Epinasty and Hyponasty of Raphaniis Cotyledons. 363 



the thallus of Marchantia are directly in this line, and tend to up- 

 hold the position of De Vries. The observations of Darwinlf have 

 shown us that dorsiventral organs tend to place themselves at 

 right angles to the direction of the light rays, and further that the 

 phenomena of epinasty and hyponasty are to be considered as a 

 modified form of circumnutation. One of the most important 

 contributions to our knowledge of the subject is that of Detmer.** 



By means of a series of observations in which dorsiventral 

 organs were subject to varying intensities of illumination, Det- 

 mer comes to the conclusion that the position assumed by such 

 are due not to the photonic, but to the paratonic action of light ; 

 and therefore instead of a condition of epinasty, it is in reality one 

 of "photo-epinasty." 



Coming now to the observations of Vinesft we find that he 

 states the primary object of his experiments to be : 



(i) "To ascertain whether epinasty and hyponasty are 

 spontaneous movements, or are induced by light or other causes 

 as stated by Detmer; and (2) whether the curvatures of dorsi- 

 ventral members which have hitherto been ascribed to negative 

 geotropism, are or are not due to this cause." He repeats the ex- 

 periments of Detmer with the cotyledons of Cuciirbita seedlings 

 and with the primordial leaves of Phaseolus, and comes to the 

 conclusion that *'the effect of light is not 'paratonic/ as Detmer 

 would have it to be, but it is 'phototonic ;' " or in other words, 

 that epinastic growth can take place in darkness. 



It will be noted that these conclusions render the term **pho • 

 to-epinasty" of Detmer useless. 



To further establish his position, Vines notices that in seed- 

 lings of Helianthus, Dahlia, Fuchsia, and Urtica, epinasty is stim- 

 ulated by the absence of light rather than bv its presence. 



Continuing his experiments with Plantago media and Tarax- 

 acum officinale, he finds that specimens of these plants kept in 

 darkness for 72 hours become decidedly hyponastic, and this hap- 

 pens whether the plant was placed in its normal position, or ro- 

 tated on the clinostat. From this he comes to his second con- 

 clusion viz : that "Dorsiventral members are not negatively geo- 



HF. Darwin: Journal Linnean Society, xviii, London, 1881. See also 

 "Movements of Plants," 1880. 

 **Detmer: Bot. Zeitg, 1882. 

 ttVines, I. c. 



