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



cotyl. When this happens the roots can no longer supply the coty- 

 ledons with water and they become withered. Frequently the flax 

 plant appears normal above the ground line except for a slight purple 

 band and constriction in the hypocotyl, but when the plant is pulled 

 up the taproot is found to be destroyed by fungi (see Fig. 2). The 

 power of resistance of the roots to fungi appeared to have been 

 lowered by a partial starvation as a result of the slight constriction 



Fig. 2. — Frost injury to flax seedlings : 5, Tlie tissue of both cotyledons and hypocotyl s 

 has been destroyed. Note the shriveled condition. The root is apparently uninjured. 

 6, One week after frost injury. Part of the seedling above ground is normal except for 

 the purple band and the constriction of the hypocotyl. The root tissue has been partly 

 destroyed by the fungus. 



of the hypocotyl. The same varieties of flax were not attacked by 

 fungi in the germination boxes unless exposed to frost. These ob- 

 servations were made use of later in the process of selecting frost- 

 resistant plants; only those flax plants that survived the frost tests 

 with healthy roots and without any trace of purple or constriction 

 of the hypocotyl were transplanted to breeding plats for increased 

 resistance. 



