in various ways and infect new host cells. (Fig. 2). The family Chytridiaceae (Fig. 3) which are mostly parasitic in aquatic alga and fungi are probably closely related to these or to the next forms.

Water Molds (Saprolegniacea) which are minute filamentous, colorless plants living in the water on living and dead plants and animals. (Fig. 4). Each plant is a more or less branched thread, some portion of which penetrates the host and thus obtains food, while the other part is external and bears the reproductive organs. The filaments are cylindrical, and are peculiar in having no cross partitions in the vegetative portions. They are to be regarded as composed of many cells which have

FIG. 3. Rhizidiomyces apophysatus, another of the lower fungi (Chytridiacea); the root-like organs are parasitic in a cell of a water mold. Highly magnified. FIG. 4. Sa prolegnia thureti, A, fly with reproductive filaments; B, end of a filament forming zoospores. C. zoospores escaping. A, natural size; B and C, highly magnified.

not separated themselves by partitions. nuclei are numerous, and very small.

The

The more common mode of reproduction is as follows: A terminal portion of a branch forms a partition at some distance from the extremity and the protoplasm in this segment becomes denser, and a little later divides into a great number of small cells, each of which remains naked (that is, no cell wall is formed around it), and soon escapes by a rupture of the end of the segment. (Fig. 4). These escaped cells are known as zoospores, since they have a very active swimming motion, very like that of some of the lower microscopic animals. The similarity to the lower animals is shown still more by the identity in their locomotive organs, which consists of one or two slender

FIG. 5.— Achlya racemosa, showing antherids and oogones. Highly magnified.

plant from which they came. Reproduction by means of zoospores is very rapid, since they are formed in such great numbers when conditions are favorable.

The sexual organs, which are rather rarely formed, consist first of an enlarged and rounded end segment in which the protoplasm is quite dense. From the sides of the branch below the end segment (or from elsewhere on the body of the plant) slender branches grow up and in turn their ends become cut off by cross partitions. (Fig. 5). The first end segments (the rounded ones) are oögones, or in plainer words they are egg-organs, and in them one or more eggs are produced. The second segments (slender) are male organs called antherids, and the protoplasm they contain has the function of the spermatozoids of many plants (and animals). At the proper time the antherids puncture the egg-organs, and by the inflow of the contents of the former the eggs are fertilized. Later these eggs may germinate and produce new plants like those on which they were borne.

are

Downy Mildews (Peronosporacea) much like the water molds, but instead of being aquatic, they live in the tissues of land plants. Like the water molds they are composed of branching, non-septate filaments. The main body of the plant usually grows in the intercellular spaces of the host, where there is nearly as much moisture as under aquatic conditions. In a few species, however, including the organism of the Late Blight of the potato (Phytophthora infestans), the filaments grow directly through the cells of the host, killing them in advance by a poisonous secretion sent out by the fungus. (Fig. 6). From this inter

FIG. 6. Portion of a filament of Albugo candida, with its haustoria penetrating host cells. Highly magnified.

nal part of the fungus short branches grow out into the air, and these become swollen terminally into rounded segments, which are in fact short zoosporangia. Instead of forming zoospores at once, they first fall off and then

those that fall into water develop zoospores, much as in the water molds. As these structures are very minute, a droplet on a leaf is large enough for the germination of hundreds of the detached zoosporangia. Here again, the zoospores, after coming to rest, develop into new plants, which at once penetrate the host. In some species the zoosporangia grow at once into a filament, without forming zoospores.

The sexual organs of downy mildews are much like those of water molds, the differences being quite immaterial for the present discussion. (Fig. 7).

It is evident from a comparison of the structure and reproductive organs of water molds and downy mildews, that the latter are derived from the former. Just as the water molds have been derived from the green plants of the Green Felt family (Vaucheriacea) by the adoption of parasitic and saprophytic habits, so by the change from strictly aquatic conditions to those found in the intercellular spaces of land plants, water molds have been changed to downy mildews. Every difference between the two families may be accounted for by this difference in the environment of the plants.

Black Molds (Mucoracea) show an additional modification of the water mold type. They are non-aquatic, mostly saprophytes, a few only being parasites. They live for the most part on dead organic matter, animal or vegetable, which is still moist, and but few species can live in the water. The commonest species live on the starchy and sugary substances in pantries, cellars and other places where these substances are found in the presence of sufficient moisture. Organic substances which are dry are not attacked by black molds.

Each black mold plant is a branching tubular filament, which has few cross partitions. One part of the plant usually grows in the substance of the organic matter, and another grows

FIG. 7. Peronospora alsinearum, showing antherid penetrating the egg-cell. Highly magnified. FIG. 8.- Mucor stolonifer. Highly magnified. upward into the air. (Fig. 8). The former absorbs food matter, while the latter bears reproductive organs, as in the water molds. The ends of the aerial branches enlarge as in the two preceding families, but instead of forming zoospores, the protoplasm in the terminal segments forms many small spores, each covered with a cell wall. These spores are the homologues of the zoospores in previous families, but as the plants are not aquatic, these zoo

FIG. 9.- Mucor fusiger; A, young sexual organs; B, after fertilization. Highly magnified.

favorable conditions they quickly give rise to a new crop of mold plants. On the filaments which penetrate the nutrient substance, or grow over its surface, are to be found (rarely, however, in the common species) sexual organs somewhat resembling those of the two preceding families. (Fig. 9).

