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 
43 
