Stkuctuee and Growth. 25 



All seeds will not equally produce vigorous plants ; but the 

 healthiness of the seedling will correspond with that of the 

 seed from which it sprang. Where vigor is required, the 

 plumpest and heaviest seeds should be selected. 



A seed always produces a plant of the same species as that 

 from which it was derived, but is not certain to reproduce any 

 peculiarity that may have existed in its paren^. For instance, 

 the seed of a Green Gage plum wiU grow into a new individual 

 of the plum species, but it is not certain, or even likely, to pro- 

 duce the variety known as the Green Gage. The variety must 

 be propagated in some other way. 



YI.— THE FOOD OF PLANTS. 



The gardener should know precisely what substances plants 

 require for their growth and the matm'ation of their fruit — 

 that is, their natural food. This is ascertained by analysis. 

 When we have learned of what plants are composed, we know 

 what their food must necessarily contain. 



The constituents of plants, as shown by analysis, are of two 

 kinds, organic and inorganic. Only the organic constituents, 

 however, are universally indispensable. These are oxygen, 

 hydrogen, nitrogen, and carbon, which make up at least from 

 eighty-eight to ninety-nine per cent, of every vegetable sub- 

 stance. The hiorganic constituents, which are essential to the 

 perfection of any but the lowest grade of plants, consist mainly 

 of potash, soda, lime, magnesia, alumina, silex, sulphur, and 

 phosphorus. 



Now, where and how are the different kinds of food which 

 plants require obtained ? Mainly, no doubt, from the soU, and 

 by means of the roots, which, we have seen, are the proper 

 feeding organs. The air mny, however (and evidently does, in 

 some cases, as in the epijjliytes^ or air-plants), either directly or 

 indirectly, supply aU the organic elements. 



But whether derived from the earth or from the air, the 

 vlanfs nourishment is icholly received either in tJie gaseous or 

 the liquid, form ; for the leaves can imbibe air or vapor only 



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