fact of a plant being more fertile with pollen from a distinct individual than
with its own pollen, is common to very many species, as I have shown in my work
'On the Effects of Cross and Self-fertilisation.'

Hottonia palustris.

This aquatic member of the Primulaceae is conspicuously heterostyled, as the
pistil of the long-styled form projects far out of the flower, the stamens being
enclosed within the tube; whilst the stamens of the short-styled flower project
far outwards, the pistil being enclosed. This difference between the two forms
has attracted the attention of various botanists, and that of Sprengel, in 1793,
who, with his usual sagacity, adds that he does not believe the existence of the
two forms to be accidental, though he cannot explain their purpose. (1/15. 'Das
entdeckte Geheimniss der Nature' page 103.) The pistil of the long-styled form
is more than twice as long as that of the short-styled, with the stigma rather
smaller, though rougher. H. Muller gives figures of the stigmatic papillae of
the two forms, and those of the long-styled are seen to be more than double the
length, and much thicker than the papillae of the short-styled form. (1/16. 'Die
Befruchtung' etc. page 350.) The anthers in the one form do not stand exactly on
a level with the stigma in the other form; for the distance between the organs
is greater in the short-styled than in the long-styled flowers in the proportion
of 100 to 71. In dried specimens soaked in water the anthers of the short-styled
form are larger than those of the long-styled, in the ratio of 100 to 83. The
pollen-grains, also, from the short-styled flowers are conspicuously larger than
those from the long-styled; the ratio between the diameters of the moistened
grains being as 100 to 64, according to my measurements, but according to the
measurements of H. Muller as 100 to 61; and his are probably the more accurate
of the two. The contents of the larger pollen-grains appear more coarsely
granular and of a browner tint, than those in the smaller grains. The two forms
of Hottonia thus agree closely in most respects with those of the heterostyled