GEOWING PLANTS WITHOUT SOIL 



By Earl S. Johnston 

 Division of Radiation and Organisms, Smithsonian Institution 



[With 4 plates] 



Over 300 years ago Johan Baptista van Helmont carried out a very 

 simple and interesting experiment at Brussels. The following is 

 a record of the experiment as given by Russell : 



I took an eartben vessel in which I put 200 pounds of soil dried in an oven, 

 then I moistened with rain water and pressed hard into it a shoot of willow 

 weighing 5 pounds. After exactly five years the tree that had grown up 

 weighed 169 pounds and about 3 ounces. But the vessel had never received 

 anything but rain water or distilled water to moisten the soil when this was 

 necessary, and it remained full of soil, which was still tightly packed, and, 

 lest any dust from outside should get into the soil, it was covered witli a sheet 

 of iron coated with tin but perforated with many holes. I did not take the 

 weight of the leaves that fell in the autumn. In the end I dried the soil once 

 more and got the same 200 pounds that I started with, less about 2 ounces. 

 Therefore the 164 pounds of wood, bark, and root arose from the water alone. 



The experiment is simplicity itself and may be repeated by anyone. 

 The language describing it is clear and lacks the many technical 

 terms which are common in modern descriptions of experiments. In 

 spite of the many good qualities commending this famous old experi- 

 ment, Van Helmont's conclusion is illogical and incorrect. As we 

 shall note directly, the 164 pounds of wood did not arise from the 

 water alone. 



If he had taken the young tree and dried it, thus driving off the 

 water, its weight would have been reduced 40 to 50 per cent. If he 

 had then burned this dried wood, ash or noncombustible material 

 would have remained, though but a small fraction of the final weight 

 he recorded. 



Almost half the weight of woody plants can be attributed to the 

 water contained in the plant cells and tissues. The other half con- 

 sists mainly of organic matter which can be burned, forming carbon 

 dioxide, one of the gases in the air. If approximately 50 per cent of 

 the plant can be returned to the air as carbon dioxide, it seems reason- 

 able to suppose that this gas might have been withdrawn from the air 



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