174 



OASSELL'S POPULAR GAEDENING. 



HmCESSITT OF PEBFBOT PLANT-FOOD. 



The fundamental principle upon ■which a manure 

 is employed is that of adding to the soil an abundant 

 supply of the elements necessary to the full develop- 

 ment of the plants grown, and in such a condition 

 as shall he best fitted for absorption by the plant- 

 roots. 



"When a horticulturist has obtained a general 

 knowledge of the nature of manures and the 

 wants of different plants, it will be of great ser- 

 vice in guiding his practice if he determine, by 

 actual experiment, what is the relative effect of 

 different manures upon his various soils and plants ; 

 the influence of climate and season, with the 

 previous manurial condition of the land, being 

 always taken' into account when interpreting the 

 results. 



When land is cropped and the produce removed, 

 a gradual diminution of the fertility of the soil 

 takes place, until at length, according to the natural 

 resources of the soil, it becomes almost incapable of 

 maintaining a crop. The exhaustion thus brought 

 about is rarely if ever due to the simultaneous con- 

 sumption of aU the different constituents of plant- 

 food, but generally depends upon that of one or two 

 individual substances. 



The old theory, that seven elements are always 

 necessary to the full development of a plant, is now 

 exploded ; but still, unless proper and suitable food 

 is supplied in sufficient quantity, the plant suffers. 

 If a soil be supplied with a manure containing a 

 very small quantity of one of the important ingre- 

 dients of plant-food, along with abundance of all 

 the others, the amount of growth and increase which 

 is produced must obviously be measured not by 

 those which are abundant, but by that which is most 

 deficient ; for the plant which grows luxuriantly so 

 long as it obtains a supply of all its constituents, is 

 arrested as effectually by the want of one important 

 item as of all. 



The engraving in Fig. 11 exhibits the results of 

 an experiment by Professor "W. O. Attwater, Director 



of the Connecticut Agricultural Station, U.S.A. 

 The experiments were undertaken to demonstrate 

 the effect of withholding certain elements of plant- 

 food separately, and comparing each case with an 

 example in which the plant was supplied with every 

 ingredient necessary to its full development. Ten 

 wooden boxes were taken and filled with pure sand, 

 the boxes being numbered I., II., III., IV., V., 

 respectively. In the first five Buckwheat was sown, 

 and in the second five, Oats. To fertilise these, 

 several solutions were prepared by dissolving suitable 

 chemical salts in water. One of these solutions, 

 containing all the ingredients which plants require 

 for building up their vegetable fabric, was called the 

 normal solution, and was applied to No. V. of each 

 series. Another solution, containing the same in- 

 gredients, except that the constituent of nitrogen 

 was omitted, was used to water the plants of No. IV. 

 A solution, with everything but phosphoric acid, 

 was applied to No. III. of each set. Potash was 

 in like manner omitted from No. II. And finally 

 No. I., of both Buckwheat and Oats, received rain- 

 water only. 



The engraving presents to the eye at once the 

 character of growth obtained uiider these various 

 treatments ; the omission of any one of the more 

 important elements of plant-food reduced in a re- 

 markable degree the healthiness and vigour of the 

 plant operated upon. In lack of potash, everything 

 else being supplied, the plants suffered to a certain 

 degree ; leaving out phosphoric acid injured them 

 more, especially in seed-production, as may be 

 learnt from the table wWh follows. "Without 

 nitrogen, even though everything else was fui'- 

 nished, the growth was no better than with rain- 

 water only. 



When the plants were ripe they were harvested, 

 the roots being freed from sand by careful washing, 

 and the dissected parts weighed. The following 

 table gives the air-dried weights in grammes of 

 both Buckwheat and Oats under the various ISiauu- 

 rial applications : — 



