Pethybridgk and Laffkrtv — A Disease of Flax Seedlings. 383 



It was discovered that mycelium of the fungus hibernates within the 

 cells of the epidermis of the seed-coat, and it was proved that this was the 

 source from which the disease was transmitted, the seedlings becoming 

 infected during or subsequent to germination. 



Transmission of the disease by infected seeds can to some considerable 

 extent be overcome by sowing the seed deeply so that, on germination, the 

 seed-coats are kept below ground, but this is scarcely a practicable method 

 of control. 



Disinfection of infected seed with formalin and with hydrogen peroxide 

 reduces the number of seedlings to a marked degree, but does not completely 

 eliminate the disease. Treating slightly moistened infected seed with a 

 mixture of finely powdered copper sulphate crystals and dry sodium carbonate 

 suppressed the disease entirely. 



Flax-seed from Russia, Holland, Canada, the United States of America, 

 and Japan has been found to give rise to diseased seedlings, and it is believed 

 that the disease is widespread over the globe. 



XL— Explanation of Plates. 



Plate XIX. 

 Fig. 



1. Four flax seedlings naturally affected with the Colletotrichum disease. 



From the one on the extreme left, one cotyledon has already fallen 

 off, while the other one and the cotyledons of the three remaining 

 seedlings are severely attacked. A few of the older lower leaves of 

 the seedlings are also affected. The constricted areas on the hypo- 

 cotyledonary stems are points of attack by the fungus. (Slightly 

 reduced.) 



2. Young flax seedlings photographed from above, showing the disease on 



their cotyledons. In the cases of the middle seedling in the upper 

 row, and the right hand one in the lower row, the seed-coat is still 

 adhering to one cotyledon. These seedlings were raised from healthy 

 seed, artificially contaminated with conidia of Colletotrichum linicolum. 

 (Natural size.) 



3. Portion of the superficial tissues scraped from a naturally infected 



hypocotyledonary stem, showing the acervuli and setae of the 

 fungus, (x 60.) 

 -1. Section through portion of the endosperm and seed-coat of an infected 

 flax-seed mounted in water, and not stained, showing hyphae of 

 0. linicolum in the much-swollen epidermal cells, (x 200.) 



SCIENT. PKOC. R.D.S., VOL. XV.. NO. XXX. 3 p 



