part of mucilage or like fine particles in a muddy pond. These various sub- 

 stances are constantly undergoing chemical changes. 



Chemical processes inside a plant or animal, like those in a test tube or 

 a soap kettle, can take place only in a fluid state. In living things this 

 fluidity is maintained by the large amount of water. 



Unlike the test tube or kettle, however, the living cells of leaves and 

 stems, of muscles and nerves, require a constant flow of water. For the 

 water itself takes part in some of the chemical transformations of proto- 

 plasm, so that it is constantly being destroyed. In other cases the activities 

 involve a loss of water through the walls or membranes of the cell. There 

 is in fact a constant flow of water between a living cell and its surround- 

 ings — water coming in and water going out. 



Sprouting of Seeds In the spring the gardener or the farmer places his 

 seeds in the ground, and they sprout. Since our common cultivated plants 

 normally grow in soil, we are likely to assume that the soil somehow starts 

 the seeds to begin their active growth after their long rest. The soil is a 

 mixture of many kinds of stuff, some of which may have something to do 

 with the sprouting, but not the others. 



Most of us know that seeds kept in jars will not sprout, whether they 

 are kept in the dark or exposed to light. Hence it is not on account of dark- 

 ness that seeds germinate in the ground. Seeds kept in a warm place and 

 seeds kept in a cool place will both fail to sprout so long as they remain in 

 our jars or boxes. It cannot be temperature alone that makes them sprout 

 in the ground. Perhaps the soil keeps some of the air away from the seeds } 

 But keeping air out of the jar will not make the seeds sprout. 



In regard to the chemical substances in the soil, our usual experience tells 

 us nothing at all. If we place the seeds in boxes containing the various in- 

 gredients of the soil, such as sand, clay and various salts, we shall find that 

 not one of the seeds sprouts. 



This suggests that even if any of the substances might cause sprouting, 

 none can get into the seeds in the dry state. We should therefore try these 

 substances with water. But has water by itself any effect on the* sprouting 

 seeds ? 



An experiment in which some seeds are placed with various amounts of 

 water, while other seeds from the same lot are kept under similar conditions 

 of air, light and temperature — but without water — will easily convince us 

 that a certain amount of water is a necessary condition for starting the 

 germination of the seeds. 



We shall find also that some kinds of seeds will fail to sprout if they 

 are completely covered with water, although other kinds will sprout under 

 those conditions. This suggests that water may have injured the seeds, or 

 that they drowned because of lack of air. 



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