104 THE ART OF CULTURE. 



in those people who live almost exclusively upon pctatoes; theii 

 excrements contain a large quantity of unchanged granules of 

 starch. Potatoes, which, when mixed with hay alone, are 

 scarcely capable of supporting the strength of a horse, form with 

 bread and oats a strong and wholesome fodder. 



It will be evident from the preceding considerations, that the 

 products generated by a plant may vary exceedingly according 

 to the substances given it as food. A superabundance of carbon 

 in the state of carbonic acid conveyed through the roots of plants, 

 without being accompanied by nitrogen, cannot be converted 

 either into gluten, albumen, or wood ; but either it will be sepa- 

 rated in the form of excrements, such as sugar, starch, oil, wax, 

 resin, mannite, or gum, or these substances will be deposited in 

 greater or less quantity in the wide cells and vessels. 



The quantity of gluten, and of vegetable albumen, will 

 augment when plants are supplied with an excess of food con- 

 taining nitrogen, if certain other conditions be fulfilled ; and 

 ammoniacal salts will remain in the sap, when, for example, as 

 in the culture of the beet, we manure the soil with a highly 

 nitrogenous substance, or when we suppress the functions of the 

 leaves by removing them from the plant. 



We know that the ananas is scarcely eatable in its wild state, 

 and that it shoots forth a great quantity of leaves when treated 

 with rich animal manure, without the fruit on that account ac- 

 quiring a larger amount of sugar; that the quantity of starch in 

 potatoes increases when the soil contains much humus, but de- 

 creases when the soil is manured with strong animal manure, 

 although then the number of cells increases, the potatoes acquir- 

 ing in the first case a mealy, in the second a soapy, consistence. 

 Beet-roots taken from a barren sandy soil, contain a maximum 

 of sugar, and no ammoniacal salts; and the Teltowa parsnip 

 loses its mealy state in a highly manured land, because there 

 all the circumstances necessary for the formation of cells are 

 united. 



An abnormal production of certain component parts of plants 

 presupposes a power and capability of assimilation to which the 

 most powerful chemical action cannot be compared. The best 

 idea of it may be formed by considering that it surpasses in 



