POLLEN FLOWERS 107 
been mentioned (p. 95), also Kerner’s explanation of this—i.e. that the odour 
characteristic of this plant is perceived only by this particular bee. 
Hermann Miller regards the glowing red hue of Papaver Rhoeas (‘ Alpenblumen,.’ 
p- 479, note) not only as serving to allure insects, but also as a terrifying or defen- 
sive colour, by which grazing animals are made aware of the poisonous juices of the 
flower, so that they avoid it. As evidence of this assumption Miiller notes that on 
the ‘ Kampen’ (i.e. the enclosed meadows near Lippstadt, on which the cows pass 
the whole summer) the flowers of the corn-poppy remain untouched, while almost 
all others are grazed down. (What is true for Papaver Rhoeas also holds for 
Ranunculus acris.) 
Certain pollen flowers are particularly noteworthy in that they exhibit a division 
of labour among their stamens, which enables them to make sure of crossing with 
fewer stamens. According to Ludwig (‘Biologie der Pflanzen,’ pp. 481-3) we are here 
principally concerned with pollen flowers possessing ‘wo kinds of stamens with different 
form, but similarly-coloured anthers and pollen —i.e. with shorter alluring stamens 
with nutrztive anthers and longer alluring stamens with reproductive anthers. ‘Todd, 
Fritz Miiller, and Herm. Miiller have proved for a small number of plants that this 
division of labour is related to Lxantiostyly, i.e. the occurrence of right-styled and 
left-styled flowers (comparable to the long-styled and short-styled forms of hetero- 
stylous dimorphous flowers). Solanum rostratum is an example of the kind. The 
lowest anther in this plant is greatly elongated, and narrows into a curved point that 
is turned upwards at the end; the style is also upwardly curved. Both, however, 
are curved away from the direction of the floral axis in opposite directions. In the 
same raceme right-styled and left-styled flowers alternate regularly, and flowers on 
the same branch which ofen simultaneously are either all right-styled or all left-styled. 
The humble-bees effecting cross-pollination, while stripping the nutritive anthers 
of the four short stamens, receive a cloud of pollen on the right side of their body in 
left-styled flowers, and a similar shower on their left side when in right-styled flowers, 
Obviously, therefore, they must always transfer this pollen on to the stigmas of 
flowers in which the style turns in the opposite direction. Cross-pollination therefore 
results in the same way as in the heterostylous flowers of Pulmonaria, Primula, and 
others. In Cassia (Caesalpiniaceae) the following relations occur :— 
1. Enantiostyly (dextro and sinistrostyly) without division of labour among the 
anthers—in Cassia Chamaecrista (according to Todd). 
2. Enantiostyly with division of labour among the anthers, but without preferen- 
tial crossing of opposite floral forms—in Cassia neglecta (according to Fritz Miiller). 
3. Enantiostyly with division of labour among the anthers, and regular crossing 
between flowers of opposite form—in Cassia multijuga (according to Fritz Miiller). 
- 4. Division of labour among the anthers (reproductive and nutritive) without 
enantiostyly—in a form related to Cassia laevigata (according to Fritz Miiller). 
According to Robertson, Cassia marylandica has three kinds of stamens. The 
three uppermost are reduced to dark scaly bodies, which take the place of the nectar- 
guides of honey flowers, and the red markings on the upper petals of Cassia 
Chamaecrista. Four stamens afford pollen to visitors, and are stripped by humble- 
bees. Two long stamens, one on either side of the style, are concerned with 
cross-pollination. 
