AIR AND LIFE. 173 



among" other families of plants. This is but an hypothesis, however, 

 and no definite statement can yet be made concerning this attempted 

 generalization. Some facts, indeed, go against it, and show that cer- 

 tainly not all plants have the functions which we have noted in the 

 papilionaceous family. Messrs. Schloesing and Laurent infer from 

 experiment that some species at least are unable to make use of 

 atmospheric nitrogen, and require to have it provided to them under 

 the form of different compounds contained in the fragments and debris 

 of other plants, which thus play the part of manure and food. While 

 the lion and tiger eat -the sheep and deer, some plants eat, so to say, 

 their congeners, and exhibit a form of cannibalism. The latter obtain 

 nitrogen from the atmosphere, and after death their remains serve as 

 food for other plants. Such is the case with mosses and many crypto- 

 gams. So, observe the gradation : Inferior plants 1 draw nitrogen from 

 the atmosphere; superior plants feed upon the remains of the lower; 2 

 and, lastly, animals feed on other animals or plants. Man eats both 

 animals and plants, and crowns the edifice of life, as he supposes; but 

 the solid substructure upon which all the building rests is merely an 

 agglomeration of humble unnoticed forms, often invisible to the naked 

 eye, whose functions are to provide the animal and vegetable king, 

 doms with an essential part of their food. Whether there is here a 

 plan is not for me to decide, but most assuredly the connections ;md 

 interactions are of interest. 



This exposition may seem somewhat long, but it was necessary. It 

 shows that certain plants, at least, can either directly or indirectly fix 

 atmospheric nitrogen without having recourse to the nitrates of nitrog- 

 enous manures. Here again it is shown that air is indispensable to 

 life. A gas that at first seems inert and useless is found, after careful 

 investigation, to play a most important part in the nutrition of living 

 organisms. Without nitrogen there would be no plants, no food, 

 no animals, no mankind, in brief, no life at all. And if atmospheric 

 nitrogen were to disappear, life would soon be extinguished. Who, 

 then, will consider this element of the air as useless? 



We now come to carbonic acid. 



We all know that it is an essentially noxious compound, and doubt- 

 less there is little in its history to redeem its reputation. One-half of 

 our respiratory function is concerned especially with the task of ridding 



'And some superior plants also, such, as those of the papilionaceous group; but 

 even with them the process is indirect, as it is through very low organisms (bacteria) 

 that nitrogen is brought to them. 



-When Melchior Treub visited Krakatoa after the disaster of 1884, in order to 

 investigate the floral repopulation of the island — seeds being brought by currents 

 and winds from the surrounding parts in abundance — he noted that the first plants 

 to appear were alga 1 , and lichens. And it was only some time after the latter had 

 taken a foothold, and, so to say, prepared a suitable soil, that higher plants were seen, 

 and lastly phanerogams. This jjrogression is quite in accordance with physiological 

 facts. 



