2o6 



MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



ity of plants exhibit divergences from normal growth and development 

 whenever cultivated under conditions in which the customary occur- 

 rence of illumination and darkness is varied. The effect of one 

 departure, in which plants are cultivated in complete darkness, has 

 been the subject of an enormous number of investigations as pre- 

 viously indicated. The amount of experimental evidence at hand 

 bearing upon the influence of continuous illumination upon plants is 

 comparatively meager, the most important contribution to the subject, 

 from a botanical point of view, having been made by Bonnier in 1895 



(see page 27 of this Mem- 



oir). >" 



The continuous electric 

 illumination to which Bon- 

 nier subjected the plants 

 used in his experiments was 

 of suchintensitythat a liber- 

 ation of oxygen from aqua- 

 tic plants under the same 

 conditions took place at 

 about one third the normal 

 rate at which the process 

 ensued in sunlight. Par- 

 ticular emphasis is to be 

 laid upon this fact in view 

 of the well-grounded con- 

 clusions, to which refer- 

 ence is made above (p. 

 204), that the separate 

 stages of development of 

 a plant, or of the different 

 organs, are associated with 

 certain intensities of illumi- 

 nation. An intensity below 

 the normal of full sunshine 

 would be favorable for cer- 

 tain action and unfavorable 

 for others, and it is to this continuous and long-continued con- 



FiG. 158. Carpinus Betiilus. iC, leafy branch 

 from small tree in continuous electrical illumina- 

 tion. ID, leafy branch in normal discontinuous 

 illumination. After Bonnier. 



1^* Bonnier, G. Influence de la lumiere electrique continue sur la forme et la struc- 

 ture des plantes. Rev. Gen. d. Bot. 7 : 241, 269, 332, 407. 1895. 



