1 1 20 THE BOOK OF GARDENING. 



These analytical results, which are well worthy of careful 

 study by 1 every practical gardener, give an insight into the 

 composition and the food-requirements of some of the many 

 different plants with which he has to do. And a system of 

 manuring may be called well-devised or rational when it is 

 based upon the results of a careful examination into the 

 composition of the plants under cultivation, and on a due 

 consideration of the natural capabilities of the plant for 

 availing itself of the needed plant-food, both from the atmo- 

 sphere and from the soil. 



The gardener, however, has to remember that the essential 

 elements of plant-food are not required by different plants in 

 the same invariable proportions at the various stages of growth, 

 but are wanted at different periods of their life, in different 

 absolute amounts, and in different proportions, according as to 

 whether stems, leaves, flowers, fruit, or seed are required to 

 be brought into prominence. 



The gardener is therefore taught that all his cultivated plants, 

 whether in the open garden, the orchard, or the conservatory, 

 contain the same elementary constituents, yet no two of 

 them are in exactly the same proportions. Each plant has its 

 especial wants at different stages of its development. Succu- 

 lent and rapidly-growing vegetables require an abundant supply 

 of nitrogenous food in an easily available form during their 

 early periods of growth ; flowering plants and fruit-trees require 

 phosphoric acid when blossoming and developing fruits and seeds; 

 Grape-vines need a large amount of available potash during the 

 formation and maturing of the Grapes, for the production of a 

 rich and sugary juice ; whilst Potatoes require nitrogen and 

 potash in combination for the production of starch in the tubers. 



It is found that the proportions of sugar and starch, and other 

 constituents, can be considerably changed by the judicious use 

 of special fertilisers. For example, in one of the experiments at 

 R.othamsted, Hertfordshire, on root crops, the amount of sugar 

 in the roots of Beet has been increased in one experiment from 

 78olb. to 16321b. per acre ; and in another experiment, from 

 9861b. of sugar, the amount has been raised to 25121b. per 

 acre— an increase of more than half-a-ton of sugar on each 

 acre of land. 



In practical gardening, four only of the chemical constituents 

 of plants are in the majority of cases supplied to the crop under 

 the form of fertilisers, and these are nitrogen, phosphoric acid, 

 potash, and sometimes lime. The first three especially are 

 the most sparsely distributed in soils, are the most easily 

 exhausted, and the most costly to replace. 



With every crop of vegetables, fruit, or flowers removed from 

 the soil, the available stores of potash, phosphoric acid, and 

 nitrogen are diminished; therefore, if a gardener proportions his 



