306 



GROWTH 



Take some vigorously growing specimens of Taraxacum from 

 the soil and wrap the roots with wet sphagnum. Support in an 

 upright position. Note positions assumed by the leaves. In- 

 vert and make same observations. Are 

 the positions of the leaves due to epinasty 

 or hyponasty, or to geotropism ? L 



391. Carpotropic and Gametropic Move- 

 ments. A large number of movements are 

 carried on by the primary or accessory re- 

 productive organs for the purpose of pro- 

 moting fertilization, dissemination of seeds 

 or spores or protection from climatic ele- 

 ments. These movements may be directed 

 by external stimuli, principally that of 

 gravity, or may be epinastic or hyponastic. 

 Movements of this character entail an ac- 

 cession of sensibility to the external stim- 

 ulus at a certain stage of development, 

 or a change of form of reaction to this 

 stimulus. Thus a petiole may be apogeo- 

 tropic until fertilization or pollination is 

 accomplished, when it may become pro- 

 geotropic. Similar irritability to light is 

 found, and instances are not lacking in 

 which a second change is made. The 

 stimuli by which auto-carpotropic move- 

 ments are set up, are released by develop- 

 mental changes. Opening and closing of 

 (^^ IfW calices, movements of stamens and pistils, 



M V \^w ^ IG ' *43' Inflorescence of Bulbine longiscapa show- 



ing carpotropic movements. The unopened flower buds 

 stand approximately erect, appressed lo the axis : the pedi- 

 cels of open flowers are horizontal and the pedicels curve 

 downward after the seed-capsules begin to develop. After 

 Hansgirg. 



1 Day, R. N. The forces determining the position of 

 dorsiventral leaves. Minn. Bot. Stud. I :743- 1894-1898 



