the length of time (expressed as the number of tv;o-week periods^ 

 during which it was acting. The length of time during which 

 the average growth rate is active would be the length ':^f the 

 growing season, which, for soy-bean and most agricultural 

 plants, would be the length of the frostless season. 



The plant producing power of any station may thus be re- 

 garded as equal to the product of two factors, CLn intensity 

 factor and a duration factor, the first derived from the read- 

 ings of the standard olant and the|second the length of the 

 frostless season. A large value for either of both of these 

 factors at a given station would result in a high plant pro- 

 ducing power and a low value for either or both of them would re- 

 sult in a low plant producing power. 



The two-week seasonal averages for the nine exposed sta- 

 tions of the two growth measurements taken represented graphi- 

 cally in Plate XIII show that the plant producing power of the 

 climatic complex is about the same whether it is measured by 

 stem height ot leaf-product. The range of variation for the 

 former measure/pent is from 76 for Monrovia to 125 for ■Baltimore, 

 In terms of stem height thus the average intensity of the 

 Monrovia climatic complex is 61 per cent of that of the 

 Baltimo e complex. Similarly, leaf-product varies from a 

 minimum of 77 at Oakland to a maximtim of 119 for Baltimore. 

 As measured by leaf-prodiict therefore, the Oal<land climate is 

 65 per cent as efficient as the Baltimore climate. If we in- 

 troduce the duration factor, however, the plant producing 

 power of Oakland will be still further reduced since the grow- 

 ing season at this station ts short, including only 9 two-v/eek 

 periods as compared to the lengths of the growing season at 



