guish it from them. The rest of the described species have smaller sporidia. A few of the germinated examples forwarded by Mr. Wilson are illustrated, natural size, at Fig. 6. It will be FIG. 6. Peziza postuma, B. and W. seen that the Sclerotia give rise to long, slender, tortuous stems, and that each stem at length bears a shallow pallid head, which ultimately becomes flat or slightly recurved. The stems are about two inches high, and the cup-like expansion at the top about half-an-inch across. On closely observing these expanded tops in sunlight, especially when held in favourable positions, as against a black background, a slight sudden cloud resembling a puff of smoke or steam may be seen to gradually sail away through the air from the top surface. This almost invisible cloud really consists of millions of minute spores, in this instance technically termed sporidia for a reason to be mentioned immediately. The whole interest of the fungus now centres on the expanded top, and especially to its surface, whence the clouds of sporidia sail away. If we cut one of the cups in two, and look on the cut surface with a magnifying power of five, and twenty diameters, we shall see the structure as shown at A and B, Fig. 7. We now notice Peziza postuma, B. and W. Section through cup. that the whole of the upper stratum of the expanded top consists of elongated perpendicular cells as illustrated, whilst the under surface is a mass of spherical cells of various sizes; but to see this curious structure well a much higher magnifying power is required, and a small fragment only of the top must be examined in section, as at Fig. 8, magnified 400 diameters. We now distinctly see the basal stratum of transparent globular cells of various sizes, and a few of the hundreds of thousands of vertical transparent bladders forming the top stratum, and from which the cloud of dust consisting of oval transparent sporidia arises. With a lancet we will now remove a few of these vertical asci or long bladders, and magnify 500 diameters. Each colourless bladder, sack, or bottle, is termed an ascus, from askos, a bag, bladder, or bottle. Each ascus, as at Fig. 9, contains eight oval spores or sporidia. These bodies, one of which is farther enlarged to 1000 diameters at B, are termed sporidia because they are not supported on threads or fine branches like many other spores, but are carried free in an ascus or transparent bladder, in which position they have arisen from a dif ferentiation of the protoplasmic contents of the ascus. Mixed with the asci are numerous slender, often septate organisms, termed paraphyses (as at A, Fig. 9), or organs which grow about or in company with organs of greater importance. The word is derived from para, about, and phuō, I grow. The right hand ascus in the illustration is shown in the act of discharging its sporidia into the air. At a given moment, depending upon unknown conditions, possibly of the air, of light or heat, the ascus opens at the top, as illustrated (in some fungi an operculum or lid flies off), and discharges the eight sporidia which it invariably contains into the air. In the genus of fungi named Ascobolus, the ascus itself, with its contained spores, as the name indicates, is shot into the air. Each transparent sporidium is furnished with two or three lustrous spots. The asci are so inconceivably small, slender, and attenuated that there are more than 300,000 packed side by side on the top of each expanded cap, which on the average measures about half-an-inch in diameter; and as each ascus contains eight sporidia there are no less than 2,500,000 sporidia produced by every cap. Now, as every infected potato plant will produce at least fifty Sclerotia, it follows that a plant killed by this new disease is capable, by means of its germinating Sclerotia during the following season, of discharging more than 100,000,000 reproductive bodies into the air. It must now be specially noted that after a year's rest the Sclerotia germinate on the ground, and there produce their sporidia exactly at the time in July when potatoes are making their best growth. A vast number of the sporidia must perish, but such as fall upon potato plants (and possibly some other plants, as carrots) germinate at once, cover the stems with spawn, obliterate the organs of transpiration, and speedily reduce the haulm either to a mass of putrescence or to dry tinder. During this rapid and exhaustive growth the spawn again gradually compacts itself into the black nodules of condensed mycelium termed Sclerotia, and these nodules are destined to germinate and produce the Peziza disease the following year. No The remedy for this state of disease is obvious. infected stems should be allowed to rot in the fields, but all should be carefully gathered together and burnt. If the stems are allowed to rot on the ground the disease is almost certain to recur; but if they are burnt not only will the Sclerotia of the Peziza be destroyed, but the spawn, germs, eggs, and spores belonging to numerous other parasites, perhaps equally bad with the Peziza itself, will be destroyed at the same time. If, on an examination of the potato stems, it is found that many of the Sclerotia have dropped from them, the top surface of the ground should if possible be raked and burnt. Nothing is more common than to find hibernating reproductive bodies falling readily to the ground. This is clearly a natural provision for their preservation. |