376 



ing this end. It is always best to close the vessel used in such experiments 

 to prevent the entrance of Algse not at the depth at which it is desired to 

 take the samples or to keep some in the bottle from being lost in raising 

 the bottle to the surface. In this way it is easily possible to obtain speci- 

 mens that are floating from any part of the body of water. By this method, 

 too, it was shown that numerous forms of Algae were distributed all through 

 this body of water. The living ones were found in greater abundance at 

 or near the surface, as would be expected, but they were also found in the 

 deeper water as well. In some places the number of forms was often very 

 small, but in order to make a study of the greater number from such a 

 locality the following method was used : A suitable quantity of water 

 was obtained in the above described way from the desired location, and 

 this allowed to filter through a small surface. A funnel, the lower end of 

 whose tube was closed with closely woven cloth, served quite well, and in 

 this way enough forms would be obtained for a convenient study. Such 

 concentration of forms, we may term it. also brings about a great saving 

 of time in looking for forms that would otherwise be found only after much 

 searching, and at the same time was more representative for any given 

 depth. 



The effectiveness with which various of the Algre forms could be re- 

 moved by means of sand was attempted. This will vary with the kind 

 of sand employed. The kind of sand here employed was very fine, white 

 sand, especially employed for the microscopic examination of water. The 

 following are some of the results : 



Twenty-five ccm. of water from the bottom of the reservoir, in five 

 cm. of this sand, required seven minutes to filter. 



One thousand ccm. of water from the surface of the reservoir required 

 forty-three minutes to filter, through a closely woven cloth tied over the 

 end of a very small glass tube. A considerable depth of very fine, clear 

 sand is necessary to entirely remove all of the smaller Algre forms from 

 the water, for I found after only twenty-five ccm. of the water from this 

 reservoir had been filtered through five ccm. of fine sand, a considerable 

 number of some forms came through. In one instance, in tap water, com- 

 ing from this same source, some small forms came through four cm. of this 

 fine, white sand, which to filter twenty ccm. it required one hour and twen- 

 ty-five minutes. 



In another case only eighty-five minutes was required to filter twenty- 

 five ccm. of this water through four cm. of sand, due in this case to the less 



