STUDIES OF SEED-PLANTS 155 



for months until freezing or decay of seed-coats cause cracks 

 into which water can enter. Gardeners often crack certain 

 hard seeds, like peach and various nuts, or file or cut notches 

 in others, and still other kinds are soaked and softened in 

 hot water before planting. By soaking seeds for various 

 lengths of time in red ink it is possible to trace the paths 

 taken by entering water, usually the same as that taken by the 

 sap while the seed was developing. 



Proper Temperature. This also requires no special demon- 

 stration. Any one who has ever been interested in a garden 

 knows that warm weather is necessary, and that some kinds 

 of seeds will germinate in early spring when the soil is still 

 cold and that others require warm soil. By simply placing 

 some seeds on a moist paper in an ice-box and others of the 

 same kind in warmer places one could show the effect of 

 temperature, and after many trials it would be found that 

 there is a best or optimum temperature for each kind of seeds. 

 Seed-catalogues and books on gardening usually give the 

 necessary information regarding best temperatures for germi- 

 nating common vegetable and " flower " seeds. 



Air, Oxygen. That the oxygen of the air is necessary 

 might be expected because a germinating seed is a living 

 plant, and we have learned that all protoplasm must have 

 oxygen. It can be proved by placing seeds in a bottle and 

 pumping out the air with an air-pump, or by filling the bottle 

 with pure nitrogen gas made with a chemist's generator. 

 That carbon dioxide is formed in germinating seeds can be 

 proved by the lime-water test simply stand a small cup 

 or vial containing lime-water in a larger, carefully stoppered 

 bottle containing germinating seeds. Or use the method 

 described in 26, suspending seeds in a bag of netting during 

 germination, and then after lifting out the bag, pour lime- 

 water into bottom of the jar. 



The student is advised to consult Chapters I and II of Oster- 

 hout's "Experiments with Plants" for numerous experiments and 



