Fungus

FUNGUS. To the botanist the fungi are a most interesting class of plants. Their seeds, (spores) and many of the resulting plants are so small that they must be examined with the microscope to bring out their character. What are understood as funguses by the ordinary observer, are toad- stools and puff-balls Smut, mildew and rust are generally termed blight; yet they all belong to the larger class of fungi, the more minute forms below those of mildew, being largely in excess of those larger than mil dew. Fungus attacks all plants, especially those in a more or less diseased or disorganized condition. Fungus sometimes does attack apparently healthy trees. It attacks all living trees, and also is one of the means of the decom position and decay of dead plants. It is propa gated by spores, minute grains which perform the function of seeds. These, says a writer on. fungus life, begin to germinate by sending out numerous filamentous rootlets, composed of a succession of small cells, which perform the office of roots in supporting the plant in an erect position, and supplying it with nourishment. These rootlets are called the mycelium. They also send up stems (stipes) of various shapes, according to the class to which they belong. The Botrytis infestans, more recently called the Peronospora infestans, is one of the most destruc tive of the fungi that cause the potato-rot. It has the form of a spreading tree, hearing some three thousand ovoidal spore-cases (arrospores) on the ends of the branches, somewhat resembling, when taken collectively, clusters of grapes, and hence its generic name Botrytis. The seeds of the fungi, which are contained in the spore-cases, usually have a brown color, like fine dust, and are almost infinite in number. A single plant is said sometimes to produce millions, so small and light as scarcely to be affected by gravity. They cover everything around them—earth, plants, and animals. The air is filled with them, and they wait only for a state of the atmosphere favorable to their growth to seize upon every object within their reach. They live principally upon decaying substances, but the living do not always escape them. The conditions best the potato. Long-continued, warm, damp weather, often causes them to appear in great numbers; but a single day of dry weather will arrest their progress. They mature with won derful rapidity. Puff-balls sometimes grow six inches in diameter in a single night. Certain species have been found growing on the surface of iron that had been heated in the forge only a few hours before. They have also been found growing on the surface of glass. Peronospora infestans matures in a few days, sometimes in fif adapted to their growth are, first, a debilitated or morbid state of the plant; and, secondly, a proper degree of heat, moisture, and electric influence to induce germination. They do not germinate readily, and the conditions must be very nicely balanced to insure germination at all. They frequently remain inert for a long time, and, when the conditions are complete, fall upon plants like an epidemic, and after a time disap pear almost entirely. Such may, perhaps, some times have been the case in their attacks upon teen to eighteen hours even, when conditions are most favorable to its growth, and scatters its seeds by thousands and tens of thousands, to prey, with each successive brood, from day to day, upon the expiring plant. The seeds are supposed to enter the pores (stomata) of the leaves and stems, and also to be taken up by the spongioles of the roots; and carried along in the circulation of the sap through the plant. They take root in the cellular tissues of the stems and leaves, stop up the pores with their roots, pre-• vent the proper elaboiation of the crude sap, and exhaust large portions for their own support, besides probably exerting a deleterious chemical influence on the plant. That the seeds of this fungus are capable of destroying the potato has been demonstrated by Dr. DeBary, who mixed some of them in a drop of water and applied them to the leaves and tuhers, when brown and livid spots appeared, and afterward decay. All the members of this genus, peronospora, are parasitic on living plants, inducing in them speedy decay, of which they are themselves the cause. To those who wish to study cryptogamic botany, the following from a lecture by Prof. McNab, delivered in the Royal Agricultural College, England, will be found interesting: The study of the lower order of plants is attended with many and great difficulties. This is owing chiefly to the minute size of the objects them selves, requiring as they do the microscope for their investigation. Then, again, most of our botanical text-books give only the most superfi cial description of the lower groups, and fix the whole time and attention of the student on the higher or flowering plants. The consequence of this is that the study of the higher plants is car ried to such a length in our lectures on botany that little or no time is given to the lower orders, a plan of procedure as philosophical as that of teaching zoology merely from the vertebrates and omitting all other divisions. To the more or less flattened or rounded cellular expansion of these plants, which may consist of only one or of thousands of cells, the term thallus has been applied; and the three groups possessing this may be united, to form a large division of the vegetable kingdom, called the Thallophytes. The thallus may consist of one cell or of many cells ; these may be either similar or dissimilar. In some of these Thalloph,ytes we have plants con sisting of one cell, which performs the functions of nutrition during the day, and those of repro duction during the night. In others we have .one part of the plant set aside to perform the function of nutrition, while another part per forms the function of multiplication only. In most of the sea-weeds the part of the thallus set apart for the purpose of nutrition is large, while the reproductive organs occupy only a small por tion. In the funguses we have plants which obtain most of the nutriment ready made, and, and as a consequence, an elaborate nutrient sys tem is not required. Hence that portion of the thallus in funguses set aside for the purposes of nutrition, called the mycelium or spawn, is com paratively small, while the organs for perform ing the functions of reproduction predominate. The same law holds in the animal kingdom, as in many parasites we have a low type of the nutritive system and a largely developed repro ductive system. In most of the Thaltophytes we

