22 THE GLORY OF THE GARDEN 



hindrance the wonderful work of food manu- 

 facture. 



The daily work and routine of this green part of 

 the plant is one of the most interesting phenomena 

 in nature, and yet by the greater number of people, 

 one of the least-thought-of facts. It is, of course, 

 a commonplace piece of knowledge that plants do 

 exactly the opposite thing to the atmosphere, to 

 that done by human beings and animals — viz., they 

 purify the air during the daytime by breathing out 

 pure oxygen and taking in the carbon dioxide from 

 the surrounding air. This gas, whose chemical 

 formula is CO2, is at once seized upon by the chloro- 

 phyll grains, or chloroplasts (the green colouring 

 matter of the plant), and " assimilated." 



After entering into the cells of the leaf, the CO2, 

 together with a certain amount of water, undergoes 

 a chemical change, which results in the formation 

 of a soluble carbohydrate. 



The word Carbohydrate simply means a substance 

 composed of carbon, hydrogen, and oxygen. Starch 

 and sugar are carbohydrates, and the first to be 

 formed after this " carbon-fixation " is sugar, 

 probably cane sugar, which is in soluble form, and 

 in this form the leaves send it along by special cells 

 and vessels down to the stem and roots. 



The next process that this sugar undergoes is to 

 be converted into starch grains, which latter, being 

 solid, are more easily compressed into a small space. 

 Normally, the night-time storage form is sugar, 

 and each morning, directly it is light, the proto- 

 plasm seizes on the sugar, elaborates it, and once 

 more converts it into starch for the daytime storage 

 form. 



