. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. 396 A NGIOSPERMAE—DICOTYLEDONES flower increases to twice its original diameter or even more, so that the visits paid by any particular insect will usually be in the order most favourable for crossing. We are indebted to A. Engler for an excellent monograph on the genus. He regarded all the species as protandrous. Treviranus (Bot. Ztg., Leipzig, xxi, 1863) had already observed the movement of the stamens towards the middle of the flower, and inferred that au
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. 396 A NGIOSPERMAE—DICOTYLEDONES flower increases to twice its original diameter or even more, so that the visits paid by any particular insect will usually be in the order most favourable for crossing. We are indebted to A. Engler for an excellent monograph on the genus. He regarded all the species as protandrous. Treviranus (Bot. Ztg., Leipzig, xxi, 1863) had already observed the movement of the stamens towards the middle of the flower, and inferred that automatic self-pollination takes place. As some species of this genus possess nectar-guides, while others do not, Engler called in question the correctness of Sprengel's interpretation of these markings. Hermann Miiller remarks in this connexion ('Fertilisation,' p. 243), that in plants where the nectar is sometimes fully exposed, and at other times concealed, there is very naturally a corresponding variation in the nectar-guides, so that this peculiarity of the genus cannot be regarded as opposed to Sprengel's view, while there is no other explanation to take its place. 938. S. Aizoon Jacq. (Herm. Miiller, ' Alpenblumen,' pp. 100-2.)—The flowers of this species are markedly protandrous, and in the Alps self-pollination is almost or entirely prevented. The abundant pollen and readily accessible nectar. Fig. 124, Saxifraga Aizooii^ Jacq. (after Herm. Miiller). A. Flower at the beginning of the first (male) stage. B. The same, at the end of the first stage. C. Flower in the second (female) stage (x 3J). 7/, nectary. attract numerous visitors, especially flies. In Greenland, where insects are few, the flowers are also strongly protandrous, but here effective automatic self-pollination is ultimately possible by contact of the anthers (still covered with pollen) with the widely divergent stigmas (Warming, Bot. Tids., Kjobenhavn, xvi, 1888, pp. 27-9). Visitors.—Herm. Miiller obse
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