FUNGUS OF HOLLYHOCK DISEASE
Puccinia malvacearum
A fragment of a Hollyhock leaf is illustrated at A, dotted with the characteristic brown pustules; these pustules cover the stems as well as the leaves. At B is shown the edge of a pustule enlarged one hundred diameters and seen in section; to show the whole of a pustule in section from six inches to a foot of space would be required. Bursting through the skin of the plant may be seen a dense forest of threads, each thread bearing a spore with a joint across the middle. One pustule alone will produce thousands of these double spores. At C some of the threads and spores are still further enlarged to two hundred diameters, and at D one ripe spore is shown falling from the thread and breaking asunder—each piece is a reproductive body or spore. When mature, these minute spores or ‘seeds’ are carried in the air by millions. At E one of the compound spores is enlarged to four hundred diameters. As this disease is seated within the tissues of the plant, remedies are difficult of application, and in many cases attempts at cure have failed. No doubt the fungus is nursed by malvaceous weeds. Infected Hollyhock plants and allied weeds should be destroyed by fire or by deep burying.
Poppy Disease.—Garden Poppies are often attacked by a fungus pest closely allied to the fungus of the Potato disease, and named Peronospora arborescens. It grows sometimes in abundance on the common Red Poppy of cornfields (Papaver Rhoeas), and it badly attacks P. somniferum and all its garden varieties. The fungus grows within the leaves, and emerges with a tree-like growth through the organs of transpiration (the stomates) on the under side of the leaves. Like the fungus of the Potato disease, it speedily sets up decomposition, and destroys the host-plant.
FUNGUS OF POPPY DISEASE
Peronospora arborescens
At A is illustrated one of the stems of the Poppy Peronospora emerging from the leaf, enlarged seventy-five diameters. The fungus of the Poppy is very much more branched than that of the Potato, and every minute branchlet carries a spore. To save confusion, a large number of spores are omitted from the branchlets in the illustration, and the branches growing from the stem both before and behind are for the same reason left out. At B a tip of a single branch is shown further enlarged to four hundred diameters. The spores in the Poppy fungus are unusually large and numerous: an infected plant will throw off many millions of such spores. All the putrefactive spawn of this fungus is inside the host-plant; cure, therefore, is difficult. This disease, like every other plant disease, is always at its worst in ill-kept places where red field Poppies are abundant. Field Poppies are often sown with unclean corn. As prevention is better than cure, all we can advise is, buy the best and cleanest garden and field seeds, cultivate in the best way, and look out for and burn, or deeply bury as soon as detected, all disease-stricken plants, whether wild or cultivated. When diseased plants of any sort are left to decay on the refuse-heap, it is the most certain way of propagating a plant disease for the next year.
Diseases of Violets.—Violets are subject to fungoid diseases, both in spring and autumn. The disease of autumn is caused by the brown Puccinia violæ, allied to the P. graminis of Corn and to the P. malvacearum of Hollyhocks and various malvaceous plants. The Puccinia of Violets has its yellowish or orange-coloured stage; it is then known as Trichobasis, or Uredo violarum. In spring and early summer Violets are often badly affected by a fungus named Æcidium violæ, which is apparently identical, however, with Puccinia violæ. This disease attacks leaves, stems, and sepals, and it is best examined on the leaves. In this position it is seen to consist of a considerable number of minute yellow pustules, each pustule less in size than a pin’s head, and all congregated into one flat circular mass of about a quarter of an inch in diameter. This pest is very frequent on the Dog Violet, but it is perhaps equally common on the Sweet Violets of our gardens in early spring, and it not infrequently spreads to other species of Viola. One of the most destructive pests of Violas is found in Æcidium depauperans, so called because its effect is first to starve and attenuate, and then to totally destroy, plants of Viola cornuta. It is a close ally of Ae. violæ, but it differs in having its minute cups or pustules irregularly distributed all over the green parts of the host-plant instead of being congregated in circular patches, as in Ae. violæ. Our illustration shows, at A, a small portion of the stem of Viola cornuta attacked by Æcidium depauperans. The minute pustules are seen (natural size) distributed all over the stem, leaf-stalks, and ruined leaves; the effect of the fungus growth is to decompose the tissues of the plant. At B, a transverse section through the stem is illustrated and magnified twenty diameters. The section cuts through several of the abscess-like pustules, and it is seen how completely embedded they are in the flesh of the plant. At C, a pustule is seen in section, enlarged sixty diameters to show more clearly the innumerable spores, or ‘seeds,’ disposed in necklace-like fashion, which are destined to reproduce the pest in future seasons. Another disease of Violets in autumn is caused by a fungus named Urocystis violæ. This fungus causes gouty swellings to form on the stalks and principal veins. These swellings at length burst, exhibit black patches, and discharge sooty spores. The fungoid disease named Phyllosticta violæ is frequently common on Violet leaves in June. In this the spots are whitish. No cure is known, and it is always well to burn or deeply bury all infected leaves or plants.
VIOLET DISEASE
Æcidium depauperans