588 SELECTIONS FROM ADDRESSES. 



given ingredient in a soil to the production of a plant, in which 

 the same component had been proved to exist, the way was 

 open for direct and unmistakable tests of the theory in the 

 large way of practice. 



Observation and experience had already shown much of that, 

 which the theory above briefly outlined gave a ready and sat- 

 isfactory explanation. It has, for example, been long noted? 

 Virgil even indicates it, that where a particular crop had been 

 grown for a series of seasons on the same fields, the land had 

 become tired of it. The practice of longer or shorter rotations 

 natarally followed, and it was found that so entire and irre- 

 trievable had been the exhaustion in some cases, certain crops 

 must be left entirely out of the series of rotations. The agri- 

 culturist could, a few years ago, only explain these facts by 

 stating them in other phraseology. The soil was said to be 

 exhausted, and so it was, but not in that indefinite meaning he 

 attached to the word. It was clover sick., or 'wheat sick, when 

 these crops gave out. Now when wheat, which requires a 

 large figure of phosphoric acid, having drawn all that sub- 

 stance out of the ground which was in it, declined to grow, 

 and turnips which did not contain but little of that ingredient 

 did well, the rationale seems obvious enough to us. 



Sagacious cultivators did not fail to notice another singular 

 state of facts, for which they were wholly at fault for explana- 

 tion. They saw that a very few pounds to the acre, of some 

 mineral substances augmented the crop to a surprising degree. 

 Pounds of such manure brought off hundred weights of crop, 

 in one place, and was useless m another. Gypsum was an 

 example. In Nova Scotia, where it was brought from, it was 

 so useless on land that the people fancied it actually did mis- 

 chief. Of course, conjectures were made to account for what 

 seemed a crapricious action, and the conclusion generally 

 reached was, that gypsum did not do any good near the sea, 

 and the next part of the philosophy was, that it was the salt- 

 ness of the air which interfered with it. Unluckily, it proved 

 that it did do good near the sea, in some places, and then it 

 was certain that no salt ever leaves the ocean from evapora- 

 tion, none in fact, but the spray mechanically driven inland, 

 and lastly, salt, or salt water had not the slightest decomposing 

 or altering eft(3ct on gypsum, which is a sulphate of lime. 



