. 



4 THE PRINCIPLES OF 



adulteration in mixtures of grass-seeds, the knowledge of 

 plants which may be introduced into our agriculture, and the 

 identification of injurious plants, either in the form of per- 

 nicious weeds, or as impurities in mixtures of seeds presented 

 for sale by unscrupulous seedsmen, or it may be in the 

 tracing of the life history of those cryptogamic or fungoid 

 forms, which so often are the cause of loss to farmers as, for 

 example, the potato disease and other blights and mildews 

 which affect our crops. This brings us naturally to the 

 domain of vegetable nosology, a most important branch of 

 botany, so that whether we view this great subject in relation 

 to the structure of plants, the classification of plants, or the 

 diseases of plants, we see its bearings upon the pursuit of 

 agriculture. Scarcely less important is the subject of physi- 

 ology, dealing as it does with the functions of animal and 

 vegetable life. So also it would be difficult to convey any- 

 thing like an adequate idea as to the history and attributes 

 of soils without importing a good deal of knowledge which 

 belongs essentially to the science of geology. It is not my 

 object to pass in review every natural science which throws 

 light upon agricultural problems or agricultural practice ; it 

 is sufficient to show that there are many branches of natural 

 science which cannot be overlooked by any intelligent student 

 of agriculture. But while the natural sciences are of vast 

 importance in elucidating difficulties and suggesting improve- 

 ments, it can scarcely be denied that the great subject of 

 agriculture requires for its full explanation a knowledge of 

 mathematics, of political economy, of statistics, of engineering, 

 and of physics, and there is perhaps scarcely a branch of 

 knowledge which might not be easily shown to have a 

 practical and important bearing upon the usages and customs 

 of agriculture. Take, for example, > meteorology, and even 

 astronomy. Consider for one moment the influence of the 

 sun as a factor in the germination of seed, and then reflect 



