10 



Starch, is always definite in cliaraeter, and possesses tlie same 

 properties from whatever plant it may be obtained. It is composed 

 of carbon, hydrogen, and oxygen, in the proportion of 0^ H^^ Og. 

 The carbon is derived by plants from the carbonic acid which is 

 found in small quantity in the air. This fact was first shown by 

 Liebig ; before his time it was erroneously believed that the source 

 of the carbon was the soil. Wlien a seed is placed to germinate in 

 sand, and supplied with water and air which have been deprived of 

 carbonic acid, it ceases to grow, but growth at once recommences 

 when carbonic acid is supplied. The carbon of the carbonic acid in 

 the air is derived principally from the respiration of animals, and from 

 the combustion of coal, gas, &c. That carbonic acid exists in the air 

 expired from the lungs was shown by the Lecturer, who breathed 

 some air from his own lungs into a bottle containing lime-water. 

 The lime-water became turbid from the conversion of the soluble 

 lime into an insoluble carbonate of lime or compound of lime with 

 carbonic acid. The oxyyen of starch is also partly deiived from 

 carbonic acid, but its liijclror/en comes from water, the composition of 

 which is H„0. Thus it is found that carbonic acid and water are 

 necessary to the growth of a plant. But, in order to separate the 

 carbon from the oxygen. Energy is required, and that energy is 

 found in Light. 



The Lecturer then stated that when a ray of white light, such 

 as a beam of sunlight, is passed through a wedge-shaped piece of 

 glass, it becomes spread out like a fan, and broken up into several 

 rays coloured like the rainbow. These coloured rays — red, orange, 

 yellow, green, blue, indigo, and violet — appear invaiiably in the 

 same order, and, when thrown upon a screen, exhibit what is known 

 as the "spectrum." Now, of these rays, the red, orange, yellow, 

 and part of the green are necessary to the growth of a plant ; the 

 remaining rays, being inactive, are not necessary, and plants will 

 grow if depi-ived of such rays. The yellow exhibits the greatest 

 amount of energy in decomposing carbonic acid, and the intensity of 

 action of the various colours was shown to be E = 25, = 63, 

 Y = 100, G = 37, B = 22, I = 13, V = 7. This conclusion has 

 been arrived at by an estimation of the number of bubbles thrown 

 off in a given time by the leaves of a water-plant when exposed to 



