334 THE STORY OF PLANT LIFE 



The plant is a herbaceous perennial. Few aquatic 

 plants are annual. The plant varies in height from i 

 to 2 ft. 



Honey is secreted at the base of the flower. The 

 inflorescence is conspicuous, so that Flies and 

 Hymenoptera visit the flowers. 



There are two forms of flower as in the allied 

 Primrose. These have been described above. The 

 tube in each is 4 to 5 mm. long. The pollen-grains 

 of the long-styled form are spherules 'oii to '014 mm. 

 in diameter, those in the short-styled form are 'oiSto 

 •023 mm. in diameter, and in the latter case the style 

 is 4 to 5 mm. long, in the former 7 to g mm. In 

 legitimate pollination the larger pollen-grains are 

 deposited on the stigma of the long-styled form, in 

 which the stigma is rough and velvety, and has 

 larger papillae than in the short-styled form, which 

 has a smooth stigma. 



In legitimate pollination the stamens and stigma 

 of equal height in the tubes are touched by insects in 

 search of honey. Pollen seekers only dip their heads 

 as far as the stamens in the short-styled forms, and 

 if they visit many of this type may bring about 

 illegitimate pollination ; and in visiting several long- 

 styled forms may bring about illegitimate crossing 

 in that case also. The long-styled forms are more 

 productive in the case of illegitimate crossings than 

 the short-styled, the former not so often occurring. 



In some cases the flowers are cleistogamic, and in 

 the case of the short-styled form self-pollination 



