2 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



is formed as usual in etiolated leaves, that aquatic plants may be 

 etiolated, that perfect seed formation does not occur in darkness 

 except in subterranean plants, that flowers which open in darkness 

 perish more quickly than similar ones in light, that growth is more 

 rapid during the first stages of etiolation, and that etiolated plants 

 take up and transpire less water than the normal/ It is remarkable 

 that these earlier observations agree almost point by point with those 

 which will be described in the concluding section of this memoir. 



Duhamel recounted the observations of Bonnet in i758» t)ut it 

 can not be learned that he made any independent experimental 

 investigation of the subject.^ 



Knowledge of etiolation was notably increased as a result of 

 Senebier's observations, which were first published in 1782. Sene- 

 bier found that etiolated stems of the bean were greater in diameter 

 and developed more hairs than the normal plant. The epidermal cells 

 were seen to be more irregular in outline than those of etiolated 

 plants, and were separated from the underlying tissues by smaller 

 intercellular spaces, and the pith was greater in amounts in etiolated 

 plants. The emergence of the flowers of certain monocotyledonous 

 plants in normal and etiolated specimens was thought to be depend- 

 ent upon qualities of the sheath induced by etiolation or illumination. 

 Peduncles were seen to undergo excessive elongation in darkness 

 and some changes in colors were observed. Mosses were seen to 

 blanch when placed in darkness for long periods.® 



Twenty-eight years later Senebier gave a comprehensive sum- 

 mary of the subject, in which he noted minor observations by Lin- 

 naeus, Humboldt, and others. He made the first estimations from 

 which it was seen that the dry weight of etiolated plants is less than 

 the normal, and formulated a hypothesis to account for the phenom- 

 ena of etiolation, which asserted that the basal or primitive color of 

 plants was yellow, and that coloration was due to the fixation of car- 

 bon and elaboration of the carbon compounds. The absence of 

 illumination prevented the assimilation of carbon dioxide and the 

 construction of coloring and other matter.'' 



*Mees' observations were published after his death bj Van Swinden in the Jour- 

 nal de Physique, 6: 445. 1776, and 7: 112, 193. 



5 Duhamel du Monceau. Des plantes etiolees, in La physique des arbres, 2 : 155. 



1758. 



6 Senebier, J. Memoires physico-chimiques, 2 : 51-116. 1782. 

 ' Senebier, J. Physiologie vegdtale, 4 : 264-308. 1800. 



