STORAGE OF FOOD IN THE SEED 21 



a strong magnifying glass, then with a moderate power of 

 the compound microscope. To see how dead, dry cell- 

 walls, with nothing inside them, look, examine (as before) 

 a very thin slice of elder pith, sunflower pith, or pith from 

 a dead cornstalk. Look also at the figures in Chapter VI 

 of this book. Notice that the simplest plants (Chapter XX) 

 consist of a single cell each. The study of the structure 

 of plants is the study of the forms which cells and groups 

 of cells assume, and the study of plant physiology is the 

 study of what cells and cell combinations do. 



25. Absorption of Starch from the Cotyledons. Examine with 

 the microscope, using a medium power, soaked beans and the cotyle- 

 dons from seedlings that have been growing for three or four weeks. 

 Stain the sections with iodine solution, and notice how completely 

 the clusters of starch grains that filled most of the cells of the un- 

 sprouted cotyledons have disappeared from the shriveled cotyledons 

 of the seedlings. A few grains may be left, but they have lost their 

 sharpness of outline. 



26. Oil. The presence of oil in any considerable 

 quantity in seeds is not as general as is the presence of 

 starch, though in many common seeds there is a good 

 deal of it. 



Sometimes the oil is sufficiently abundant to make it 

 worth while to extract it by pressure, as is done with flax- 

 seed, cotton-seed, the seeds of some plants of the cress 

 family, the " castor bean," and other seeds. 



27. Dissolving Oil from Ground Seeds. It is not possi- 

 ble easily to show a class how oil is extracted from seeds 

 by pressure ; but there are several liquids which readily 

 dissolve oils and yet have no effect on starch and most of 

 the other constituents of seeds. 



