20 THE BOOK OF NATURE STUDY 



water turns milky. As lime-water always turns milky when 

 carbon dioxide is mixed with it, it is clear that human beings 

 breathe out carbon dioxide, and thus the air in a room in which 

 people are sitting for some time gets laden with carbon dioxide. 

 In order to ascertain whether seeds also breathe out this gas, 

 the air in a glass bottle in which germinating seeds have been 

 placed for twenty-four hours may be tested in the same way, by 

 pouring a little clear lime-water into it and shaking it up. The 

 lime-water becomes milky. The conclusion, therefore, is that 

 germinating seeds give out carbon dioxide. 



Experiments such as these are very simple, but they serve 

 to develop the reasoning power, and help children to understand 

 that respiration goes on in seeds as it does in human beings and 

 in all animals ; for the taking in of oxygen and the giving out 

 of carbon dioxide always accompany respiration. What is true 

 of seeds is also true of the fully grown plant ; all the ordinary 

 plants, as long as they are alive, are taking in oxygen and giving 

 out carbon dioxide. 



(ii.) Water Essential. Seeds must have water; as long as 

 they are in a dry condition they will not germinate. Some 

 seeds can retain their vitality in a dry condition for years. Just 

 lately Becquerel has experimented on the seeds of 500 species 

 of plants belonging to 30 of the most important families of 

 Monocotyledons and Dicotyledons. The age of the seeds was 

 known from the records of the Museum of Natural History in 

 Paris. He found that 18 species, 87 to 28 years old, of Legum- 

 inosse ; 3 species of Nelumbium, 56 to 18 years ; one Lavatera, 

 64 years old ; and a Stachys, 77 years of age, germinated. 1 

 Gardeners say that the best seeds to sow, best because most 

 certain of producing good plants, should be a year old. There 

 is nothing in the external appearance of a seed to denote whether 

 it is dead or living, but as soon as it is soaked in water the living 

 seed will begin to germinate; the dead seed will not. Seeds 

 may be killed by boiling them, and then they will not germinate. 

 Both living and dead seeds will take up water, but it is only in 

 the living seed that the radicle will begin to protrude. It takes 



1 This, however, is not universally true ; some seeds very soon lose their power of 

 germination, and require to be sown the same year in which they are ripened. 



