce- 



