* Lapsana, Nymphaea alba, Calendula. l. 165. And many other flowers close and open their petals at certain hours of the day; and thus constitute what Linneus calls the Horologe, or Watch of Flora. He enumerates 46 flowers, which possess this kind of sensibility. I shall mention a few of them with their respective hours of rising and setting, as Linneus terms them. He divides them first into meteoric flowers, which less accurate∣ly observe the hour of unfolding, but are expanded sooner or later, according to the cloudiness, moisture, or pressure of the atmosphere. 2d. Tropical flowers open in the morning and close before evening every day; but the hour of the expanding becomes earlier or later, as the length of the day increases or decreases. 3dly. Aequinoctial flow∣ers, which open at a certain and exact hour of the day, and for the most part close at another determinate hour.
Hence the Horologe or Watch of Flora is formed from numerous plants, of which the following are those most common in this country. Leontodon taraxacum, Dandelion, opens at 5—6, closes at 8—9. Hieracium pilosella, mouse-ear hawkweed, opens at 8, closes at 2. Sonchus laevis, smooth Sow-thistle, at 5 and at 11—12. Lactuca sativa, cultivated Lettice, at 7 and 10. Tragopogon luteum, yellow Goatsbeard, at 3—5 and at 9—10. Lapsana, nipplewort, at 5—6 and at 10—1. Nymphaea alba, white water lily, at 7 and 5. Papaver nudicaule, naked poppy, at 5 and at 7. Hemerocallis fulva, tawny Day-lily, at 5 and at 7—8. Convolvulus, at 5—6. Malva, Mallow, at 9—10, and at 1. Arenarea purpurea, purple Sandwort, at 9—10, and at 2—3. Anagallis, pimpernel, at 7—8. Portulaca hortensis, garden Purslain, at 9—10, and at 11—12. Dianthus prolifer, proliferous Pink, at 8 and at 1. Cichoreum. Succory, at 4—5. Hypochaeris, at 6—7, and at 4—5. Crepis at 4—5, and at 10—11. Pi•ris, at 4—5, and at 12. Calendula field, at 9, and at 3. Calendula African, at 7, and at 3—4.
As these observations were probably made in the botanic gardens at Upsal, they must require further attention to suit them to our climate. See Stillingfleet's Calendar of Flora.
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