A widespread disease known as pocket-plums or bladderplums is due to an ascomycetous fungus, Exoascus pruni, the mycelium of which lives parasitically in the tissues of the host plant, passes into the ovary of the flower and causes the characteristic malformation of the fruit which becomes a deformed, sometimes curved or flattened, wrinkled dry structure, with a hollow occupying the place of the stone; the bladder plums are yellow at first, subsequently dingy red.
In Arthrobotrys side-branches of the mycelium sling themselves around the host (Tylenchus) much as tendrils round a support.
Some make their way through the cells of the outer part of the cortex towards the root-tip, and form a mycelium or feltwork of hyphae, which generally occupies two or three layers of cells.
Mycelium with haustoria (h); 2, Erysiphe; A and B, mycelium (m), with haustoria (h).
In lepto and micro forms both aecidiospores and uredospores are absent, the sporidia producing a mycelium which gives rise directly to teleutospores; in the lepto forms the teleutospores can germinate directly, in the micro forms only after a period of rest.
Klebs has shown that the development of zoosporangia or of oogonia and pollinodia respectively in Saprolegnia is dependent on the external conditions; so long as a continued stream of suitable food-material is ensured the mycelium grows on without forming reproductive organs, but directly the supplies of nitrogenous and carbonaceous food fall below a certain degree of concentration sporangia are developed.
In the rotting tissues branches of the older mycelium similarly swell up and form antheridia and oogonia (fig.
The asci are borne directly on the mycelium and are therefore fully exposed, being devoid from the beginning of any investment.
The disease spreads by the mycelium growing ever the epidermis of the plant.
This is the lifehistory of the most complicated forms, of the so-called eu forms. In the opsis forms the uredospores are absent, the mycelium from the aecidiospores producing directly the teleutospores.