Tilden: pilinia and stigeoclonium. 605 



Pilinia thalli were taken from the bottom of the spring with a 

 long handled rake. 



Miss Levy informs me that at the present time the spring is 

 surrounded by a walk of crushed limestone and the stone ex- 

 tends down into the basin a foot or more. There are now no 

 rocks around the edge and but few in the basin. 



Many similar springs occur in the vicinity, one as large and 

 others much smaller. The Pilinia occurred on pebbles found 

 in some of these. As far as I can judge it only grows in quiet 

 water, and in no instance was it discovered on wood. 



Microscopic Structure of Plant: — The first installment of 

 pebbles was received from Miss Levy on January 24th, 1896. 

 They had been taken from the bed of the spring three days 

 previous and packed in damp cotton together with some of the 

 Chara found growing in the spring. Upon being placed in 

 water they were seen to be covered on the top and sides with 

 a slippery coating of algae, apparently healthy in color — a 

 peculiar dark, lustrous, velvety green. The pebbles were 

 pronounced by Mr. Elftman of the geological department of 

 the University of Minnesota, to be a silicious dolomite. 



The thalli of the algae consisted of circular, flat masses, 

 from 1 to 1.5 mm in diameter and were solitary, or confluent, 

 or piled upon each other. On the top and more exposed parts of 

 pebble "1" (PI. XXXI, Fig. 1) the algal layer was of the green 

 color described above and was mucilaginous to the touch. On 

 the sheltered surface however, the thalli were of a bluish- 

 gray color, decidedly calcareous in aspect and when rubbed 

 with the finger felt "sandy". The thalli were so numerous 

 that they formed an almost continuous stratum. This pebble 

 was placed in a glass tank, frequently replenished with fresh 

 water, but the plant survived only a few days. At the end of 

 three days the coating had changed to an olive-green color. 

 On pebble "2" as can be readily observed in the photograph 

 (PI. XXXI, Fig. 2), the discs are solitary and scattered. This 

 was allowed to dry. while yet in good condition, for herbarium 

 material. 



An attempt to procure a second supply of Pilinia, brought 

 only Oscillatoria material. The pebbles were collected from 

 the northwest corner of the spring where the outflow caused a 

 current. 



On April 3rd, Miss Levy again collected and sent material. 

 Two pebbles, "3" and "4", procured from the bottom of the 

 main spring and four pebbles and a couple of bits of glass 



