Plate XIV.

1, 2. Sporangia with stalk detached × 800.

3. Sporangium with contained spores × 800.

4, 5, 6, 7, 8. Spores with and without attached fragments of sporangia × 1,000.

9, 10. Spores germinating within a sporangium × 600.

11, 12, 13. Spores germinating × 1,000.

14, 15. Mycelium produced by germinating spores × 500.

16, 19. Mycelium with immature conidial fruit; 16 × 700; 19 × 500.

17, 18. Mycelium with granulated protoplasm; 17×700; 18×1000.

20. Mature conidial fruit × 1,000.

21. Conidium germinating × 1000.

The disease has also been studied in Ceylon by Mr. Morris, Assistant Director of the Royal Botanic Gardens, Peradeniya, from the practical point of view of finding some means of combating its attacks. Mr. Morris was eventually detached entirely to this duty, with the permission of the Government and the approval of Dr. Thwaites. The following is a brief summary of his results:—The Hemileia is, of course, propagated from year to year by spores which, if Mr. Abbay is correct, are contained in the sporangia forming the orange-coloured dust on the under surface of the leaves of diseased plants. These sporangia become detached, and are powdered over the leaves, twigs, branches, and stems of the coffee plants, and on the ground beneath. They are also blown about by the wind, but, except this is very strong, are probably not carried to any very great distance.

The spores germinate and produce the filamentous or thread-like mycelium described by Mr. Abbay. Mr. Morris found that in infected plantations, although invisible to the naked eye, it could be shown by the microscope that in what may be called its first stage, the filaments of the Hemileia, covered—however little this might be suspected—the ground and every part of the stems, branches, and leaves of the coffee trees growing upon it. It continues generally in this stage from December to March. During this period, besides the vigorous growth of the mycelial filaments, the fungus possibly multiples itself by the forma- page 34 tion of reproductive bodies called conidia, which are detached from the filaments, and germinate and grow precisely in the same manner as spores.

The second stage begins where the filaments enter the stomata on the under surface of the leaves. They now assume a thicker, more branched, and coral-like aspect as they ramify amongst the loosely packed intercellular tissue of the interior of the leaves. The ends of the branches of the mycelium come in contact with individual cells, tap their contents, and progressively destroy them, feeding on their contents.

This continues till the last or third stage is reached. The filaments having reached maturity once more, push their way through the stomata and produce on the outside the clusters of orange-coloured kidney-shaped sporangia.

Mr. Morris has clearly shown that it is only in the first stage, when the Hemileia is purely external in its mode of life, and has inflicted little or no injury upon the coffee plants, that it can be advantageously attacked. To the extent to which the mycelium can be destroyed in this stage without interfering with the health of the coffee plant will be proportioned the alleviation of the further and injurious stages of the disease and its chance of perpetuation to another season. The most important of the numerous remedies which have been proposed may be briefly noticed.

1. Mr. Wall's method of Fumigation.—Mr. Morris finds that "the fumes of burning sulphur, whether applied by the aid of umbrellas or in the open field, have invariably had an injurious effect upon the trees, and, by causing them to shed their leaves, have aggravated the disease they were intended to cure. What is still more conclusive with regard to this method is that fumigation has not in the least degree diminished the amount of leaf disease."

2. Mr. Northmore's Salt-water Treatment.—Mr. Morris has found that neither sea-water nor solutions of sea-salt have any effect in killing the Hemileia.

3. Mr. Morris' Sulphur-lime System.—Mr. Morris writes:—"I have obtained very important results with a mixture of sulphur and coral-lime in the proportion of one to three. The action of the sulphur seems to be much quickened and the cost reduced to almost a third. In addition to this, no special blower is required, for a cooly supplied with the mixture in a bag can powder the tree very effectually by hand, and the smallest quantity of the powder deposited on the under side of the leaves is sufficient to destroy the filaments very thoroughly. The planters can now treat the whole of their estates in a week or 10 days, and at a cost not exceeding 50s. per acre. I cannot hope to see anything more satisfactory than this. The coral-lime used, which must be unslaked, will prove a valuable dressing to the soil, and thus the leaf-disease specific, pure and simple, viz., the sulphur will cost only 20s. to 25s. per acre."