cleanliness in a pathological sense means, and yet success in growing a crop often hinges on the proper application of this very point.

The gradual shifting of plant industries from one region to another offers very interesting material for study. While the causes may be grounded in economic adjustments these adjustments are frequently made necessary by failure to appreciate or properly understand plant sanitation in a broad sense. Not long since I was told by one of the largest nurserymen on the Pacific Coast that he could no longer afford to buy land for nursery work. Fighting certain cumulative soil pests, such as crown gall, nematodes, and gummosis, cost so much that it was cheaper to rent land and move on every few years. This practice can not, of course, be continued indefinitely. Means must be found for correcting the difficulties in other ways.

While a great deal of beneficial sanitation is within the power of the individual, the State must be brought to see the importance of the matter if far-reaching results are to be secured. The State never moves in such matters until there is a ground swell of public opinion behind it, and this ground swell can best be created by bringing to the individual grower the importance and value of sanitary practices in all his work.

There is a phase of crop hygiene that so far as we are aware has received little attention as yet in this or any other country. For want of a better title we might call it plant-disease detection. It would be in the nature of crop insurance, It would differ from a plant disease survey in that the disease would be detected before it had assumed sufficient importance. to be surveyed. We can apply this work to our field stations, but it should be applied to the country at large. The work presupposes central directive power. It would be national. Is it not reasonable to believe that were a properly organized corps of men engaged in the field in this kind of work many of our most serious and widespread pests would have been discovered in their incipient stages and could have then been stamped out?

The State is slow to move in such matters. It is rather prone to wait until things happen and then act. Public sentiment was a long time in crystallizing to the extent that such precautionary measures were made practicable in connection with some of the most serious diseases of man, and it has not yet reached the point where it is willing to require the State to undertake this kind of work with the diseases of our domestic animals. There is no adequate force of men constantly on the lookout for foot-andmouth disease. Such a force of men might cost the Government fifty to sixty thousand dollars a year, but if the disease was discovered and stamped out in its incipient stages it would be money well spent.

Finally, we would like to speak briefly on what appears to be two very

broad fields of usefulness in plant hygiene. The first has to do with the relation of weather to outbreaks of plant diseases and the relation of weather to plant-disease control, and the second is concerned with soil and fertilizer requirements as affecting pathological phenomena. We know that the weather plays a most vital part in all crop production. We do not want to discuss this broad subject now. Suffice it to say that there would appear to be enough data and experience to warrant attempts at plant-disease-outbreak forecasting in a limited way at first, same to be increased as knowledge is gained. This would need to be taken up by men trained not only in pathology, but also possessed of broad knowledge of crops, crop production, and crop economics.

Coupled with crop-disease forecasting would be timely warnings as to action in preventive measures. In a number of the midwestern, lake region, and northern Atlantic States the movement of cyclonic areas is so well defined, especially during the spring, early summer, and fall that it would appear feasible to use them as a basis for timely warnings as to when to spray or not to spray plants. I believe such use is already being made of weather data in a limited way. Our point is that it should be developed into a broad National service.

As to the soil and fertilizer requirements in their relation to plant hygiene, we have many striking examples of the broadness of the field. The losses through plant diseases due to maladjustments of crops to soils and through malnutrition, the result of misuse of so-called plant foods, are strikingly large. Can these losses be met or mitigated through broad phytopathological studies? We believe that they can, but to get the large, essential facts and to properly group them so that they can be used in a broad way will require unity of action.

We have here in the eastern United States and also extending into many States of the South a vast area of soil capable of producing immense quantities of food under proper agricultural management. I refer to the acid lands of the Coastal Plain Region. For centuries we have been handling this land and cropping it without due regard to the fact that many of the introduced plants are out of place there. It would seem that with our present knowledge we might do much toward a proper adjustment of crops to soil and thereby greatly increase the production of the region..

