MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 285 



MORPHOGENIC INFLUENCE OF LIGHT AND 

 DARKNESS. 



An examination of the groups of facts obtained by absolute etiola- 

 tions shows most clearly that no one of the theories recorded in the pre- 

 ceding section is capable of general application to the behavior of all 

 plants in darkness. The unusual ductility of the bodies of plants in 

 darkness is a consequence, or accompaniment of the abnormal forms 

 produced by etiolation, not a cause of them, and the extended existence 

 of shoots in darkness and their subsequent behavior when exposed to 

 illurtiination is signal proof that a shoot absolutely etiolated is not in a 

 pathological condition in the ordinary acceptance of the term, although 

 when a mature green leafy shoot is confined to darkness the leaves 

 and other chlorophyl-bearing members may become more or less 

 pathological, in a manner which might be expected when any active 

 tissue is forced into prolonged inactivity. The " self-nutrition theory " 

 has been abandoned for equally obvious reasons, among which the 

 most important are that leaves (to which this theory principally ap- 

 plies) may be induced to make nearly the full amount of growth, 

 but not of morphological differentiation when stimulated by the re- 

 moval of concurrent organs. All attempts to establish a direct con- 

 nection between the action of light on tissues, and the behavior of 

 these tissues in consequence, have so far failed, and the former con- 

 clusions as to exaggeration or multiplication of epidermal and other 

 elements are found to be wholly worthless. Furthermore the exten- 

 sion of this idea by which laws of etiolation were formulated as to 

 the behavior of leaves and stems in darkness is found to be entirely 

 unsupported since no classification of the etiolative reactions may be 

 made on an organographic basis. As may be seen from the sections 

 in which this matter has been discussed in the present paper the 

 phenomena exhibited by both leaves and stems are extremely diversi- 

 fied and widely divergent. Lastly, as to the proposal that etiolative 

 reactions are adaptive in their nature it is to be said that the forms 

 presented by the shoots of a greater majority of the species examined 

 do not exhibit any beneficial adjustments by which the plant might 

 free itself from encompassing darkness, and lift its leaves and repro- 

 ductive organs past the obstruction that intercepts the rays. It needs 



