NECTAR OF FLOWERS 97 
such flowers they disappear more or Jess completely in the double variety, where they 
have become mere useless markings. Insects are certainly attracted from a distance 
by these flowers, but as soon as they come near they notice that here there is nothing 
for them (for as a rule the formation of pollen and the secretion of nectar cease when 
flowers become double), and turn away without searching for food. 
2 
Fic. 14. Weciar-pguides. (1) Dotted marks of Saxifraga-aspera Z. (2) Ring-shaped nectar-guide 
of Myosotis'alpestris Schazd¢. (3) Spots and streaks of Gentiana acaulis Z. (4) Streaks on the lower 
lip of Teucrium Chamaedrys Z. (5) Streaks and ring-shaped nectar-guide of Veronica Chamaedrys. 
Delpino (‘Ult. Oss., Atti Soc. ital. sc. nat.,’ Milano, xvi, 1874, pp. 234 et seq.) 
distinguishes between 7z/ra-floral nectaries, occurring in the flower, and c7rcum- 
floral nectaries on its outer side, as e.g., in Euphorbia, where the honey is secreted 
by crescentic or rounded appendages of the cup-shaped involucre. There may also 
be extra-floral nectaries outside the flower altogether, but situated near it, as in the 
case of the above-mentioned (pp. 73-4) Marcgraviaceae, which investigations of 
Thomas Belt (‘The Naturalist in Nicaragua,’ 1874) made known to us. In this 
family nectar is secreted by bracts of striking form and colour by which the 
humming-birds that effect pollination are attracted, 
Besides these three kinds of nectaries occurring in the region of the flower, and 
DAVIS H 
