Initial localization and subsequent spread of curly-top symptoms in the sugar beet

does not appear. First page follows. Introduction Studies made by (Bennett (1934)) on tobacco plants affected by curly top of the sugar beet indicate that the virus causing this disease moves within the phloem tissue, spreading through this channel from the site of inoculation to other parts of the plant. If this is true, the path of the virus depends on the vascular connection between the inoculated leaf and the other organs. According to anatomical studies on curly-top-diseased beets, the first internal and external pathologic changes are definitely localized in the plant and their position is determined by the site of inoculation. The first part of the present paper discusses this localization of symptoms. The second part deals with the course of phloem degeneration in the root. These studies give additional information on the spread of internal symptoms and strengthen the conclusions drawn in previous papers (Esau, 1933), (1934a), and 1935), especially as regards tissue relations of the curly-top virus. The observations upon protoplast degeneration in diseased root tips contribute toward the knowledge of the role of sieve tubes on the spread of the injurious agent in curly-top infection. A description of the structure of healthy organs and tissues furnishes a basis for interpreting the phenomena observed in diseased plants. Material and Methods The methods employed in preparing material for microscopic study, as well as the origin and treatment of such material prior to fixation, were essentially the same as described in an earlier publication (Esau, 1933). The plants were grown in a greenhouse and were inoculated with curly top by means of the beet leafhopper, Eutettix tenellus (Baker). Most of the material was killed in a chromo-acetic-formalin mixture (Esau, 1933); but some root tips were treated with a mitochondrial bichromate fixative made up as follows: 1 per cent solution of potassium bichromate, 1 per cent solution of chromic acid, and commercial formalin mixed just before using in a proportion of 5:5:1.