424 ANNUAL EEPORT. 



It is consequently of the first importance that we should ascer- 

 tain whether or not, we are within the zone or limits to which the 

 cultivation of these fruits is confined. 



That we are in the zone of the fruits named, facts, I think, dem- 

 onstrate. Our failures have been doubtless owing to want of expe- 

 rience in cultivation, to Avant of proper adaptation, and to lack of 

 knowledge in selecting varieties. 



The essential conditions of temperature to insure success, are a 

 sufficiency of heat in the growing season to ripen the fruit and of 

 subsequent cold to force hibernation — or compel the tree to stop 

 growing without killing it. Our summer heat is sufficient; our 

 winter cold too intense, for most of the varieties we have tried. 



I venture the proposition that in any climate where the summer 

 heat is sufficient to ripen the fruit of any given kind, that there 

 are varieties of trees of such fruit, or new varieties may he originated^ 

 which will withstand the winters and seasonal extremes of temper- 

 ature in such climate. 



The fruits named have been carried by civilized man in his 

 migrations from milder climates northward. The change in the 

 constitution of the tree has been gradual. Naturalization from 

 mild to much colder regions has been accomplished by the production 

 of neiv varieties, the essential characteristics of which have been 

 earlier ripening of the fruit, and greater hardiness of the tree to 

 enable it to endure severer cold or greater differences of seasonal 

 temperatures. 



It is a mistake to suppose that trees adapted to a southern cli- 

 mate and requiring a long growing season, can ever be acclimated 

 to one raucli shorter. 



As a general rule applicable to our continent, every additional 

 degrcd northward shortens the growing season about four days. 

 Our season at St. Paul is therefore twenty days shorter than that 

 of Philadelphia. 



Some varieties of fruit which ripen at Philadelphia must fail here 

 in consequence of our shorter growing season. 



But length of growing season is not the only condition — every 

 variet}' of vegetation requires for its maturity of leaf or fruit a cer- 

 tain sum of heat. Wheat, for example, requires, according to the 

 observations of Boussingault, from 2,000 to 2,200 degrees of heat, 

 centigrade, which, with a mean temperature of 20 degrees centi- 

 grade, would require from 100 to 110 days to ripen. 



But, in ascertaining the requisite quantity for plants growing 

 exposed to the sun, the thermometer consulted should also be 



