228 Thirty-fifth Annual Meeting 
pond, would be good policy—that is in a climate like Minnesota, 
letting the pond remain dry all winter? 
Mr. Clark: I am not prepared to state. 
Prof. Reighard: It is the practice to do that with the Ger- 
man carp ponds. Exposing the vegetation and the soil in the 
bottom of the pond to the air helps decay, and the freezing loos- 
ens up the soil more or less, so that altogether the method has a 
tendency to break down the more complicated chemical com- 
pounds in the plant material, and make them more available for 
plant growth the next year. I think Mr. Lydell has had a little 
experience in that line. 
Mr. Lydell: Our ponds were dry from about the first of Sep- 
tember until the latter part of November, and our plant life in 
there did not come on quite as early this season as it has in 
former years but it is just as abundant now as it is in the other 
ponds. 
While I am talking I would like to ask Dr. Birge or Prof. 
Reighard in regard to the introduction of foods in our ponds. I 
noticed that the ponds that were dry the longest last fall were 
the ponds that produced the most food this spring for fry and 
young fish, and I was greatly surprised because I supposed that 
the frost would kill everything, and did not expect anything at all 
from the ponds whereas I got the most food from them. If it is 
beneficial I will draw all my ponds dry this fall and leave them 
dry all winter if it will bring me more food. If it is beneficial 
to leave them dry during the winter to get daphnia and this food 
I should lke to know it. 
Dr. Birge: That is one of the things you have got to try a 
good many experiments on before you know what is best. But 
I should say that the exposure of the bottom of the pond to the 
air, and perhaps to freezing, loosened up the material and put it 
into a more soluble form, so that when the water came back on it 
along in the spring there was more rapid growth of the minute 
organisms on which these feed, and so they had a better chance to 
develop. It does not seem to me at all unnatural that that should 
be the case, but I think you want a good many comparisons. This 
