224 Brown : Algal periodicity 



September the work was again taken up, additional ponds and 

 streams added to the number under observation, and continued 

 until August, 1907. Collections were made twice a month, material 

 being taken from several different parts of each pond or stream, 

 both on the surface and on the bottom, placed in separate vials, and 

 brought to the laboratory for identification. This was done to 

 avoid error so far as possible in determining the amount of any 

 particular alga present. In nearly every case when an alga was 

 found in any quantity in one part of a pond, it was found in other 

 parts also. 



It was thought best to select a limited number of ponds and 

 streams and study these closely. The ones chosen were selected 

 on account of the variety of conditions they presented and the 

 ease with which they might be reached. Five different ponds and 

 two small streams were under observation. The ponds will be des- 

 ignated as ponds nos. 1, 2, 3, 4, and 5, and the streams as streams 

 nos. 1 and 2. 



Pond no. 1 is a small body of water in an old sink-hole de- 

 pression, the bottom of which has become clogged and partly filled 

 with soil. It is about 40 feet across and 4 feet deep during the 

 greater part of the year. During August and September the water 

 becomes low, leaving the bottom bare in places. The pond is fed 

 mainly by underground water flowing through openings in the lime- 

 stone, which is near the surface in this region. The depth of the 

 water varies with the season but is not much affected by a single 

 rain. A small amount of surface water flows into it, carrying in 

 some red clay from the surrounding plowed field. The water must 

 be changed frequently, for it never seems to be impure. The pond 

 is on a hill in an open field, so there is no shade. On November 

 io, there were .006 g. of solid matter in 54 g. of the water, or 

 .00011 per cent, of the water was solid matter. Typha, A/iswa, 

 Eleocharis, Potamogeton, and 'Callitriche grow in the pond rather 

 abundantly, but the animal life is not very extensive, consisting of 

 a few salamanders, frogs, tadpoles, dragon-fly larvae, and a few 

 smaller forms. 



nd 



Pond no. 2 is a small, shallow pond, about two feet deep a 

 50 feet wide, fed by a spring near by. This pond is not subject t 

 much variation in depth of water. The flow from the spring > s 



to 



