14 SEEDS : STRUCTURE AND GERMINATION 



of the air is absorbed, and in its place carbon dioxide is given off 

 into the surrounding air, for this is what happens in the breathing 

 of a living animal. 



Ex. T. — Carbon dioxide is produced when beans germinate. Place twenty 

 soaked beans in a wide-mouthed bottle, and cork them up after showing that 

 a match burns freely in the bottle. Leave them in a warm place for twenty- 

 four hours, and try if a match will now burn in the bottle. 



The carbon dioxide gas can be poured out into a beaker containing lime 

 water ; on shaking, its presence is proved by the lime water becoming 

 ' milky ' owing to the precipitation of carbonate of lime. 



The particular use of the water, heat and air to the plant we 

 cannot at present discuss. It may, however, be mentioned that 

 without water the embryo would have little chance of becoming 

 free from the tough and hard seed-coat surrounding it; water 

 softens the latter, and makes it more easily torn by the extending 

 radicle and plumule. 



In the early stages of the life of the bean plant, from the com- 

 mencement of germination up to the time when the first green 

 leaves are unfolded, the development and building up of the 

 elongating rootlet and shoot depend upon the thick cotyledons. 

 At first the latter are thick and fleshy, but as the radicle and 

 plumule grow the cotyledons become softer and thinner, ulti- 

 mately shrivelling considerably. The cotyledons are leaves, the 

 interior of which is .packed with food for the rest of the growing 

 embryo, and a large amount of the water absorbed by the seed 

 is used for the purpose of dissolving the nutrient material in 

 them, and carrying it from them to the various parts of the root 

 and shoot of the young plant where growth is going on. 



Ex. 8. — Germinate beans in damp flannel as in Ex. 3, and show that the 

 cotyledons are essential to the development of the root and shoot of the em- 

 bryo by cutting them off as soon as the two latter parts have emerged from 

 the seed-coat. Try separating one cotyledon and then two at various stages 

 of development, and see if the axis (root and shoot) can be made to develop 

 without them. The growth should be allowed to continue some time in 

 order to obtain well-marked efifects. 



7. Not only do the changes observed in the embryo of a ger- 



