GERANIACEAE 



2 33 



Visitors. During the day Plateau only saw a small Muscid. The time when 

 the flowers are odorous suggests that they are probably pollinated by nocturnal 

 insects. 



592. P. zonale L'Herit. Darwin states that this species is self-sterile. 



174. Tropaeolum L. 



Protandrous hymenopterid flowers, the spurred calyx of which secretes and 

 conceals nectar. 



593. T. majus L. (Sprengel, ' Entd. Geh.,' pp. 213-27 ; Delpino, ' Sugli appar. 

 d. fecondaz. nella piante autocarp.,' p. 30; Knuth, ' Bloemenbiol. Bijdragen.') This 

 species bears markedly protandrous humble-bee flowers. There is a red blotch, 

 serving as a nectar-guide, on the base of the lamina of each yellow petal. When the 

 flower opens, the stamens are all curved downwards, with anthers still unripe, 

 the style is still very short, and the stigmas are closely apposed. Now one stamen 



Fig. 71. Tropaeolum majus, L. (From nature.) A. Flower in the first (male) condition : an 

 anther (a) stands in the entrance of the flower. B. Flower in the second (female) condition : the stigmas 

 (_s) occupy the entrance of the flower. Natural size. 



becomes erect, and its anther dehisces exactly opposite the flower-entrance, the 

 filament again curving downwards when, on the second day, a second stamen raises 

 itself so that its pollen-covered anther occupies the mouth of the flower. After 

 all the eight stamens have successively executed these movements, and are all bent 

 downwards with empty anthers, the style has become so long that the gradually 

 maturing stigmas take up the position previously assumed by the dehiscing anthers. 

 An insect visiting one of the younger flowers in search of nectar, will therefore dust 

 the under-surface of its body with pollen, and when subsequently visiting older 

 flowers will necessarily transfer some of this to the stigmas. 



Visitors. Sprengel observed an ant (in the spur), also small spiders (' which 

 presumably chase the little insects that creep into the flowers'), and a fly ('which, 