have two modes of reproduction, one a true sexual process, in which we have parts equiva lent to the stamens and pistils of the higher plants, while the other is asexual, and therefore to be considered as a process of budding. These two modes of reproduction either alternate or else we may have budding taking place two or more times in succession before sexual reproduc tion again occurs. This fact is of the greatest importance, and must not he lost sight of. In many of the sea-weeds we have this alternation of sexual generation with budding. At one period in the life-history of the plant true sexual organs may be produced, while at the other periods we have numerous small cells given off, each armed with two or more hair-like appendages. As these appendages are capable of moving, they propel the whole mass, to which, on account of its peculiar animal-like motions, the term zoospore has been applied. The zoospore may therefore be considered as a movable bud of the simplest possible construction. The same alternation of sexual generation with budding is to be met with in the funguses, and the. Peroaospora affords a very good example of it. Many of our readers must have observed dead flies floating in water in the autumn, with their bodies all covered with fine hair-like threads. This appearance is pro du6ed by a plant, which was formerly believed to be a sea-weed, but is now placed among the funguses. If we examine the thread with the microscope, we observe a cellular mycelium or portion of the thallus. At the end of some of the portions of the mycelium we may probably observe a single large cell, the contents of which become broken up into small portions. These small portions of the protoplasm become liberated, and are zoospores or rounded masses of protoplasm, with two hair-like appendages. When free, they are capable of moving about contents of the small male branches, one or more Mispores being in this way produced. The Mispores are in fact comparable with the fertil ized seed of the higher plants. After a period of rest the oospore germinates and produces a new plant. The reproductive process in the fungus resembles that of many sea-weeds which form Migonia and o8spores, the Mispores being formed after fertilization from the contents of the for some time, and then growth takes place, and each one will form a new plant ; but in another we may observe that the ends of the branches of mycelium form a club-shaped cell. This club .shaped body is the female reproductive organ, and is called by botanists oogonium. At each _side of this club-shaped body two smaller bodies Migonium. Then, in the production of the moving buds, the zoospores, which multiply the plant asexually, these funguses closely approach the sea-weeds. The passage from Achyla (the fungus possesses the sea-weed like character just described) to the fungus producing the potato disease is but a single step. In Peronospora can be seen, which spring from the same portion •of mycelium as the otigonium, but below it ; they are two small branches, which grow upward until they come in contact with the Migonium, being, in fact, the male reproductive organs, called by antheridia. Inside the Migonium are the granular contents, or protoplasm, forming the Misphere. The Mosphere is fertilized by the infestans we have a thallus with the nutritive portion of it, the mycelium, ramifying through the potato-plant. It has also two modes of reproduction, sexual and asexual. In the asex ual form we have a branching tree-like form of the mycelium, making its way through the sto mata or breathing pores of the leaf. This branching portion bears rounded swellings, arranged in a somewhat beaded manner, and called conidia. They do not produce zoospores, but develop a mycelium distinctly. Other observers, however, assert that the conidia never produce a mycelium directly, but always from several, in general ten, zoospores. The zoo spores, after moving freely about, attach them selves to the cuticle of the plant, and surround themselves by a delicate wall; they then bore through the outer wall of the epidermic cell, and form a mycelium ramifying through the intercellular spaces of the potato-plant. If the young mycelium is formed in the tuber or potato, it may remain dormant during the winter, and then spread through the young plant as it grows. The sexual organs of Peronospora develop inside the tissue of the infested plant. The extrem ities of certain of the threads of mycelium form rounded bodies—the o6gonia. Inside the oOgo nia a portion of the protoplasmic contents form the o6sphere On another branch of mycelium the antheridium is produced, which adheres to the wall of the oogonium. the contents passing into the o6sphere, which is thus fertilized, and the olispore formed. The oospore is surrounded by a thickened skin, which is rough and dark brown in color. After a period of rest, the ferti lized oospore germinates and produces mycelium. The fungus producing the potato-disease is thus interesting botanically from its peculiar relations to certain of the sea-weeds, in its mode of repro duction, and in the production of moving zoo spores. From the effect of rain or dew in liber ating these zoospores it is not difficult to under stand how the disease spreads in damp weather. Since it is easier for the unscientific reader to catch ideas by the eye more readily than from scientific descriptions, we give cuts showing some principal forms of fungi. On page 377 we have illustrated the potato disease or fungi. A disease spot appears in a potato. The micros cope will show the disease commencing where the vascular bundles concentrate. There the air is in greater volumes than elsewhere, such spots exposed to the atmosphere causes the blue mold fungus to appear. This however, has no relation to the potato rot. Blue Mold, is Peni cillium glaueum. F, represents the mycelium or roots, at G, is shown that of potato rot, (Perowspora infestans). The following defini tion is from the report of the Microscopist of the Department of Agriculture at Washington: 2, and 3, 3, potato disease, represent the com bination of the spiral and dotted ducts; A, the root stem ; B, a new growth or tuber from 1. Viewing their connection in this way, it will be seen that any germinal disease entering through the root-stem A, will necessarily communicate through all the connecting links, viz., A, 2, 3, 3, 0 0 1,4_ F.. :4