In distinguishing wall color the workers in this laboratory have adopted a simple system which has been found to be very useful in working with rust spores. Nine different colors, or groups of colors, are recognized, namely, colorless, light-yellow, yellow, orange-yellow, golden-brown, cinnamon-brown, chestnut-brown, chocolate-brown, and blackish, and any rust spore may be quite readily placed in one of these divisions. Like any other scheme for interpreting or matching colors this leaves a wide latitude for individual interpretation, but it works very satisfactorily, since a comparison of descriptions by different observers has usually shown a close agreement.

When the wall is noticeably colored it is usually an easy matter to measure its thickness. Difficulty arises when the wall is either faintly or too densely colored. In the former case some cell-wall stain is used, the important consideration being to use a stain which will differentiate the wall from the spore contents. For this purpose chloral-hydrate-iodine is frequently utilized. When the wall is densely colored, so that no clear optical section is visible, lactic acid is used as a clearing agent, a drop of the acid being placed at the edge of the cover-glass of an ordinary water mount and the slide then heated. In some species of rusts, especially those having a waxy spore-wall, wall thickness cannot be ascertained in water mounts, since such walls usually gelatinize and swell considerably in water. In such cases alcohol is used as the dispersion medium. Sometimes the rust sorus is so waxy that it is very difficult to scrape whole spores from it. It may be worth while to cite the case of a rust, Sphenospora pallida, in which the telial sori are so waxy and so unlike any ordinary, pulverulent, rust sori that after making several water mounts and finding no spores the writer was about to conclude that it was not a rust. It was only after boiling some of the sori in a dilute solution of potassiumhydroxide that the true nature of the fungus was established.

Surface markings are usually distinctive and are ordinarily rather easily recognized; when they are difficult to observe a dry mount of the spores will often be of considerable help in recognizing and distinguishing them, but interpretation of the types of markings is frequently a rather difficult task. In order to harmonize descriptions of various species having the same type of markings it has seemed best to limit the use of some terms, especially the terms verrucose and echinulate. The word verrucose is applied to those markings which are wart-like and have rounded apices. Markings on aeciospore-walls are usually of this type. The word echinulate is used in describing those markings which are needle-like or spiny with more or less sharply-pointed apices. Urediniospore-walls frequently have markings of this type. These markings are placed at various distances apart and in order to insure conciseness and harmony in describing the various species,

the following scheme is used. Those markings which are 1 μ or less apart are described as very close, those which are 1μ to 2μ apart are called close, 2μ to 3μ apart moderate, 3p to 5μ apart sparse and 5μ or more apart very sparse. This scheme is used merely as a guide in writing up descriptions and ordinarily no attempt is made to measure the distances between the markings.

THE PORES

The number, position, and character of pores, especially in urediniospores, have shown themselves to be exceedingly valuable features in defining and distinguishing species. To any one who questions this statement the writer desires, for example, to point out the three species of grass rusts, Puccinia Clematidis (P. triticina), P. glumarum, and P. montanensis, which are usually accepted as good species. A study by the writer of the material of these rusts in the Arthur herbarium has shown that such characters as type of spotting (frequently a difficult thing to distinguish in dried specimens), linear arrangement of sori, and other features are often found to be associated with at least two and sometimes all three of these closely related species. When telia are present, P. montanensis may readily be distinguished from the other two, but when uredinia only are available, the writer has found that the best distinguishing character is the number of pores in the urediniospore-walls, which is 6 to 8 in P. Clematidis, 8 to 10 in P. montanensis, and 10 to 15 in P. glumarum. (It is beyond the scope of this paper to give further details on these rusts.)

Frequently the pores are difficult to locate and to count, as in the three rusts mentioned above, especially if the wall coloring is too faint or too dark or if the cell contents is made up of oil globules or other refractive bodies. The easiest way of distinguishing pores from spore inclusions is to obtain the pores in optical section when they will appear as passage-ways in the wall. Then by rotating the spore, which is done by gently tapping or moving the cover-glass, the number and position of pores can be ascertained. When the walls are densely colored the use of lactic acid and heat is very helpful in bringing out the pores, and when the walls are lacking in color the use of chloral-hydrate-iodine, of the formula given by Stevens in his Plant Anatomy, p. 300, is frequently very beneficial. By these methods there are very few species of rusts in which urediniosporeor teliospore-pores cannot be ascertained.

No attempt is here made to discuss all the characters and terminology used in describing rusts in the Arthur herbarium but rather to explain the methods used in studying the more obscure characters.

UNIVERSITY OF ARKANSAS

AGRICULTURAL EXPERIMENTAL STATION

PHYTOPATHOLOGICAL NOTES

An epidemic of corn smut following hail. There is a small district of some six by ten miles directly east of Greeley, Colorado, where hail storms occur frequently, and often with severity. On the afternoon of July 29, 1918, a storm occurred which did much damage. Beans were pounded into the ground and killed outright; sugar beets and potatoes were defoliated; corn was badly bruised and the leaves shredded. On August 14, sixteen days after the storm, several fields of smutted corn were observed averaging 19 per cent infection. Other fields outside of this hail area, but subject to high winds, averaged only 1 per cent infection. According to testimony of the farmers owning the corn, the smut (Ustilago zeae (Beckm.) Unger) had appeared following the hail, and none had been observed before it. It is safe to assume that the fields contained at least the 1 per cent commonly found. This would have provided a source of infection.

Hail storms in this region are usually preceded by wind and rain. Little or no wind may accompany the hail, though some rain usually falls for the first few minutes. A severe hail such as occurred on July 29 would easily have broken and shattered any smut sporophores and scattered the spores or raised them in clouds. Presumably wind accompanied this storm, though there is no definite information on this point.

