GEOGRAPHY OF PLANTS. 507 



The above resulting aggregates of heat, derived from the very meagre data 

 our extensive research has brought to light, do not entirely agree with the 

 amount which appears to be required for maturing the crop in Britain. For 

 "W'csteru New Yoi':, where the climate is more moist and cooler than that of 

 New Jerse}^ or Virginia, the aggregate accords very well ; but, in the dry dis- 

 tricts of the south, the early varieties of "Japan wheat" and "Mediterranean" 

 appear to demand smaller aggregates of heat, as we would reasonably expect 

 they would require from their quality of early ripening. 



In England the periods of growth varied from sixty-nine days in 1860, when, 

 for ten days, the thermometer did not rise above 5S^ Fahrenheit, and fifty -nine 

 days were thus required at an average daily mean of 61 1° and. an aggregate 

 of 3,629^ were received, to fifty days in 1861, when an average was noted of 

 64i°, and an aggregate of 3,225^ were required to ripen the grain. Again, in 

 1862 fifty-six days, at a mean of 61°, and an aggregate 3,406°, were required to 

 produce the game result. As the wheat in Enghind did not head until the 12th 

 of June, and this process commences here from the 1st to the middle of May, 

 and later, the time as observed in Monroe county, New York, though it nearly 

 corresponds to that of Britain, ripens the crop about one month earlier. The 

 differences observed in the above results may be ascribed to different degrees 

 of cloudiness, which, Avhile it affects the dkect heat of the sun, cannot be indi- 

 cated by the thermometer with precision. 



The foregoing observations indicate that, during the period that the wheat 

 plant is passing from the bloom to the ripe fruit, the temperature must be above 

 60°, or that spring and winter wheat should be sown at such a time that they can 

 take advantage of this mean for the heading process, which commences in the 

 northern States generally about fifty to fifty-five days before maturity. 



To the English wheat-grower the most important researches of the English 

 experimenter are those which respect the temperature of the soil at the time of 

 sowing in autumn. As the temperature of the soil does not differ perceptibly 

 from that of the mean temperature of the air for a series of days, observations 

 on the soil may be dispensed with. The results of om- own experiments indi- 

 cate that such is the case for short terms. The observer considers it unsafe to 

 sow autumn wheat until the temperature of the earth has been reduced to 50°, 

 a mean temperature which is seldom reached in the United States in latitude 

 40° north until the second or third week of October, or until a frost has occuiTed. 

 His reasons for the opinion are founded on the experience that the best crops 

 of wheat have been grown from seed that remained in the ground upwards of 

 thirty days, which term was required in order to enable the seed to root properly 

 before sprouting luxuriantly, and employing its strength in forming leaves at 

 the expense of the roots. The foregoing observations on the proper time for 

 sowing wheat, we apprehend, are not immediately applicable to our climate, but 

 we have presented them in the hope that they may induce corrcspouding ob- 

 gervatious on our own soil and crops, which possibly may enable us to select 

 the proper time for committing the seed to the ground with the best promise of 

 success. 



THE RANGE OF THE WHEAT PLANT. 



Meyen, in his Geography of Plants, asserts that wheat requires a mean 

 annual heat of 39° Fahrenheit, a summer heat of 56° Fahrenheit, and that 

 much inferior mean heats suffice in the extreme climates of sub-arctic America, 

 provided the summer heat of one hundred to one hundred and twenty days be 

 enough. 



At Sitka, in Russian North America, latitude 57°, the mean of 39.7° for the 

 year has been observed, and a summer mean of 51.5°, yet wheat will not ripen, 



