DEVELOPMENT OF PLANTS 



437 



The buckwheat order, Polygonales, containing such familiar 

 weeds as the sorrel, dock {Rumex), and kno tweed or smartweed 

 (Polygonum), has perfect regular flowers with a distinct perianth. 

 These characters also appear in the allied goosefoot order, Cheno- 

 podiales, with its great array of common weeds, as the goosefoot 

 (Chenopodium) , orache (Atriplex), tumbleweed and pigweed 



Fig. 304. Advanced type of the Chenopodiales: A, shoot of Melandry- 

 num bearing flower with perianth differentiated into calyx, ca, and corolla, 

 c. B, section of flower, showing the relation of calyx to corolla and the con- 

 cealment of the nectar glands at the base of the ovary. Access to the corolla 

 tube is guarded by an outgrowth on the petals, as shown in C, which, assisted 

 by the styles or stamens, so effectually closes the mouth of the tube that 

 only insects with long tongues can reach the honey. 



{Amaranthus) . The flowers are arranged in loose clusters and 

 are for the most part small and wind pollinated (Fig. 303). How- 

 ever, it is noteworthy that some of the genera are adapted to 

 insects, the calyx becoming larger and brightly colored and nectar 

 glands are associated with it. In the higher members of the 

 order, as in the purslane and pink families (which include the 

 spring beauty, Claytonia), the perianth becomes differentiated 

 into a calyx and showy corolla, and the flowers have become in a 

 marked degree adapted to insect visitors (Fig. 304). These 



