NA TUBAL HISTORY OF MARL 49 1 



into account before we finally abandon plants as the agents of 

 precipitation. Of these, two groups, differing widely in structure, 

 habits, and method of precipitation, will be found. The first and 

 most conspicuous, and probably the most important as well, is 

 the Characeae or Stoneworts. These plants are well known to 

 botanists, and may readily be recognized by their jointed stems, 

 which have at each joint a whorl of radiating branches, which 

 are also jointed. In some species the stems and branches are 

 covered with a thick coating of mineral matter, are almost white, 

 and very brittle because of this covering. These plants not only 

 grow near the surface in shallow water, where it is unoccupied 

 by other plants, but in the deeper parts as well of our ponds 

 and lakes, and, as they thrive where light is feeble, they 

 continue to grow throughout the year, although in winter 

 they must grow less rapidly than in summer, because ice and 

 snow on the surface of the lakes make less favorable light 

 conditions. 



The sufficiency of these plants alone to fix and deposit cal- 

 cium carbonate in large quantities is indicated by the following: 

 In November 1899 the writer collected a large mass of plants of 

 Chara sp ?, from which five stems with a few branches were 

 taken at random and without any particular care being taken to 

 prevent the brittle branches from breaking off. The stems were 

 each about 6o cm long, and after being dried for some days they 

 were roughly ground in a mortar and dried for one half hour at 

 ioo° C, dried and weighed until the weight was constant. The 

 weight of the total solid matter obtained in this way from five 

 plants was 3.6504 grams, 0.73 grams per plant. This was 

 treated with cold hydrochloric acid diluted, twenty parts of water 

 to one of acid, filtered, washed, and the residue dried at ioo° 

 C, on a weighed filter paper, until weight was constant. The 

 weight of insoluble matter was 0.5986 grams; of the total 

 soluble matter 3.0518 grams, or .6103 grams per plant. In the 

 lake from which the material analyzed was derived from 50 to 80 

 plants were counted to the square decimeter of surface in the 

 Chara beds. 



