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 Muller 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 (' Biologic der Pflanzen,' pp. 481-3) we are here 

 principally concerned with pollen flowers possessing Iwo kinds 0/ stamens with different 

 form, but siviilarly-coloured anthers and pollen- — i.e. with shorter alluring stamens 

 with nutritive anthers and longer alluring stamens with reproductive anthers. Todd, 

 Fritz Miiller, and Herm. Muller have proved for a small number of plants that this 

 division of labour is related to Enantiostyly , 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 open 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 Muller). 



3. Enantiostyly with division of labour among the anthers, and regular crossing 

 between flowers of opposite form — in Cassia multijuga (according to Fritz Muller). 



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. 



