1920.] Cockayne. —Yellow-leaf Disease in Phormium tenax. 195 
The May, 1919, examination puts the healthy plants at 338, and the 
diseased plants at twelve. Generally the flax was 5 ft. high, but in a few 
of the plots the plants were stunted. 
This freedom from yellow-leaf of flax fifteen months old since cutting 
(cut February, 1918) is very satisfactory, since, although diseased flax puts 
forth green leaves for a time after cutting, yellow-leaf may be expected 
to appear in about six months, while one-year-old flax is frequently badly 
diseased. 
7= History of a Considerable Number of Marked Plants of a Badly 
Diseased Area from Cutting up to a Period of Fourteen and 
Fifteen Months. 
The area in question is situated on the Aside a Estate, near its junction 
with Tane. The flax was badly diseased when cut ; indeed, almost every 
plant was diseased more or less. Some of the old plants had died outright. 
In order to watch the progress of events in this critical area I marked no 
less than 45 plants. Also, it was easy to observe the general condition of 
this originally badly diseased area on each periodical visit. 
There is no need to cite the detailed statistics, for there was great 
uniformity exhibited by the plants at each examination. The following 
shows the general history of the plants : — 
By July the growth of each plant was from about 1J ft. to 2 ft. True 
yellow-leaf was virtually absent, but there were slightly tinged leaves 
on almost every plant. Growth had been very feeble. The September 
examination revealed a similar state of affairs: there was still abundance 
of tinged leaves and, except in a few cases, no growth of moment. By 
December there was much browning of leaves, but not much actual yellow- 
leaf. Growth had still remained almost at a standstill, 3 ft. being perhaps 
the average of the best. It looked, indeed, as if the giant-fescue grass 
would wipe out this stunted flax. By May, 1919, the improvement was 
most marked. There was hardly any vellow-leaf ; good growth had set in, 
the change for the better being, indeed, remarkable. 
8. The Question of Races of Phormium tenax which are Proof 
against Yellow-leaf. 
When it is considered that out of 147 healthy plants more than one- 
half never took the disease for a period of considerably more than fourteen 
months when plants on all sides of them were affected, the question of 
their immunity from the disease at once arises. These plants were quite 
healthy at the time of marking ; many gave every proof that they had 
been healthy for months. Can such immunity be accidental ? The answer 
to this question, bearing in mind the teachings of science, must be in the 
negative. It stands out clearly, then, that in some of the above healthy 
plants there is the best material available at the present time for raising 
a race incapable of contracting yellow-leaf. Such a race once segregated 
would be of great monetary value. Nor does the work of producing such 
a race appear to me of extraordinary difficulty. Such work, however, is 
not suited for a private individual. There is no patent law with regard 
to plants. Work of this kind should be undertaken either by the State or 
by such a body as the Flax-millers ’Association. But the latter might well 
hesitate in view of the uncertainty still existing regarding the spread of 
yellow-leaf, the favourable opinion of this report notwithstanding. 
However, if once yellow-leaf proves to be not so hurtful as it once 
promised to be, the quest for a race of flax which could not take the disease 
would be a legitimate commercial venture. Undoubtedly, the future of 
