MICHIGAN ACADEMY OF SCIENCE. 
39 
dimension represents crop yield. A. represents the theoretical critical 
temperature. The curve of yield which may be a straight line to the 
left of the critical temperature becomes a rapidly ascending curve 
beyond the point A. If B. the mean temperature of the soils stand 
fairly close to the critical temperature it may be possible by proper 
methods of soil management to raise the mean temperature beyond the 
critical point. The benefits are represented by the rapidly ascending 
curve. There are numerous means at hand by which the farmer nf.^v 
materially improve the temperature of his soil. 
If there be such a critical temperature it may be that this critical 
temperature will prove an average mean. If however, it should prove 
to be a mean of maximum temperatures the question becomes a more 
important one. It is barely possible this critical temperature may prove 
to be the extreme maximum, that is the highest temperature that is 
reached at any time. Then the question becomes even more important 
yet. 
If there be such a critical temperature it makes little difference 
whether it be a direct cause or whether it be an indirect cause acting 
through one to a dozen phenomena. 
Michigan Agricultural College, East Lansing, Mich., April, 1911. 
