colors will be observed. So successful has this little instrument proved in practice that it is now coming into general use. Agents of the United States Bureau of Interal Revenue are being furnished with pocket polariscopes by the Chief of the Bureau.

EXHIBIT 60.-Taylor combination freezing microtome.

The freezing microtome invented by Dr. Thomas Taylor, United States Department of Agriculture, supplies a long-felt want. The instrument, as its name implies, combines the valuable properties of several microtomes, by means of which vegetable or animal tissues may be quickly frozen, using ice water and common salt, ether, or rhigolene. Tissues embedded in wax or paraffin may be as readily cut. Notwithstanding its several adaptations the arrangement is remarkably simple consisting of an adjustable knife (curved in this illustration, although a straight knife may be used) and a freezing chamber which when removed admits of the substitution of a cork or other suitable substance on the top of which the material to be cut in section is held by means of paraffin or wax.

EXHIBIT 60.- represents the freezing chamber, a metallic box with arms, to both of which rubber tubing is affixed for the access and exit of water or ether. The exit tube is furnished with a glass tube terminating in a bore one-sixteenth of an inch in diameter, which prevents a too rapid flow of the freezing liquid. This passing into a separate vessel may be used over again, especially if freezing water. Ether may be condensed in ice water in a close jar and thus reserved for future use, a precaution hitherto overlooked. ' A sectional view of the freezing chamber; s the revolving table. The freezing chamber is prevented from turning by a back plate, facing the mahogany block, which arrests the movement of the arms coming in contact with it. EXHIBIT 61.-Taylor instrument for testing the tensile strength of textile fibers.

CHAPTER XXXII.

FUNGUS DISEASES OF PLANTS.

By B. T. GALLOWAY.

The Section of Vegetable Pathology was organized in July, 1887. Its purpose is to investigate the causes of and remedies for the diseases of cultivated plants caused by parasitic fungi, and to disseminate information concerning them. The first has been done by the work of specialists in the laboratory and in the field, and the second by the publication of bulletins and annual reports, both illustrating and describing the fungi causing these diseases. In these there are always suggestions as to treatment, and especial attention has been given to any experiments with fungicides which have been made by the Department or reported to it by outside parties. The fact that a successful remedy has been found for black rot of the grape, and that there are indications that bitter-rot and scab of apples as well as other destructive diseases may also be prevented, is sufficient to show that the section is of practical value to the country.

The following illustrations and photographs of the leading fungus diseases of cultivated plants, together with maps indicating distribution, comprised the exhibit of this section at the Exposition.

ILLUSTRATIONS OF FUNGI.

No. 1.-Apple scab (Fusicladium dendriticum, Fckl.).

Fig. 1. Diseased apple.

Fig. 2. Leaf with spots caused by the fungus.

Fig. 3. Spores, some of which are germinating.

Fig. 4. Section of a diseased portion of the fruit.

The distribution of the disease is coextensive with the cultivation of the apple. It is found in nearly every orchard in the Eastern and Central States and is frequent in California; has been known in Europe for over fifty years, and is a serious pest in Australia and New Zealand.

It attacks certain varieties more than others, but in some seasons respects neither soil, culture, nor variety. In the United States it causes great annual losses, to the extent of one-half the crop in some States.

No. 2.-Cotton leaf-blight (Cercospora gossypina, Cke.).

Fig. 1. Tuft of spore-bearing hypha, with detached spores.

Fig. 2. End of branch with diseased leaves.

One of several fungi that infest the cotton plant; probably occurs in all the cottongrowing States. It is more prevalent in wet weather, and is sometimes sufficiently serious to materially diminish the vitality of the plant.

No. 3.-Pear leaf-blight (Entomosporium maculatum, Lev.).

Fig. 1. End of branch with diseased leaves.

Fig. 2. Diseased fruit, showing crack.

The fungus attacks the leaves, stems, and fruit, sometimes defoliating the trees as early as the middle of July, and causing the fruit to crack, as shown in the figure. It is widely distributed, and in some places destroys three-fourths of the crop annually.

No. 4.-Strawberry leaf-blight (Sphærella fragariæ, Tul.).

Fig. 1. Diseased strawberry leaf.

Fig. 2. Germinating summer spores.

Fig. 3. Several asci with a portion of the pseudoparenchyma to which they are attached.

Fig. 4. Ascospores, much enlarged.

Fig. 5. Section through the upper surface of a leaf, showing a tuft of conidiophores with spores attached.

Fig. 6. Section of a perithecium, showing asci within.

Fig. 7. Perithecium, external view, with conidiophores and conidia at the apex.

