92 



ment of the conspicuous flowers and also because insects 

 failed to pollinate the flowers during bad weather. 



FIG, 37. 

 Figr. 37. CleistogramouK flower of 

 Lamium amptextcatde. (After Lub- 

 buok). 



PIG. 37 A. 

 Fig. 37 A. Section of cleiatogamoHS 

 flower of dead nettle (Lamium amplexi- 

 caule). (After Lubbuck.) 



Arlstolochiaceae. 



Birthwort (Aristolochia clematitis) is an 

 example of flowers pollinated by small 

 flies; the arrangement is quite unique. The yellow flowers 

 are arranged in whorls. The long, tubular flowers consist of 

 a wide, funnel-shaped throat and a long and narrow tube 

 which is lined with stifle hairs. The lower part is enlarged 

 and contains the stamens and part of the pistil. In Aristolo- 

 chia ringens the calyx has developed a lower and upper lip. 

 In the birthwort there is a flattened expansion which serves 

 as a resting place for insects. The colors as well as the disa- 

 greeable odor make these flowers attractive to certain kinds 

 of insects. Flies find no difliiculty in going into the flower, 

 since the hairs all point in an oblique direction away from 

 the opening. When the insect reaches the expansion it is 

 comfortably housed. The temperature is several degrees 

 warmer than the surrounding air. They now try to escape, 

 and in doing so come in contact with the stigma where they 

 leave some pollen from other flowers, but they cannot es- 



