Climate of Middle Illinois. 



21 



It may be doubted whether it be advisable to include the tempera- 

 tures of January. 



In continuously cold winters a temperature rising only a few day a 

 few degrees above freezing point, may be inactive; but we have, not 

 rarely, quite warm winter months in which the buds of the trees consid- 

 erably swell, and, when cold weather follows, rest stationary for a time. 



The time of blooming of a number of woody plants were noted, 

 amongst which Amelanchier canadensis. From seventeen years an aver- 

 age sum of heat of 450 degrees (centigrade) was found from the 1st of 

 January to the day of blooming, which is in average the 21st of April. 

 In this period of one hundred and eleven days the temperature rises on 

 seventy-eight days above freezing point. The earliest time of blooming 

 was observed in 1871, on the 4th of April, with a sum of 414 degrees; 

 the latest in 1857, on the 8th of May, with a sum of 496 degrees. The 

 difference of 82 degrees may be accounted for, when we consider that the 

 heat is not the only agent. The time of blooming may partly depend on 

 the moisture in the ground, the dryness of the atmosphere, and, before all, 

 on the quantity of light and direct insolation. 



The above figures indicate not the absolute, but the relative value of 

 heat, i. e,: When the sum of daily means above freezing point reaches 450 

 degrees in the shade, then the Amelanchier is in flower, or is in flower since 

 several days, when we had much sunshine and the air is dry, or will be 

 in flower in a few days, when we had less sunshine and the air is moist. 



Of fifteen other species, the necessary heat and the time of blooming 

 was calculated. 



MEANTIME OF 

 BLOOMING. 



SUM OF HEAT 



IN 



CENTIGRADE 



DEGREES. 



NUMBER OF 

 OBSERVA- 

 TIONS. 



Acer dasycarpum . . . 

 Ulmus americana . . 

 Negundo aceroides . 

 Acer saccharinum . . 

 Prunus americana . . 

 Cercis canadensis . . . 



Aesculus glabra 



Pyrus coronaria .... 



Morus rubra 



Prunus virginiana.. 



Asimina triloba 



Prunus serotina .... 

 Robinia pseudacacia 



Catalpa speciosa 



Tilia americana 



March 27th. 

 March 31st. 



April 21st. 



April 28th. 



April 29th, 



May 3d. 



May 6th. 



May 11th. 



May 13th. 



May 13th. 



May 15th. 



May 22d. 



May 23d. 



June 7th. 



June 26th. 



210 

 230 

 440 

 530 

 550 

 600 

 650 

 740 

 760 

 770 

 800 

 920 

 940 

 1270 

 1700 



11 



13 

 7 



12 

 6 



12 



15 

 5 

 5 

 7 

 7 

 5 



15 

 6 



11 



That the temperature of December is not of great influence, as one 

 might suppose, shows the December, 1877, with a sum of 225 degrees 

 above freezing point. The American Elm was in bloom on the 8th of 

 March, 1878, with a sum of 235 starting from the 1st of January, and the 

 same on the 10th April, 1866, with a sum of 240. The December, 1865, 



