716 BIOLOGICAL EFFECTS OF RADIATION 



garden plants growing in northwestern Canada near the mouth of the 

 Mackenzie River to a point 80 miles north of the Arctic circle. The 

 mean July temperature in this region varies from 56.6°F. at Aklavik 

 to 59°F. at Fort McPherson, This compares with a similar mean of 

 68.8°F. at Ottawa, Canada, and according to the New York Observatory- 

 records, a mean for New York City for 64 years of 75°F. Twelve to 

 24 in. below the surface the soil remains permanently frozen. Yet on 

 account of the long days of sunlight many plants grow very rapidly and 

 manage to mature in the short growing season. Crops such as the potato, 

 favored by comparatively low temperatures and long days thrive espe- 

 cially well in this region. Albright records a single tuber grown at Fort 

 Good Hope in 1927 which weighed 17 ounces. Higgins (14) of the 

 Motanuska Alaska Station reports potato yields on well-fertilized land 

 ranging up to 412 bushels per acre depending upon the variety grown. 

 Other garden plants, such as beets, turnips, peas, and cabbage, grow 

 remarkably well there. 



Darrow (8) has recently called attention to the records of the rapid 

 growth of tomatoes and berries in Alaska. Albright (1, 2) has presented 

 numerous instances of grains and other crop plants developing at an 

 ever-increasing rate when the height growth at a southern station is 

 compared on the same day with that at a station farther north. Evans 

 (9) found that timothy plants propagated vegetatively from the same 

 plant and grown at various stations from Savannah, Georgia, to Fair- 

 banks, Alaska, reached the flowering stage at a constantly accelerated 

 rate from southern to northern stations. A late variety in 1929 flowered 

 at Jackson, Tennessee, on July 5, at Beaverlodge, Alberta, Canada, 

 July 10, and at Sitka, Alaska, August 2nd. Local temperature and soil 

 conditions affect the time of maturity of plants at such widely separated 

 points of observation. In addition the temperature is lower in the early 

 spring and late summer in the north. Even in July, the month when all 

 temperatures at the various stations should be most nearly alike, northern 

 stations have the disadvantage of a slightly lower temperature as com- 

 pared with those farther south. Yet because of the longer days in the 

 north, plants reach maturity at about the same time, or at most only a 

 few weeks later than similar varieties growing in the south. Probably 

 a much more accurate test of the effects of continuous sunlight could be 

 obtained by growing the same varieties of plants in greenhouses at each 

 station where temperature and soil factors could be more carefully con- 

 trolled. Then only the one main factor, sunlight, would need to be 

 considered in studying the growth rate produced. To date greenhouse 

 facilities in the far north have not been available for such a comprehensive 

 series of experiments so that this study must be left for the future. It 

 should be pointed out, however, that the studies already cited indicate 

 clearly that plants develop much more rapidly on long days; the longer 



