244 SUMMARY OF CURRENT RESEARCHES RELATING TO 



chamber was illuminated at night only by the electric light. Five 

 series of comparative observations were made, viz. : — 



1. Plants exposed night and day to the electric light alone. 



2. Plants exposed during the day to the diffused daylight, and 

 during the night to the electric light. 



3. Plants living during the day in the open air, and receiving the 

 electric illumination at night. 



4. Plants passing the day in the diffuse daylight, and the night 

 in darkness. 



5. Plants living normally in a garden. 



The plants submitted to experiment were barley, flax, beans, and 

 a number of garden and greenhouse plants. 



Action of the Unprotected Light. — At the end of seven days the 

 naked electric light was seen to have an injurious effect both on those 

 plants which were constantly subjected to it, and in a less degree on 

 those which were exposed to it during the night only. The leaves 

 blackened, withered, and dropped off; the injury was confined to the 

 epidermal layers, and was due to the direct impact of the luminous 

 radiations (and not to the formation of nitrogen oxides) ; for where 

 one leaf was partly shaded by another, a sharp line was photographi- 

 cally impressed. 



Experiments on Elodea canadensis, submerged in flasks of water, 

 showed that while the diffuse daylight of the building was unable to 

 cause decomposition of carbonic anhydride and evolution of oxygen, 

 the direct rays of the electric light were able to do so, about as much 

 oxygen being obtained during an exposure of four or five days and 

 nights to the electric light as could be obtained in an hour or so in 

 bright sunlight. At the end of fifteen days the arc-lights were 

 inclosed in globes of transparent glass, Siemens' just published 

 experiments having shown that the injurious action of the direct radi- 

 ations was thereby modified. 



Action of the Protected Light. — A number of fresh and uninjured 

 plants were placed in the greenliouse, and in addition sowings of barley, 

 oats, peas, maize, beans, which had just aj)peared above the ground. 

 All the seedlings exposed exclusively to the electric light perished 

 sooner or later, and the leaves of some of them were blackened as 

 with the naked light, The mature plants, on the other hand, con- 

 tinued to vegetate, but in no case, save a plant of barley, were flowers 

 and seeds produced, the vegetation being purely foliaceous. The 

 barley grains were normal, and germinated on being sown. The 

 electric light employed was clearly insufiicient by itself to determine 

 the assimilation of any considerable quantity of material ; direct 

 experiments also proved that it is not more powerful in exciting 

 transpiration of water, a leaf exposed to it giving off in an hour only 

 about one-fiftieth of the quantity of water evaporated under similar 

 circumstances in sunlight. As the evaporation of water by the leaves 

 is one of the chief agencies in causing the migration of material 

 necessary for the maturation of seeds, the failure of the plants to 

 produce flowers and seeds receives its explanation. It is known that 

 yellow and red rays are most powerful in causing transpiration, whilst 



