On the Effects of Heat and Moisture on Vegetation. 433 



alluded to. He will also find many of the successful modes 

 of operation satisfactorily accounted for, which, I may observe, 

 untutored sagacity had stumbled on, and which experience 

 has sanctioned. 



That heat is a prime agent in forwarding, and bringing to 

 maturity the vegetable productions of the soil is well under- 

 stood ; but the degree of heat requisite to bring certain 

 plants into flower, or to mature their fruits or seeds in the 

 open air, and in a given time, or the effect which a greater 

 or less supply of moisture at different periods has in acce- 

 lerating or retarding the progress of vegetation, has not yet, 

 so far as I know, been ascertained ; nor am I aware that any 

 observations have hitherto been made, at all calculated to 

 elucidate an enquiry so generally interesting. 



The observations which I have made and noted during 

 the last three seasons at this place, which is situated in the 

 Carse of Gowrie, enable me to point out some facts indicating 

 the combined influence of heat and moisture, on the progress 

 of vegetation, which may be deemed worthy of notice, and 

 may induce the institution of similar observations in other 

 parts of Great Britain. 



The vegetating season, according to Professor Playfair, 

 in his remarks on Temperature and Vegetation, inserted in 

 the Transactions of the Royal Society of Edinburgh for 

 1800, commences about the 20th of March, and ends about 

 the 20th of October : I suppose he means in the vicinity of 

 Edinburgh. He divides that period into twenty-one decades, 

 and gives the mean temperature of each. He assumes 40° 

 as the lowest temperature, at which corn will vegetate, and 

 56° as the mean temperature of a good vegetating season. 



