



BRIEFER ARTICLES 



RELATION OF FLAX TO VARYING AMOUNTS OF LIGHT 



Certain features of a plant's metabolism take place in sunlight or' 

 diffuse daylight, while other changes go on during the period of dark- 

 ness. In this connection the question arises, Is the amount of light 

 (measured in duration, but not in intensity) received by a plant at any 

 part of the earth's surface ever so prolonged as to serve as a check to the 

 plant's growth? In other words, if the duration of the periods of 

 darkness and light were approximately equal, would the plant make 

 as much growth as in those cases where the light period is greatly in 

 excess of the darkness period? In other words, does the prolonged 

 exposure of a plant to light in a more northern latitude compensate to 

 a considerable extent for the loss in temperature occasioned by distance 

 from the equator? As an instance of this difference, Fort Simpson in 

 latitude 6 2° N. has, between May 1 and August 31, 342 hours of daylight 

 in excess of that received at Ottawa in latitude 45 . 5 N. A similar condi- 

 tion as regards light holds good on the higher slopes of mountains. 



Pfeffer, in his Physiology of Plants (Engl, transl., 2: p. 98) writes 

 as follows: 



Plants are able to grow when continuously illuminated both in the polar 

 regions and under artificial conditions, but the future must show whether 

 all plants grow normally under light of constant intensity. For various 

 reasons the same total quantity of light will not produce the same physio- 

 logical effects when spread over the entire twenty-four hours, as when restricted 



* 



to twelve hours of the day, or an even shorter period. 







To determine the effect of shading plants during a short period each 

 day at the time of year when the sun is longest above the horizon, 

 certain experiments were made in 1916 at Ottawa, and repeated again 

 during 1918. Linum usitatissimum was chosen, for the reason that it 

 is shallow rooting, and has little tendency to branch when sown moder- 

 ately thick, both of which are important considerations when plants 

 have to be grown in pots. 



The procedure followed in 19 16 differed considerably from that of 

 1 91 8, and will be described first. Four pots, each being 10 inches in 

 diameter, were filled with the same kind of soil and were sunk in the 



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[Botanical Gazette, vol. 70 



