78 ANATOMY AND PHYSIOLOGY OF 



Tlie questions, whetlier plants iniibt take up from witlioiit the element- 

 ary substances wloicli analysis discovers in them, or wlietlier tliey liave the 

 power of transforming the elements one into another, to live upon pure 

 water, &c., are no longer worth discussion in these days. Whether it be 

 thought probable or not, that the elements of modern chemistry are actu- 

 ally elementary substances^ it has been placed beyond doubt, from Saus- 

 sure's researches onwards through all accurate subsequent observations, 

 that no other substances occur in plants besides those which they take up 

 from without (.ee, especially, Wiegmann and Polstorff " Ueher d, anorgmi, 

 Bestcmdih. d, Fflanzerh'). 



Of all the elementary substances which enter into plants, 

 oxygen is the only one that is taken up in a pure condition; 

 plants can only appropriate the others out of chemical compounds, 

 which they for the most part decompose. Here at once arises 

 the question, whether the elementary substances when they are 

 to serve as food for plants, must be abeady combined into oiganic 

 compounds, or whether plants possess the power of feeding upon 

 inorganic compounds? On no question of vegetable physiology 

 has so active a strife existed as on this, especially since Liebig 

 (" Ghe-mistry applied to Agricultitre and Physiology ") appeared 

 as a defender of one of the extreme answers to it. 



No universally valid answer can be given to this question. It 

 is beyond any doubt, that plants, if not as a whole, yet in an 

 overwhelming majority, possess the power of forming organic out 

 of inorganic substances, and that inorganic substances mostly 

 play the principal part in the nutrition. This is evident, both 

 from observations made on a large scale in free nature, and in 

 small artificial experiments. It is a perfectly universal expe- 

 rience, repeated in the same manner in the primaeval forests of 

 the tropics, on the peat bogs, meadows, and heaths of temperate 

 regions, and on the rocky soil of the Alps, that where the vege- 

 tation is left to itself upon a particular soil, and its products are 

 not removed from the ground, masses of decaying organic sub- 

 stances are formed, in consequence of the death of the plants, accu- 

 mulating from year to year, which can of course only be the case 

 through each generation of plants producing a greater quantity 

 of organic substances than it consumes. In a similar way, when 

 an estate is cultivated on proper principles, a certain amount of 

 organic substance is taken away, in the form of grain, cattle, &c., 

 having its origin in the plants grown upon the estate, without 

 the necessity of adding organic matters from elsewhere, and 

 without diminishing the fruitfulness of the soil. 



The experiments of Saussure also, which are above all to be de- 

 pended on in questions relating to the nutrition of plants, shewed 

 that plants which he grew with water, in a closed space, in an 

 atmosphere rich in carbonic acid, increased their organic substance. 

 He calculated in a manner which does not indeed admit of exact- 

 ness, but still of an approximation to the true condition, that a 



