2 Department Circular 26^, U. S. Dept. of Agriculture. 



complete germination or by a severe frost that strikes the flax after 

 germination and stunts the growth or depletes the stand. It has 

 been observed that in the experimental plats at East Lansing, Mich., 

 some varieties give a very poor stand when planted early, while 

 others germinate well whether planted early or late. Severaf agrono- 

 mists have noted varietal differences in flax on frost resistance, but 

 there does not appear to have been any attempt to take advantage 

 of this and select for increased resistance. C. H. Clark, formerly 

 of the Office of Cereal Investigations, Bureau of Plant Industry, 

 and H. Hunter - both noted that some varieties of flax were injured 

 more than others by frost during early growth. 



THE TEMPERATURE RANGE FOR FROST TESTS WITH FLAX. 



Kepresentative groups of flax were chosen for tests, with the 

 object of determining the extent of the differences in frost injury 

 that might be present and if possible the nature of this injury in 

 flax. The tests included imported fiber flaxes, several seed-flax 

 selections, two commercial varieties of fiber flax, and a group of tal] 

 fiber-flax selections developed by the Office of Fiber Investigations. 

 Seven tests were conducted in all, two in the fall of 1921, which were 

 planted out of doors, and five in the spring, in which the flax was 

 germinated in boxes of sand and then exposed out of doors. 



Table I. — Frost-resistance tests with flax. 



[The 1921 test plats were covered with 1 foot of snow, which melted after two weeks, leaving the flax 



uninjured.] 





Date 

 exposed. 



Number of 

 days. 



Minimum temper- 

 atures (• F.). 



Percentage 

 of plants 

 that sur- 

 vived. 





Season and test. 



After 

 seed- 

 ing 

 when 

 ex- 

 posed. 



Period 

 of ex- 

 posure. 



Nonin- 

 juri- 

 ous. 



Injurious. 



Remarks. 



Fall of 1921: 

 No.l 



No.2 



Spring of 1922: 



Nov. 18 

 Dec. 1 



Feb. 21 

 Mar. 6 

 Mar. 11 



Mar. 22 

 Mar. 30 



52 

 42 



6 



7 

 10 



4 

 5 



8 

 8 



6 

 2 



7 



10 



4 



27 

 27 



39 

 34 

 26 



26 

 26 



24 to 23.... 

 24 to 23.... 



18 



Oto 37.5., 

 1 to 12.5.. 



Oto 15.... 

 17 to 54...- 

 Oto 7.... 



21 to 92.... 

 8to48.... 



Second leaves formed when 



frosted. 

 In cotyledon stage when 



frosted. 



No.2. 



21.. 



Soil verv cold when seeded. 



No.3 



No.4 



21 to 19.... 

 25 



Strong wind, accompanied 

 by freezing temperatures. 



No. 5 



25 



Heav\' sleet on Mar. 31. 







Seedlings weighted do\^^] 

 with ice. 



In spite of a great variety of weather conditions, such as freezing 

 temperatures from 19° to 32° F., accompanied at times by high 

 winds or heavy sleet and snow storms, the effect on the flax was 

 fairly uniform. In no case did a temperature of 26° F. or above 

 cause injury (see Table 1), and a temperature of 25° F. or below 



3 Hunter, H. Improvement of the flax crop by propagation from selected plants. 

 Dept. Agr. and Tech. Instr. Ireland Jour., v. 15, p. 237-246, 1 fig. on pi. 1915. 



In 



