1920.] Cockayne.—Yellow-leaf Disease in Phormium tenax. 193 
aspect of the flax areas according to increase or decrease of general yellow¬ 
ness. The figures now to be given, however, supply information as to 
the progress of the disease which could never be gained by observing the 
conditions of the flax areas as a whole. In fact, these figures, especially if 
taken in conjunction with what follows under heads 6 and 7, give some 
definite information regarding the likelihood of a plant being affected, its 
chance of recovery, its chance of deterioration as milling-flax, and so on. 
Apart from a considerable number (85) of marked plants or plots 
belonging to two different categories treated of below under separate 
headings, the number of individual plants examined during my final 
examination of the marked plants at the beginning of May, 1919, and their 
condition when first marked at the end of February and the beginning of 
March, 1918, were as follows 
Number of marked plants examined at final examination, 338. 
Condition of these 338 plants when first marked, in February, 1918 : 
Healthy, 147 (43 per cent.) ; diseased, 177 (52 per cent.) ; doubtfully healthy, 
14 (4 per cent.). 
History of the Originally Healthy Plants.— Taking the originally healthy 
plants and the doubtfully healthy together, the following is their history 
during the period of observation of about fourteen months — 
(1) Remained healthy all the time, 88 (54 per cent.) ; (2) became more 
or less, diseased, 73 (45 per cent.). These figures may be a little too high 
in the case of (1) and a little too low in the case of (2), as some of the plants 
were noted on one occasion only during the periodical examinations. 
Taking next the 73 originally healthy plants which became diseased, 
the following is their history :— 
(1) Recovered, 37 (50 per cent.) ; (2) were recovering, 16 (22 per cent.) 
[total (1) and (2), 72 per cent.] ; (3) were a little better, 2 (3 per cent.) ; 
(4) remained more or less badly diseased, 16 (22 per cent.) ; (5) were 
evidently dying, 2 (3 per cent.). 
With regard to the value of the flax of the foregoing for milling purposes, 
it must be pointed out that at least 88 plants (54 per cent.) were growing 
vigorously, and that 45 plants (27 per cent.) were exceptionally good. 
History of the Originally Diseased Plants. —The history of the 177 origin¬ 
ally diseased plants is as follows :— 
(1) Got worse at some time or other, 114 (64 per cent.) ; (2) dying and 
dead, 16 (9 per cent.); (3) got better and then worse (included in (1)), 67 
(38 per cent.) ; (4) remained much as at first, 14 (8 per cent.) ; (5) recovered, 
83 (47 per cent.); (6) recovering, 53 (30 per cent.) [total (5) and (6), 77 
per cent.]; (7) now worse, 11 (6 per cent.). 
With regard to the value of these originally diseased plants for milling 
purposes, it is interesting to learn that at least 88 (50 per cent.) were 
growing well, and that 45 (25 per cent.) were exceptionally good. Also, 
a considerable number, although still deseased, were quite suitable for 
milling, while others, though partly diseased, were otherwise extremely 
healthy and showing every sign of developing into excellent plants. 
5. A Few Cases of Remarkable Recovery. 
That a plant is badly diseased is far from being a certain indication 
that it will not eventually recover and make good milling-flax. It is no 
uncommon circumstance to find that when the prostrate stem (rootstock, 
or rhizome) of a badly diseased or, it may be, moribund plant reaches the 
flat ground alongside the hummock on which the plant originally grew 
new fans of the greatest vigour, and apparently most perfect health, are 
produced. So, too, many plants were noted which, though badly diseased 
13—Science. 
