The First Land Plants 



water but from the atmosphere. No plant can live on 

 carbonic acid alone, for its living material contains 

 nitrogen, sulphur, phosphorus, iron, and other elements 

 which are usually obtained in solution by its roots. 



There has always been a difficulty about explaining 

 the nitrate supply of the vegetable world. The gas, 

 nitrogen, in the atmosphere is not usually available for 

 plants which can only, in most cases, absorb it in the 

 form of nitrates dissolved in water. 



The entire mass of dead vegetables and animals 

 represent a sort of capital stock from which a living 

 plant draws what it requires during life ; its dead body 

 and waste products go back to replenish the fund of 

 available nitrogen. The chief object in the world of 

 fungi and especially bacteria is to look after such dead 

 matter and work it back into a form in which it can be 

 absorbed by living roots. 



Dr. Bunge has some very eloquent remarks upon 

 this point. He complains of the wickedness of man- 

 kind in burning forests and so robbing the flower-world 

 of its painfully acquired stores of invaluable nitrogen. 

 He objects especially to cremation, which, in his view, 

 is economically a crime. All explosives, such as gun- 

 powder, are derivatives of nitric acid. So one might 

 say that every shot fired, whether the bullet reaches a 

 living being or not, destroys life, for it is a wanton 

 destruction of combined nitrogen. All life depends 

 upon this nitrogenous capital fund.^ 



,_ But it is quite certain that vegetable life had a be- 

 ginning, and this capital must have slowly accumulated 

 out of very small excesses of income over expenditure. 

 It is in this connection that our nostoc becomes 

 particularly interesting, for it was soon discovered that 

 a certain bacterium (azotobacter) which lives upon this 

 blue-green alga has the power of getting hold of the 



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