PLANT FOOD 31 



the living substance of a plant, only the plant makes 

 them first for itself. 



Sow seeds of any quickly-growing herb, and when 

 three or four leaves have appeared on each, cut them 

 all off from some of the plants, leaving the others 

 entire. In a few days the mutilated plants will prob- 

 ably be dead ; or if they are still alive after a week, 

 it will be very apparent that they have not grown as 

 those which have still their leaves. 



This shows us that the leaves are essential to the 

 life of the plant, that they in fact supply its food. 



Now grow in pots some more of the same or any 

 other plant that naturally grows in the open, such as 

 Cotton, Sunn-hemp, or Castor. When they have come 

 up, put some of them out in the sun, giving them 

 plenty of water, and keep the others in a dark 

 room. 



In a few days' time those in the dark room will 

 be very likely a little taller, especially if the plant be 

 naturally a climber (the reason for this we shall come 

 to later on), but they will be weak and sickly in 

 appearance, and if left for some time will probably 

 die, while the others will be sturdy and strong and 

 have a healthy green colour. 



We learn by this that light is necessary for green 

 plants, and that without light they cannot obtain their 

 food, but starve and die. It is, therefore, only during 

 the day that the making of carbohydrates can go on, 

 and for that reason this process is also called photo- 

 synthesis (photos = light, synthesis = combination). 



Since carbon is taken from the gas carbon dioxide 

 in the process of assimilation, oxygen must be set 



