4 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



but became green later, no doubt due to defective methods of ex- 

 clusion of light. 



J. E. Smith ^" records that when light was admitted to leaves 

 through glasses of different colors, the plants became paler as the 

 glass approached violet in tint. He reiterates the mistaken idea that 

 blanched plants become green when exposed to the action of hydro- 

 gen. From a consideration of currently accepted descriptions he 

 concludes that light acts beneficially on the upper surfaces of leaves, 

 and hurtfully on the lower sides, hence the upper is always turned 

 toward the illumination. 



DeCandolle '^ also exposed a number of plants to the light from 

 six argand burners, which was insufficient to cause the release of 

 oxygen, yet it was found that this illumination would cause the for- 

 mation of chlorophyl in etiolated specimens. 



Re '^ used the term " clorosi " to denote the blanching of plants 

 when deprived of light, as distinct from the modern usage, and re- 

 lated that many "salads" were treated to induce this condition 

 (" asparagi, sedani, e cardi"). 



Knight'^ was cognizant of the effects of deprivation of illumina- 

 tion, and he developed a new method of culture of rhubarb in dark- 

 ness and diffuse light in order to increase its succulence and edibility. 

 His experimental results upon the influence of light upon the for- 

 mation of the tubers of the potato have also become of great impor- 

 tance in experimental morphology and physiology. 



Sir Humphrey Davy"' made analyses of normal and etiolated 

 material in which he found that 400 grains of leaves grown in sun- 

 light yielded 53 grains of woody fiber after being subjected to the 

 action of boiling water and alcohol, and that an equal amount of 

 etiolated material gave but 31 grains of " woody fiber." Poggioli *^ 

 found that plants developed better in violet rays than in red, probably 



''Smith, J. E. An Introduction to Systematic and Physiological Botany. Pp. 206, 

 207. 1807. 



'^DeCandolle, A. P. Physiologic veg^tale, 3 : 1069. 1832. 



'*Re, F. Saggio di nosologia vegetabile. P. 23. 1807. 

 Re, F. Saggio Teorico-Pratico sulle Malat ie delle piante. P. 147. 1807. 



"Knight, T. A. On a method of forcing rhubarb in pots. Trans. Hort. See. 

 Lond. 3: 154. 1820. See also a selection from the physiological and horticultural 

 papers published in the Transactions of the Royal and Horticultural Societies. 

 1841. 



'6 Davy, H. Elements of Agricultural Chemistry. Pp. 208, 209. 1815. 



'^ Poggioli, S. Opuscules scientifiques de Bologne. i: 9. 



