THE INFLUENCE OF LIGHT ON LIFE. 235 



If we SOW some seeds in a pot and place it in a dark cupboard 

 we shall find that in due season these seeds will sprout, but we shall 

 also find that the small seed-leaves will remain of a yellowish colour. 

 If left in the dark, the young plants will, perhaps, lengthen out a 

 little, but, after the food which was stored up in the seed has been 

 exhausted, no increase of the plant's substance will lake place. 

 They will become swollen with water and soon droop down and 

 die. If at the same time as we make that experiment we also 

 place a pot containing seeds in the Hght, we shall find that the 

 young plants will hea.r green leaves, and that, instead of becoming 

 water-logged and limp, they will every day fix more carbon in their 

 tissues, so that the plant substance will daily increase. In these 

 two experiments we have the same seeds, the same quantity of 

 water provided, and the same air, containing in each case the same 

 quantity of carbonic acid ; but the great difference in the circum- 

 stances is, of course, that in one case we have no light at all and 

 the plant dies, while in the other case the plant enjoys the influence 

 of the mysterious light, and therefore lives and grows. If we 

 removed the plant which was trying to grow in the dark into the 

 light, we should find that its colourless leaves would soon become 

 green, and that in every way the plant would turn from its state of 

 sickness to one of verdant health. The seeds germinated in the 

 dark, of course, because the necessary food was present in the 

 seed, and light was therefore not required for the fixation of 

 carbon. Indeed, light is objectionable at that stage, as it tends to 

 fix the carbonic acid which the young sprout wishes to throw off. 



The same proof of the necessity of light for plants is obtained 

 by exposing one glass of spring water to the sunshine, and hiding 

 another one in a dark chamber. In the former glass, green films 

 of algae life will by-and-by appear, owing to the action of light on 

 the germs which were present in the water, whereas, as might be 

 expected, no such growth will appear in the other glass. From 

 these simple experiments we see that it is absolutely necessary, in 

 order to have vegetation, that we must have light, and we find our 

 experiments fully corroborated in Nature, for in coal-mines and 

 caves where there is no light at all there is no plant life at all. 

 We may just call to mind, in passing, that in the cultivation of 

 .celery the altering effect of darkness is taken advantage of; the 



