Grain and Chaff from an English Manor

by Arthur Herbert Savory

"First the flea, then the fly,
Then the lice, and then they die,"

is a couplet repeated in all the hop districts to-day, but the damage done by the flea is not to be compared to that caused by the next pest, the fly. The latter is one of the numerous species of aphis which begins its attack in the winged state, and after producing wingless green lice in abundance—which further increase by the process known as "gemmation"—reappears with wings in the final generation of the lice, and hibernates in readiness for its visitation in the spring next year.

So long as the hop plant maintains its health the aphis is comparatively harmless, for the plant is then able to elaborate to the full the bitter principle which is its natural protection. On a really hot day in July it is sometimes possible to detect the distinctive scent of the hop quite plainly in walking through the plantation, long before any hops appear, and when this is noticeable very little of the aphis blight can be found. There is however nearly always a small sprinkling lying in wait, and a few days of unsuitable weather will reduce the vitality of the plant so that the blight immediately begins to increase.

There is little doubt that all the distinctive principles of plants or trees have been evolved, and are in perfect health elaborated, as a protection from their most destructive insect or fungoid enemies; just as physical protective equipment, such as thorns, prickles, and stinging apparatus, is produced by other plants or trees as safeguards against more powerful foes. If it were not so, plants that are even now seriously damaged and kept in check by such pests would long ago have become extinct.

Pursuing this theory it seems likely that the solanin of the potato is its natural protection against the disease caused by the fungus Phytophthora infestans. The idea is suggested by the invariably increasing liability to the potato disease experienced as new sorts become old. The new kinds of potatoes are produced from the seed—not the tubers—of the old varieties, and the seed, when fully vitalized and capable of germination, may be assumed to contain the maximum potentiality for transmission of the active principle to the tubers immediately descended from it. During the early years of their existence these revitalized tubers contain so much solanin that they are not only injurious, but more or less poisonous, to man, and it is only after they have been cultivated, and have produced further generations of tubers from tubers, that they become eatable, showing that in the tuber condition the plant gradually loses its efficient protection.

In the case of the hop the most effective remedy is a solution of quassia and soft soap. The caustic potash in the soap neutralizes the oily integument of the lice and dries them up, but the quassia supplies a bitter principle not unlike that of the hop, though without its grateful aroma, which acts as a protection in the absence of the bitter of the hop itself. So closely does the hop bitter resemble that of quassia, that in seasons of hop failure it is said to be employed as a substitute in brewing, and at one time its use for that purpose was prohibited by law.

As a further proof that the bitter principle of the hop is distasteful to the aphis, it is noticeable that when the fly first arrives it always attacks the topmost shoots of the bine where the leaves have not developed, and where the active principle is likely to be weakest. The same position is selected by the aphis of the rose, the bean, and every plant or tree subject to aphis attack—it is the undeveloped and therefore unprotected part which is chosen.

It is remarkable that when a destructive blight is proceeding—generally in a wet and cold time—and a sudden change occurs to really hot dry weather, the hop plant often recovers its tone automatically, shakes off the disease, and the blight dies away, a fact which strengthens the assumption that in normal weather the plant can protect itself. Again, the blight is always most persistent under the shade of trees or tall hedges, or where the bine is over luxuriant, when owing to the exclusion of light and air the plant is unable to elaborate its natural safeguard.

Fertilizers not well balanced as to their constituents, and containing an excess of nitrogen, act as stimulants without supplying the minerals necessary for perfect health. The effect is the same as that produced in man by an excess of alcohol and a deficiency of nourishing food, the health of the subject suffers in both cases, leaving a predisposition to disease.

Reasoning by analogy, these causes affecting the success or failure of plants give us the clue to the remedies for bacterial disease in man. Disease is the consequence and penalty of life under unnatural or unfavourable conditions, which should first receive attention and improvement. When in spite of improved conditions disease persists, specifics must be sought. The conditions which produce disease in the vegetable world are fought by the active principle of each plant, and inasmuch as the germ diseases of man are probably, though distantly, related to those which affect vegetable life, the specific protections of plants should be exploited for the treatment of human complaints. This, of course, has for long been a practice, but possibly more success might be achieved by careful research to identify each distinct bacterial disease in man with its co-related distinct disease in plants, so as to utilize as a remedy for the former the natural protection which the latter indicates.