INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 293 



prising a fair proportion of sunlight) presented their usually healthy 

 green appearance ; those exposed to electric light alone were, in most 

 instances, of a somewhat lighter, but, in one instance, of a somewhat 

 darker hue than those exposed to daylight ; and all the plants that 

 had the double benefit of day and electric light far surpassed the 

 others in darkness of green and vigorous appearance generally, the 

 specimens of mustard and of carrots exhibited to the Society showing 

 this difference in a very remarkable way. 



These experiments are not only instructive in proving the suffi- 

 ciency of electric light alone to promote vegetation, but they also go 

 to prove the important fact tliat diurual repose is not necessary for 

 the life of plants, although the duration of the experiments is too 

 limited perhaps to furnish that proof in an absolute manner. It may, 

 however, be argued from analogy, that such repose is not necessary, 

 seeing that crops grow and ripen in a wonderfully short space of time 

 in the northern regions of Sweden and Norway, and Finland, where 

 the summer does not exceed two months, during which period the sun 

 scarcely sets. 



Dr. Siemens only considers himself as yet on the threshold of the 

 investigation, but thinks the experiments already made are sufficient 

 to justify the following conclusions : — 1. That electric light is effica- 

 cious in producing chlorophyll in the leaves of plants, and in pro- 

 moting growth. 2. That an electric centre of light equal to 1400 

 candles placed at a distance of two metres from growing plants, 

 appeared to be equal in effect to average daylight at this season of 

 the year ; but that more economical effects can be obtained by more 

 I)oweiful light-centres. 3. That the carbonic acid and nitrogenous 

 compounds generated in diminutive quantities in the electric arc, 

 produce no sensible deleterious effects upon plants enclosed in the 

 same space. 4. That plants do not appear to require a period of rest 

 dui'ing the twenty-four hours of the day, but make increased and 

 vigorous progress if subjected during daytime to sunlight and during 

 the night to electric light. 5. That the radiation of heat from power- 

 ful electric arcs can be made available to counteract the effect of night 

 frost, and is likely to promote the setting and ripening of fruit in the 

 open air. 6. That while under tlie influence of electric light plants 

 can sustain increased stove heat without collapsing, a circumstance 

 favourable to forcing by electric light. 7. That the expense of 

 electro-horticulture depends mainly upon the cost of mechanical 

 energy, and is very moderate where natural sources of such energy, 

 such as waterfalls, can bo maile available. 



The paper gave rise to a highly interesting discussion, in which 

 Sir J(jscph Hooker pointed out that the evidence aflbrded of the 

 I)ractical identity, as regards vegetation, of sohir and electric light, 

 besides the probability that it would bo turned to immediate account 

 by horticulturists, would afford great facilities for the scientific inves- 

 tigation of tlie influence exerted by light, as compared with other 

 agencies, in promoting the formation of the active principles or most 

 valuable constituents of plants, sucli as the quinine of the cinchona 

 bark, the gluten of wheat, and so forth. 



