Phloem structure in the grapevine, and its seasonal changes

Abstract

The present investigation of the phloem of the grapevine Vitis vinifera L., was undertaken to provide a background for a study of the anatomical effects of the virus-induced Pierce's disease upon this plant. According to the previous studies of Pierce's disease (Butler, 1910; Houston et al, 1947), the xylem appears to be the tissue affected primarily, but the irregularity in the maturation of the bark suggests a possible disturbance in the phloem also. The close relation of the causal agent of Pierce's disease to the xylem places this virus in an uncommon category. With regard to their tissue relationships, viruses have been divided, thus far, into those that are largely restricted to the phloem and those that are not so restricted and invade various types of parenchyma (Bennett, 1940). To determine whether Pierce's disease affects the phloem at all, a detailed study of this tissue in healthy and diseased vines was carried out. The present article deals with the phloem of plants that showed no symptoms of any disease. A study of the grapevine phloem promised to be of interest also from the standpoint of phloem anatomy in general. The phloem of Vitis shows an unusually long life. Its sieve tubes function more than one year, becoming inactive during the winter and resuming activity in the spring. Though the general structure and development of the grape phloem was thoroughly investigated by Wilhelm (1880), the phenomenon of reactivation of this tissue seemed to merit a renewed consideration in the light of the modern concepts of phloem structure. Moreover, it seemed that information relating the seasonal changes in the phloem to the various manifestations of growth and reproduction in the plant would further explain the connection between structure and function of the sieve tubes.