The injury to strawberry culture resulting from this disease appears to have been on the increase during the past 5 or 6 years. It seems to be pretty thoroughly distributed throughout the United States, and appears to be most severe in Illinois, Michigan, Wisconsin, Minnesota, Iowa, Missouri, Kansas, and Kentucky.

Its effects, even in mild cases, must be detrimental to the processes of assimilation, and when the attack is severe it results in the death of the plants.

No. 5.-Cedar apples, and apple Ræstelia, (Gymnosporangium macropus, Link.).
Fig. 1. Leaves showing the rust spots on upper and under surfaces.
Fig. 2. Cedar apples.

A disease which appears in different forms on different hosts, producing the growth usually known as cedar apples on cedar trees, and apple rust on the cultivated apple. It is a widespread disease and the injury which it does to apple trees seems to be on the increase. It attacks the fruit as well as the leaves.

No. 6.-Orange leaf-scab (Cladosporium, sp.).

Fig. 1. End of a twig bearing leaves attacked by the "scab."
Fig. 2. Portion of the leaf magnified, showing "scab" spots.

Fig. 3. Section through a scab spot, showing fungus on the surface.

Orange scab is a disease of recent appearance in the South, and is usually confined to sour stocks and lemons. It is very destructive to the growth of trees and ruinous to young nursery stock,

No. 7-Anthracnose of the bean (Glæosporium lindemuthianum, Sacc. & Mag.). Fig. 1. Diseased pods.

Fig. 2. Section through a diseased pod, the dark portions representing the diseased

spots.

Fig. 3. Section through a diseased pod in a more advanced stage of the disease, one side of the pod and the bean within being completely shriveled.

Fig. 4. Section through a pustule containing the basidia and spores of the fungus. Fig. 5. Spores.

The disease sometimes called "rust" attacks wax or butter beans, and often causes serious injury to melons by attacking the leaves and rind.

It occurs in Germany, France, Italy, England, and the United States. In the

latter country it seems to be very generally distributed, as specimens have been sent to the Department of Agriculture from Maine, Massachusetts, Wisconsin, Pennsylvania, Louisiana, and the District of Columbia.

No. 8.-Black spot of the peach (Cladosporium carpophilum, Thüm.)

Fig. 1. End of twig bearing diseased leaves.

Fig. 2. Diseased peach with crack caused by the fungus.

The peach spot is so prevalent and so uniformly present on certain varieties that some peach-growers consider it as a portion of the peach itself. It may and does cause serious injury in many cases. When it covers any considerable portion of the surface of the fruit it retards the growth of the outer parts and causes it to crack, thus making it very liable to decay.

No. 9.-Rose rust (Phragmidium mucronatum, Wint.).

Fig. 1. Diseased stem and leaves. Ecidium stage. Stem showing characteristic bend caused by the fungus.

Fig. 2. Diseased leaf, showing Uredo and Phragmidium stages.

Fig. 3. Section through a diseased spot on the back of a vein, showing the spores in rows. Ecidium stage.

Fig. 4. Æcidium and Uredo spores.

Fig. 5. Phragmidium spores.

Fig. 6. Section through a diseased spot, Uredo stage.

A fungus belonging to the same class as the one causing the apple rust, but, unlike that, producing all the different forms on the same plant. The disease is especially severe on hardy hybrid perpetuals. It is common in Europe and widely distributed in the United States, where it has recently been observed in California.

No. 10.-Spot disease of the maple (Phyllosticta acericola, C. & E.).

Figure showing both the upper and under side of the leaves of the silver maple attacked by the parasite.

The disease attacks both the red and the silver maples, sometimes rendering the foliage unsightly. It is especially severe on nursery stock. Found in the Eastern and Western States.

No. 11.-Anthracnose of the raspberry (Gloeosporium venetum, Speg.).

Fig. 1. Diseased branch, showing the diseased spots on the stem, leaves, and petioles, and the effects on the berries.

Fig. 2. Spores, two of which have sent out germ tubes.

Fig. 3. Section through a disease spot on the stem, showing the manner in which the fungus breaks down the tissues.

This disease, sometimes popularly known as "raspberry cane rust," has caused serious injury in Illinois, New Jersey, Texas, Wisconsin, and Missouri. In southern Missouri the loss amounted to from 10 to 12 per cent in 1887.

No. 12.-Black spot of the rose (Actinonema rosæ, Fr.).

Fig. 1. Diseased leaf.

Fig. 2. Enlarged portion of a leaf at the edge of a black spot, showing the mycelium and two fruit pustules of the fungus.

Fig. 3. A strand of mycelium.