. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. Figure 1.—Uredospores on uredia of four North American Melampsora species. A. M. abietis-canadensis. B. M. occidentalis. C. M. medu- sae. D. M. albertensis. (SEM X 1000) intermediate M. medusae and M. albertensis and the small M. abietis-canadensis are evident. Echinulation was very prominent in SEM photos. Spores which were spiny over their entire surface were easily distin- guished from those having a bald spot. The ure- dospores of
. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. Figure 1.—Uredospores on uredia of four North American Melampsora species. A. M. abietis-canadensis. B. M. occidentalis. C. M. medu- sae. D. M. albertensis. (SEM X 1000) intermediate M. medusae and M. albertensis and the small M. abietis-canadensis are evident. Echinulation was very prominent in SEM photos. Spores which were spiny over their entire surface were easily distin- guished from those having a bald spot. The ure- dospores of M. medusae (fig. 1C) show the prominent equatorial bald spot characteristic of this species while those of M. occidentalis (fig. IB) and M. abietis- canadensis (fig. 1 A) are entirely spiny, lacking a bald region. Melampsora medusae and M. albertensis differ in the uredial stage mainly by the extent of the bald spot. This difference is visible by comparing figure 1C (M. medusae) and ID (A/, albertensis). Since SEMs show only one side of any particular spore, the observation of a small feature present only at one point on the circumference becomes a matter of probability. The chances of a spot being seen in a sample of spores can be calcualted by spots of differ- ent sizes, and increase as the spots become larger. This calculated relationship is shown by the dotted line in figure 2. To see if this theoretical relationship would hold up, bald spots were measured from SEM photos. The measured size and frequency of observation for each sample were then plotted against the theoretical line. Reasonably good agreement was found (fig. 2).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Merrill, William; Ostry, Michael E; United States. Forest Service; International Union of Forestry Research Organizations. Worki
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