Insect Fungi (Entomophthoracea) are somewhat similar to black molds, but are parasitic in the body tissues of insects, and accordingly show considerable structural modifications. (Fig. 10).

Phylum Carpomyceteæ. The Higher Fungi. This immense phylum, containing over 60,000 recognized species and probably twice as many, if not more, not yet studied, seems to have arisen from chlorophyll-bearing plants of the phylum Rhodophyceae, the Red Seaweeds. These are mostly marine, although many fresh-water species are known. They reproduce sexually by the union of a non-motile : sperm with the elongation of the oogone, termed trichogyne. The male nucleus passes down this to the egg nucleus with which it unites. The fusion nucleus thus produced divides very freely and the daughter nuclei pass out into many branching threads whose terminal cells (carpospores) are the reproductive cells of the plant. The whole structure of oogone, branching threads and carpospores is a "spore-fruit" and may or may not be surrounded by a protective structure of vegetative cells. In the Higher Fungi we find similarly a spore-fruit arising as a result of the sexual process. The ultimate cells are of three kinds, depending upon which one of the three classes is under consideration. (See VEGETABLE KINGDOM and PLANTS, MORPHOLOGICAL EVOLUTION OF). These classes are the Ascomyceteæ, Basidiomycetea and Teliosporeæ. Beside these there is a large group of fungi, certainly belonging to this phylum but which in the lack of knowledge as to their sexual reproduction cannot with certainty be assigned to any one of these classes. These are the Imperfect Fungi. All the plants of this phylum possess branching threads with numerous cross walls (septa) and usually one or two nuclei to a cell. Asexually they produce by conidia, cells cut off from the ends of

FIG. 10.- Empusa musca; filaments from body of fly. Highly magnified. FIG. 11. A, several spore-sacs (asci) in different stages of development; B, a mature spore-sac. Highly magnified. is that the spores which occur in their fruits develop in certain end cells and remain enclosed within the cell wall until matured. (Fig. 11). These spore-containing cells have been aptly likened to sacs (Latin asci; singular, ascus) and from this we derive the name of the class.

There are more species of sac fungi than of all other kinds. Their fruits range in size from very minute to many inches in extent. They include some of the most harmfully parasitic plants as well as many which live saprophytically upon refuse organic matter. Among the many families (more than 100) in this class, the following may be noticed:

FIG. 12. Sexual organs of Erysiphe and formation of fruit. Highly magnified.

Powdery Mildews (Erysiphacea) are the cause of many serious diseases of wild and cultivated plants; e.g., rose, apple, cherry, gooseberry, ash, etc. The plant body consists of branching filaments which creep over the sur

faces of their hosts, from which they obtain food by means of root-like absorbing organs, which penetrate the host cells. Certain branches form spores by the simple process of separating their terminal cells in succession and this is done so abundantly that the spores form powdery masses on the surface of the hosts. These spores float away on wind currents, and those that germinate on similar hosts give rise to new plants.

The sexual organs (egg-cells and antherids) occur on the creeping filaments, and are short lateral branches, the former somewhat thicker than the slender antherids. (Fig. 12). The two come in contact with each other, and the protoplasmic contents of the antherid pass into the egg-cell fertilizing it. As a result the eggcell sends out one or more branches, the end cells of which develop into asci, while from below the egg-cell there grows up a cellular, globular covering, constituting the outer wall of the fruit, and enclosing the asci. The spores in the asci, when set free by the rupture of fruit and ascus walls, germinate and on similar hosts give rise to new plants. These fruits are usually blackish and may be seen by the naked eye as minute globular bodies on the mass of filaments. (Fig. 13).

Truffles (Tuberacea) are eagerly sought for as table delicacies, their large subterranean fruits being highly favored by epicures. Their life history is not well known. They are saprophytic, living on the decaying organic matter in the soil in forests. Little is known as to their early life, and the formation of their non-sexual spores, but these are thought to be somewhat like those of the powdery mildews. nd sell sig blom d

FIG. 13. Mature fruit of powdery mildew, with escaping spore-sac. Highly magnified.

Their fruits are formed under ground. The sexual organs, which possibly precede the development of the fruits, have not yet been discovered. The fruits of the common truffles of Europe are from one to two inches in diameter, and warty and dark colored externally. (Fig. 14). Internally they consist of a soft, whitish tissue, in which are numerous cavities, each containing several asci. Practically nothing is known as to their propagation. A few little known species occur in America, but in Europe they are common. See TRUFFLE.

Black Fungi (Sphæriacea and numerous related families) are typically parasites which grow in the tissues of higher plants, and whose small black fruits are formed on the surface of the host. Here again we are evidently dealing with plants related to the powdery mil

A

FIG. 14

19118 A

FIG. 15

FIG. 14.-Truffle; fruit, natural size. FIG. 15.-Nectria cinnabarina; A, bark with enlarged fruits; B, spore-sacs. Highly magnified. reproduction are similar to the same phenomena in the Sphæriales. Several species of Nectria (Fig. 15) cause serious cankers on apple twigs, etc. Ergot of grains (Spermædia or Claviceps) also belongs in a closely related family.

