MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. II 



plant might accomplish normal growth, food formation and devel- 

 opment. 



Darkness-7'ig07' was used to denote the stable and non-motile 

 condition of protoplasm after continued deprivation of illumination, 

 under which circumstances all periodic movements and other activi- 

 ties were said to cease. 



Variations in intensities of illumination were supposed to induce 

 the assumption of day and night positions of leaves, and other organs 

 in a phototonic condition, by the paratonic action of the rays. 

 Leaves and internodes which have grown under normal alternations 

 of day and night grow more slowly in temporary illumination than 

 in darkness, due to the retarding action of light. 



Etiolation is a pathological condition, and the diminished stature of 

 leaves is due to defective nutrition, and not to lack of illumination 

 alone. 



Only chlorophyl-bearing organs might be etiolated ; floral organs, 

 customarily free from chlorophyl, fruits and seeds, may develop in a 

 fairly normal manner in darkness. 



It is notable that the investigations of Sachs and the workers in 

 his laboratory resulted in the record of an enormous number of facts 

 concerning growth and the relation of light to plants, and that these 

 researches led the way to nearly all of the modern work upon the 

 subject, yet scarcely a single one of his conclusions concerning etiola- 

 tion, and the influence of light upon growth are tenable at the present 

 time except in modified form. Some of his imperfect interpretations 

 must have been due to a failure to comprehend the bearing of the 

 reactions of fungi to light and darkness. 



G. Kraus'^^ conclusions published in 1869 ascribed the undevel- 

 oped stature of etiolated leaves to a lack of nutrition, upon the sup- 

 position that leaves were dependent upon the products of their own 

 chlorophyl apparatus for food. The excessive elongation of etiolated 

 stems was supposed by Kraus to be due in part to a slight multipli- 

 cation of the cells, and to an exaggerated elongation of these ele- 

 ments. Stress was laid upon the predominating influence of turgid 

 parenchyma cells as a positive factor in such stretching. The walls 

 of the fundamental system were seen to remain unthickened for a 

 month or more, in etiolated stems. Torsions were found in all 



3' Kraus, G. Ueber die Ursachen der Formanderungen etiolirender Pflanzen. 

 Jahrb. Wiss. Bot. 7: 209. 1869. 



