56 MASSACHUSETTS HORTICULTURAL SOCIETY. 



exert some exciting intlueuce upon the physiological processes, 

 and not to the action of greater warmth or more food, or to any 

 intensification of the ordinary conditions of existence. I insist 

 upon this distinction here because it enables me to contrast two 

 phenomena which are often confounded in their effects upon 

 plants, but which are in essence far apart : namely, the eft'ect of 

 electric light, which simply adds light to light or, in other words, 

 increases the daytime, and the electric current, or electrification, 

 which in some way disturbs or excites the normal functions. 



I. The Application op Electrical Illumination to Plant- 

 Growing. We are now ready to approach the subject of the influ- 

 ence of electrical forces upon vegetation in a philosophical spirit. 

 These forces or agencies are of two general types — the electric 

 light, which is simply a method of illumination, and electric currents, 

 which are a means of electrification. The former of these agen- 

 cies is the one to which I invite your chief attention. We may 

 feel sure, at the outset, that illumination at night will not injure 

 the plant ; and as it has long been proved that artificial lights 

 exert much the same influence upon plants as the sunlight does, 

 only in smaller degree, we shall expect that good results will 

 follow, and in proportion as the energy of the artificial light 

 approaches the energy of solar light. The electric arc light com- 

 mends itself above other common artificial lights because it is the 

 most powerful. The spectrum of this light is that of carbon, 

 combined, probably, with certain products of combustion. It 

 contains the same parts as the solar spectrum and in approxi- 

 matel}^ the same proportions ; but it is richer in the ultra-violet 

 rays and probably somewhat weaker in the orange rays, which 

 accounts for its dazzling blue- whiteness. It is pretty well ascer- 

 tained tliat the orange portion of the solar spectrum is particularly 

 promotive of the assimilative power in plants. This fact suggests 

 that the use of an orange globe for the electric light would bring 

 its spectrum nearer to that of sunlight. Our experiments with 

 color-screens show that an amber glass — which is the nearest 

 approach to orange in commercial glass — gave more rapid growth 

 or earlier results than other colors ; but it is doubtful whether the 

 assimilative power of the ordinary electric light is sufficient to 

 render minor modifications of tlie visil)le portions of its spectrum 

 practically appreciable in plant growth. Incandescent electric 

 illumination has not been carefully studied in its effects upon 



