PERIOD AT WHICH A CROP IS REAPED. 



easily dissolved by the water which is to convey it into the 

 plant is more readily acted upon directly by the extremities of 

 the roots themselves and produces more quickly and completely 

 those chemical changes on which its beneficial action, in respect 

 either of the soil or of the plant, always in a great degree 

 depends. 



Hence, if one man apply a substance in hard and sparingly 

 soluble lumps, and another in the form of a fine and more 

 soluble powder if one apply it in a solid and the other in a 

 liquid form if one apply a concentrated and the other a largely 

 diluted solution in each case the effects of the same applica- 

 tion in the different forms may be different, and results appa- 

 rently contradictory may therefore be obtained.* 



To produce maximum effects we must apply substances in 

 a finely divided state ; to produce analogous and properly com- 

 parable effects, we must use them under like circumstances and 

 in a similar state. 



4. The period at which a crop is reaped or lifted may also 

 influence the result. The effect of many applications being not 

 only to promote but also to prolong the growth of plants, or to 

 cause it go on till a later period of the year, it is obvious that the 

 season or month in which the crop is reaped or gathered must in 

 such cases affect the actual amount of produce. This is especially 

 the case with root-crops, such as turnips, which, under the influ- 

 ence of some manures, may continue to grow as long as the 

 season is sufficiently mild, while, under the stimulus of others, 

 they may attain a more early maturity. Hence, if turnips be 

 lifted in early winter, that a crop of winter-corn may be sown, 

 not only may all the parts of an experimental field yield a less 

 return of this crop than if they had been left longer in the 

 ground, but especially those portions which are still in a state 

 of sensible growth may weigh less than they would other- 

 wise do. 



In these modes of treatment, therefore, exists a cause of diver- 

 sity or discordance in comparative experimental results, which 

 ought not to be lost sight of by the experimenter and the critic. 



* For experimental proof of this statement, see my Elements of Agricultural 

 Chemistry and Geology, 5th Edition, p. 185. 



