474 



THE POLEMONIALES 



mine, Strychnos, yielding the alkaloid strychnine, oleander 

 (Nerium), the gentians, marsh pink (Sabbatia), the aquatic float- 

 ing heart {LimnanthemtLm) and the highly specialized plants of 

 the dogbane and milkweed families. The latter family is dis- 

 tinguished by the microspores being united into club-shaped 

 pollinia that are attached, one from each of the two adjoining 

 anthers, to a peculiar hook, so that the leg of the insect becomes 

 caught in the hook and withdraws the pollinia in pairs. 



Fig. 328. Primulales and Gentianales: A, flower of loosestrife {Steiro- 

 nema). Above flower in section, showing cohesion of single row of stamens 

 to base of corolla and the numerous ovules on a free central placenta. These 

 are the most important characteristics of the order. B, fringed gentian 

 (Gentiana), showing leaf arrangement and twisting of petals in bud, b, char- 

 acteristics of the order. C, section of flower. D, fruit, the two carpels 

 separated. 



152. Polemoniales, or Phlox Order. — This group is the richest 

 in the number of species, over 14,600, of any order of angio- 



