DISEASES OF PLANTS. . 245 



of the head until the grain is mature. According to weather conditions and the 

 length of tinio tliat the dead top of the stallc is subject to the action of 

 weather, it may appear bleached, blackened, or discolored in various ways. 

 Very frequently the stalk breaks off at the point of attack, and in 70 per cent 

 of all cases observed the point of infection was at the lowest joint on the 

 rachis, or what is pojmlarly known as the neck. If the lesion is below the 

 neck, the first sign of the disease is one or more miiuite spots, which appear 

 on the sheatli node directly above the joint. At first the tissues appear water- 

 soaked and sunken and later the spots become discolored, brownish, or black. 

 This discoloration spreads up the sheath, but usually for not more than an 

 inch, and downward for a distance of one-fourth to one-half inch. The spot 

 becomes more shrunken and extends laterally, girdling the stem. The skin 

 becomes broken, resulting in an open wound, which may appear blackened from 

 the growth of various organisms on the dead tissues. A microscopical 

 examination of the neck shortly after the appearance of the spot reveals the 

 presence of the spores of a fungus, but as yet it has not been positively identi- 

 fied. Thus far experiments have not determined the exact cause of the disease. 



The rice blast does its damage by arresting the development of grain, which 

 may be done at any time. The financial losses due to this cause are very great, 

 and in some localities the disease has resulted in the abandonment of rice cul- 

 iivation. 



Investigations conducted to determine whether the disease might be distrib- 

 uted by other plants than rice seem to indicate that while it may affect a few 

 species of plants, such, as Panicum crus-galU, yet it is improbable that the 

 disease can originate or spread from this source. 



A number of typical cases of blast, as observed in plantations, ai'e described, 

 after which the author discusses the conditions of spread and methods of con- 

 trol. So far, there does not appear to be any connection between the disease 

 and weather conditions, nor is there any evidence that the blast is transmitted 

 by seed. There does appear, however, to be a distinct relationship between the 

 soil conditions and the disease. It has been shown that the blast may be readily 

 produced by inoculating healthy plants directly from diseased ones, but so far 

 it has not been produced by pure cultures of any one organism. The disease 

 occurs in its most virulent form on rested land, land that has been recently 

 reclaimed, or land that is fei'tilized with nitrogenous fertilizers. 



In considering methods of control, the author discusses water treatment, the 

 use of fertilizers, spraying, securing immune plants, etc. The best results have 

 been obtained where marl or lime were used as fertilizers. It is believed that 

 the disease has practically run its course in South Carolina and will not spread 

 further unless nitrogenous fertilizers are used or resting is practiced on these 

 lands that are annually producing poorer and poorer crops. Such lauds should 

 be treated with great cai-e and should not be rested under any circumstances, 

 nor should nitrogenous fertilizers be applied to them. 



So far as known, there are no varieties of rice that are entirely inuuune to 

 this disease, and variety tests and selections for immunity have thus far failed. 



Brief notes are given on other diseases of rice, among them smut, rust, damp- 

 ing off, spotted blight, etc., most of these diseases being fairly well known and 

 capable of control. 



A brief list of works relating to rice diseases completes the bulletin. 



Diseases of sweet potatoes in Alabama, E. M. Wilcox (Alabawa College 

 Sta. Bill. 13-'), pp. IC. fif/s. .'/I. — A preliminary report is given on some of the 

 diseases to which the sweet potato is subject in Alabama, the principal ones 

 described being black rot, dry rot. scurf, soft rot. soil rot. stem rot. and white 

 rot. Where preventive treatments are known the author has described them. 



