474 



THE POLEMONIALES 



mine, Strychnos, yielding the alkaloid strychnine, oleander 

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

 ing heart (Limnanthemum) 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- 



