. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. 128 INTRODUCTION To this group therefore belong all flowers of Classes E and EC, having ' indoloid ' odours, and many that possess ' aminoid ' odours (cf. pp. 91-2). Certain flowers with a ' parafl5noid' odour are also included here, Ruta graveolens. B. Pitfall Flowers (Fpf). A transitional stage from Nauseous Flowers, which are visited only by very small Diptera, is represented by Asarum europaeum (Fig. 41). The proterogynous. Fig. 41. Asarum europaeum
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. 128 INTRODUCTION To this group therefore belong all flowers of Classes E and EC, having ' indoloid ' odours, and many that possess ' aminoid ' odours (cf. pp. 91-2). Certain flowers with a ' parafl5noid' odour are also included here, Ruta graveolens. B. Pitfall Flowers (Fpf). A transitional stage from Nauseous Flowers, which are visited only by very small Diptera, is represented by Asarum europaeum (Fig. 41). The proterogynous. Fig. 41. Asarum europaeum^ L. I. Younpf flower after removal of half the perianth. II. Older flower in outline, ti', Longer and, a^, shorter stamens ; Ji^ filaments ; J/, stigmas. flowers, which are externally brownish and internally of a dirty, dark purple, smell hke camphor, and entice minute flies and midges to visit them. These insects creeping about, sometimes in older flowers at other times in younger ones, effect cross-pollination. For in just-opened flowers the stigmas are already developed, standing right in the middle of the flower, so as to be touched by the Diptera that creep in. If these are already covered with pollen from a flower in the second (male) condition, pollination must result. The tips of the perianth are inwardly curved, so that the small visitors, though they can easily get into the flower, find it difficult to escape. ' It may very well happen, therefore,' says Hermann Mtiller (Kosmos, ii, 1877, p. 324). ' that one or other of the guests is unable to get out of the flower before the anthers have dehisced, at which time the tips of the perianth have curved more towards the exterior.' Should this occur, there is here the beginning of the development of a Pitfall Flower, and Asarum europaeum would thus form a transition to the remarkable pitfall arrangement of Aristolochia Clematitis (Fig. 42), the floral adaptation of which Sprengel ('Entd. Geh.,' pp. 418-29) sketches in a mas
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