Cup Fungi (Pezizacea and related families) are typically saprophytes (Figs. 16 and 17), growing in the tissues of decaying plants, as rotten logs, sticks, etc. In these fungi the plant is filamentous and grows through the decaying tissues as slender white, branching threads. Non-sexual spores resembling those of the powdery mildews are known for some species. Sexual organs, consisting of a globular egg-cell and a slender anthenid are found on the creeping filaments. (Fig. 19). Fertilization takes

B

FIG. 17.- Humaria rutilans; A, three fruits, natural size; B, vertical sections of fruits of different ages.

face of which are found many asci (Fig. 18). It will readily be seen that were these cupfruits to remain closed, their structure would be closely similar to that of the fruits of the powdery mildews or black fungi. However, the fruits of the cup fungi are often of considerable size, sometimes being as large as five or six inches in diameter.

Lichens (see article LICHENS) are now regarded as nearly related to the cup fungi and black fungi. (Fig. 20). In the essentials they agree with those fungi, but they are usually treated separately because their parasitism on various small algæ leads to the production of for powever

1170

FIG. 18

FIG. 19

FIG. 16.- Diagrammatic vertical section of a cup fungus. place as in powdery mildews, with a similar result, the fruits, however, being at length cupshaped instead of globular. In many species

FIG. 18.- Humaria rutilans; spore-sac, and three paraphyses. Highly magnified.

FIG. 19.- Egg-cells and antherids of a cup fungus. Highly magnified.

peculiar vegetative structures, the study of which for a long time led botanists to neglect their evident relationship to fungi which were not parasitic on algæ. There are several families of the lichen-forming fungi, aggregating between 2,500 and 3,000 species.

are here

Yeasts (Saccharomycetacea) briefly referred to in order to call attention to the excessive degradation which they have suffered. Although they consist of single cells, or

FIG. 20.-Physcia stellaris, a common lichen. Natural size. while at the same time carbon dioxide is set free. It is for the alcohol that yeasts are used in breweries and distilleries, and it is for the escaping carbon dioxide gas that they are used in the making of bread. See YEAST.

Phylum Teliosporeæ. The fungi of this phylum consist entirely of parasites upon higher plants. They are often exceedingly destructive. The characteristic distinction from the preceding phylum is the formation of a thick-walled teliospore. This is formed as the ultimate product of a sexual union. From this teliospore there arises sooner or later a short thread (Bromycelium) upon which are produced four (sometimes more) small "sporidia" which give rise to the new fungus when they fall upon the right host. In this phylum we find parasitism brought to its highest development. The fungus has so adapted itself to the host that it continues to live within the host tissues for a long time without causing much inconvenience, only proving destructive when it enters upon its fruiting stage. The two chief groups (orders) are the rusts and smuts.

Rusts (order Uredinales) are minute plants, parasitic in the tissues of higher plants. (Fig. 21). They consist of branching filaments which grow through and live upon the host tissues. Certain branches cluster together and form rows of spores by terminal abstriction, each row being initiated by a sexual union of the terminal

spores germinate each produces a short filament (promycelium) on which four minute spores (sporidia) develop. There are thus four kinds of spores in a typical rust plant, and these have been taken to characterize as many stages in the plant's life history, namely: (1) Cluster-cup stage (aciospores); (2) Red Rust (urediniospores); (3) Black Rust (teliospores); (4) Promycelium (sporidia). In many rusts these stages occur on the same host in the order given, but in some the first stage occurs on one host, and the remaining stages on another. The latter is the case with the stem rust of wheat, in which the cluster-cups, occur on barberry leaves, and the æciospores then germinate upon and infect the leaves of the wheat, on which the red rust, black rust and promycelium then follow in succession.

Smuts (order Ustilaginales) are still more parasitic than the rusts, and as a consequence have suffered still greater degeneration (Fig. 23). They grow wholly within their hosts, and do not even bring their spores to the surface. They consist of branching filaments which penetrate the tissues of their hosts, and at last form spores homologous with the teliospores of the rusts. The latter in germinating produce sporidia. Comparing the rusts with the smuts we note that while there are four stages in the

FIG. 21.- Puccinia caricis, a common rust on sedges. or subterminal cells of two adjacent filaments. (aciospores) (Fig. 22 A). The fungus arising from the germination of these spores forms at first large numbers of red or orange colored single terminal spores (urediniospores) (Fig. 22 B), and still later, the one- to several-celled thick-walled, usually dark colored teliospores. (Fig. 22 B). These all begin within the host tissues, but they eventually break through the epidermis into the air. Lastly, when the telio

FIG. 22. Puccinia graminis, a common rust of wheat. A, Cluster-cup stag on Barberry leaf; B, three urediniospores and one teliospore from a leaf of wheat. Magnified.

former, there are but two in the latter, the first and second having apparently disappeared Imperfect Fungi.- At this point should be mentioned the so-called imperfect fungi, an im