HISTORICAL AND INTRODUCTORY 5 



unmanured land to the circumstance that " the vegetable 

 matter that it at first abounded in being extracted from it by 

 those successive crops, is most of it borne off. . . . The land 

 may be brought to produce another series of the same vege- 

 tables, but not until it is supplied with a new fund of matter, 

 of like sort with that it at first contained ; which supply is 

 made several ways, either by the ground's being fallow some 

 time, until the rain has poured down a fresh stock upon it ; or 

 by the tiller's care in manuring it." The best manures, he 

 continues, are parts either of vegetables or of animals, which 

 ultimately are derived from vegetables. 



In his celebrated textbook of chemistry Boerhaave (41) 

 taught that plants absorb the juices of the earth and then work 

 them up into food. The raw material, the " prime radical 

 juice of vegetables, is a compound from all the three kingdoms, 

 viz. fossil bodies and putrified parts of animals and vege- 

 tables ". This " we look upon as the chyle of the plant ; being 

 chiefly found in the first order of vessels, viz., in the roots and 

 the body of the plant, which answers to the stomach and intes- 

 tines of an animal ". 



For many years no such outstanding work as that of 

 Glauber and Woodward was published, if we except Hales' 

 Vegetable Staticks (119), the interest of which is physiological 

 rather than agricultural.^ Advances were, however, being 

 made in agricultural practice. One of the most important 

 was the introduction of the drill and the horse hoe by Jethro 

 Tull (286), an Oxford man of a strongly practical turn of 

 mind, who insisted on the vital importance of getting the soil 

 into a fine crumbly state for plant growth. Tull was more 

 than an inventor ; he discussed in most picturesque language 

 the sources of fertility in the soil. In his view it was not the 

 juices of the earth, but the very minute particles of soil 

 loosened by the action of moisture, that constituted the 

 ^' proper pabulum " of plants. The pressure caused by the 

 swelling of the growing roots forced these particles into the 

 " lacteal mouths of the roots," where they entered the circula- 

 tory system. All plants lived on these particles, i.e. on the 



^ He shows, however, that air is " wrought into the composition " of plants. 