The smut boils as seen on August 14 were of remarkably uniform size. They were about two inches in diameter and beginning to break down into conidia. In spite of the fact that the corn plants showed abundant bruises and shattered leaves, infection had taken place only at the leaf axils. There was no infection through wound or bruise. Piemeisel1 has reported that infection may take place readily without injury of the tissues, and is purely local. He makes no mention of having caused infection through wounds. Potter and Melchers, however, consider that the conidia do not infect directly, but that infection results from the development of a virulent culture in the leaf axil. As noted above, infection following the hail was evidenced only at the leaf axils. This infection was probably as general and violent as ever occurs in nature. It seems reasonable to suppose that the wounds on the corn plant were liberally sown with smut spores, and that direct infection might have followed had direct in1 Piemeisel, Frank, J. Some facts of the life history of Ustilago zeae (Beckm.) Unger. Phytopath. 4, No. 6: 411-412. December, 1914.

Potter, Alden A., and Melchers, Leo E. Ecological observations on Ustilago zeae. Phytopath. 40, No. 1: 73-74. February 191′′

feetion been the rule. The answer to this may be that at the axil only would enough moisture collect to cause spore germination and make fungous growth readily possible, especially in an arid climate.

H. G. MACMILLAN.

Plant pathologist desired in Brazil. A communication from Mr. Adolph Hempel (Secretaria da Agricultura, Commercio e Obras Publicas, do Estado de S. Paulo, Directoria de Agricultura, Brazil) states:

"The State Government wishes to install a new department of economic entomology and plant pathology, and would prefer to have men from North America and some that have had some experience in their specialties and who are capable of doing research work, and who would be willing to work under my direction here in S. Paulo, and contract for several years, at a salary of about $150.00 a month, and traveling expenses paid."

Personals. Mr. Fred C. Werkenthin has resigned his position as assistant professor of biology at the New Mexico College of Agriculture and Mechanic Arts to accept a position as associate professor of botany at the New Hampshire Agricultural College.

Dr. Charlotte Elliott of Dell Rapids, South Dakota, has been appointed as assistant pathologist in the Laboratory of Plant Pathology, Bureau of Plant Industry.

Mr. G. H. Martin, Jr., formerly a teaching fellow in plant pathology at the University of Washington, has accepted the position of plant pathologist in the Plant Disease Survey, Bureau of Plant Industry.

Dr. V. H. Young has resigned his position in the Office of Cotton, Truck, and Forage Crop Disease Investigations, Bureau of Plant Industry, to become the head of the department of botany in the University of Idaho.

Dr. F. A. Wolf, for several years in charge of the botany and plant pathology work at the North Carolina Agricultural College and Experiment Station, has been given a commission as first lieutenant in the sanitary corps of the Army.

LITERATURE ON PLANT DISEASES1

COMPILED BY EUNICE R. OBERLY, LIBRARIAN, BUREAU OF PLANT INDUSTRY, AND FLORENCE P. SMITH, ASSISTANT

August, 1918

Africa, Emilio Macasaet. The minimum Bordeaux application for the control of Hemileia. Philippine Agr. and Forester 6: 251-271. My. 1918.

Bibliography, p. 271.

Thesis.

American Phytopathological Society. Cereal pathologists. Fourth annual field Science, n. s. 48: 148-150. Ag. 8, 1918.

conference

Boyce, J. S. Advance rot and latent defects on aeroplane timber. Aerial Age Weekly 7: 674-675, 691. Je. 17, 1918.

Bibliography, p. 691.

Brierley, William Broadhurst. The microconidia of Botrytis cinerea. Roy. Gard. Kew, Bul. Misc. Inform. 1918: 129-146, pl. My. 1918.

Cook, Melville Thurston. Common diseases of berries. New Jersey Agr. Expt. Sta. Circ. 88, 11 p., illus. [1918?]

Common diseases of garden vegetables and truck crops. New Jersey Agr. Expt. Sta. Circ. 89, 22 p., illus.

[1918?]

and Martin, William H. Leaf blight of the tomato. New Jersey Agr. Expt. Sta. Circ. 96, 4 p., illus. 1918.

Dodge, Bernard Ogilvie. Studies in the genus Gymnosporangium. II. Report on cultures made in 1915 and 1916. Bul. Torrey Bot. Club 45: 287-300, pl. 8. Jy. 1918.

Literature cited, p. 299.

Edson, Howard Austin, and Shapovalov, Michael. Potato-stem lesions. Jour. Agr. Research 14: 213-220, pl. 24-26. Jy. 29, 1918.

Elliott, John Asbury. Arkansas peach diseases. Arkansas Agr. Expt. Sta. Bul. 149, 9 p., 5 pl. 1918.

Grove, William Bywater. The British species of Melanconium. Roy. Gard. Kew Bul. Misc. Inform. 1918: 161-178, illus. Je. 1918.

Hall, Constant Johan Jacob van. De bescherming der cultuurgewassen tegen nieuwe ziekten en plagen uit het buitenland. Teysmannia 29: 62-95. 1918. Reprinted.

1 This list includes references, both American and foreign, to the literature of plant pathology and mycology of interest to pathologists. Foreign references published since January 1, 1917, have been included beginning with the list appearing in v. 7 no. 3, June 1917.

All authors are urged to coöperate in making the list complete by sending their separates and by making corrections and additions, and especially by calling attention to meritorious articles published outside of regular journals. Reprints or correspondence should be addressed to Miss E. R. Oberly, Librarian, Bureau of Plant Industry, U. S. Dept. Agric., Washington, D. C.