Further Notes on the Witches' Brooms and the Substomatal Pycnia of Melampsorella

Abstract

During the past year investigations on the Melampsorella problem have been concerned largely with field work during the summer at the Rocky Mountain Biological Laboratory at Gothic, Colorado, and with examination of the Melampsorella material on Abies and Picea from the Arthur Herbarium. The results of this work lend support to the previous observations (Pady, 1940.) that there are two distinct species of Melampsorella as opposed to the recent monotypic conception of the genus (Arthur, 1934). FIELD WORK Photographs were made of the prominent witches' brooms caused by this rust in order to show some of the differences that are present. Since the brooms are conspicuous not only for their size but also for their color all of the photographs were made with Kodachrome. During the winter the witches' brooms are usually dark and appear to be dead, but when the growing season begins, usually in June, the buds enlarge and the young leaves begin to appear. Since the mycelium is systemic the leaves are heavily infected and almost at once the pycnia appear. The infected leaves of Picea are paler in color than the normal leaves, giving the groom a pale-green cast. The brooms on Abies are somewhat similar in color at this stage. It is when the aecia begin to develop that the color differences become striking. During July and August the aecia develop slowly. There is considerable variation in time when the secia mature, some brooms showing mature aecia while other brooms are still in the pycnial stage. The large broom shown in Figure 3, one of the largest single brooms that the writer has ever observed, measuring over 6 feet in length and two to three feet in width, was still in the pycnial stage when the photograph was taken on July 20th, 1940. Even on this broom a few aecia had already started to mature. Figure 8, taken on July 16th shows that a few aecia are already mature on both specimens, the one on the right being from a broom on Picea, the one on the left from Abies. It may be noted here that the secia on Abies are much more mature than those on Picea. This is generally true, the aecia of Abies maturing usually by the end of July while the aecia of the Picea form mature during August. Seasonal variations apparently occur, along with individual variations, and a warm, dry summer, such as that of 1940 in the Gothic area, seemed to induce early maturity at the same time causing the death of many of the infected branches. On Picea engelmanni the witches' brooms in the aecial stage are very striking since the numerous orange-red aecia give the entire broom an orange to orange-reddish color, which shows up particularly well against the dark green foliage of the normal branches. This was true of the two brooms shown in Figure 1 at (a) and (b). Incidentally, this infection occurred at a very h'gh