MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 3 



A number of scientists made observations of various kinds upon 

 the relations of light to plants in the closing period of the eighteenth 

 century, which resulted in the discovery of the simple elements, and 

 the foundation of chemistry. Attention was chiefly directed to the 

 evolution and absorption of gases in darkness and in light, but inci- 

 centally some information was acquired as to changes in form as 

 induced by various degrees of illumination, oi by darkness. Tes- 

 sier ^ tested the formation of green color in red yellow, and white 

 light and of illuminations from lamps and the moon. Some strik- 

 ing effects in phototropism were obtained. Senebier exposed 

 plants to isolated portions of the spectrum, and to illuminations of 

 various intensities, finding that growth was more rapid in violet rays 

 than in red, and that white light was more active than any of its con- 

 stituents. De Saussure^ concluded as a result of his own work and 

 the results of others that light was without effect upon growth as 

 manifested by germinating seeds. 



DeCandolle^° describes some work done by him upon etiolation in 

 1799, in which he notes the blanched appearance of the undeveloped 

 leaves formed by etiolated seedlings of Sinafis album, Lepidium 

 sativum, and Miagrum sativum, together with the phenomena attend- 

 ant on the excessive elongation of stems, which ensued in darkness. 

 Several years later he gave the matter somewhat more comprehensive 

 treatment in his text-book on plant ph^^siology. In the latter essay 

 he sets forth that sunlight increases the suction of roots and causes 

 transpiration. Cessation of illumination, as in etiolation, stops trans- 

 piration, while absorption continues and the plant becomes highly 

 charged with water or " hydropique." The formation of coloring 

 matter in flowers in the darkness was observed. Non-green organs 

 were supposed to be but little affected by etiolation. He also made 

 partial etiolations by thrusting the tips of branches into dark chambers, 

 although he was not the first to try this experiment as asserted by 

 G. Kraus, Bonnet having made similar tests a half century before. 



Link" reported that etiolated shoots were pale in the earlier stages 



^Tessier. Experiences propres a develloper les effets de la lumi^re sur certaines 

 plantes. Mem. I'Acad. d. Sc. Paris, p. 133. 1783- 



^De Saussure, Th. De I'influence de la lumiere sur la germination. Recherches 

 chimiques sur la vegetation, p. 21. 1S04. 



•"DeCandolle, A. P. Experiences relatives a I'influence de la lumiere surquelques 

 veg^taux. Mem. Math, et phys. Inst. Nat. Paris, i : 332. 1S06. (Presented in 1799-) 



11 Link, D. H. F. Grundlehren der Anat. u. Phvsiol. d. Pflanzen. p. 291. 1807. 



