276 NATUKE OF SEEDS. 



may by artificial means readily make some forms of 

 organic matter, and convert them into others; but 

 he cannot make organized matter ; the latter is a 

 product of vital action, and has never been formed 

 by artificial means. 



723. The first change efi'ected by plants, is to con- 

 vert carbonic acid and water, under the influence of 

 light, into starch and similar forms of organic matter; 

 the second operation is to form these substances into 

 the various cells and tubes which compose the struc- 

 ture of plants. The former is a purely chemical 

 operation ; the latter requires something more, 

 namely, the exertion of vital power. 



724. As starch, though it is very easily convertible 

 into other substances under the influence of a fer- 

 ment, is nevertheless one of the most stable of all 

 the products which a plant forms ; so it is also that 

 one best fitted to serve as nutrition to a young plant, 

 and is the substance always prepared in plants, to 

 act as a store of nutriment for any future growth. 

 Whenever a growing point or embryo is formed, a 

 quantity of starch also is, at the same time, deposited. 



725. Thus starch is found in all seeds and buds, 

 as well in those which are formed on underground 

 stems and tubers, as in those which are formed at 

 the extremities of the branches. Whenever an 

 embryo or point of growth begins to develop, the 

 chemical action, in the first instance, is the same. 

 The azotized matter begins to change, diastase or 

 some similar substance is generated ; this acts on the 



