1921.] 
New Zealand Institute Science Congress. 
35 
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. R. 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 insects found on or in the flax- 
plants, and mentioned the work of Mr. Miller on the Xanthorrhoe 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 sugar in Honolulu, and 
the Americans were very anxious to learn all they could about all the 
scales on New Zealand flax. Specimens shall be collected and sent to 
America for determination. It had been shown that the work on 
* N.Z. Jour. Sci. db Tech., vol. 3, No. 4, pp. 190-96, 1920. 
