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AUG 



AAA. 



A DISEASE OF FLAX SEEDLINGS CAUSED BY A SPECIES OF 

 COLLETOTRICHUM, AND TRANSMITTED BY INFECTED SEED. 



By GEOBGE H. PETHYBEIDGE, B.Sc, Ph.D., 



Economic Botanist to the Department of Agriculture and Technical 



Instruction for Ireland ; 



AND 



H. A. LAFFEETY, A.E.C.Sc.L, 

 Assistant in the Seeds and Plant Disease Division of the Department. 



(Plates XIX. and XX.) 



[Read May 2S ; published August 19, 1918.] 



I. — Introductory. 



Farmers in the North of Ireland who cultivate flax complain not infre- 

 quently of trouble with the crop (when in the seedling stage) which they 

 describe as " yellowing." Very little attention has, up to the present, been 

 devoted to this trouble from a scientific standpoint ; but it is almost certain 

 that both the nature and causes of this so-called " yellowing " in flax are not 

 in every case the same. 



There is one form of "yellowing" in which the seedling plants exhibit 

 a general paleness or yellowing of their normally green parts — a kind of 

 chlorosis — and in which search for a parasite as the causative agent has given 

 only negative results. Since this form of " yellowing " can be cured by the 

 application of an artificial manure, rich in potash salts, it is usually supposed 

 that the chlorotic condition is due to potash starvation. 



Another form of " yellowing " in flax has been attributed to attacks on 

 the roots of seedlings by Asterocystis radicis, a parasite belonging to the 

 Chytridiaeese. 1 A short note 8 on this matter was published in August, 1900 ; 



1 This organism has also been found in yellowing flax in France (Arnaud 6. La 

 Brulure du Lin. Bull. Soc. Path. Veg. de France I (1) 1914, p. 38), and, according to 

 Arnaud, the brulure attributed by Ladureau in 1880 to Thrips may perhaps in reality 

 have been caused by Asterocystis. 



2 Anon. The Yellowing of Flax Plants. Journ. Dept. Agric. and Tech. Inst, for 

 Ireland, vol. L, 1900-01, p. 151. 



SCUSNT. PBOC. R.D.S., VOL. XV., NO. XXX. 3 M 



