510 Proceedings. 



the swamps get very dry the disease spreads very rapidly. Unless the 

 disease can be eliminated the industry is doomed. The fungus had been 

 isolated, developed in pure cultures, reintroduced into healthy plants, and 

 had produced yellow- leaf disease. Three methods of combating soil- 

 diseases were known : (1.) Soil-treatment, of which well-known cases were 

 the use of lime for club-root in cabbages, and sulphur for onion-smut. 

 On the whole, few diseases could be controlled by this method. (2.) Crop- 

 rotation, a method used successfully with a large number of diseases, such 

 as " take-all " in wheat. All such cases were diseases attacking annuals, 

 and the method was not possible with flax, which was a perennial. (3.) The 

 use of disease-resistant strains. Wonderful success had been secured by this 

 method in a great variety of diseases, including some caused by other 

 species of Ramularia — e.g., Irish-flax wilt, tomato-wilt, cotton-wilt, &c. 

 Healthy plants growing in diseased areas had been selected for breeding, 

 and the diseases had been combated. The control of yellow-leaf disease 

 must be found along this line. 



Mr. TC. Waters, who had conducted the isolation of the fungus under the 

 direction of Mr. Cockayne, mentioned the difficulty of sterilizing the exterior 

 of so porous a root. In the end slightly infected roots were selected, a jelly 

 was infected, and a growth obtained, of which he exhibited specimens. 

 The results of infection of healthy plants was at first negative until 

 seedlings were tried, when the disease quickly appeared. In answer to 

 Professor Easterfield, who asked whether disease-resisting plants showed any 

 root-infection, Mr. Waters stated that no work on disease-resistant strains 

 had yet been done, but root-infection was absent from healthy plants. 



Dr. L. Cockayne stated that flax grew under almost all conditions — 

 dry areas, wet areas, sweet soils, sour soils, rocky slopes, wet clay, dry 

 clay, &c. No one could say yet under what circumstances we get the 

 best flax, and so an accurate survey of the plant as it grew in nature was 

 needed. The question to be settled was whether flax would not be a 

 profitable crop on poor lands. In his opinion, quite possibly the sand- 

 dune areas might be turned into flax-fields. He briefly alluded to his 

 previous work on the flax,* and stated that he did not at first believe it 

 to be a disease, but merely an effect of a non-correct system of swamp- 

 management. 



Dr. C. Chilton asked whether Koch's conditions as to proof of patho- 

 genicity had been fulfilled, whether spores of the fungus had been obtained, 

 and whether treatment of the soils might not also help. 



In reply, Mr. Waters stated that all of Koch's conditions had not yet 

 been fulfilled, owing to the short time since the discovery. Spores of two 

 kinds had been obtained, both from the cultivated fungus and from diseased 

 plants. 



Dr. Tillyard referred briefly to the inspcts found on or in the flax- 

 plants, and mentioned the work of Mr. Miller on the Xanthorhoe grub. 

 A noctuid grub, a species of Melanchra, also bit out the sides of leaves, 

 but did not do serious damage. Syrphid grubs were found in the rotting 

 jelly inside the leaves, and a mealy bug at the leaf-bases. Mr. Miller 

 was ably investigating these insects. A scale insect, Pseudococcus, had 

 been described many years ago from New Zealand flax by the late Mr. 

 Maskell, but his type specimen was in very bad condition and practically 

 indeterminable. A similar scale was found on supar in Honolulu, and 



* N.Z. Jour. Sci. & Tech., vol. 3, No. 4, pp. 190-96, 1920. 



