Laffhrtv — Disease of Cultivated Flax. 251 



they are still green, but as they ripen they lose their green colour naturally, 

 and become golden or light brown in colour. At this stnge the recognition 

 of the disease becomes almost impossible without the aid of the microscope. 

 On the green fruits the diseased areas may arise at any point, but they are 

 generally located at the apex or along one of the five raised ribs. They are, 

 at first, light fawn in colour, and often surrounded by a darker zone due to 

 the development of anthocyan. Gradually, as the disease advances, the 

 darker zone becomes involved, and the colour of each area may then vary 

 from fawn to brown. Fruits showing various stages of attack are illustrated 

 in the two upper rows of fig. 3, Plate VIII. Whether infection originates at 

 the apex or along a ridge, the diseased tissues lose moisture and contract, with 

 the result that affected fruits show a strong tendency to gape open, especially 

 in very dry weather. 



As the fruits become ripe and dry, the progress of the disease is retarded ; 

 hence many of them show infection on one side only, or on a restricted area 

 about the apex. But in cases of early infection the entire fruit may become 

 diseased, and, if opened, the young seeds within are found to be shrivelled 

 and dead. In cases of slight infection the seeds may appear normal to the 

 naked eye ; but, as will be shown later, the majority of them, though still 

 retaining their vitality, are, nevertheless, heavily infected with the disease. 



(&) Stem-hreak. — In a crop suffering from " browning " there are to be 

 found individuals here and there which, instead of standing upright like the 

 majority of their neighbours, have their stems bent over and lying on the 

 ground. The recumbent position of these stems is due to the fact that at or 

 in the region of the first node they are diseased, and have, therefore, become 

 more or less completely broken across (Plate VIII, fig. 5). 



When the fracture is practically a complete one, the plants turn yellow, 

 die, and finally become brown. If, however, the stems are already fairly 

 well developed before the attack becomes severe, and if, therefore, a con- 

 siderable development of woody tissue has already occurred, only partial 

 fracture occurs. The stems bend over, but since the conducting tissues are 

 not entirely severed, the portions above the breaking-point continue to live 

 and grow for a time. They develop negatively geotropic curvatures, as is 

 shown in Plate IX, fig. 1, but ultimately they succumb prematurely. The 

 connexion between "stem-break" and "browning" was not at first recog- 

 nized ; but, as will be explained later, it has now been proved that these two 

 dissimilar phenomena are due to one and the same cause. 



2. Histological features. — Microscopical preparations of the tissues from 

 any of the affected parts of flax plants show the presence of hyaline, septate, 

 and branched fungus hyphae in the diseased tissues. The cell contents are 



2 M 2 



