28o MEMOIRS OF THE NEW YORK BOTANICAI. GARDEN. 



the sporophores of Dictyosteliiim is retarded when cultivated in the 

 open air, but when confined within a damp chamber a growth above 

 the average normal is made, showing that light does not retard 

 growth in this species, and that the lessened growth in the open air 

 under the action of light may be ascribed to transpiration, although 

 interpreted in another manner by Potter. 



THEORIES AS TO THE NATURE OF ETIOLATION.'^* 



Various explanations have been advanced to account for the ab- 

 normal form, stature, color, structure, growth and development of 

 plants in darkness, beginning with the time of Hales (1727), and the 

 theories formulated constitute a most interesting index of the state of 

 knowledge of the physiology and morphology of plants during 

 the last two centuries. Hales ascribed the greater length of the 

 attenuated etiolated stems which came under his observation to the 

 increased ductility of the tissues, a view which A. P. DeCandoUe, 

 shared a century later (1832). Very naturall}' the earlier investi- 

 gators laid the greatest stress upon the more apparent physical fea- 

 tures in which alterations were to be easily observed, and con- 

 sequently the matter of color came in for an undue share of attention, 

 while the lack of information as to the character of the photosyn- 

 thetic functions, and of the general morphology of the plant made 

 it impossible that the functional and anatomical alterations due to the 

 absence of the morphogenetic and other influences of light should be 

 appreciated. To Senebier perhaps (1800) may be ascribed the first 

 serious attempt at an explanation of the abnormal manifestations 

 shown by etiolated plants. ^^^ He assumed that the primitive or funda- 

 mental color of plants was yellow, and that etiolation inhibited the 

 processes of oxygen-separation and carbon-fixation that were neces- 

 sary for the construction of the various colors. The lesser dry weight 

 of etiolated plants when compared with those grown in light was as- 



18* Presented before the New York Weekly Botanical Convention, Museum of the 

 New York Botanical Garden, November 5, 1902. 



1'^ Senebier. Hypothese pour expliquer I'etiolement. Physiol, vegetale. 4: 295- 

 308. 1800. 



