THE LEAF 139 



simple inorganic substances carbonic acid and water 

 into the organic substance starch represents the sole 

 natural process by which organic matter is formed upon 

 our planet. All organic substances, however diverse 

 they may be, and wherever they are found, whether in 

 plant, animal, or man, had their origin in the leaf, 

 have been formed from substances manufactured by the 

 leaf. Nature does not possess any other laboratory for 

 the formation of organic matter, except the leaf, or, 

 more strictly, the chloroplast. In every other organ 

 and organism, organic matter is merely transformed ; 

 only here does it arise anew from inorganic matter. 



From starch, for instance, is formed soluble sugar 

 which reaches the furthest parts of the plant by passing 

 from one cell to another. From this sugar the hard 

 skeleton of the plant called cellulose is formed. And, 

 lastly, from this same sugar and the inorganic substance, 

 ammonia, the most complicated organic substances, 

 such as proteids, can be formed. 



Thus the leaf assimilates carbon, and within itself 

 forms an organic compound with which not only the 

 plant itself but the whole animal kingdom is also 

 supplied. 



We have at last arrived at the source of carbon in 

 the plant, and have explained how it penetrates into it. 

 We have thus explained the first stage of the phenomenon 

 of nutrition ; we now know whence and by what means 

 all the elements that enter into the composition of the 

 plant are obtained, carbon being the last of the series. 



So far we have been examining the activity of the 

 leaf and of the plant in general, exclusively from the 

 chemical point of view from the point of view of the 

 transformation of matter. Starting from the funda- 



