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, e.g. 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 

 masterly way, only overlooking the proterogyny and the resulting cross-fertilization. 

 He sums up his observations in the following characteristic account : — ' The flower 

 occurs so long as it vegetates in three diff'erent conditions. After having attained its 

 definitive size and opened, it appears to bloom, but yet actually does not do so, 

 i. e. it is not yet ready to be fertilized, for neither are the anthers properly ripe, 

 nor has the stigma attained to proper development. During this first condition, the 



