. Practical botany. Botany. 126 PRACTICAL BOTANY display is all made by an enlarged and conspicuous set of specialized leaves (bracts) which surround the flower, as in the flowering dogwood and many euphorbias (Fig. 292), or even by highly colored ordinary leaves, as in the poinsettia. 120. Degrees of specialization for insect visitors. Flowers with a spreading perianth and radial symmetry — like those of the stonecrop (Fig. 92) and the live-forever, the buckwheat (Fig. 114) and the caraway (Fig. 295), buttercups, poppies, roses, and hun- dreds of other familiar kinds— are open to all comers,
. Practical botany. Botany. 126 PRACTICAL BOTANY display is all made by an enlarged and conspicuous set of specialized leaves (bracts) which surround the flower, as in the flowering dogwood and many euphorbias (Fig. 292), or even by highly colored ordinary leaves, as in the poinsettia. 120. Degrees of specialization for insect visitors. Flowers with a spreading perianth and radial symmetry — like those of the stonecrop (Fig. 92) and the live-forever, the buckwheat (Fig. 114) and the caraway (Fig. 295), buttercups, poppies, roses, and hun- dreds of other familiar kinds— are open to all comers, and are frequented by many sorts of in- sects, from flies to bees. Flowers with bilateral symme- try — like vio- lets, wild balsam (Fig. 119), most flowers of the Pea family (Fig. 98), mints, and many others — are usually not suited to indiscriminate visitors, but only to those insects which can get at the nectar, the pollen, or both. In violets, for example, the pollen is abundant, but is concealed within the throat of the corolla, and the nectar is deep down in the spur of the corolla. Both pollen and nectar are easily reached b}- the tongues of bees, but not by small insects. In the snap- dragon the mouth of the corolla is firmly closed, so that small insects cannot enter it. Larger ones, such as bees, can, how- ever, readily overcome the elasticity of the hinge at the junc- tion of the lips and enter the flower (Fig. 115). There are some flowers which appear to be dependent on pollination by a single kind of insect only, and therefore are. Fig. 115. Flowers of snapdragon A, with lips of corolla tightly closed; JB, with the lips forced open by a visiting bee. 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 Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell, Otis William, 1869- joint author. Bos
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