DISEASES OF PLANTS. 857 



plant with which it comes in contact. The presence of a white mold 

 at the base of the plant, rotting the leaf bases and the stem, and a sud- 

 den collapsing of plants, distinguish this disease from the Botrytis 

 diseases with which it has been confused. 



Another disease which is due to a species of Rhizoctonia, in which 

 the lower leaves are first attacked, moist brown spots occurring, and 

 the leaf blade rapidly rotted away, is briefi}^ described. In this dis- 

 ease the center of the head becomes a black, slimy mass. A brief note 

 is also given on a bacterial disease, which so far the authors have not 

 met with in their investigations. 



An extended account is given of experiments conducted for the con- 

 trol of the ' ' drop " and Rhizoctonia diseases by sterilizing soil. 

 Experiments show that where f to f of an inch of sterilized sand or 

 earth is used as a covering to the buds the amount of disease is reduced 

 47 per cent; 1 in. of sterilized sand or earth reduces it 87 per cent; 

 and when 2, 3, or 4 in. have been sterilized there is no disease what- 

 ever, when the plants had not been infected from contaminated material. 

 The sterilization of soil is affected by heating it to about 160° F. 

 Other methods of preventing these diseases were investigated, but 

 aside from sterilization none were efficient. Freezing the soil had no 

 effect upon the drop disease, and the development of the sclerotia was 

 considerably accelerated by freezing. Drjing the soil has a similar 

 effect. The sterilization method of treatment will have no value upon 

 such diseases as the Botrytis, mildew, bacterial rot, etc., which can be 

 readih' prevented by proper management of the crops, spraying, etc. 



Orange culture and diseases, J. Borg {Bui. Bot. Dept. Jamaica^ 

 n. ser., 7 {1900), JS^o. 9, pp. 129-lJi^). — This paper gives an account of 

 orange culture and diseases in Malta. The principles of culture are 

 briefly outlined and the diseases treated under the heads of insect dis- 

 eases, those caused by fungus parasites, those due to errors in assimi- 

 lation or unsuitable surroundings. Among the insects noted c^ most 

 troublesome are 2 species of flies {IIalterop>hora capitatct and j,L Jiis- 

 panica), and numerous scale insects. Of the fungus diseases described, 

 the black blight or fumago, due to Meliola penzkji, the gummosis due 

 to a number of species of Fusarium, Cladosporium, etc., and to the 

 attacks of Polijporm oMupius., are described at some length. The dis- 

 eases due to imperfect assimilation and improper surroundings are 

 briefly described. Among these diseases are mentioned withers or 

 lupa, which is the sudden death of part or the whole of a tree caused 

 by the sudden occurrence of cool breezes after a protracted sultry 

 calm in the hottest days of summer. It is said to be purely a phys- 

 ical disease, and frequent irrigation is suggested as the only remedy. 

 Other diseases are brontosis, which is a name given to a disease caas- 

 ing the sudden death of trees in the winter; anthomania, the produc- 

 tion of an extraordinary quantity of flowers; anthoptosis, the fall of 



17622— No. 9 5 



