THE NATURAL HISTORY OF MARL 503 



Studies were undertaken to determine the method of concen- 

 tration and precipitation of the calcium carbonate by Chara. 



As has already been indicated elsewhere, the calcium car- 

 bonate is present on the outside of the plant as an incrustation, 

 and this is made up of crystals, which are rather remote and 

 scattered on the growing parts of the plants, and form a com- 

 plete covering on the older parts, which is uniformly thicker on 

 the basal joints of the stems than it is on the upper ones. Con- 

 sidering the hypothesis that the deposition of the salt was the 

 result of purely external chemical action as not fully capable of 

 satisfying all the existing conditions, the formation of the 

 incrustation was taken up as a biological problem, and an inves- 

 tigation was made upon the cell contents of Chara, first, micro- 

 scopically by the study of thin sections. Various parts of the 

 plant were sectioned while still living, and the attempt was 

 made to find out if the calcium carbonate was present as a part 

 of the cell contents in recognizable crystalline form. Various 

 parts of the plant were examined, but no crystals undoubtedly in 

 place among the contents of the cells were observed, although 

 numbers were to be seen on outside walls of all cells. 



Next an attempt was made to determine the presence of the 

 calcium in soluble form in the cell contents, by the use of dilute 

 neutral solution of ammonium oxalate. An immediate response 

 to the test was received by the formation of large numbers of 

 minute, characteristic, octahedral crystals of calcium oxalate 

 on the surface and imbedded in the contracted protoplasmic 

 contents of the cell. The number of these crystals was so 

 large, and they were so evenly distributed through the cell con- 

 tents, that it was evident that a large amount of some soluble 

 calcium salt was diffused through the cell sap of the plant. 

 The next step was to isolate this compound and to deter- 

 mine its composition. A considerable quantity of the growing 

 tips of Chara were rubbed up in a mortar and the pulp was 

 thoroughly extracted with distilled water. This water extract was 

 filtered and tested to determine the presence of calcium and an 

 abundant precipitate obtained by using ammonium oxalate, 