One of the field stations of the Office of Foreign Seed and Plant Introduction is located at Brooksville, Florida. This station was established primarily as a place to grow, test, and propagate bamboos. It is in a section, such as may be found in many parts of the South, in which numerous crop enterprises have been launched in times past and most of which have failed, about the only ones persisting being those that are not seriously affected by the ravages of nematodes. Corn, velvet beans, and several

promising grasses may eventually make live-stock production, especially the raising of hogs, a profitable business.

Here we find ourselves asking other far-reaching questions. Can we look forward to a successful liye-stock agriculture in certain parts of the South if we have to depend wholly upon the crops produced there? May not calcium be the limiting factor in the successful raising of certain kinds of live stock in this region, and can calcium be supplied to the plants in such quantity and form as to give them the maximum development and supply the necessary cell-building materials? We may be overstepping the bounds of phytopathology when we open up such problems, but after all we are seeking the truth. Are we to follow the rule of the Chinese and secure truth only through century-long trials and retrials, or are we to secure it through the channels of science, which after all recognize no hard and fast lines between those who labor in its fields?

THE ALTERNARIA LEAF-SPOT OF COTTON

R. C. FAUL WETTER

WITH THREE FIGURES IN THE TEXT

A disease of cotton leaves, due to a species of Alternaria, is common in South Carolina and very probably in other of the cotton-growing states. So far as is known it has never been described, though the disease was recognized and some studies made by Beal of the Mississippi Agricultural College in 1914. Investigation of the subject was undertaken by the writer because of its relation to the angular leaf-spot, a disease which has been under close observation for some time.

The fungus causing the disease is not a virulent parasite when compared to other species of the same genus, A. panax Whetzel,' for instance, which is said to be able to destroy entire gardens of ginseng. The lesions of this disease of cotton arise in and spread from earlier injuries of the leaf in the great majority of instances. In the early part of the summer these are most frequently the angular spots caused by Bacterium malvacearum Smith. Other injuries may serve for this purpose, and occasionally the disease develops where no previous wound can be detected.

The Alternaria spot when developing from a bacterial spot first appears at one side as a pale green area, having an indefinite and irregular margin. As this area increases in size the color of the older portion becomes strawyellow and finally rusty brown. By this time the spot contains a number of irregular concentric zones, resembling those diseases of other plants ascribed to species of Macrosporium and Alternaria (fig. 1). The largest spots formed in this way have a breadth of 1.5 to 2 cm. and are usually of irregular shape with nearly equal breadth and length. It very often happens that the fungus grows outward from the bacterial spot in all directions and finally surrounds the former. In such cases the definitely angular spot may be detected in its center by holding the leaf to the light. The bacterial spot is translucent while the fungous spot is opaque. The same dark brown, papery spot is common in the region of red spider injuries upon the leaves (fig. 2). The principal point of difference in the two types of spots lies in the fewer and less, conspicuous zones in the latter case. When examined with a hand lens the zones are easily seen, but usually lie close to the margin. Entomologists agree that

1 Whetzel, H. H. and Rosenbaum, J. The diseases of ginseng and their control. U. S. Dept. Agr., Bur. Plant Industry Bul. 250: 9–17, 1912.

this condition is not caused by the spiders alone. Such areas are very common in the angles of the main ribs and often spread over a large part of a sector of a leaf.

During the latter part of the summer cases of the disease have been found in which neither angular leaf-spot, red spider or other injuries seem to be present. It is difficult to determine conclusively the necessity of such wounds for the entrance of the fungus, but judging from the material examined it seems probable that conditions exist under which the fungus is able to invade uninjured tissues. Whether these condi

tions involve the physiology of the host or parasite, or the external environment, the writer is not prepared to say.

Water mounts of scrapings from the surfaces of these spots always contain Alternaria-like spores (fig. 3 left). In such mounts they have only been found singly. Examination of the surfaces by means of a binocular microscope show the spores frequently in chains of two. On material collected during a particularly rainy period and examined immediately, chains of spores were found containing three and four each. The surfaces of petri dish cultures also show such chains, though this evidence is less important than that found under more natural conditions.