120 BROOKLYN BOTANIC GARDEN MEMOIRS 



ing soil temperature, air temperature, humidity, number of hours of 

 sunshine, wind velocity, precipitation, evaporation, etc. 



The fundamental problem, however, presents itself after the analy- 

 sis has been made of the elements which enter into the compound 

 "weather." It is the experimental determination of the effect of 

 those elements, singly and collectively, as measured by the data 

 compiled, upon the physiological activities of the plant under con- 

 sideration. This effect can only be measured by means of accurately 

 conducted experiments in which very expensive apparatus is used. 

 One of our problems is so to outline the work and to set forth its 

 fundamental importance that those in authority will be moved to 

 purchase the ecological equipment without which these agricultural 

 and silvicultural problems cannot be studied. 



In the attempt to solve the problem above outlined some workers 

 have used a "plant instrument." A given kind of plant has been 

 grown by the side of atmometers, etc., at stations established under 

 different climatic conditions and an attempt has been made to interpret 

 their effect as registered by the "plant instruments." As an illustra- 

 tion of the attempt to interpret meteorological data in terms of plant 

 development let us take the work dealing with temperature. One 

 method contemplates the subtraction of a constant from the tempera- 

 tures recorded and considers that thermometric degrees in excess of 

 this constant are available for purposes of plant development. A 

 second method seeks to express growth-rate in terms of the velocities 

 of chemical reactions. A third — the physiological method — attempts 

 to take into account the optimum and maximum temperatures as 

 related to plant growth, and the attempt has been made to develop 

 one formula which will express the combined effect of rainfall, evapora- 

 tion and temperature on plant growth. This represents but little 

 more than an attempt to show what might be done if we had sufificient 

 experimental data on the reaction of plants to the complex conditions 

 known as the weather. 



Much of this work has been based on averages — averages for a 

 month, a year, or a number of years. We read that a large amount 

 of data assists in "smoothing out the curve" or that the "spas- 

 modically jerky graph may be smoothed." It is certainly true that 

 in some cases the curve should not be smoothed out, because it is the 

 spasmodic graph that shows sudden changes and the extremes. The 

 burden of this paper is to show that, in some cases at least, averages 

 for long periods are of little value as compared to the importance of 

 the data obtained for certain critical periods in the conditions of the 

 environment as shown by the "spasmodic graph." Data collected 

 for a short period in the summer may be very important, but are by 



