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. g1-2). Certain 
flowers with a ‘ paraffinoid’ odour are also included here, e.g. Ruta graveolens. 
B. Pitraty Frowers (Fpf). 
A transitional stage from Nauseous Flowers, which are visited only by very 
small Diptera, is represented by Asarum europaeum (Fig. 41). The proterogynous 
Fic. 41. Asarvum europaeum, L. 1. Young flower after removal of half the perianth. II. Older flower 
in outline. a’, Longer and, a’, shorter stamens; /, filaments; s¢, stigmas. 
flowers, which are externally brownish and internally of a dirty, dark purple, smell 
like 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 Miiller 
(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 different 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 
