46 INTRODUCTION 
mentioning these examples, goes on to say (‘Nat. Hist. Pl.,’ Eng. Ed. 1, II, p. 396) :— 
‘It may be taken to be a general rule that the flowers adapted to cross-fertilization in 
which no autogamy takes place are larger than those in which the accomplishment of 
autogamy is assured. This phenomenon has been explained by the circumstance that 
flowers destined to be crossed with others require to be more plentifully equipped 
with the means of attracting insects than those which are certain to undergo pollina- 
tion even if no insects visit them.’ 
Fic. 4. Lythrum salicarta, L. (after Herm, Miller). (1) Long-styled flower. Seen from above, 
after removal of the upper third of the calyx, corolla, and stamens. (2) Flower with style of medium 
length similarly treated. (3) Flower with short style similarly treated—a. Long stamens and style. 
5. Medium stamens and style. c. Short stamens and style. (4) Flower with medium style seen obliquely 
from the right front. 
Trimorphous flowers differ from one another in similar ways to the dimorphous, 
as regards size of stigmatic papillae, pollen-grains, and the like. In the typical trimor- 
phic plant Lythrum Salicaria, the pollen-grains of the long stamens are the largest, those 
Fic. 5. Diagram of the possible legitimate and tlleg?- 
timate unions tn a dimorphous pliant (Primula) (after 
Darwin). The arrows indicate the anthers from which pollen 
must be brought to the stigma of either of the two forms, so 
as to give a legitimate union (the straight horizontal lines), 
or an illegitimate union (the curved lines on right and left). 
(Loew.) 
of the medium stamens are of inter- 
mediate size, and those of the short 
stamens the smallest; the anthers of 
the long stamens are green, those 
of the medium and short are yellow; 
the filaments of the long stamens 
are red, those of the medium and 
short are green; the stigmatic pa- 
pillae of the long-styled flowers are 
noticeably longer than those of the 
medium, and these are a little longer 
than those of the short-styled; the 
seeds of long-styled flowers are 
larger than those of medium-styled 
flowers, and these again are larger 
than those of short-styled flowers. 
Epigaea, according to Asa Gray, 
has even tetramorphous flowers, 
differing from one another partly 
in the length of the style, partly 
in regard to the stigma and anthers. 
