CHAPTER VIII 

 PLANT FOOD IN THE SOIL 



WE learned in previous paragraphs that the roots 

 of plants take food from the soil, and that a condi- 

 tion necessary for the root to do its work for the 

 plant was the presence of available plant food in 

 sufficient quantities. 



What is plant food? For answer let us go to 

 the plant and ask it what it is made of. 



Experiment. Take some newly ripened cotton 

 or cotton wadding, a tree branch, a cornstalk, and 

 some straw or grass. Pull the cotton apart, then 

 twist some of it and pull apart; in turn break the 

 branch, the cornstalk and the straw. The cotton 

 does not pull apart readily nor do the others break 

 easily; this is because they all contain long, tough 

 fibres. These fibres are called woody fibre or cel- 

 lulose. The cotton fibre is nearly pure cellulose. 



Experiment. Get together some slices of white 

 potato, sweet potato, parsnip, broken kernels of 

 corn, wheat and oats, a piece of laundry starch 

 and some tincture of iodine diluted to about the 

 color of weak tea. Rub a few drops of the iodine 

 on the cut surfaces of the potatoes, parsnip, and 



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