198 PLANT GROWTH SUBSTANCES 



Paatela (40) made intensive studies of the relation of increase in height 

 of flax to its susceptibility to methoxone and 2,4-D, In experiment i, 

 flax plots sown on the same day were sprayed over a period of six weeks 

 as they reached seven stages of development. Thus treatment I was 

 made when the flax was in the cotyledon stage; II, when 4.6 cm. tall; 

 III, 7.8 cm. tall; IV, 12.5 cm. tall; V, 17.1 cm. tall; VI, in bud; and VII, 

 in flower. 



In experiment 2, stages I, II, V, and VI were obtained by sowing the 

 flax at successive dates. All plots were sprayed on the same day. Since 

 the date of spraying was July i, growth conditions were favorable for 

 more rapid growth of flax in all stages as compared to experiment i. 

 This fact was determined by height measurements of unsprayed flax 

 for a period of six days following the spraying of the remaining plots. 

 Injury was markedly greater in experiment 2 than in experiment i, with 

 one exception, even though the flax was in the same stage of development 

 in each case. The one exception was the flax sprayed in the cotyledon 

 stage. Data illustrating this result were selected in cooperation with 

 Paatela and are presented in Table i. 



In a more recent study at Minnesota, Paatela and Dunham grew three 

 varieties of flax under conditions conducive to slow growth in one 

 instance and rapid growth in the other. The following treatments were 

 used: i) Flax was grown 3-4 inches tall with 12 true leaves at approxi- 

 mately 50° F. and sprayed with (a) methoxone and (b) amine salt of 

 2,4-D. One half the population remained in the cool room; the other half 

 was removed to the greenhouse at time of spraying. 2) Flax was grown 

 to the same stage as in i at high (approximately 85° F.) temperatures 

 in the greenhouse. One half the population remained in the greenhouse; 

 and the other half of the population was removed to the cool room at 

 time of spraying. Response was measured by the bending and twisting 

 of the stems, a characteristic reaction of flax to the growth-regulating 

 herbicides. Both the number of afl"ected plants and the degree of epinasty 

 were recorded. The number of plants multiphed by the degree of bending 

 as indicated by a scale of o to 3 was divided by the total number of 

 plants. The resulting decimals are the data reported in Table 2. Dif- 

 ferences appear small when expressed in decimals until comparisons are 

 made. Thus 6 oz. of methoxone on Dakota started in the warm room 

 and moved to the cool room caused 8 times as much bending as when 

 the plant was grown continuously in the cool room (0.8 and o.i). It is 



