. Bursa bursa-pastoris and Bursa heegeri biotypes and hybrids. Bursa heegeri; Plant hybridization. Fig. 1.—Enlarged sections of buds and flower of Bursa bursa pastor is, show- ing three stages in anthesis. A. Exposure of the stigtnatic surface for the reception of foreign pollen. B. Anthers opening in contact with the stigma, thus insuring self-pollination. C. The flower fully open, allowing the access of the visiting insects to the pollen. All magnified 20 diameters. The conditions which favor cross-fertilization are : («) Slight prote- rogyny, which allows the stigma to receive foreign polle
. Bursa bursa-pastoris and Bursa heegeri biotypes and hybrids. Bursa heegeri; Plant hybridization. Fig. 1.—Enlarged sections of buds and flower of Bursa bursa pastor is, show- ing three stages in anthesis. A. Exposure of the stigtnatic surface for the reception of foreign pollen. B. Anthers opening in contact with the stigma, thus insuring self-pollination. C. The flower fully open, allowing the access of the visiting insects to the pollen. All magnified 20 diameters. The conditions which favor cross-fertilization are : («) Slight prote- rogyny, which allows the stigma to receive foreign pollen some hoiirs before the anthers of the same flowers dehisce. The distal portion of the globular or disk-shaped stigma is exposed between the tips of the unopened sepals and petals (fig. 1, a) . ib) Although the fully developed inflorescence is a typical raceme, the flowers and buds are arranged in a nearly flat-topped corymb having the flowers at the circumference, giving this part of the inflores- cence a condition quite analogous to that of the head of the Compositee, in which the whole inflorescence appears to act the part of a single flower in the attraction of insects. Small insects, particularly flies and small bees, visit the flowers freely. These rest upon the top of the inflorescence as a whole while visiting the several individual open flowers about the circum- ference. In these fully open flowers forming the exterior circle of the inflo- rescence the anthers have opened, while in the second circle the summits of the stigmas are exposed on the same general level as the rest of the corymb. As the insect walks about over the top of the inflorescence, the. 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 Shull, George Harrison, 1874-1954. Washington, Carnegie Institution
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplanthybridization
